Mack AIR AND BRAKE SYSTEM SERVICE MANUAL(16-104) - PDF DOWNLOAD

AIR AND BRAKE SYSTEM SERVICE MANUAL

JULY 2007 (REVISED)

16-104

AIR AND BRAKE SYSTEM SERVICE MANUAL

JULY 2007 (REVISED — SUPERSEDES ISSUE DATED OCTOBER 2005)

© MACK TRUCKS, INC. 2007 16-104

ATTENTION The information in this manual is not all inclusive and cannot take into account all unique situations. Note that some illustrations are typical and may not reflect the exact arrangement of every component installed on a specific chassis.

The information, specifications, and illustrations in this publication are based on information that was current at the time of publication.

No part of this publication may be reproduced, stored in a retrieval system, or be transmitted in any form by any means including (but not limited to) electronic, mechanical, photocopying, recording, or otherwise without prior written permission of Mack Trucks, Inc.

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TABLE OF CONTENTS

TABLE OF CONTENTS

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TABLE OF CONTENTS INTRODUCTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 SAFETY INFORMATION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 Advisory Labels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 Service Procedures and Tool Usage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 EXPLANATION OF NUMERICAL CODE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 ABOUT THIS MANUAL . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 DESCRIPTION AND OPERATION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 AIR SYSTEM OVERVIEW . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 Air Compressor and Reservoirs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 Dash-Mounted Pressure Gauges . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 Application Valve (Treadle Valve) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 Brake Chambers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 AIR SYSTEM THEORY OF OPERATION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 System Pressurized with Parking Brakes Applied . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 System Pressurized with Parking Brakes Released . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 Applying the Service Brakes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 Releasing the Service Brakes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 AIR SYSTEM SAFETY FEATURES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 Low-Pressure Warning . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 Single Check Valves . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 Double Check Valves . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 Spring Brake Modulating Relay Valve . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 Spring Brake Control Valve (LE and MR Models) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19 Redundant Signal Relay Valve . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20 Anti-Compounding Circuits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22 Tractor Protection Valve . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26 AIR SYSTEM COMPONENTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27 Air Reservoir . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27 Drain Valves . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30 Automatic Drain Valve . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30 Air Compressor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32 Governor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34 Low-Pressure Indicator Switch . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36 Single Check Valves . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37 Double Check Valves . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38 Pressure Protection Valve . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39 Stoplight Switch . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40 Treadle Valve . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42 Park Brake Control Module . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46 Single Park Brake Control Valve with Double Check Valve . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51 Push/Pull-Type Park Brake Control Valves . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54 Trailer Air Supply Valve . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56 Tractor Protection Valve — MR and DM Models with Full Trailer Connection . . . . . . . . . . . . . 59 Tractor Protection Manifold — CXN/CHN/CH/CL/CX/CV/CT Models . . . . . . . . . . . . . . . . . . . . 62 Hand Control Valve (Trolley Valve) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65 Spring Brake Modulating Relay Valve . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 67 Spring Brake Control Valve . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 74 Quick Release Valve . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 82 Tractor — Rear Brake Proportioning/Front Axle Ratio Valves . . . . . . . . . . . . . . . . . . . . . . . . . . 83 Inversion Valve . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 87 Relay Valves . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 88 iv

TABLE OF CONTENTS Bobtail Proportioning Relay Valve . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 94 Hose Couplings (Glad Hands) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 101 Brake Chambers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 101 Single-Diaphragm Brake Chambers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 102 Multiple-Diaphragm Spring Brake Chambers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 104 Rotochambers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 110 Long-Stroke Air Chambers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 111 AIR DRYERS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 113 Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 113 Air Dryer Service . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 115 Anchorlok “Moisture Lok” Dry Air Tank (Aftercooler Type) . . . . . . . . . . . . . . . . . . . . . . . . . . . 115 Bendix AD-9 and AD-9 Soft Seat Air Dryers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 121 Bendix AD-IP Air Dryer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 126 Bendix AD-SP Air Dryer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 130 CR Brakemaster Models 62 and 68 (Aftercooler Type) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 134 CR Brakemaster T2000 and T3000 Air Dryers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 136 Cyclo-Gard Air Dryer Models 17 and 22 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 140 Haldex Dry E.S.T. Air Dryer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 142 Midland Pure Air Plus Air Dryer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 146 ArvinMeritor™ WABCO System Saver 1000, 1200, 1200E and 1200P . . . . . . . . . . . . . . . . . 148 Isolation (ECON) Valve . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 153 ANTI-LOCK BRAKE SYSTEM (ABS) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 155 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 155 System Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 155 Dyno-Testing Vehicles with ATC Option . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 156 ANTI-LOCK BRAKE SYSTEM COMPONENTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 157 Electronic Control Unit (ECU) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 157 Engine Brake Disable Relay . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 160 ABS Relay Panel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 161 Tone Wheel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 161 Wheel Speed Sensors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 162 Modulator (ABS) Valve . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 163 ATC Valve . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 163 ABS Indicator Lamp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 165 ATC Indicator Lamp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 165 Diagnostic Blink Codes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 166 ABS/ATC Diagnostic Tools . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 167 TROUBLESHOOTING . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 169 TROUBLESHOOTING BRAKE SYSTEM PROBLEMS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 170 BRAKE NOISE INVESTIGATION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 174 DUAL-NEEDLE TEST GAUGE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 175 AIR SYSTEM DIAGNOSTIC PROCEDURES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 176 Measuring Supply Pressure at the Service Brake Relay Valve (If Equipped) . . . . . . . . . . . . . 176 Measuring Supply Pressure at the Treadle Valve . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 177 Measuring Relay Valve Control Pressure Versus Delivery Pressure . . . . . . . . . . . . . . . . . . . . 177 Measuring Drive Axle Delivery Pressure Versus Steering Axle Delivery Pressure . . . . . . . . . 178 Measuring Drive Axle Control Pressure Versus Trailer Control Pressure (Tractors Only) . . . . 178 Measuring Drive Axle Delivery Pressure Versus Trailer Axle Delivery Pressure (Tractors Only) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 178 Air System Diagnostic Check . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 179

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TABLE OF CONTENTS MAINTENANCE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 181 AIR SYSTEM MAINTENANCE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 182 Service Tests . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 182 Preventive Maintenance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 183 Dual-Circuit Brake System Function Test . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 185 REPAIR INSTRUCTIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 187 ANTI-LOCK BRAKE SYSTEM COMPONENT REMOVAL AND INSTALLATION . . . . . . . . . . . . . 188 Front-Axle Speed Sensor Removal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 188 Front-Axle Speed Sensor Installation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 188 Rear-Axle Speed Sensor Removal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 189 Rear-Axle Speed Sensor Installation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 190 ABS Valve Removal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 191 ABS Valve Installation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 192 ATC Valve Removal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 192 ATC Valve Installation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 193 WHEELBASE CHANGES ON ABS-EQUIPPED VEHICLES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 193 REPLACEMENT OF ABS CHASSIS HARNESSES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 193 BRAKE ADJUSTMENT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 196 Manual and Automatic Slack Adjusters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 196 Slack Adjuster Maintenance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 197 Slack Adjuster Lubrication . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 203 Adjusting Stroke . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 204 BRAKE SYSTEM OVERHAUL . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 210 Asbestos Fibers Danger . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 210 Non-Asbestos Fibers Danger . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 211 Wheel Removal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 211 Drum/Rotor Inspection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 212 Cam Brake Shoe Removal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 216 Cam Brake Component Inspection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 223 Cam Brake Shoe Installation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 229 AIR SYSTEM CONTAMINANT REMOVAL . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 240 BALANCED AIR BRAKES ON TRACTOR/TRAILER COMBINATIONS . . . . . . . . . . . . . . . . . . . . 241 Testing for Balanced Brakes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 241 AIR LINE HOSE — INSTALLATION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 246 Air Fittings — Quick Disconnect . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 247 Air Lines — Routing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 249 Air Lines — Clamping . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 253 Air Lines — Minimum Allowable Radius . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 258 SCHEMATIC & ROUTING DIAGRAMS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 259 AIR SYSTEM BASIC CHASSIS AND CAB PIPING DIAGRAMS . . . . . . . . . . . . . . . . . . . . . . . . . 260 CXN, CHN, CT Series Truck with 4S/4M ABS/ATC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 265 CXN, CHN, CT Series Truck with 4S/4M ABS/ATC with Full Trailer Connection . . . . . . . . . . . . . 266 CXN, CHN, CT Series Truck with 4S/4M ABS/ATC with Full Trailer Connection and Dual Function Hand Control Valve . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 267 CXN, CHN, CT Series Tractor with 4S/4M ABS/ATC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 268 CV Series Truck with 4S/4M ABS/ATC (January 1, 2004 and Later) . . . . . . . . . . . . . . . . . . . . . . 269 CV Series Truck with 4S/4M ABS/ATC with Full Trailer Connection (January 1, 2004 and Later) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 270 CV Series Truck with 4S/4M ABS/ATC with Full Trailer Connection and Dual Function Hand Control Valve (January 1, 2004 and Later) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 271

vi

TABLE OF CONTENTS CV Series Truck with 4S/4M ABS/ATC (Prior to January 1, 2004) . . . . . . . . . . . . . . . . . . . . . . . . 272 CV Series Truck with 4S/4M ABS/ATC with Full Trailer Connection (Prior to January 1, 2004) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 273 CV Series Truck with 4S/4M ABS/ATC with Full Trailer Connection and Dual Function Hand Control Valve (Prior to January 1, 2004) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 274 CV Series Tractor with 4S/4M ABS/ATC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 275 CH/CL Series Truck with 4S/4M ABS/ATC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 276 CH/CL Series Truck without ABS/ATC with Full Trailer Connection . . . . . . . . . . . . . . . . . . . . . . . 277 CH/CL Series Truck with 4S/4M ABS/ATC and Full Trailer Connection . . . . . . . . . . . . . . . . . . . . 278 CH/CL Series Truck with 4S/4M ABS/ATC and Full Trailer Connection with Dual Function Hand Control Valve . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 279 CH/CL Series Tractor without ABS/ATC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 280 CH/CL Series Tractor with 4S/4M ABS/ATC ArvinMeritor™ WABCO “C” Version ECU . . . . . . . . 281 CH/CL/CX Series Tractor with 4S/4M ABS/ATC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 282 R Series Truck without ABS/ATC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 283 R Series Truck with 4S/4M ABS/ATC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 284 R Series Truck without ABS/ATC with Full Trailer Connection . . . . . . . . . . . . . . . . . . . . . . . . . . . 285 R Series Truck with 4S/4M ABS/ATC with Full Trailer Connection . . . . . . . . . . . . . . . . . . . . . . . . 286 R Series Tractor without ABS/ATC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 287 R Series Tractor with 4S/4M ABS/ATC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 288 R Series Truck with 4S/4M ABS/ATC with Full Trailer Connection and Dual Function Hand Control Valve . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 289 DM, DMM Series Truck without ABS/ATC with Full Trailer Connection . . . . . . . . . . . . . . . . . . . . 290 DM, DMM Series Truck with 4S/4M ABS/ATC with Full Trailer Connection . . . . . . . . . . . . . . . . . 291 MR Series Truck without ABS/ATC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 292 MR Series Truck with 4S/4M ABS/ATC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 293 MR Series Truck without ABS/ATC with Full Trailer Connection . . . . . . . . . . . . . . . . . . . . . . . . . . 294 MR Series Truck with 4S/4M ABS/ATC with Full Trailer Connection . . . . . . . . . . . . . . . . . . . . . . 295 MR Series Tractor without ABS/ATC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 296 MR Series Tractor with 4S/4M ABS/ATC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 297 LE Series Truck without ABS/ATC without Work Brake . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 298 LE Series Truck with 4S/4M ABS/ATC without Work Brake . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 299 LE Series Truck without ABS/ATC and with Work Brake . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 300 LE Series Truck with 4S/4M ABS/ATC with Work Brake . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 301 Liftable Axle Air Brake Piping — One Tag or One Pusher . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 302 Liftable Axle Air Brake Piping — Two Pusher Axles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 303 Liftable Axle Air Brake Piping — One Tag and One Pusher Axle . . . . . . . . . . . . . . . . . . . . . . . . . 304 Liftable Axle Air Brake Piping — Two Pusher Axles and One Tag Axle . . . . . . . . . . . . . . . . . . . . 305 Rear Axle Relay Valve Configuration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 306 Bendix TU-FLO Piping . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 310 Cab Manifold Piping . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 311 SPECIAL TOOLS & EQUIPMENT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 351 SPECIAL TOOLS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 352 INDEX . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 353

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NOTES

viii

INTRODUCTION

INTRODUCTION

Page 1

INTRODUCTION SAFETY INFORMATION Advisory Labels Cautionary signal words (Danger-Warning-Caution) may appear in various locations throughout this manual. Information accented by one of these signal words must be observed to minimize the risk of personal injury to service personnel, or the possibility of improper service methods which may damage the vehicle or cause it to be unsafe. Additional Notes and Service Hints are used to emphasize areas of procedural importance and provide suggestions for ease of repair. The following definitions indicate the use of these advisory labels as they appear throughout the manual:

Danger indicates an unsafe practice that could result in death or serious personal injury. Serious personal injury is considered to be permanent injury from which full recovery is NOT expected, resulting in a change in life style

Warning indicates an unsafe practice that could result in personal injury.

Personal injury means that the injury is of a temporary nature and that full recovery is expected.

Caution indicates an unsafe practice that could result in damage to the product.

Note indicates a procedure, practice, or condition that must be followed in order for the vehicle or component to function in the manner intended.

A helpful suggestion that will make it quicker and/or easier to perform a procedure, while possibly reducing service cost.

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INTRODUCTION Service Procedures and Tool Usage Anyone using a service procedure or tool not recommended in this manual must first satisfy himself thoroughly that neither his safety nor vehicle safety will be jeopardized by the service method he selects.

Individuals deviating in any manner from the instructions provided assume all risks of consequential personal injury or damage to equipment involved.

Also note that particular service procedures may require the use of a special tool(s) designed for a specific purpose. These special tools must be used in the manner described, whenever specified in the instructions.

1. Before starting a vehicle, always be seated in the driver’s seat, place the transmission in neutral, be sure that parking brakes are set, and disengage the clutch.

2. Before working on a vehicle, place the transmission in neutral, set the parking brakes, and block the wheels.

3. Before towing the vehicle, place the transmission in neutral and lift the rear wheels off the ground, or disconnect the driveline to avoid damage to the transmission during towing.

Engine-driven components such as Power Take-Off (PTO) units, fans and fan belts, driveshafts and other related rotating assemblies, can be very dangerous. Do not work on or service engine-driven components unless the engine is shut down. Always keep body parts and loose clothing out of range of these powerful components to prevent serious personal injury. Be aware of PTO engagement or nonengagement status. Always disengage the PTO when not in use.

REMEMBER, SAFETY . . . IS NO ACCIDENT!

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INTRODUCTION EXPLANATION OF NUMERICAL CODE

GROUP 400 — STEERING, AXLES, WHEELS AND TIRES, DRIVELINE

The organization of MACK service manuals has been upgraded to standardize manual content according to a reference system based on component identification. The new reference system will help link the information contained in this publication with related information included in other MACK service/warranty publications, such as associated service bulletins, warranty manuals, and MACK Service Labor Time Standards.

GROUP 500 — BRAKES, AUXILIARY SYSTEMS

The system is based on a numerical code, the first digit of which identifies the general component grouping as listed here: GROUP 000 — GENERAL DATA GROUP 100 — CHASSIS GROUP 200 — ENGINE GROUP 300 — CLUTCH, TRANSMISSION, TRANSFER CASE AND PTO

GROUP 600 — CAB, TRUCK BODY GROUP 700 — ELECTRICAL The second two digits of the three-digit code are used to identify the system, assembly or subassembly, as appropriate, within each of the groupings. The codes applicable to this publication are shown at the COMPONENT HEADINGS, as necessary, and may also appear in the TABLE OF CONTENTS, to guide you to specific component information.

Additionally, a two-character alpha code (i.e., [CP] RESERVOIR, AIR SUPPLY) may be shown with each operation. This alpha code, in combination with the three-digit Group number, identifies the specific assembly, sub-assembly or part, and directly relates to the first five positions of the operation code listed in MACK Service Labor Time Standards.

Examples:

Numerical Code

Page 4

INTRODUCTION ABOUT THIS MANUAL This manual assists the technician in properly diagnosing and repairing the air and brake system of a MACK Class 8 highway chassis. To provide an understanding of how an air system operates, a basic discussion of air system operation, along with a detailed explanation of air system components, is included. As an aid in identifying the various air system components in relation to the chassis, illustrations are used, where possible, to show the location of each component on the truck. Piping diagrams are designed to be easy to follow while accurately illustrating airflow through the system.

Every effort has been made to ensure the accuracy of the presented information. However, due to constant product improvement, not all information is applicable to every chassis.

Additionally, because of various customer-specified options, not all chassis are equally equipped.

Follow recommended service and maintenance procedures to ensure air and brake system integrity and proper operation. Read and understand this manual before attempting any extensive air and brake system service or repair.

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NOTES

Page 6

DESCRIPTION AND OPERATION

DESCRIPTION AND OPERATION

Page 7

DESCRIPTION AND OPERATION AIR SYSTEM OVERVIEW

The wet tank supplies compressed air to two service reservoirs:

Air-actuated brakes are standard equipment on all MACK chassis. Air brakes use the power generated by pressurized air to force the brake shoes (or disc pads if the chassis is equipped with disc brakes) against the brake drums (or rotors) to stop the vehicle. A typical air brake system is composed of an air compressor which is driven by the engine, air reservoirs to store the compressed air, air chambers which apply the force to the brake assemblies, and a method of distribution (piping, hoses, valves, etc.) to direct the pressurized air throughout the system. The air system is also used to power various air-operated accessories which may be used on the vehicle.

앫

Primary Reservoir — supplies the rear brakes

앫

Secondary Reservoir — supplies the front brakes

1

All MACK chassis use a dual air system which is actually two separate braking systems, with either system capable of stopping the vehicle should one system fail. The system is composed of a primary circuit which supplies air pressure to the rear brake assemblies, and a secondary circuit which supplies air pressure to the front brake assemblies.

The air system is designed and built to conform to all applicable Federal Motor Vehicle Safety Standards in effect at the time of manufacture.

Tractor air systems are designed for tractor operation only. If a tractor is going to be converted for operation as a straight truck, the air system must be reconfigured accordingly, for safe braking operation of the vehicle. Refer to “AIR SYSTEM SAFETY FEATURES” on page 15 for illustrations of the differences between straight truck and tractor air systems.

Figure 1 — Compressor, Governor and Reservoirs

Air Compressor and Reservoirs Air pressure is generated by the air compressor and stored in the air reservoirs. The air compressor pressurizes the supply reservoir (which is also called the “wet tank” because it traps moisture, oil, etc.) to a pressure of 120 pounds per square inch (psi). Reservoir pressure is maintained between 105 to 135 psi by a governor which is mounted on or near the compressor, and works in conjunction with a compressor unloader valve. The supply reservoir is protected from over-pressurization by a safety valve that is set to open at 150 psi in the event of compressor or governor failure.

Page 8

Different reservoir configurations are available, depending upon chassis model. The primary and secondary reservoirs on some models may be combined into one reservoir containing two separate chambers, while other models may combine the supply and secondary reservoirs into one tank with two separate chambers. Some chassis may also be equipped with two primary reservoirs to provide additional capacity for the primary circuit.

DESCRIPTION AND OPERATION Dash-Mounted Pressure Gauges

Application Valve (Treadle Valve)

A dash-mounted, dual air-pressure gauge provides the driver with information on how the system is functioning. The gauge monitors pressure in both primary and secondary systems.

The green pointer indicates air pressure in the primary air circuit, and the orange pointer indicates air pressure in the secondary circuit.

A foot-operated brake application valve (treadle valve) provides the driver with modulated control of the air system for applying or releasing the brakes. The treadle valve is a dual air valve that controls air pressure in both primary and secondary circuits in one motion. The portion of the valve closest to the pedal directs air pressure to the primary air circuit (rear brake assemblies), and the portion of the valve furthest from the pedal directs pressure to the secondary circuit (front brake assemblies).

2

3

Figure 2 — Dashboard Pressure Gauge

Some vehicles are equipped with a separate gauge for each circuit. The gauge with the green pointer indicates primary circuit air pressure and the gauge with the orange pointer indicates secondary circuit air pressure.

Figure 3 — Treadle Valve

Page 9

DESCRIPTION AND OPERATION Brake Chambers Brake diaphragm chambers convert the energy of the pressurized air into the mechanical energy necessary to operate the brake assemblies. In most applications, single-diaphragm brake chambers are used on the front axle brake assemblies, and multiple-diaphragm spring brake chambers are used on rear axle brake assemblies. The spring brake chambers provide

a parking brake function, along with an emergency brake function in the event of a pressure loss.

Spring brakes automatically apply when air pressure in both primary and secondary circuits drops to approximately 40 psi.

4

Figure 4 — Air Chambers

Page 10

DESCRIPTION AND OPERATION AIR SYSTEM THEORY OF OPERATION System Pressurized with Parking Brakes Applied

and the various auxiliary control valves that make up the system. The multiple diaphragm spring brake chambers apply the rear brakes if system pressure is below approximately 40 psi in both primary and secondary circuits, or the parking brake valve is pulled out (applied).

5

The air system becomes operational when the air reservoirs are sufficiently pressurized and compressed air is delivered to the treadle valve

Figure 5 — System Pressurized, Parking Brakes Applied

Page 11

DESCRIPTION AND OPERATION System Pressurized with Parking Brakes Released At approximately 70 psi, sufficient pressure exists in the air system to shut off the low air buzzer and the low air warning lamp. When the parking brake

valve is pushed IN, air pressure is directed to the spring brake chambers to compress the power spring and release the spring brakes.

6

Figure 6 — System Pressurized, Parking Brakes Released

Page 12

DESCRIPTION AND OPERATION Applying the Service Brakes Pushing the brake pedal applies the service brakes by opening a path through the treadle valve for pressure to flow to the front and rear service brake chambers. The flow of pressure is proportional to the amount of force applied to the brake pedal.

Many chassis are equipped with a relay valve that speeds up the application of the rear service brakes by providing reservoir pressure in close proximity to the rear axle brake chambers. The relay valve is mounted near the rear axle(s), and responds to signal pressure received from the treadle valve.

7

Figure 7 — Applying the Service Brakes

Page 13

DESCRIPTION AND OPERATION Releasing the Service Brakes Releasing the brake pedal relieves the pressure against the brake chamber diaphragms, allowing the return springs to force the diaphragms into the released position, thus releasing the service brakes.

Pressure from the brake chambers exhausts either through the treadle valve or through the relay valve, if the chassis is so equipped.

Exhausting air through the relay valve allows the brakes to release more quickly than having to

exhaust air back through the treadle valve. Signal pressure to the relay valve exhausts through the treadle valve.

Most chassis are equipped with a quick release valve on the front axle brake circuit that allows the front axle brakes to release more quickly.

When the treadle valve is released, pressure from the front chambers exhausts through the quick release valve rather than through the treadle valve. Air in the line between the quick release valve and the treadle valve exhausts through the treadle valve.

8

Figure 8 — Releasing the Service Brakes

Page 14

DESCRIPTION AND OPERATION AIR SYSTEM SAFETY FEATURES A series of check valves, control valves and other features provide a measure of safety if the air system should fail.

Low-Pressure Warning If air pressure in either circuit drops below 70 psi, a low air pressure warning lamp and an audible buzzer activate to alert the driver of an air system malfunction.

Single Check Valves Check valves prevent a total loss of air pressure if an air line ruptures or a similar malfunction occurs. A check valve allows air to flow in one direction, but closes if the flow of air should reverse. If a malfunction resulting in a loss of air pressure occurs anywhere between the air compressor and the primary and secondary air reservoirs, the higher pressure in the reservoirs forces the check valve to close and allows the system to retain air pressure.

10

9

Figure 9 — Pressure Gauge Indicating Low Pressure

Stop the vehicle and immediately service if pressure in either air system drops below 70 psi. Pressure lower than 70 psi can result in reduced braking performance and may lead to vehicle or property damage.

Figure 10 — Check Valves Prevent Total Air Pressure Loss

Page 15

DESCRIPTION AND OPERATION Double Check Valves A double check valve provides dual air function by isolating the primary and secondary air systems while directing pressure into a common line between the two reservoirs. With both systems functioning normally, pressure from whichever reservoir is at the higher pressure is fed into the common line and supplied to the spring brake chambers to keep the spring brakes released.

If primary system pressure drops below secondary system pressure, the double check valve shuttle shifts position and allows secondary system pressure to be fed to the spring brake chambers. If the primary system experiences a total loss of pressure, secondary system pressure keeps the spring brakes released. Double check valves are designed so that the outlet port is never blocked.

11

Figure 11 — Dual Air Circuit, Primary System Air Loss

Page 16

DESCRIPTION AND OPERATION Spring Brake Modulating Relay Valve A method of providing modulated control of the spring brakes through the treadle valve is standard on straight trucks, and can be optional on tractors. On CV, CT, CXN and CHN model chassis this is accomplished using a spring brake modulating relay valve; whereas on current LE and MR models, a spring brake control valve is used. The spring brake modulating relay valve combines the functions of both the spring brake control valve and the spring brake relay valve.

The spring brake modulating relay valve was implemented into production January 1, 2004 on CV model chassis, and was used on CXN and CHN models from the beginning of production.

With the air system functioning normally, the spring brake modulation valve monitors pressure in both the primary and secondary circuits. When the park brake valve is pushed in to release the parking brakes, the relay valve opens a path for reservoir pressure to the spring brake chambers to keep the spring brakes released.

A loss of primary pressure at the spring brake modulating relay valve results in an unbalanced condition inside the valve. In this condition, a service brake application allows secondary control pressure to enter the valve in proportion to the amount of force applied to the pedal. In response to the applied control pressure, the modulating relay valve allows a proportionate amount of spring brake hold-off pressure to exhaust from the spring brake chambers.

Typically, a 30 psi service brake application will exhaust spring brake hold-off pressure to approximately 60 psi.

In the event of a pressure loss in the primary circuit, the spring brake modulating relay valve allows the spring brakes to be applied by application of the treadle valve rather than having to use the instrument panel-mounted park brake control valve.

Page 17

DESCRIPTION AND OPERATION 12

Figure 12 — Spring Brake Modulating Relay Valve

Page 18

DESCRIPTION AND OPERATION Spring Brake Control Valve (LE and MR Models) On LE and MR models, the spring brake control valve allows a modulated application of the spring brakes through the treadle valve in the event of a primary air system pressure loss. When the system is functioning normally, the spring brake control valve is balanced by pressure from both the primary and secondary circuits. System pressure is supplied through the valve to the spring brake chambers to keep the spring brakes released.

A pressure loss in the primary circuit causes an unbalanced condition at the spring brake control valve. In this condition, applying the brake pedal directs signal pressure in proportion to the

amount of force applied to the pedal from the secondary circuit to the spring brake control valve. In response to the applied signal pressure from the secondary circuit, the control valve proportionately closes the supply line. The drop in supply line pressure causes a proportionate amount of air to exhaust from the delivery line. By exhausting pressure from the delivery line through the spring brake relay valve, a proportionate amount of pressure is exhausted from the spring brake chambers, allowing the spring to gradually expand and apply the brakes.

Releasing the brake pedal removes the signal pressure from the relay valve, and system pressure is again returned to the spring brake chambers to release the brakes.

13

Figure 13 — Spring Brake Control, Primary Circuit Air Loss (MR and LE Models)

Page 19

DESCRIPTION AND OPERATION Redundant Signal Relay Valve On a straight truck, if a leak should develop in the primary signal line between the treadle valve and the rear axle relay valve, the chassis must still be able to meet emergency stopping distance requirements mandated by Federal Motor Vehicle Safety Standards. This is accomplished through the use of the spring brake modulating relay valve. On chassis having the spring brake control valve, this requirement is met through the use of a redundant signal relay valve in the rear axle service brake circuit. This relay valve (R-12DC) incorporates a double check valve in the relay valve control port which allows a redundancy of signals (both primary and secondary), thus allowing the chassis to meet the stopping distance requirements in the event of a primary signal line failure.

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The double check valve is designed so that primary control pressure always activates the valve during a normal brake application. Primary control pressure is supplied from the treadle valve primary delivery port, and secondary pressure is supplied by the front axle brake system (either “tee’d” into the system at the front axle quick release valve or at the control line for the spring brake control valve). If a leak develops in the primary signal line, secondary control pressure delivered to the relay valve activates the rear axle brakes.

DESCRIPTION AND OPERATION 14

Figure 14 — Redundant Signal Relay Valve, Primary Control Pressure Air Loss

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DESCRIPTION AND OPERATION Anti-Compounding Circuits

Anti-Compounding, Spring Brakes Applied

To prevent compounding the force against the rear brake assemblies when the service brakes are inadvertently applied while the parking brakes are set, pressure is directed from the treadle valve into the spring brake circuits. Most tractors accomplish this with a double check valve, while trucks use a spring brake relay valve with an anti-compounding function.

When the spring brakes are applied, air is exhausted from the spring brake chambers allowing the compression springs to expand and set the brakes. If the treadle valve is applied, air pressure is directed to the service section of the brake chamber, and to the anti-compounding double check valve. The parking brake circuit is not delivering pressure to the double check valve.

TRACTOR ANTI-COMPOUNDING CIRCUIT

Brake application pressure, therefore, enters the double check valve and forces the valve shuttle to one side, opening a path for pressure to enter the spring brake section of the brake chamber.

Pressure entering the spring brake chamber forces the compression spring to compress and relieve some of the pressure against the brake chamber push rod as application pressure enters the service section of the brake chamber.

In a tractor air system, a double check valve directs pressure into a common line in the spring brake circuit between the park brake valve and the treadle valve.

15

Figure 15 — Tractor Anti-Compounding Circuit (Spring Brakes Applied)

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DESCRIPTION AND OPERATION Anti-Compounding, Spring Brakes Released When the parking brake control valves are pushed in to release the spring brakes, system pressure is directed to the anti-compounding double check valve. This forces the valve shuttle to the opposite side, opening a path for pressure

to enter the spring brake chambers and cage the compression springs. Because system pressure is generally higher than brake application pressure, the double check valve will not respond to pressure applied from the treadle valve when the service brakes are applied.

16

Figure 16 — Tractor Anti-Compounding Circuit (Spring Brakes Released)

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DESCRIPTION AND OPERATION STRAIGHT TRUCK ANTI-COMPOUNDING CIRCUIT (SPRING BRAKE MODULATING RELAY VALVE) 17

Figure 17 — Straight Truck Anti-Compounding Circuit — Spring Brake Modulating Relay Valve

Anti-Compounding — Spring Brake Modulating Relay Valve On straight truck air systems, the spring brake modulating relay valve provides an anti-compounding function. When the park brake valve is pulled out, control pressure at the modulating relay valve is exhausted and the spring brakes are applied. Applying the service brakes directs pressure to the modulating relay valve balance port. Pressure entering the balance port opens the relay valve and allows reservoir pressure to enter the spring brake chamber to relieve tension against the compression spring.

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DESCRIPTION AND OPERATION STRAIGHT TRUCK ANTI-COMPOUNDING CIRCUIT (SPRING BRAKE RELAY VALVE) 18

Figure 18 — Straight Truck Anti-Compounding Circuit — Spring Brake Relay Valve

Anti-Compounding — Spring Brake Relay Valve The spring brake relay valve reacts to control pressure from either the parking brake control valve or the rear service brake circuit. With the park brake valve pulled out, control pressure at the spring brake relay valve is exhausted and the spring brakes are applied. Applying the treadle valve directs brake application pressure to the control port of the spring brake relay valve. This causes the valve to open, allowing reservoir pressure to enter the spring brake chambers and relieve some of the tension against the compression spring.

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DESCRIPTION AND OPERATION Tractor Protection Valve On tractor and trailer combinations, a tractor protection valve is used to prevent an air loss in the tractor air system should an air loss occur in the trailer air system. In the event of a trailer

breakaway, or similar malfunction, the tractor protection valve immediately seals off the trailer air system. This allows the tractor air system to retain pressure so that the vehicle can be stopped.

19

Figure 19 — Tractor Protection Valve Circuit

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DESCRIPTION AND OPERATION AIR SYSTEM COMPONENTS

Air Reservoir 20

Before servicing the air brake system, the following precautions must be taken to prevent personal injury:

앫

Block the wheels to prevent the vehicle from rolling.

앫

Spring brakes must be mechanically caged, or they will automatically apply when air pressure drops to 40 psi.

앫

Drain air pressure completely before performing any maintenance on the air system. DO NOT disconnect any hoses, lines, fittings, etc., unless all pressure has been exhausted from the system.

앫 앫

Follow the manufacturer’s recommended procedures when working on components having internal springs.

After performing any brake system service, always check brake system operation before putting the vehicle back into operation.

Figure 20 — Typical Reservoir Configuration

DESCRIPTION Compressed air is stored in the air reservoirs, which are nothing more than storage tanks.

However, they perform the additional function of cooling the air as it is delivered by the compressor. As the air cools, water vapor that may be present, is condensed into a liquid and trapped in the reservoir. Oil that may be passed by the air compressor while in operation, is also trapped and held in the reservoir until it can be drained.

Single- or double-compartment reservoirs may be used. Double-compartment reservoirs have an integral check valve between compartments to allow the free passage of air from one compartment to the next, but block the flow if a rupture should occur downstream from the second compartment.

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DESCRIPTION AND OPERATION 21

Figure 21 — CH/CL Reservoir Piping with Primary Extension Reservoir

The integral check valve may either be mounted externally on the outside diameter surface of the reservoir, or inside the reservoir compartment on the inner compartment wall. On earlier production reservoirs, access to the internally mounted check valve is through the reservoir end port. The port is labeled “CHECK VALVE ACCESS.”

The internal check valve on current production air reservoirs is not serviceable. If the reservoir end port is not labeled “CHECK VALVE ACCESS,” the internal check valve cannot be replaced.

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For reservoirs having the replaceable internal check valve, a 1/2-inch, 6-point, thin-wall, deep-well 3/8-inch drive socket and a long 3/8-inch drive extension are required to remove the check valve. To remove the check valve, drain the reservoir and remove the fitting or plug from the end port. Insert the socket and extension into the reservoir, over the hex head of the check valve, and then unscrew the valve. Carefully withdraw the socket, extension and check valve from the reservoir. Reinstallation is the reverse procedure of removal.

DESCRIPTION AND OPERATION OPERATIONAL AND LEAKAGE TESTS

22

Testing the Integral Check Valve in a Double-Compartment Reservoir 1. Determine the direction of airflow through the reservoir (airflow from the compressor, through the first compartment to the second compartment).

2. Start the engine and allow the air system to build pressure until it reaches governor cutout.

3. Stop the engine.

4. Completely drain the first compartment.

5. Determine if the second reservoir compartment is retaining air pressure by: 앫

Checking the dash gauge and noting if the secondary air system is retaining pressure

OR 앫

Momentarily opening the drain valve of the second chamber and noting if any air is expelled.

DO NOT allow the second compartment to completely drain.

6. Apply a soap-and-water solution to the open drain ferrule of the first compartment. Slight bubble leakage is permitted.

Figure 22 — Integral Check Valves

A lanyard drain valve must be held opened.

If it is evident that the second compartment of the double air reservoir is leaking, or if excessive leakage at the open drain ferrule of the first compartment is indicated, the integral check valve is suspect. Inspect and replace as necessary.

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DESCRIPTION AND OPERATION PREVENTIVE MAINTENANCE Moisture and contaminants should be drained from the air reservoirs daily. When draining moisture and contaminants, open the drain valve slowly to prevent the formation of an air channel which would empty only air from the reservoirs and prevent any moisture and contaminants from being expelled. DO NOT completely drain the reservoirs on a daily basis. Reservoirs should only be completely drained once per month.

Automatic Drain Valve 24

Drain Valves 23

Figure 24 — Automatic Drain Valve

DESCRIPTION

Figure 23 — Reservoir Drain Valve

DESCRIPTION Reservoir drain valves provide a means of manually draining moisture and other contaminants from the reservoirs.

When the reservoir drain valve is opened, air should drain proportionately to the amount that the valve is opened.

LEAKAGE TESTS With the reservoirs fully pressurized and the drain valves closed, coat the drain valves with a soap-and-water solution and check for leakage.

No leakage is allowed.

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This reservoir drain valve automatically expels moisture and other contaminants from the reservoir into which it is installed. To provide flexibility for different mounting arrangements, automatic drain valves contain two reservoir inlet ports. When mounted on the bottom of the reservoir, the top port of the drain valve is used.

The side port is used if the valve is mounted in the end of an end drain reservoir.

DESCRIPTION AND OPERATION When there is no pressure in the air system, the inlet and exhaust valves are closed. Slight pressure build-up opens the inlet valve and allows moisture and other contaminants to collect in the sump cavity. The inlet valve remains open until maximum system pressure is reached, at which point, spring tension of the valve guide assembly closes the inlet valve. Both the inlet and exhaust valves are then closed.

25

27

Figure 27 — Inlet Valve Opened

Figure 25 — Automatic Drain Valve Cutaway

To operate, the valve needs no outside control or manual assistance. The die-cast aluminum valve body contains a sump cavity (to collect moisture and other contaminants) and an inlet/exhaust valve assembly.

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Figure 26 — Inlet/Exhaust Valve Closed

Page 31

DESCRIPTION AND OPERATION A slight pressure drop (approximately 2 psi) in the reservoir allows the pressure in the sump cavity to open the exhaust valve and drain moisture and other contaminants through the exhaust port.

With the air system charged and pressure stabilized, there should be no leakage through the automatic drain valve exhaust port.

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A constant, slight exhaust of air through the automatic drain valve may, however, be caused by excessive leakage elsewhere in the system and not the result of a faulty drain valve.

PREVENTIVE MAINTENANCE 앫

B, C, D Inspections — Check for proper operation and excessive leakage. Replace if necessary.

Air Compressor 29

Figure 28 — Exhaust Valve Opened, Moisture Expelled

The exhaust valve remains open until the pressure in the sump cavity drops enough to allow the valve to close. The length of time that the exhaust valve remains open and the amount of moisture and contaminants expelled from the system depends upon the pressure in the sump cavity and the drop in reservoir pressure that occurs each time the air system is used.

Figure 29 — Typical Air Compressor

OPERATIONAL TESTS With the air system fully pressurized, make several brake pedal applications. Make sure that an exhaust of air occurs at the automatic drain valve exhaust port each time the brake pedal is applied. If no air is exhausted, push the wire stem located inside the exhaust port. If air still does not exhaust, there may be a plugged filter in the adaptor. Remove and discard the filter.

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DESCRIPTION AND OPERATION DESCRIPTION

30

The air compressor generates the compressed air needed for the air system to operate.

Compressors used on MACK chassis may either be one- or two-cylinder, single-stage types and are driven by the engine. Water for cooling and oil for lubrication are both provided by the cooling and lubricating systems of the engine.

The compressor is continuously operating (as long as the engine is running) and compresses air by the reciprocating action of the piston in the cylinder. On the piston downstroke, air is drawn into the cylinder through the compressor inlet valve. As the piston begins its upward stroke, the increased air pressure inside the cylinder forces the inlet valve to close. As the upward stroke continues, air pressure forces the discharge valve open. The compressed air flows past the discharge valve into the discharge line and into the supply reservoir. At the end of the piston stroke, the discharge valve closes (by spring pressure and the higher pressure in the discharge line) to prevent the flow of compressed air back into the cylinder.

Air compression stops when reservoir pressure is directed to the air compressor unloader mechanism by the governor. Pressure entering the unloader cavity moves the unloader pistons down to hold the inlet valves open. With the inlet valves open, air is pumped back and forth between the two cylinders and the discharge valves remain closed. As air system pressure drops, compression resumes when the governor closes and allows the pressure in the unloader cavity to exhaust. When the air in the unloader cavity exhausts, the unloader pistons move up, and the inlet valves close.

Figure 30 — Compressor Cutaway

On the Holset QE single-cylinder air compressor, the unloader mechanism has a different design than those used on conventional-style air compressors. The unloader mechanism on the Holset compressor is pressurized with air system pressure, typically 95–125 psi. This pressure holds both the inlet and exhaust valves closed during unloaded operation. The trapped air pressure inside the cylinder bore creates an air spring effect as the piston reaches the top of its travel, and provides a downward force against the piston as direction of travel changes.

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DESCRIPTION AND OPERATION OPERATIONAL TESTS For vehicles operating under FMVSS 121, the air compressor must be capable of building air pressure from 85 to 100 psi in 25 seconds or less with the engine running at full governed speed.

To test the operation of the air compressor, totally drain all pressurized air from the system. With the engine running at full governed speed, observe the time it takes for pressure to build from 50–90 psi. After the air pressure has reached at least 100 psi, rapidly cycle the treadle valve to decrease pressure below 85 psi. Observe the time it takes for the pressure to build back up from 85–100 psi. Time should not exceed 25 seconds.

Governor 31

Time may exceed 25 seconds if the chassis is equipped with increased air reservoir capacity.

LEAKAGE TESTS Testing and service procedures vary between different compressor manufacturers. If the compressor is not functioning properly or excessive leakage is detected, refer to the appropriate manufacturer service literature for service and repair procedures.

PREVENTIVE MAINTENANCE 앫

B, C, D Inspections — Check that the compressor is securely mounted.

MACK chassis may be equipped with a Bendix, Holset, ArvinMeritor™ WABCO or other air compressor. For maintenance, service or repair information of a particular compressor, refer to the specific manufacturer service literature.

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Figure 31 — Remote-Mounted Air Governor

DESCRIPTION Although the compressor is continuously running as long as the engine is operating, actual air compression is controlled by the governor. The governor works in conjunction with the compressor unloader mechanism to maintain pressure between a specific minimum and maximum setting.

The governor consists of a piston, an inlet and exhaust valve assembly and a pressure setting spring. Air pressure from the supply reservoir enters the governor through the reservoir port. As reservoir pressure builds, pressure entering the governor overcomes the force of the pressure-setting spring and moves the piston and valve assembly up. As reservoir pressure reaches the cutout setting (130–135 psi), the upward movement of the piston assembly seats the exhaust stem against the inlet/outlet valve assembly, seals the exhaust passage and opens the inlet passage. Air pressure entering the governor through the reservoir passage then flows past the inlet valve, through the air passage in the piston and out through the unloader port to the compressor unloader mechanism. When the unloader mechanism is activated, air compression stops.

DESCRIPTION AND OPERATION OPERATIONAL TESTS

32

Start the engine and allow the air system to build pressure. Observe that the governor cuts out when air pressure reaches between 130–135 psi.

Make a series of brake applications to reduce air system pressure, and observe that the governor cuts in when pressure falls between 105–110 psi.

LEAKAGE TESTS The governor should be tested for leakage in both cut-in and cutout operations. 앫

With the governor in cut-in operation, apply a soap-and-water solution to the exhaust port of the governor. Slight bubble leakage is acceptable, but excessive leakage is not. If leakage is excessive in the cut-in position, a faulty inlet valve or lower piston O-ring is indicated.

앫

With the governor in cutout operation, apply a soap-and-water solution to the exhaust port. Again, slight bubble leakage is permissible, but excessive leakage is not.

Excessive leakage in the cutout position indicates a faulty exhaust valve seat, exhaust stem, exhaust stem O-ring, or upper piston O-ring.

Figure 32 — Air Governor Cutaway

As reservoir pressure drops toward the governor cut-in setting (100–105 psi), the force of the pressure-setting spring overcomes the force of the air entering the governor and pushes the piston and valve assembly down. The downward movement of the piston seals the passage to the unloader port and allows the air pressure in the unloader line to exhaust through the exhaust port.

The pressure drop in the unloader line deactivates the unloader mechanism, and air compression resumes.

PREVENTIVE MAINTENANCE 앫

A, B, C, D Inspections — Check governor cut-in/cut-out operation, and test for leaks.

Replace if necessary.

For chassis built prior to March 15, 1995, governor cutout is set at 120 ± 5 psi and governor cut-in is set at 100 + 5 psi.

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DESCRIPTION AND OPERATION Low-Pressure Indicator Switch

34

33

Figure 33 — Low-Pressure Indicator Switch

DESCRIPTION The low-pressure indicator is a pressure-sensing device used to monitor air system pressure.

Figure 34 — Low-Pressure Switch Cutaway

Operating as an air-actuated electrical switch, the low-pressure indicator functions when air pressure, applied to the supply port, pushes against the diaphragm, piston and spring assembly to hold the electrical contacts apart.

When pressure entering the supply port drops below 70 ± 5 psi, spring tension overcomes the drop in pressure and forces the diaphragm and piston to move, causing the electrical contacts to close. The closed contacts complete the electrical circuit to activate the low air warning lamp and buzzer.

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DESCRIPTION AND OPERATION OPERATIONAL TESTS With the ignition switch on, reduce air system pressure and observe that the low air warning lamp and buzzer activate when the air system gauge indicates a minimum 65 psi. 앫

If the warning buzzer does not activate, test both terminals of the low-pressure indicator with a volt/ohm meter to determine if voltage is present. As an alternate method, bypass the switch by installing a jumper across the terminals. If the low-pressure warning activates when the jumper is installed, or the volt/ohm meter indicates voltage is present, the low-pressure indicator is defective and must be replaced.

앫

If the low-pressure warning fails to activate when the jumper is installed, or the volt/ohm meter indicates there is no voltage, a problem with the electrical circuit is indicated which must be located and corrected.

Single Check Valves 35

Figure 35 — Ball Type 36

LEAKAGE TESTS With the air system pressurized, apply a soap-and-water solution to the low-pressure indicator connection and observe. NO bubble leakage is permissible.

PREVENTIVE MAINTENANCE 앫

B, C, D Inspections — Check the electrical connections at the low-pressure indicator.

Determine that the indicator is functioning properly by performing the operational checks as described above. Replace as necessary.

Figure 36 — Disc Type 37

Figure 37 — Disc Type with Replaceable Seat

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DESCRIPTION AND OPERATION DESCRIPTION

39

A single check valve allows airflow in one direction, and blocks the path if airflow reverses.

A check valve consists of a seal assembly and spring. Spring tension holds the seal on its seat.

Air pressure applied to the inlet side of the valve overcomes the spring tension and lifts the seal assembly off its seat, allowing the free passage of air from the inlet port through the outlet port.

When pressure on the inlet side is removed, spring tension pushes the seal back onto its seat, sealing the air path and preventing the passage of air from the outlet port through the inlet port.

OPERATIONAL AND LEAKAGE TESTS

Figure 39 — Shuttle Type

DESCRIPTION It may be easier, or necessary, to completely remove the check valves in order to perform the following checks.

Connect an air supply to the outlet side of the check valve, and leave the inlet side open to atmosphere. Apply air pressure, and coat the inlet side of the valve with a soap-and-water solution. A one-inch bubble in five seconds is allowable.

Double check valves (also called shuttle valves), are used to direct airflow into one common line from either of two sources. The double check valve contains two inlet ports and one outlet port.

Inside the valve is a movable shuttle. Air pressure entering either one of the two inlet ports pushes the shuttle against the opposite port to seal the air passage, allowing the free flow of air through the outlet port. The valve shuttle always reacts to the higher pressure. Double check valves are designed so that it is impossible for the shuttle to block the outlet port.

PREVENTIVE MAINTENANCE 앫

C, D Inspections — Check for proper operation and excessive leakage. Replace as necessary.

Double Check Valves 38

OPERATIONAL TESTS

Double check valves are best checked and leak tested by removing the valve from the vehicle and bench testing using two separately controlled air supplies.

1. Install an accurately calibrated pressure gauge in the outlet port.

2. Apply and release air pressure to one of the inlet ports and note that the air pressure gauge installed in the outlet line registers application and release.

3. Repeat the above procedure for the opposite inlet port.

Figure 38 — Disc Type

Page 38

DESCRIPTION AND OPERATION LEAKAGE TESTS

41

1. Disconnect the inlet line from one inlet port.

2. Apply a soap-and-water solution to the disconnected inlet port while applying air pressure to the other inlet port. Leakage should not exceed a one-inch bubble in five seconds.

3. Repeat the above test for the opposite inlet port.

If the double check valve fails either of the above tests, replace it with a new valve.

PREVENTIVE MAINTENANCE 앫

C, D Inspections — Check for proper operation and test for excessive leakage.

Replace as necessary.

Pressure Protection Valve 40

Figure 41 — Pressure Protection Valve Cutaway

The valve consists of a piston and spring assembly contained inside the valve body. When supply pressure is below 65 psi, spring tension holds the piston assembly on its seat to restrict the free flow of air through the valve. As pressure increases, spring tension is overcome, allowing the piston assembly to move off its seat and permit the flow of air to the auxiliary system.

Figure 40 — Pressure Protection Valve

DESCRIPTION The pressure protection valve is designed to prevent the supply of pressure to an air-operated device or system, while the air supply is below a specified rating. These valves are generally used when air-operated auxiliary attachments are installed on the chassis to prevent a total loss of pressure should a leak in any part of the auxiliary system occur.

If air pressure falls to approximately 20 psi below the opening pressure of the valve, spring tension forces the piston back onto its seat to seal the air supply and protect the system against further pressure loss through continued use of the auxiliary system.

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DESCRIPTION AND OPERATION OPERATIONAL TESTS

PREVENTIVE MAINTENANCE

1. Drain the main air supply.

앫

2. Disconnect the outlet side of the valve and install a tee fitting, a shut-off valve and an accurately calibrated pressure gauge.

3. Start the engine and allow system pressure to build.

B, C, D Inspections — Check for proper operation and test for excessive leakage.

Replace as necessary.

Stoplight Switch 42

4. Observe the pressure gauge on the instrument panel, and the gauge installed in the outlet port of the pressure protection valve.

5. No pressure should register on the gauge installed in the outlet port until the gauge on the dashboard reaches between 75–95 psi.

At that time, the pressure protection valve should open, and both the test gauge and the dashboard gauge should indicate the same pressure.

6. Stop the engine and open the shut-off valve.

Air should exhaust through the valve until the pressure gauge inside the cab reaches approximately 65 psi, at which point the valve should close and no more air should exhaust.

After completing the above operational check, drain the main air reservoir, remove the test gauge and shut-off valve, and reconnect the valve to the auxiliary system.

LEAKAGE TESTS 1. With the valve properly connected, start the engine and build full system pressure.

2. Apply a soap-and-water solution to the cap of the pressure protection valve and observe. A one-inch bubble in three seconds is allowable.

3. Drain the air pressure from the system on the outlet side of the pressure protection valve.

4. Disconnect the line from the outlet side of the pressure protection valve and apply a soap-and-water solution to the outlet port. A one-inch bubble in five seconds is acceptable.

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Figure 42 — Typical Stoplight Switch

DESCRIPTION The stoplight switch is an air-actuated electrical switch that works in conjunction with the treadle valve and the hand-control valve (if so equipped) to illuminate the stop lamps when the brakes are applied. The switch operates when an application pressure of at least 6 psi acts against the diaphragm inside the switch to complete the electrical circuit and illuminate the stop lamps.

DESCRIPTION AND OPERATION 2. Slowly depress the treadle valve and note the pressure gauge reading at which the stop lamps illuminate. The gauge should read 6 psi.

43

3. Release the treadle valve and note that the stop lamps turn off.

4. Repeat the above tests for the secondary system, and for any other stoplight switch that may be installed in the air system.

The above tests verify the operation and the electrical function of the stoplight switches. If the stop lamps fail to function during the above tests, the following electrical checks are necessary.

ELECTRICAL CHECKS 앫

If the stop lamps do not illuminate, test both terminals of the stoplight switch with a volt/ ohm meter to determine if voltage is present.

As an alternate method, bypass the switch by installing a jumper across the terminals. If the stop lamps illuminate when the jumper is installed, or the volt/ohm meter indicates voltage is present, the stoplight switch has malfunctioned and must be replaced.

앫

If the stop lamps fail to illuminate when the jumper is installed, or the volt/ohm meter indicates there is no voltage present, a problem with the electrical circuit is indicated and must be located and corrected.

Figure 43 — Stoplight Switch Cutaway

OPERATIONAL TESTS

In order to illuminate the stop lamps, even if one system experiences a pressure loss, the stoplight switches must be actuated by both the primary and secondary air systems. Chassis have either a switch in each air system, or a single switch and a double check valve. Additionally, some tractors have a stoplight switch installed at the trailer brake hand control valve so that the stop lamps illuminate when the valve is used to actuate the trailer brakes. When checking operation of the stoplight switches, they should be checked independently by disconnecting the electrical connections and checking one switch at a time to be sure each switch is functioning.

1. Install an accurately calibrated pressure gauge in the primary system service line near the stoplight switch.

The function of certain air system switches, such as the stop lamp switches, can be checked using the switch status function in the V-MAC Service Support Software. Refer to the applicable V-MAC User Guide for information.

LEAKAGE TESTS With the brakes applied, coat the stoplight switches with a soap-and-water solution. No leakage is acceptable.

PREVENTIVE MAINTENANCE 앫

B, C, D Inspections — Check the electrical connections at each stoplight switch. Check the operation of each switch, and test for excessive leakage. Replace as necessary.

Page 41

DESCRIPTION AND OPERATION Treadle Valve

44

DESCRIPTION The treadle valve provides the driver with a means of graduated control of the air system for applying and releasing the service brakes. The valve is divided into two separate sections. The upper portion operates the primary brake circuit and the lower portion operates the secondary brake circuit. The upper portion of the treadle valve contains a graduating spring, spring seat, primary piston and an inlet and exhaust valve assembly. The lower portion of the valve contains a relay piston and an inlet and exhaust valve assembly. Both the upper and lower portions of the valve share a common exhaust port.

Figure 44 — Treadle Valve Cutaway

Page 42

DESCRIPTION AND OPERATION 45

Figure 45 — Typical Treadle Valve Piping Diagram

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DESCRIPTION AND OPERATION On CH, CL, CX and CV models, the treadle valve is mounted on the firewall. On all other models, it is mounted to the floor.

OPERATION Application 48

46

Figure 46 — CH, CL, CX and CV Models

Figure 48 — Application

47

Depressing the brake pedal exerts a force on the spring seat and graduating spring. With applied force, both the primary piston and the relay piston are moved down. Downward movement of the two pistons closes both the primary circuit and secondary circuit exhaust valves. As the primary exhaust valve closes, the primary inlet valve opens and allows pressure to flow through the primary delivery port to the rear axle brake chambers. The rear service brakes apply.

Figure 47 — Other Models

Page 44

With the primary inlet valve opened, air passes through the bleed passage between the upper and lower valve bodies, enters the relay cavity and exerts a force on the relay piston. The relay piston then moves further to open the secondary inlet valve, allowing air pressure to flow through the secondary delivery port to apply the front service brakes.

DESCRIPTION AND OPERATION Balanced

Released

49

50

Figure 49 — Balanced

Figure 50 — Released

As pressure being delivered through the treadle valve begins to equal the force applied to the brake pedal, the primary piston moves up and closes the primary inlet valve, preventing further passage of air through the delivery port. The relay piston also moves up to seal the secondary inlet valve and prevent airflow through the secondary delivery port. Both the primary and the secondary exhaust valves remain closed to prevent the escape of air through the exhaust port. The treadle valve in this position is balanced, and pressure being delivered to the service brake chambers is neither increased nor decreased.

Removing the force from the brake pedal removes the force applied to the spring seat and the graduating spring. Air pressure on the delivery sides of both the primary and relay pistons pushes the pistons upward to open both exhaust valves, allowing air to exhaust through the exhaust port.

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DESCRIPTION AND OPERATION OPERATIONAL TESTS 1. Using accurately calibrated pressure gauges installed in both brake circuits, check the delivery pressure in both systems. Make several brake applications between the fully released and fully applied positions, and note that the readings indicated on the test gauges vary proportionately with the movement of the brake pedal. With both the primary and secondary reservoirs at the same pressure, the test gauge reading on the primary circuit will be approximately 2–4 psi greater than the reading on the gauge for the secondary circuit.

2. After releasing a full application, the reading on the test gauges should promptly fall to zero.

LEAKAGE TESTS 앫

Make and hold a high pressure brake application. Coat the exhaust port and the brake valve body with a soap-and-water solution. A one-inch bubble in three seconds is permitted.

If the treadle valve fails any of the checks as described above, it must be removed and repaired or replaced.

앫

B, C, D Inspections — Check the rubber plunger boot for cracks, holes or deterioration. Replace if required. Check that the treadle valve is securely mounted and structurally sound. Pedal free travel should be checked to be sure the plunger is in contact with the spring seat. The stop button should be adjusted, if necessary, so that the roller just contacts the plunger.

앫

B, C, D Inspections — Inspect the treadle valve pin and plunger for wear and freedom of movement.

앫

B, C, D Inspections — Inspect the treadle valve mounting bracket for damage, cracks or wear. Replace as necessary.

BRAKE PEDAL MOUNTING On CH, CL and CX model chassis, check the brake pedal mounting support, making sure the mounting bracket is structurally sound and there is no damage, wear or cracks. Replace as necessary.

Park Brake Control Module 51

PREVENTIVE MAINTENANCE 앫

A Inspection — Clean any debris from around the treadle valve.

앫

B, C, D Inspections — Using engine oil, lubricate the treadle roller, roller pin and hinge pin.

On CV, CX, CH and CL model chassis, lift the rubber boot and lubricate the treadle valve plunger with MG-C grease.

Page 46

Figure 51 — Parking Brake Control Valve Module

DESCRIPTION AND OPERATION DESCRIPTION On CH, CL, CX and CV model tractors or trucks with a full trailer connection, the parking brake control and trailer supply valves are housed in a single module and mounted in the center console of the dashboard. The module consists of a two-button push/pull-type control valve, and includes a dual-circuit supply valve and a check valve. The red octagon-shaped knob controls the trailer air supply, and the yellow diamond-shaped knob controls the tractor and trailer spring brakes.

With no air in the system, both the trailer air supply knob and the parking brake knob will be out. The tractor and trailer spring brakes will be applied.

53

52

Figure 53 — System Parked Figure 52 — Valve Porting

Page 47

DESCRIPTION AND OPERATION During initial charge, when system pressure has reached 70 psi, the red trailer-supply knob may be pushed in to supply the trailer air system and release the trailer spring brakes.

When the yellow parking-brake knob is pushed in, air is supplied to the tractor spring brakes.

55

54

Figure 55 — Normal Run Mode Figure 54 — Trailer Air System Pressurized

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DESCRIPTION AND OPERATION In the normal run mode when both the knobs are pushed in, both the tractor and the trailer spring brakes may be applied by pulling the yellow knob out. When the yellow knob is pulled out, air exhausts from the tractor spring brakes and simultaneously causes the red trailer-supply button to pop out and apply the trailer spring brakes. When both knobs are pulled out, the red knob can be pushed in to supply the trailer air system, but the tractor spring brakes remain applied (tractor park only).

Pulling the red trailer-supply knob out exhausts the air from the trailer supply line and applies the trailer spring brakes. This mode would be used to uncouple a trailer or for bobtail operations.

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56

Figure 57 — Trailer Parking Brakes Applied

Figure 56 — Tractor Parking Brakes Applied

If supply pressure applied to the valve module is reduced to approximately 35–45 psi, the red trailer-supply knob automatically pops out and applies the trailer spring brakes. If the knob is held in, a tripper piston moves when the pressure decreases to 25–35 psi and exhausts the trailer air supply. The yellow parking-brake knob automatically pops out when air pressure decreases to approximately 20–30 psi.

The dual-circuit supply valve automatically selects the primary reservoir as the main air source for the valve module. If the pressure in the primary reservoir should drop more than 25 psi below that of the secondary air reservoir, the dual-circuit supply valve shuttle moves and establishes the secondary air reservoir as the air source.

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DESCRIPTION AND OPERATION OPERATIONAL AND LEAKAGE TESTS 1. Block the wheels to prevent the vehicle from moving.

2. Pressurize the air system to 130 psi.

3. Apply a soap-and-water solution to the area between the valve body and the cover plate and exhaust port. No leakage at the valve body is acceptable, and leakage at the exhaust port must not exceed a one-inch bubble in five seconds.

4. With system pressure maintained at 130 psi, push the red trailer air-supply knob in. The knob must stay pushed in.

5. With the knob pushed in, apply a soap-and-water solution to the control module exhaust port. Leakage still must not exceed a one-inch bubble in five seconds.

6. With both the red trailer air-supply knob and the yellow parking-brake knob pushed in, slowly reduce the pressure in both reservoirs. The red button must pop out when the supply pressure drops between 35–45 psi.

The yellow parking-brake knob must not pop out before the red button.

7. Hold the red knob in and continue reducing the pressure in the reservoirs. Air must exhaust from the exhaust port of the valve module when trailer supply pressure reaches between 20 and 35 psi.

8. Release the red knob and allow the air system pressure to build to 130 psi. Push the yellow parking-brake knob in and check for leakage at the exhaust port. The knob should remain pushed in, and leakage at the exhaust port should not exceed a one-inch bubble in five seconds.

9. With the trailer supply knob pulled out and the yellow parking-brake knob pushed in, slowly reduce air system pressure. The yellow knob must pop out when pressure is reduced to 20–30 psi.

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10. Rebuild system pressure to 130 psi. Push both the red and yellow knobs in. Pull the red knob out. The yellow knob must remain pushed in.

11. Push the red knob in and pull the yellow knob out. The red knob should pop out instantaneously.

12. With the spring brakes applied (no air in the spring brake delivery line), install a pressure gauge in a spring brake chamber supply line.

13. Pressurize the air system to 130 psi.

14. Push the yellow parking-brake knob in.

Tractor spring brake delivery pressure should equal the primary reservoir pressure.

15. Reduce pressure in the primary reservoir and observe the test gauge. Both the reservoir pressure and the tractor spring brake supply pressure should drop at the same rate until reaching between 105–95 psi. At that point, the dual-circuit supply valve shuttle should switch and establish the secondary reservoir as the air source. Observe that the test gauge monitoring the tractor spring-brake delivery pressure increases to indicate the same pressure as the secondary reservoir.

16. Continue reducing primary air pressure until there is no air remaining in the reservoir.

There should be no audible leakage coming from the primary reservoir drain.

17. Close the drain.

18. Drain the pressure remaining in the secondary air system.

19. Remove the pressure gauge and tee fitting from the spring brake chamber and reconnect the delivery line.

If the valve module fails to operate as described above, or exhibits excessive leakage, the assembly must be replaced.

DESCRIPTION AND OPERATION Single Park Brake Control Valve with Double Check Valve When removing the park brake control module from a CXN, CHN, CX, CH, CT, CV and CL model chassis, removal of the push-to-connect hoses can be made easier by using fitting release tool part No. 1538-54000100.

59

On CX and CH models manufactured prior to August 1, 2001, a 90-degree 1/4″ pipe-to-3/8″ tube fitting was used in the port located in the upper left-hand side of the module. After August 1, 2001, this fitting was changed to a 45-degree fitting. When replacing a park brake control module manufactured prior to August 1, 2001, it is recommended that the original 90-degree fitting be replaced with the 45-degree fitting.

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Figure 59 — Single Park Brake Control Valve

A park brake control valve having a double check valve is used on straight trucks having a single park brake valve except LE and MR models. This type of valve receives supply pressure from both the primary and secondary reservoirs, and functions with whichever reservoir is at the higher pressure.

Figure 58 — Park Brake Control Valve Module Fitting Change 1. 45-Degree 1/4″ Pipe-to-3/8″ Tube Fitting

PREVENTIVE MAINTENANCE 앫

B, C, D Inspections — Check for proper operation and test for excessive leakage.

Replace as necessary.

When the knob is pushed in, pressure is delivered to the spring brake chambers to release the parking brakes, and when the knob is pulled out, pressure is exhausted from the spring brake chambers to apply the parking brakes. If total system pressure drops below 20–30 psi, the knob automatically pops out, exhausting pressure from the spring brake chambers to apply the parking brakes.

With the air system functioning normally, primary and secondary pressure enter the valve through the primary and secondary supply ports. The double check valve diaphragm reacts to the higher pressure and allows air to flow into the valve body. Pushing the knob in to release the parking brakes moves the plunger down, closing the exhaust port and moving the plunger seal past the guide spool. Supply pressure then flows through the passages in the plunger and out the delivery port to the spring brake chambers.

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DESCRIPTION AND OPERATION 60

Figure 60 — Park Brake Valve — Park Brakes Released 1. Knob 2. Plunger 3. Guide Spool 4. Plunger O-Ring 5. Deliver Pressure to Park Brake Circuit

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6. Exhaust Seal 7. Exhaust Port 8. Primary Reservoir Pressure 9. Double Check Valve Diaphragm 10. Secondary Reservoir Pressure

DESCRIPTION AND OPERATION Pulling the knob out to release the parking brakes moves the plunger up, opening the exhaust port and sealing the passages inside the valve. The flow of pressure to the delivery port is blocked, and pressure from the spring brake chambers exhausts through the exhaust port.

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3. With the knob pulled out, coat the exhaust port, the plunger stem and the fitting at the secondary supply port with a soap-and-water solution. Leakage at the exhaust port and plunger stem should not exceed a one-inch bubble in five seconds.

There should be no leakage at the secondary supply port.

4. Again start the engine and allow air system pressure to build to governor cutout, and then stop the engine.

5. Drain enough air from the primary reservoir to ensure that secondary system pressure is higher than the secondary system as noted on the instrument panel air pressure gauge.

6. With the knob pulled out, coat the fitting at the primary reservoir supply port with a soap-and-water solution. There should be no leakage at the primary supply port.

7. Push the knob in, and then coat the plunger stem and exhaust port with a soap-and-water solution. Leakage at both areas should not exceed a one-inch bubble in five seconds.

Operational Tests

Figure 61 — Park Brake Valve — Park Brakes Applied 1. Knob 2. Plunger 3. Guide Spool 4. Plunger O-Ring 5. Pressure Exhausting from Spring Brake Chambers 6. Exhaust

7. Exhaust Seal 8. Exhaust Port 9. Primary Reservoir Pressure 10. Double Check Valve Diaphragm 11. Secondary Reservoir Pressure

OPERATIONAL AND LEAKAGE TESTS Leakage Tests 1. Block the wheels to prevent the vehicle from moving, and then start the engine and allow air system pressure to build to governor cutout. Stop the engine.

2. Drain enough air from the secondary reservoir to ensure that primary system pressure is higher than the secondary system as noted on the instrument panel air pressure gauge.

1. Connect an accurately calibrated pressure gauge to the delivery port.

2. With the knob pulled out, start the engine and allow system pressure to build to governor cutout. Stop the engine.

3. Push the knob in and compare the pressure reading on the gauge connected to the delivery port with the reading on the instrument panel air gauge. Pressure at the delivery port should be equal to supply pressure.

4. Pull the knob out and note the reading indicated on the pressure gauge installed in the delivery port. Pressure should drop to 0 psi.

5. Again start the engine and build system pressure to governor cutout. Stop the engine.

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DESCRIPTION AND OPERATION 6. Drain the secondary reservoir at a rate of approximately 10 psi per second as indicated by the pressure gauge on the instrument panel. Primary system pressure (as indicated by the air pressure gauge on the instrument panel) and delivery pressure indicated by the gauge connected to the delivery port should not drop below 100 psi.

7. Repeat steps 5 and 6 for the primary system.

8. Start the engine and build system pressure to governor cutout. Stop the engine.

9. With the knob pushed in, drain both primary and secondary reservoirs while noting the pressure indicated on the instrument panel air pressure gauge. The knob should automatically pop out when pressure in both systems drops below 20–30 psi.

10. Remove the pressure gauge from the delivery port and reconnect the air line for the park brake circuit.

If the valve fails to function as described above, or if leakage is excessive, the valve must be replaced.

PREVENTIVE MAINTENANCE 앫

B, C, D Inspections — Check for proper operation and test for excessive leakage.

Replace the valve as necessary.

Push/Pull-Type Park Brake Control Valves 62

Figure 62 — Parking Brake Control Valves

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DESCRIPTION Parking brake valves are manually operated push/pull-type valves. The brake valve with the yellow diamond shaped knob serves as the system park brake valve to apply and release the truck, tractor and trailer parking brakes. On a three park brake valve system (tractor or truck with a full trailer connection), the valve with the round blue knob applies the truck/tractor parking brakes only, independent of the trailer parking brakes.

The valves are two-position on/off valves that operate when pushed in. When the knob is pushed in, air pressure is directed to the spring brake chambers to release the brakes. The valves also contain an exhaust function. If supply pressure should drop to 40 psi, the control valve pops out to exhaust the spring brake supply lines and apply the spring brakes.

The parking brake control valve used on the LE series chassis contains an auxiliary piston in the lower cover that moves the valve from a full system application pressure to the exhaust position when receiving a control pressure of 18 psi or more.

DESCRIPTION AND OPERATION 63

Figure 63 — Typical Three Control Valve System Piping

OPERATIONAL AND LEAKAGE TESTS 1. Block the wheels to prevent the vehicle from moving.

2. Start the engine and build system pressure to governor cutout.

3. Stop the engine.

4. With the parking brake valve pulled out, coat the exhaust port with a soap-and-water solution. Leakage should not exceed a one-inch bubble in five seconds.

5. With a system pressure of 130 psi and the knob still pulled out, coat the area around the plunger stem and the valve body.

Leakage at the plunger stem should not exceed a one-inch bubble in five seconds, and there should be no leakage between the upper and lower valve bodies.

6. Push the knob in and check again for leakage at the exhaust port and the plunger.

Leakage in both areas should not exceed a one-inch bubble in three seconds.

7. With the parking brake valve still pushed in, reduce system pressure. The button should automatically pop out when pressure reaches between 60–20 psi (depending on the pressure rating of the valve), and air pressure from the spring brake supply lines should exhaust through the exhaust port.

PREVENTIVE MAINTENANCE 앫

B, C, D Inspections — Check for proper operation, and test for excessive leakage.

Replace as necessary.

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DESCRIPTION AND OPERATION Trailer Air Supply Valve

DESCRIPTION The trailer air supply valve is a push/pull-type valve that is mounted inside the cab and operates in conjunction with the parking brake control valve and the tractor protection valve. The valve, which has a red octagonal shaped knob, supplies air pressure to the trailer air system and, in conjunction with the tractor protection valve, protects the tractor air system in the event of a trailer breakaway or a trailer air system leak.

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65

Figure 64 — Trailer Supply Valve

Figure 65 — Typical Trailer Air Supply Valve Piping

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DESCRIPTION AND OPERATION The trailer air supply valve is actually a combination of two on/off control valves contained in a single valve body. The valve contains a manually operated plunger with an inlet and exhaust valve assembly, and a control valve assembly containing a control piston and a control inlet and exhaust valve assembly. The control piston operates when pressure is received from the parking brake control valve. Air system pressure is received at the supply port, and pressure is delivered to the trailer air system through the delivery port. Control pressure from the parking brake control valve, to signal whether the spring brakes are applied or released, is received through the control port.

The valve operates when the button is pushed in and the plunger moves down. When the plunger moves down, the inlet valve opens and the exhaust valve is sealed. The button will not stay pushed in unless there is approximately 40 psi in the air system.

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66

Figure 67 — System Park

With the air system charged to 40 psi or more and the parking brake control valve pulled out (spring brakes applied), the trailer air supply button may be pushed in, but air pressure will not be delivered to the tractor protection valve, and the trailer spring brakes will remain applied.

Figure 66 — Trailer Supply Valve Cutaway

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DESCRIPTION AND OPERATION When the parking brake control valve is pushed in to release the spring brakes, control pressure is applied to the trailer air supply valve which moves the control piston and opens the control inlet valve. When the control inlet valve is opened, air flows through the delivery port to supply the trailer air system.

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68

Figure 69 — Emergency

Figure 68 — Trailer Air System Charged

When the trailer air supply button is pulled out, the plunger is moved up to close the inlet valve and unseat the exhaust valve. Air that was present at the delivery port will then exhaust through the exhaust vent located in the mid-section of the valve. Applying the parking brakes prior to deactivating the trailer air supply valve, removes the control pressure, which then causes the control piston to move and unseat the control exhaust valve. Delivery pressure will then exhaust through the exhaust port.

In the event of a trailer breakaway, a sudden trailer air line failure, or a slow leak in the trailer air system, the trailer air supply valve automatically pops out when air system pressure leaks down to approximately 70 psi, thereby protecting the tractor air system from further pressure loss.

If the supply valve button is held in while system pressure is at 40 psi or less, the control piston moves into the exhaust position at approximately 20 psi, causing the trailer air system to exhaust and apply the trailer spring brakes.

OPERATIONAL AND LEAKAGE TESTS 1. Block the wheels to prevent the vehicle from moving.

2. Start the engine and build air system pressure to governor cutout.

3. Stop the engine.

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DESCRIPTION AND OPERATION 4. With both the trailer supply and the parking brake control knobs pulled out (spring brakes applied), apply a soap-and-water solution to the exhaust vent and the plunger stem. Leakage should not exceed a one-inch bubble in five seconds.

Tractor Protection Valve — MR and DM Models with Full Trailer Connection 70

5. Push the trailer air supply knob in and apply a soap-and-water solution to the exhaust vent and the exhaust port. Leakage should not exceed a one-inch bubble in five seconds at either point.

6. Connect an accurately calibrated test gauge into an assembled hose coupling. Then connect to the trailer supply coupling (tractor emergency line) at the rear of the tractor.

7. With the trailer air supply knob still pushed in, push the parking brake control knob in to release the spring brakes. There should be an immediate indication of pressure registered on the test gauge, and it should equal system pressure as indicated on the dash gauge.

8. Apply a soap-and-water solution to the exhaust port of the trailer air supply valve.

Leakage should not exceed a one-inch bubble in five seconds.

9. With the tractor air system at governor cutout, note the pressure indicated on the dashboard pressure gauge.

10. Quickly disconnect the assembled hose coupling and test gauge from the trailer supply line coupling. The air system will leak down to approximately 65 psi before the trailer air supply valve pops out.

11. Reconnect the hose coupling and test gauge to the trailer supply line and push the trailer air supply knob in.

Figure 70 — Tractor Protection Valve

DESCRIPTION The tractor protection valve operates in conjunction with the trailer air supply valve to direct air pressure to the trailer air system, and to protect the tractor air system from a total loss of pressure should a leak develop in the trailer system. The valve is usually mounted behind the cab.

12. Open the drain valves on the primary and secondary air reservoirs slightly.

13. As the reservoirs drain, note at what pressure the knob of the trailer supply valve pops out and exhausts the trailer supply line.

This should occur between 20 and 45 psi.

PREVENTIVE MAINTENANCE 앫

B, C, D Inspections — Check for proper operation and test for excessive leakage.

Replace as necessary.

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DESCRIPTION AND OPERATION 71

Figure 71 — Typical Tractor Protection Valve Piping

A delivery line from the trailer air supply valve is connected to the tractor emergency port, and a line from the treadle valve is connected to the tractor service port. The trailer emergency and service hoses are each connected to their respective ports.

The supply passage through the valve is always open. When the trailer air supply valve is activated (pushed in), air pressure enters the tractor protection valve through the tractor emergency port, flows through the valve and supplies the trailer air system. With 45 psi applied to the tractor emergency port, the service line shut-off valve moves off its seat and opens a passage for brake application pressure to flow to the trailer service brakes. Externally mounted dual check valves select application pressures from the primary or secondary sections of the treadle valve, or from the hand control valve. The tractor protection valve also incorporates a quick release function to speed-up trailer service-brake release response by allowing service line pressure to exhaust through the valve rather than back through the treadle valve (or hand valve).

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During normal operation with a trailer attached and the trailer air supply valve pushed in, the tractor protection valve remains open to allow the free flow of air between the trailer and tractor air systems. Should a trailer breakaway occur or a severe leak develop in the trailer air system, the drop in pressure at the tractor emergency port causes the service line inlet valve to close and seal the service port, preventing a further loss of pressure. Pressure in the trailer emergency lines exhausts to atmosphere allowing the trailer spring brakes to apply.

DESCRIPTION AND OPERATION 5. While maintaining tractor air system pressure at 60 psi and with the trailer air supply valve still pushed in, make a full service brake application. The pressure gauge installed in the trailer service line should indicate the application pressure of 60 psi.

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6. While holding the full brake application, apply a soap-and-water solution to the exhaust port. Leakage should not exceed a one-inch bubble in three seconds.

7. Release the brake pedal. The pressure gauge installed in the trailer service line should immediately indicate 0 psi.

8. Build air system pressure to 100 psi.

9. With the trailer air supply valve pushed in, make and hold a service brake application and note that the application pressure is indicated on the gauge installed in the service line.

10. Open the primary and secondary reservoir drain valves and allow the air system to bleed down.

Figure 72 — Tractor Protection Valve Cutaway

OPERATIONAL AND LEAKAGE TESTS 1. Block the wheels to prevent the vehicle from moving.

2. Install accurately calibrated pressure gauges in both the trailer service and emergency ports.

3. With a tractor air system pressure of 60 psi, push the trailer air supply valve in. Sixty psi should be indicated on the pressure gauge installed in the trailer emergency line. There should be no pressure indicated on the gauge installed in the trailer service line.

11. When air system pressure drops to approximately 45 psi, observe that the tractor protection inlet valve closes to seal the trailer service port. There should not be any pressure indicated on either pressure gauge.

If the valve fails to perform as indicated in the above test, or if excessive leakage is evident, it must be removed and repaired or replaced as necessary.

PREVENTIVE MAINTENANCE B, C, D Inspections — Test the operation of the valve and check for excessive leakage. Remove and repair, or replace as necessary.

4. Apply a soap-and-water solution to the exhaust port of the tractor protection valve.

Leakage should not exceed a one-inch bubble in three seconds.

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DESCRIPTION AND OPERATION Tractor Protection Manifold — CXN/CHN/CH/CL/CX/CV/CT Models 73

Figure 73 — CH, CL, CX and CV Models

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DESCRIPTION The tractor protection manifold performs the same functions as the tractor protection valve, but is a bulkhead-mounted unit that eliminates the externally mounted dual check valves that select primary, secondary or hand valve delivery pressures. The manifold also contains ports where stoplight switches are installed.

DESCRIPTION AND OPERATION 74

Figure 74 — Tractor Protection Manifold Schematic

The tractor protection manifold contains two dual check valves that select the highest control pressure from either the tractor primary circuit, tractor secondary circuit or the hand control valve, and actuate the trailer service brakes accordingly. An integral quick release valve is also contained within the manifold to speed-up the response time for trailer brake release.

OPERATION The tractor protection manifold uses the same operating principles as the tractor protection valve. When the trailer air supply valve is activated (pushed in), air pressure enters the manifold through the tractor emergency port and flows through the manifold to supply the trailer air system. With at least 45 psi entering the manifold through the tractor emergency port, the service line shut-off valve is moved off its seat and opens a path for brake application pressure to flow to the trailer service brakes. The tractor protection manifold remains open as long as pressure is supplied to the tractor emergency port.

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DESCRIPTION AND OPERATION 75

Figure 75 — Tractor Protection Manifold Airflow

Applying the treadle valve directs brake application pressure to the manifold. The dual check valve senses the higher pressure from either the tractor primary or secondary brake circuits and reacts accordingly. In normal operation with the primary circuit at the higher pressure, the valve shuttle moves and seals the secondary delivery port. Primary brake application pressure then flows through the internal passages in the manifold, past the opened service line shut-off valve, and out through the trailer service port to apply the trailer service brakes. Pressure is also applied to the stoplight switch port to activate the stop lamps.

If the secondary brake circuit is at the higher pressure, the dual check valve moves in the opposite direction to seal the primary delivery port, and the trailer service brakes are actuated with application pressure from the secondary circuit.

Releasing the treadle valve allows the pressure in the trailer service lines to exhaust through the quick release valve inside the manifold.

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When the trailer brakes are applied using the hand control valve, pressure enters the manifold through the trailer hand brake control (TC) port.

The second dual check valve reacts accordingly by moving to seal the passage from the primary and secondary delivery ports. Pressure flows past the opened service line shut-off valve and out through the trailer service port to apply the trailer service brakes. Pressure is also applied to the stoplight switch port to actuate the stop lamps. Releasing the hand valve allows the pressure in the service line to exhaust through the protection manifold quick release valve.

If a trailer breakaway should occur, or a severe leak in the trailer air system develop, the drop in pressure at the tractor emergency port causes the service line shut-off valve to move and seal the trailer service port, preventing a further loss of pressure. Pressure in the tractor emergency line exhausts and allows the trailer spring brakes to apply.

DESCRIPTION AND OPERATION OPERATIONAL AND LEAKAGE TESTS 1. Block the wheels to prevent the vehicle from moving.

2. Start the engine and build air system pressure to governor cutout.

3. Pull the trailer air supply valve out.

4. Disconnect the trailer service hose coupling.

5. Make a trailer hand control valve application.

6. Hold a finger over the 1/16-inch vent hole located in the manifold casting near the service line shut-off area and check for leakage. Also check for leakage at the disconnected trailer service-line hose coupling. Excessive leakage at either port indicates a faulty inlet valve.

7. With the hand control valve still applied, turn the ignition switch on and verify that the stop lamps illuminate.

15. Disconnect and plug the primary circuit delivery line from the tractor protection manifold (labeled PCD).

16. Apply the treadle valve and check for leakage at the opened primary circuit delivery port.

17. Release the treadle valve application. Then reconnect the primary circuit delivery line.

18. Repeat the above procedure for the secondary circuit delivery line (labeled SCD on the tractor protection manifold).

19. Excessive leakage at either port indicates a faulty double check valve shuttle.

20. Reconnect all lines that were disconnected before returning the vehicle to service.

PREVENTIVE MAINTENANCE 앫

8. Release the hand control valve and push the trailer air supply valve in.

9. Connect a pressure gauge to the trailer service hose coupling.

10. Apply the trailer hand control valve and note that pressure is indicated at the service hose coupling.

B, C, D Inspections — Test the operation of the manifold and check for excessive leakage. Remove and repair, or replace as necessary.

Hand Control Valve (Trolley Valve) 76

11. With the trailer hand control valve applied, check for leakage at the following locations: 앫

Service line quick release valve — Excessive leakage in this area may indicate a faulty quick release diaphragm.

앫

Treadle valve exhaust port — Excessive leakage in this area indicates a defective double check valve shuttle.

앫

1/16 vent hole located in the manifold casting — Excessive leakage indicates defective inlet valve O-ring.

12. Release the hand valve application, then make and hold a treadle valve application.

13. Check for leakage at the trailer hand control valve exhaust port. Excessive leakage at this port indicates a faulty double check valve shuttle.

14. Release the treadle valve application.

Figure 76 — Hand Control Valve — Dashboard-Mounted

DESCRIPTION The hand control valve gives the driver graduated control of air system pressure for applying the trailer brakes independently of the tractor brakes or, in the case of a platform truck, for applying the rear axle(s) service brakes independently of the front brakes.

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DESCRIPTION AND OPERATION Moving the handle in a clockwise direction from the released position exerts a force on the pressure graduating spring through the action of the cam and cam follower. The force of the spring causes the piston inside the valve to move down.

77

As the handle is moved counterclockwise, spring tension against the piston is decreased. Air pressure underneath the piston lifts it and moves it away from the exhaust valve. When the exhaust passage is opened, air pressure in the delivery line exhausts through the exhaust port, and the trailer or truck rear axle(s) service brakes release.

OPERATIONAL TESTS 1. Install an accurately calibrated pressure gauge in the delivery port of the trailer brake hand control valve.

2. Rotate the handle to the fully applied position. The pressure gauge should register full reservoir pressure.

The test gauge should indicate proportional readings when the control handle is placed anywhere between the fully applied and fully released positions.

3. Rotate the control handle back to the released position. The gauge should immediately register 0 psi.

LEAKAGE TESTS Apply a soap-and-water solution to the exhaust port or exhaust line of the valve.

Figure 77 — Hand Control Valve Cutaway

As the piston moves down, the exhaust seat, which is in the center of the piston, contacts the exhaust valve and closes the exhaust passage.

Further movement of the piston moves the inlet valve off its seat and allows reservoir pressure to flow past the open inlet valve, through the delivery port, and to the trailer brake chambers or to the truck rear axle(s) brake chambers.

Pressure flowing past the open inlet valve also acts upon the bottom of the piston. When the force of air pressure beneath the piston balances the force exerted by the depressed graduating spring, the piston lifts slightly and allows the inlet valve to return to its seat. The exhaust valve, however, remains seated so the flow of pressure through the valve is blocked, and air pressure is held in the service line.

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Typically, the exhaust port is connected to a line and exhausted away from the driver’s area.

With the valve in the released position, leakage at the exhaust port should not exceed a one-inch bubble in five seconds.

With the valve in the applied position, leakage should not exceed a one-inch bubble in three seconds.

PREVENTIVE MAINTENANCE 앫

B, C, D Inspections — Check for proper operation, and test for excessive leakage.

Replace as necessary.

DESCRIPTION AND OPERATION Spring Brake Modulating Relay Valve 78

Figure 78 — Spring Brake Modulating Relay Valve

DESCRIPTION The spring brake modulating relay valve provides rapid application of the spring brakes for parking, modulated control of the spring brakes through the treadle valve should a failure of the primary air system be encountered and an anti-compounding function to prevent damaging the brake actuators should a service brake application be made with the parking brakes applied. This valve is used on all straight truck chassis (except current LE and MR models), and is an option on certain tractor applications.

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DESCRIPTION AND OPERATION 79

Figure 79 — Typical Spring Brake Modulating Relay Valve Piping 1. Primary Reservoir 2. Secondary Reservoir 3. Front Brake Chambers 4. Quick Release Valve 5. Treadle Valve

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6. Park Brake Valve with Double Check Valve 7. Spring Brake Modulating Relay Valve 8. Spring Brake Chambers 9. Service Brake Relay Valve

DESCRIPTION AND OPERATION The spring brake modulating relay valve contains a park brake control port, balance port, supply port, exhaust port, service brake control port (secondary pressure) and four delivery ports. The elbow fitting in the supply port contains a check valve, and the exhaust port is protected from dirt entry by a diaphragm.

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80

Figure 81 — Modulating Relay Valve Cutaway Figure 80 — Modulating Relay Valve Porting 1. Control Port (Park Brake Control Signal) 2. Balance Port (Primary System Signal) 3. Delivery Ports

4. Supply Port (Secondary Reservoir) 5. Exhaust Port 6. Control Port (Secondary System Signal)

Inside the valve is a control piston that receives system pressure from the park brake control valve and acts against the force of the large main piston spring, and a main piston that reacts to force applied by the control piston. The main piston actuates the inlet/exhaust valve assembly.

The check valve contained within the secondary port elbow fitting prevents spring brake hold-off pressure from leaking to the atmosphere should a leak in the secondary air system develop. The valve also contains an internal check valve in a passage between the park brake control port and the supply port. This check valve allows the control pressure from the park brake control circuit to become the supply for the valve should the secondary air system lose pressure.

1. Control Piston 2. Upper Valve Body 3. Main Piston 4. Control Piston Spring 5. Balance Port 6. Main Piston Spring 7. Control Port 8. Valve Insert 9. Lower Valve Body 10. Delivery Port 11. Valve Retainer 12. Valve Spring

13. Inlet/Exhaust Valve 14. Lower Valve Guide 15. Exhaust Port 16. Valve Seat 17. Elbow Fitting with Check Valve 18. Check Valve Guide 19. Supply Port 20. Check Valve Spring 21. Check Valve 22. Control Port 23. Double Check Valve

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DESCRIPTION AND OPERATION OPERATION

System Fully Charged

Initial Pressure Build-Up With the air system functioning normally, pushing the park brake valve in to release the parking brakes allows pressure to enter the spring brake modulating valve through the park brake control port. Pressure entering the cavity above the control piston pushes the piston down, overcoming the tension applied by the main piston spring. Downward movement of the control piston causes the main piston to move down, which in turn, opens the inlet valve. With the inlet valve open, pressure flows to the spring brake chambers and continues to flow until reaching 107 psi (nominal).

At 107 psi (nominal), reservoir pressure entering the lower cavity of the valve pushes against the bottom of the main piston to move the piston up.

When the main piston moves up, the inlet valve seats and spring brake hold-off pressure is maintained in the circuit to keep the spring brakes released.

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82

Figure 83 — Air System Charged, Spring Brakes Released

Figure 82 — Initial Pressure Build-Up 1. Control Pressure from Park Brake Valve 2. Secondary Reservoir Pressure 3. Control Piston Moves Down

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4. Main Piston Moves Down 5. Inlet Valve Opens 6. Delivery to Spring Brake Chambers

1. Control Pressure from Park Brake Valve 2. Secondary Reservoir Pressure 3. Control Piston Remains Down

4. Main Piston Moves Up 5. Inlet Valve Seats 6. Delivery Pressure Maintained in Spring Brake Circuit

DESCRIPTION AND OPERATION Normal Service Brake Application

Parking Brake Application

A service brake application allows primary and secondary pressure to enter the valve through the balance port and the secondary control port.

Primary pressure enters the cavity above the main piston and secondary pressure enters the cavity below the main piston. With pressure above and below the main piston, the valve remains in balance and no movement of the main piston takes place. The inlet/exhaust valve assembly remains closed, and hold-off pressure is maintained in the spring brake circuit.

When both the primary and secondary systems are functioning properly and the park brake valve is pulled out to apply the parking brakes, pressure on top of the control piston exhausts which allows both the control piston and main piston to move up. When the main piston moves up, the inlet valve remains seated and a passage to allow pressure from the spring brake chambers to exhaust opens.

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84

Figure 85 — Parking Brake Application Figure 84 — Service Brake Application 1. Control Pressure from Park Brake Valve 2. Secondary Reservoir Pressure 3. Control Piston Remains Down

4. Balance Pressure (Primary System Signal) 5. Control Pressure (Secondary System Signal) 6. Delivery Pressure Maintained in Spring Brake Circuit

1. Park Brake Control Pressure — Exhausts 2. Secondary Reservoir Pressure 3. Control Piston Moves Up

4. Main Piston Moves Up 5. Pressure in Spring Brake Circuit Exhausts 6. Exhaust (from Spring Brake Circuit)

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DESCRIPTION AND OPERATION Loss of Pressure in the Secondary Circuit

Loss of Pressure in Primary Circuit

If a pressure loss in the secondary circuit occurs, the check valve inside the elbow fitting at the secondary reservoir supply port moves to seal the port against further air loss. The check valve located in the internal passage between the park brake control port and secondary supply port opens and allows pressure from the park brake control circuit to become the supply for the valve.

Spring brake hold-off pressure is maintained at 107 psi.

With a loss of pressure in the primary circuit, a service brake application will allow secondary circuit pressure to enter the spring brake modulating relay valve through the control port and flow into the cavity below the main piston.

Secondary pressure moves the main piston up, which in turn causes the exhaust valve to open.

With the exhaust valve open, spring brake hold-off pressure exhausts through the exhaust port. When the hold-off pressure exhausts, the compression springs expand to apply the rear axle brakes. The amount of pressure exhausted from the spring brake chambers is proportionate to the amount of force applied to the brake treadle valve. A service brake application of 30 psi would exhaust spring brake hold-off pressure to approximately 60 psi. When the service brake application is released, pressure is removed from under the main piston, and the main piston moves down to open the inlet valve.

With the inlet valve open, secondary pressure flows back into the spring brake circuit to release the spring brakes.

When the service brakes are applied, pressure from the primary circuit enters the spring brake modulating relay valve through the balance port and flows into the cavity above the main piston.

Without secondary pressure under the main piston, primary pressure will push the main piston down to open the inlet valve. With the inlet valve open, pressure from the park brake control circuit flows to the spring brake circuit to maintain hold-off pressure.

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87

Figure 86 — Service Brake Application, Loss of Pressure in Secondary Circuit 1. Park Brake Control Pressure (Becomes Supply Pressure) 2. Loss of Secondary Reservoir Pressure 3. Check Valve Opens 4. Control Piston Remains Down

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5. Primary System Signal Pressure (Balance Port) 6. Main Piston Moves Down 7. Loss of Secondary Pressure (No Control Pressure Enters Valve) 8. Spring Brake Hold-Off Pressure is Maintained

Figure 87 — Service Brake Application, Loss of Pressure in Primary Circuit 1. Park Brake Control Pressure 2. Secondary Reservoir Pressure 3. Control Piston Remains Down 4. Loss of Primary Pressure (No Pressure Enters the Balance Port)

5. Secondary Control Pressure 6. Main Piston Moves Up 7. Pressure from Spring Brake Chambers Exhausts 8. Exhaust

DESCRIPTION AND OPERATION Anti-Compounding

OPERATIONAL TESTS

To prevent compounding the force against the rear brake assemblies should the service brakes be inadvertently applied while the parking brakes are set, the spring brake modulating relay valve provides an anti-compounding function. When the park brake valve is pulled out, pressure at the top of the control piston is removed and pressure is exhausted from the spring brake chambers. If the service brakes are inadvertently applied, primary circuit pressure enters the modulating relay valve through the balance port and flows through internal passages to the cavity above the control piston. Pressure at the top of the control piston moves both the control piston and main piston down, which in turn opens the inlet valve.

With the inlet valve opened, secondary reservoir pressure enters the spring brake portion of the chambers to relieve some of the tension against the pushrod as application pressure enters the service section of the brake chambers. When the service brakes are released, primary circuit pressure is exhausted from the top of the control piston, which in turn allows the inlet valve to close. Pressure in the spring brake chambers exhausts and allows the compression spring to expand.

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Place blocks at the front wheels to prevent the vehicle from moving, and then start the engine and allow system pressure to build to governor cutout. Stop the engine and proceed as follows: 1. Apply the parking brakes and observe that the spring brakes apply promptly. Remove one of the lines from a delivery port on the spring brake modulating relay valve, then install an accurately calibrated test gauge into the port. Reconnect the air line.

2. Release the parking brakes and note that the spring brakes fully release. With the parking brakes in the released position, note the spring brake hold-off pressure indicated on the pressure gauge. Typical hold-off pressure is approximately 107 psi (nominal).

3. Apply the parking brakes. Hold-off pressure (indicated by the pressure gauge installed in a delivery port) should immediately drop to zero. A lag in the drop in pressure (more than three seconds) would indicate a faulty valve.

4. With the parking brakes applied, gradually apply the treadle valve and note a gradual increase in pressure as indicated on the test gauge installed in the delivery port. This checks the anti-compounding function of the spring brake modulating relay valve.

5. Release the parking brakes.

6. Drain the primary reservoir. After the reservoir has drained, apply the treadle valve several times and note the reading on the pressure gauge installed in the delivery port. The reading should decrease each time the treadle valve is applied (spring brake modulation). After several applications, pressure on the gauge will drop to the point where release of the spring brakes will no longer occur.

Figure 88 — Anti-Compounding 1. Park Brake Control Pressure Exhausted 2. Secondary Reservoir Pressure 3. Primary Pressure Enters Balance Port 4. Secondary Control Pressure

5. Control Piston Moves Down 6. Main Piston Moves Down 7. Delivery Pressure to Spring Brake Chambers

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DESCRIPTION AND OPERATION LEAKAGE TESTS Release the parking brakes. Apply a soap-and-water solution to all ports, including the exhaust port. A one-inch bubble in three seconds is allowed.

Spring Brake Control Valve 89

If the valve does not function as described under “Operating Tests,” or if leakage is excessive, replace the valve.

DO NOT attempt to disassemble a spring brake modulating relay valve. The valve contains springs under compression that could release with enough force to cause serious personal injury should disassembly be attempted.

PREVENTIVE MAINTENANCE B, C, D Inspections — Clean any accumulated road dirt and other debris from around the valve and visually inspect the exterior of the valve for physical damage or signs of excessive corrosion.

B, C, D Inspections — Inspect all air line connections for signs of wear or physical damage. Replace as necessary.

B, C, D Inspections — Perform the leakage test as described above. Tighten fittings or replace as required.

D Inspection — Perform operational tests as described above. Replace valve if it does not function as described.

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Figure 89 — Spring Brake Control Valve

DESCRIPTION AND OPERATION DESCRIPTION The spring brake control valve directs a specific amount of “hold-off” pressure (about 95 psi) to the spring brake chambers to cage the compression springs and release the spring brakes. In the event of a primary system pressure loss, the

valve allows a graduated application of the spring brakes through a treadle valve application, to bring the vehicle to a safe stop. Spring brake control valves are used in all truck applications, and may be used in some tractor applications.

90

Figure 90 — Typical Spring Brake Control Valve Piping

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DESCRIPTION AND OPERATION The valve contains a supply port, delivery port, control port, primary air reservoir port and an exhaust port. The exhaust port is protected from dirt entry by a diaphragm. Inside the valve is a large piston that receives system pressure from the parking brake control valves and acts against the force of two large piston springs, and a small piston that receives air pressure directly from the primary air reservoir and acts against the force of one small piston spring. Each piston actuates an inlet and exhaust valve assembly.

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OPERATION Initial Pressure Build-Up With little or no pressure at the control valve, the piston springs force both pistons into contact with the inlet and exhaust valve assemblies. In this position, the exhaust valves are closed and the inlet valves are opened. As system pressure begins to build, pressure entering the primary reservoir port moves the small piston upward against the tension of the piston spring. At approximately 55 psi, the small piston moves enough to close the inlet valve and open the hollow exhaust passage in the small piston. Also at 55 psi, pushing the parking brake control valves in to release the spring brakes directs pressure to the supply port of the spring brake control valve. Pressure entering the supply port pushes the large piston up slightly against the force of the two piston springs.

92

Figure 91 — Spring-Brake Control Valve Cutaway

Figure 92 — Initial Pressure Build-Up

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DESCRIPTION AND OPERATION System Fully Charged As pressure underneath the large piston builds to approximately 95 psi, it moves upward against the tension of the two large piston springs. As the

piston moves, the inlet valve closes and the exhaust valve remains closed. With the inlet valve closed, 95 psi is held in the spring brake chambers and system pressure builds in the remainder of the air system.

93

Figure 93 — Air System Fully Charged

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DESCRIPTION AND OPERATION Normal Brake Application When the air system is operating normally, applying the brakes directs air pressure from the secondary section of the treadle valve to the control port of the spring brake control valve. The

flow of air is blocked by the closed inlet valve at the small piston, so no movement of the pistons or inlet/exhaust valves takes place. In this condition, the rear service brakes apply as normal.

94

Figure 94 — Normal Brake Application

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DESCRIPTION AND OPERATION Parking Brake Application When both the primary and secondary systems are functioning properly and the parking brake valve is placed in the PARK position, pressure at the spring brake control valve, along with the pressure in the spring brake chambers, is exhausted, allowing the spring brakes to apply.

The spring brake control valve contains a single check valve that allows air pressure beneath the large piston to exhaust through the parking brake control valve. After a sufficient quantity of air has exhausted, the piston is forced down, and the inlet valve opens to provide an additional passage for air to exhaust from the spring brake chambers.

95

Figure 95 — Parking Brake Application

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DESCRIPTION AND OPERATION Loss of Pressure in the Secondary Circuit If a pressure loss in the secondary reservoir occurs, the primary circuit is protected by check valves. Applying the treadle valve supplies little or

no air pressure to the control port of the spring brake control valve. Thus, no movement of the components inside the valve takes place. The rear-axle service brakes apply as normal.

96

Figure 96 — Service Brake Application, Loss of Pressure in Secondary Circuit

Loss of Pressure in the Primary Circuit If pressure in the primary reservoir falls below 55 psi, insufficient pressure exists at the primary reservoir port of the spring brake control valve to hold the small piston against the tension of the spring. Spring tension then moves the piston downward to close the exhaust passage.

Continued downward movement of the piston opens the inlet valve. The secondary reservoir and the parking brake control valve are protected from a loss of pressure by check valves.

Applying the brake pedal directs air pressure from the secondary portion of the treadle valve to the control port of the spring brake control valve.

Air entering the control port flows past the inlet valve underneath the small piston, directed through an air passage in the valve body and applied to the bottom of the large piston. The additional pressure moves the large piston

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upward against the tension of the two large piston springs. The upward movement opens the exhaust valve and allows the air in the spring brake lines and chambers to exhaust, applying the rear-axle spring brakes. The amount of air exhausted from the spring brake chambers is proportionate to the amount of force exerted on the brake pedal.

Releasing the brake treadle removes the pressure applied to the control port of the spring brake control valve. When control pressure is removed, spring tension forces the large piston down to close the exhaust valve and trap a sufficient amount of air in the spring brake chambers to release the brakes. Each time the spring brakes are applied and released, however, pressure remaining in the chambers decreases until no longer sufficient to hold off full application of the spring brakes.

DESCRIPTION AND OPERATION 97

Figure 97 — Service Brake Application, Loss of Pressure in Primary Circuit

OPERATIONAL TESTS 1. Block the wheels to prevent the vehicle from rolling.

2. Start the engine and allow the air system to build pressure until governor cutout.

3. Stop the engine.

4. Place the parking brake control valve in the PARK position and observe that the spring brakes apply promptly.

5. Install a tee fitting and an accurately calibrated pressure gauge in the line coming from the delivery port of the spring brake control valve.

6. Place the parking brake control valve in the RELEASE position and observe that the spring brakes release fully. Note that the test gauge indicates the proper spring brake hold-off pressure of 95 psi. If the pressure is incorrect, the spring brake control valve must be repaired or replaced.

7. Place the parking brake control valve in the PARK position and note that the test gauge immediately drops to 0 psi. If the pressure drops slowly, the single check valve (inside the spring brake control valve) may be faulty.

8. Place the parking brake control valve in the RELEASE position. Then completely drain the primary air reservoir.

9. Note that the test gauge indicates the proper spring brake hold-off pressure.

10. Apply the treadle valve several times and note that the pressure reading on the test gauge decreases with each brake application. After several brake applications, the pressure should reach a point (approximately 45 psi) where hold-off pressure is no longer sufficient, and the spring brakes automatically apply.

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DESCRIPTION AND OPERATION LEAKAGE TESTS

DESCRIPTION

With the air system fully pressurized and the parking brake control valve in the RELEASED position, apply a soap-and-water solution to the exhaust port and body of the spring brake control valve. Slight leakage at these points is allowable.

The quick release valve is used to speed up the exhaust of air from the brake chambers. The valve consists of a flat, circular diaphragm installed between the upper and lower valve bodies.

99

PREVENTIVE MAINTENANCE 앫

B, C, D Inspections — Check for proper operation and test for excessive leakage.

Replace as necessary.

Quick Release Valve 98

Figure 99 — Quick Release Valve Cutaway

When the brakes are applied, air pressure enters the quick release valve supply port. The center portion of the diaphragm is forced against the exhaust port, while the outer edge moves off the upper sealing lip, allowing air to flow around the diaphragm, through the delivery ports to the brake chambers.

Figure 98 — Quick Release Valve

As pressure on the delivery side of the valve equals approximately that of the supply side, the outer edge of the diaphragm moves to seal against the sealing lip of the upper valve body.

Because air pressure is acting upon the center portion of the diaphragm from the supply side only, the diaphragm remains sealed against the exhaust port.

Releasing the brake pedal removes air pressure from the supply side of the quick release valve, which allows the diaphragm to move off the exhaust port. Pressure on the supply side of the valve exhausts back through the brake treadle valve, while air from the brake chambers (delivery side) exhausts through the exhaust port of the quick release valve.

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DESCRIPTION AND OPERATION Trailer Air Line Quick Release Valve CXN, CHN, CH, CL, CX and CV model tractors having coiled air lines for the trailer connections, are equipped with in line quick release valves at the glad hands. These valves are used to provide a faster response time for release of the trailer service brakes.

100

3. With the brakes fully applied, coat the valve body with a soap-and-water solution. No leakage through the valve body is permitted.

PREVENTIVE MAINTENANCE B, C, D Inspections — Check the valve for proper operation and test for excessive leakage.

Repair or replace as required.

Tractor — Rear Brake Proportioning/Front Axle Ratio Valves 101

Figure 100 — Trailer Air Line Quick Release Valve

OPERATIONAL TESTS Apply and release the service brakes. Observe that air exhausts through the quick release valve exhaust port.

Figure 101 — Brake Proportioning Valve

LEAKAGE TESTS 1. With the air system fully charged, make and hold a full brake application.

2. Coat the quick release valve exhaust port with a soap-and-water solution. Allowable leakage through the exhaust port is a one-inch bubble in three seconds.

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DESCRIPTION AND OPERATION DESCRIPTION Brake proportioning valves are used in tractor air systems to reduce the braking effort at the rear axle brakes when operating without a trailer.

An inversion valve provides control pressure to the brake proportioning valves to signal if a trailer is attached.

The brake proportioning valve is not used on chassis equipped with ABS. 102

Figure 102 — Brake Proportioning Valves, Typical Piping

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DESCRIPTION AND OPERATION

Brake proportioning valves may be used on both the front axle and the rear axle brake circuits.

They are similar in appearance but NOT interchangeable. The identification tags attached to one of the valve cover screws are stamped with either “BP-1 FRONT” or “BP-1 REAR” to identify in which circuit the valve is to be used.

upper and inner pistons. Because pressure is acting on the total surface area of both pistons, delivery and supply pressures are equal.

103

A rear valve may be used without a front valve, provided the chassis is NOT equipped with a ratio valve. If a ratio valve is used, it must be replaced with a “FRONT” proportioning valve.

When equipped with a rear proportioning valve only and the tractor operating with a trailer attached, equal pressure (100% of the service brake application pressure) is delivered to each axle when the service brakes are applied. When the trailer is disconnected and the service brakes are applied, 100% of the application pressure is delivered to the front axle brakes and approximately 25% is delivered to the rear axle(s) brakes. As application pressure increases, the difference in delivery pressures between the front and rear axles decreases.

If the tractor is equipped with a front and a rear proportioning valve and operating with a trailer attached, the front axle receives 50% of a service brake application for a 40-psi application, but the difference between supply and delivery pressures decreases until reaching a 60-psi application, at which point a full 1:1 delivery is attained.

With the trailer disconnected, the front axle receives 100% of the brake application and the rear axle(s) receives approximately 25%. As application pressure increases, the difference in delivery pressures between the front and rear axles decreases.

Rear Proportioning Valve The rear brake proportioning valve contains an upper piston, a lower piston and an inner piston.

When a trailer is attached and the trailer supply valve is pushed in to supply the trailer air system, pressure at the proportioning valve control port is exhausted. With no pressure at the control port, brake application pressure enters the supply port and acts upon the total surface area of both the

Figure 103 — Rear Proportioning Valve Cutaway

When the trailer is disconnected and the trailer supply valve is pulled out to exhaust the trailer air system, full reservoir pressure is delivered to the proportioning valve control port and applied to the bottom surface of the upper piston. When the service brakes are applied, application pressure enters the supply port, but force is applied to the lower and inner pistons only. Because there is now less piston surface area, only 25% of the application pressure is delivered through the delivery port. When the brakes are applied, however, the proportioning valve will not limit pressure as normal until an initial delivery pressure overcomes the tension of the spring holding the lower piston closed. This initial delivery pressure is necessary to offset the rear-axle brake relay-valve crack pressure when the tractor is operating without a trailer.

Front Ratio Valve The brake proportioning valve used for the front axle is similar in appearance to the rear valve, but different internally. The valves are not interchangeable. The front valve uses an upper piston and a lower piston. Movement of the upper piston is restricted by a spring.

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DESCRIPTION AND OPERATION 2. With the trailer supply valve pulled out, install a tee fitting and an air gauge in a front-axle brake chamber and a rear-axle brake chamber.

104

3. Start the engine and build air system pressure to governor cutout.

4. Apply the service brakes with the treadle valve and observe the readings indicated on the air gauges. When the gauge installed in the front-axle brake chamber reaches 40 psi, the gauge installed in the rear-axle brake chamber should read approximately 10 to 20 psi, depending upon rear-axle relay valve pressure differential. The difference in pressures between the front axle and rear axle should decrease as application pressure is increased.

Figure 104 — Front Ratio Valve Cutaway

As with the rear proportioning valve, pressure to the proportioning valve control port is supplied through an inversion valve. With a trailer attached and the trailer supply valve pushed in to supply the trailer air system, pressure at the proportioning valve control port is exhausted.

Brake application pressure entering the proportioning valve supply port applies force to both the upper and the lower pistons. Because movement of the upper piston is restricted with a spring, service brake applications of 40 psi or less move the lower piston only, which, due to the decreased piston surface area, allows only 50% of the application pressure through the delivery port. As application pressure exceeds 40 psi, spring tension holding the upper piston is overcome, allowing the upper piston to move.

With movement of the upper piston, the difference between supply and delivery pressure decreases. When service brake application pressure reaches 60 psi, upper piston spring tension is fully overcome, allowing the valve to deliver a full 1:1 brake application pressure to the front brakes.

OPERATIONAL TESTS 1. Block the wheels to prevent the vehicle from moving.

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5. If the chassis is not equipped with a front-axle limiting valve, connect a trailer and push the trailer supply valve in to supply the trailer air system.

6. Apply the service brakes with the treadle valve and observe the readings indicated on the gauges. Both gauges should read approximately equal throughout a range of service brake application pressures.

7. If the chassis is equipped with a front and rear limiting valve, connect a trailer and push the trailer air-supply valve in to supply the trailer air system. Apply the service brakes with the treadle valve and note the readings indicated on the gauges. When the gauge installed in the front-axle air chamber reads 20 psi, the rear axle gauge should read approximately 40 psi. As application pressure is increased, the difference in pressure between the front and rear axles should decrease.

8. Remove the pressure gauges and tee fittings and test for leakage before putting the vehicle back into service.

PREVENTIVE MAINTENANCE B, C, D Inspections — Check for proper operation, and test for excessive leakage.

Replace as necessary.

DESCRIPTION AND OPERATION Inversion Valve

106

105

Figure 106 — Inversion Valve Cutaway Figure 105 — Inversion Valve

DESCRIPTION Inversion valves are pilot-operated, two-way on-off valves that provide control pressure to the brake proportioning valves to signal whether or not a trailer is attached. The valve is so named because pressure will not flow through the valve when pressure is applied at both the control and supply ports, but when control pressure is removed, pressure flows through the delivery port.

Air pressure in the control cavity of the inversion valve overcomes the force of the piston return spring and holds the piston away from the inlet valve. The inlet valve is held closed by the inlet valve spring, and the flow of pressure through the valve is blocked. Any pressure that was present in the delivery line is exhausted to atmosphere through the hollow exhaust passage in the piston.

Removing the control pressure from the cavity allows the force of the piston return spring to push the piston into contact with the inlet valve and seal the exhaust passage through the piston.

Continued movement of the piston opens the inlet valve and opens a path for supply pressure to flow through the valve and out the delivery port.

Inversion valves are used on chassis equipped with bobtail proportioning valves. They are not used with bobtail proportioning relay valves.

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DESCRIPTION AND OPERATION The inversion valve receives control pressure from the tractor protection valve. When the trailer supply valve is pushed in to pressurize the trailer air system, pressure is directed from the tractor protection valve to the inversion valve control port. With control pressure at the inversion valve, delivery pressure is exhausted, signaling the brake proportioning valves that a trailer is attached and service brake application pressure should not be reduced. Pulling the trailer air supply valve out exhausts the pressure at the inversion valve control port. With no control pressure, the inversion valve allows reservoir pressure to be delivered to the brake proportioning valves, signaling that a trailer is not attached. Service brake application pressure will then be proportioned.

Relay Valves 107

OPERATIONAL AND LEAKAGE TESTS

Depending on installation, it may be easier or necessary to completely remove the valve to perform the following tests.

1. Install an accurately calibrated test gauge in a common control/supply line, and another accurately calibrated gauge in the delivery port.

2. Gradually apply pressure to the common supply/control line, and note at what pressure exhaust occurs.

3. With air pressure in the supply/control line, apply a soap-and-water solution around the supply-port capnut. No leakage is permitted from this area.

4. Apply a soap solution to the delivery and exhaust ports. Slight bubble leakage is permissible. Excessive leakage, however, may indicate a faulty O-ring or inlet valve.

5. Slowly decrease pressure at the control port and note at what pressure delivery is made.

If the valve fails these tests or exhibits excessive leakage, it must be repaired or replaced.

PREVENTIVE MAINTENANCE B, C, D Inspections — Check the valve for proper operation and excessive leakage. Replace as necessary.

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Figure 107 — Relay Valve

DESCRIPTION Relay valves are used to speed up the response time for the application and release of the service brakes. Acting as a remotely operated brake application valve, the relay valve opens a direct air path from the reservoir to the brake chambers after receiving control pressure from the treadle valve. The valve is generally mounted in close proximity to the brake chambers it serves.

Pressure from the brake chambers exhausts through the relay valve rather than through the treadle valve when the brakes are released.

Relay valves may be used in both the service brake and spring brake circuits.

DESCRIPTION AND OPERATION Different types of relay valves are found on MACK chassis. The R-12 relay valve is used on chassis prior to the introduction of the Anti-lock Brake System (ABS). The R-14 relay valve is used on tractors equipped with ABS, and is also used in the spring brake circuit of truck chassis,

because of its anti-compounding and quick release functions. On MR and LE straight truck air systems, the R-12DC relay valve is used in the rear axle service brake circuit. These relay valves are described in greater detail in the following text.

108

Figure 108 — Relay Valve Piping Diagram

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DESCRIPTION AND OPERATION OPERATION R-12 Relay Valve 109

Air flowing past the inlet valve also acts on the bottom of the relay piston. As delivery pressure beneath the relay piston equals control pressure applied above the piston, the piston lifts slightly and allows the inlet valve return spring to push the inlet valve back onto its seat. The exhaust valve remains closed as control pressure balances the delivery pressure of the relay valve.

Releasing the brake treadle removes air pressure from the control port of the relay valve. As air pressure above the piston exhausts, pressure below the piston, along with the tension of the return spring, lifts the relay piston to move the exhaust seat off the exhaust valve, opening the exhaust passage to atmosphere. Air pressure from the brake chambers then exhausts through the relay valve.

R-14 Relay Valve The R-14 relay valve functions in the same manner as the R-12 relay valve previously described except that the R-14 valve incorporates an anti-compounding/quick release function.

Figure 109 — R-12 Relay Valve Cutaway

110

Inside the relay valve is a relay piston assembly, a piston return spring and an inlet and exhaust valve assembly. The relay valve reacts quickly to control pressure from the brake treadle valve because of the small volume of air required to fill the cavity between the valve body cover and relay piston.

When the brake treadle is applied, air pressure enters the control port of the relay valve. Air pressure overcomes the tension of the return spring and forces the relay piston down. The exhaust valve seat moves down with the piston and seals against the exhaust portion of the inlet/ exhaust valve assembly to seal the exhaust passage. At the same time, the inlet portion of the inlet/exhaust valve assembly moves off its seat, opening a passage for air to flow directly from the reservoir to the brake chambers.

Figure 110 — R-14 Relay Valve Cutaway

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DESCRIPTION AND OPERATION The R-14 relay valve contains an additional balance/quick exhaust port on the top of the relay valve at the control port. A diaphragm that functions as a double check valve is located inside the control port. 앫

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Anti-Compounding Function — When the parking brakes are released, pressure from the parking brake control valve enters the control port of the R-14 relay valve and causes the flexible diaphragm to seal against the quick exhaust port. Control pressure then flows around the edges of the flexible diaphragm and into the cavity between the valve cover and relay piston.

From this point, the valve reacts in the same manner as the R-12 relay valve.

When a service brake application is made, pressure from the service brake relay valve is directed to the balance/quick exhaust port of the R-14 relay valve. In general, pressure from a brake application entering the balance port is not sufficient to overcome the pressure applied against the flexible diaphragm from the parking brake control valve, so there is no effect on the relay valve.

When the parking brakes are applied, however, pressure is exhausted from the R-14 relay valve control port. If a service brake application is made, pressure directed from the service brake relay valve enters the balance/quick exhaust port and flows into the cavity between the relay valve cover and piston. The piston moves down against the tension of the return spring and opens a path for reservoir pressure to flow through the relay valve to the spring brake chambers.

The exhaust line is used only with Bendix relay valves.

R-12DC Relay Valve — Straight Trucks Prior to January 2004 and All MR and LE Models The R-12DC relay valve functions in much the same manner as a standard R-12 relay valve, except that the R-12DC valve provides a redundant signal from both the primary and secondary air circuits. This relay valve is used on straight trucks or on tractors equipped with a spring brake control valve to ensure that the chassis can make an emergency stop in the required distance, even with air loss in the primary control circuit between the treadle valve and the relay valve.

The control port of the R-12DC valve contains a double check valve that is biased to ensure that the primary air system controls the relay valve. A spring keeps the edges of the check valve diaphragm sealed to prevent the passage of air from the secondary system during a normal brake application. Control pressure delivered from the treadle valve, enters the small cavity above the piston to move the piston down. Movement of the relay piston opens a path for air to flow from the reservoir to the rear axle brake chambers.

ABS Applications — On ABS-equipped tractors, the R-14 relay valve is used for the quick exhaust function. When a service brake application is released, or during an anti-lock braking event, control pressure is exhausted through the balance/quick exhaust port, thus improving control pressure exhaust timing. When used as the service brake relay valve on an ABS-equipped tractor, a 90-degree elbow and air line is installed in the balance/quick exhaust port. The air line, which is routed into the air line harness, prevents moisture and dirt from entering the relay valve through the balance/quick exhaust port.

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DESCRIPTION AND OPERATION 111

Figure 111 — R-12DC Relay Valve Cutaway

The primary control port is located on the top of the relay valve. The secondary control port is located on the side of the valve. Make sure that the control lines are connected to the proper ports. Intermixing the connections results in brake balance problems.

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In the event of a primary control line failure, control pressure from the secondary air system enters the control port of the relay valve when the brakes are applied. Secondary control pressure delivered to the relay valve moves the edges of the double check valve diaphragm against the tension of the bias spring. Secondary control pressure then flows around the diaphragm and into the small cavity above the relay piston.

Pressure applied to the relay piston moves the piston down and allows pressure to flow from the reservoir to the rear axle brake chambers.

DESCRIPTION AND OPERATION 112

Figure 112 — R-12DC Relay Valve Application

On CH, CL and CV model trucks, the secondary circuit redundant signal line for the R-12DC relay valve is tee’d into the secondary circuit at the front axle quick release valve. On all other chassis, the secondary circuit signal line is tee’d into the air system at the spring brake control valve. On all chassis, primary control pressure comes from the treadle valve. In all instances, the primary air line to the relay valve control port is routed on the left-hand side of the chassis, and the secondary air line to the relay valve control port is routed down the right-hand side of the chassis.

113

Figure 113 — R-12DC Relay Valve Control Line Routing

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DESCRIPTION AND OPERATION OPERATIONAL AND LEAKAGE TESTS 1. Block the wheels to prevent the vehicle from rolling.

Bobtail Proportioning Relay Valve 114

2. Check brake adjustment and adjust if necessary. Refer to “BRAKE ADJUSTMENT” on page 196 for proper brake adjustment procedures.

3. Pressurize the air system.

4. Make several brake treadle applications and check for prompt response of the service brakes at each wheel.

5. With the brakes released, check the relay valve for leakage through the inlet valve and O-ring by coating the exhaust port with a soap-and-water solution. A one-inch bubble in three seconds is acceptable.

6. With the brakes fully applied, check for leakage through the exhaust valve by coating the exhaust port with a soap-and-water solution. A one-inch bubble is permissible.

7. With the brakes fully applied, coat the valve body with a soap-and-water solution and check for leakage through the seal ring where the valve cover and valve body join.

No leakage in this area is allowable.

8. With the brakes released, coat the quick-release exhaust port with a soap-and-water solution and check for leakage through the quick-release diaphragm exhaust seat. Allowable leakage is a one-inch bubble in three seconds.

PREVENTIVE MAINTENANCE B, C, D Inspections — Check for proper operation and test for excessive leakage.

Replace as necessary.

Page 94

Figure 114 — Bobtail Proportioning Relay Valve

DESCRIPTION The bobtail proportioning relay valve, which is used only in tractor air systems, is actually two valves contained in a single housing. One portion of the valve functions as a standard brake relay valve. The other portion functions as a proportioning valve to automatically reduce brake application pressure to the rear brake chambers during bobtail operations and return the system to full braking power when a trailer is attached.

DESCRIPTION AND OPERATION 115

Figure 115 — Bobtail Proportioning Relay Valve Piping Diagram

Page 95

DESCRIPTION AND OPERATION Operation with Trailer Attached

116

When the air system is fully pressurized and the trailer air supply knob is pushed in to pressurize the trailer air system, pressure is also directed to the control port of the bobtail proportioning valve.

Air pressure entering the control port pushes the proportioning piston against its stop in the cover to seat and seal the exhaust passage and open the inlet valve. With the proportioning valve in this position, full application pressure will be delivered to the rear axle brakes.

117

Figure 116 — Bobtail Proportioning Relay Valve Cutaway

The proportioning section of the valve contains a proportioning piston with an integral inlet/exhaust valve, a blend-back piston, a service piston with an exhaust diaphragm and an exhaust port. The lower portion of the valve houses a relay piston and an inlet/exhaust valve assembly.

OPERATION When the air system is operational, reservoir pressure enters the proportioning valve through the supply port and flows through internal passages in the valve body and cover to exert a force against the large diameter end of the blend-back piston.

Reservoir pressure enters the bobtail proportioning relay valve through the supply ports and is directed to the service brake chambers through the delivery ports. Application pressure from the primary side of the treadle valve enters the proportioning valve through the service port and control pressure, which signals the proportioning valve that a trailer is attached, enters the valve through the control port.

Page 96

Figure 117 — Receiving Control Pressure

DESCRIPTION AND OPERATION Once past the inlet valve, air flows through a passage in the valve cover to the top of the relay piston. The relay piston moves into contact with the exhaust portion of the inlet/exhaust valve assembly to seal the exhaust passage.

Continued movement of the relay piston opens the inlet portion of the inlet/exhaust valve and allows reservoir pressure to flow through the valve to the brake chambers.

118

While the brakes are applied and pressure underneath the relay piston begins to equal application pressure, the piston moves slightly and allows the inlet valve to close. With both the inlet and exhaust valves closed, pressure is trapped in the brake chambers to hold the brake shoes in contact with the drums. Pressure delivered to the chambers is neither increased nor decreased.

Figure 118 — Applying Brakes

When the brakes are applied, pressure from the treadle valve enters the proportioning valve through the service port and flows through the service piston to the exhaust diaphragm. The diaphragm flexes and seals the exhaust passage.

Air then flows around the exhaust diaphragm, through the centers of both the blend-back and proportioning pistons, and past the opened inlet valve.

Page 97

DESCRIPTION AND OPERATION 119

Figure 119 — Releasing Brakes

When the brakes are released, air pressure at the service port of the proportioning relay valve exhausts through the treadle valve. Pressure above the relay piston then flows back through the proportioning and blend-back pistons to the exhaust diaphragm. If the brake treadle was released rapidly, the force of the returning air flexes the exhaust diaphragm and allows the pressure to exhaust through the exhaust port of the proportioning valve. If, however, the treadle was released slowly, the exhausting air pressure flows through a slot behind the exhaust diaphragm and exhausts through the treadle valve. As pressure above the relay piston exhausts, pressure beneath the piston lifts it away from the exhaust valve to open the exhaust passage and allow the air from the service brake chambers to exhaust through the open exhaust port.

Page 98

Bobtail Operation Brake proportioning takes place when control pressure is removed from the proportioning valve (by pulling the trailer air-supply valve out) and pressure holding the proportioning piston is exhausted. With the control pressure exhausted, the proportioning piston moves away from its stop in the valve cover.

DESCRIPTION AND OPERATION action opens a path for air pressure to flow from the reservoir to the rear brake chambers. The initial application pressure ensures that the brake shoes contact the drum.

120

121

Figure 120 — Bobtail Operation, Applying Brakes

Applying the brakes directs air pressure from the primary side of the treadle valve to the proportioning valve service port. Pressure entering the service port pushes against the exhaust diaphragm and seals the exhaust port.

With the exhaust port sealed, pressure flows to the blend-back piston. Brake proportioning occurs because both the blend-back and proportioning pistons have large-diameter and small-diameter ends.

At application pressures of 80 psi or less, the blend-back piston remains stationary because of the opposing force applied by reservoir pressure.

Pressure flows through the center of the blend-back piston to exert a force against the small-diameter end of the proportioning piston while simultaneously flowing through its center past the opened inlet valve. Pressure flowing past the inlet valve exerts a force against the large-diameter end of the proportioning piston.

The proportioning piston and the inlet valve remain in this position and allow air pressure to flow into the relay cavity until a preset initial application pressure moves the relay piston. This

Figure 121 — Bobtail Operation, Releasing Brakes

As pressure under the relay piston exceeds the initial application pressure, force is exerted against the large diameter end of the proportioning piston, moving it just enough to close the inlet valve without opening the exhaust valve. If application pressure increases, the proportioning piston opens the inlet valve only as necessary to deliver a proportioned amount of reservoir pressure to the brake chambers.

Application pressures above 80 psi are sufficient enough to move the blend-back piston against the opposing force exerted by reservoir pressure entering the valve. The difference between applied and delivered pressures blend back from a proportioned delivery to nearly a 1:1 delivery. A full brake application delivers a full 1:1 delivery regardless of the reservoir pressure acting against the blend-back piston.

Page 99

DESCRIPTION AND OPERATION When the brakes are released, pressure exhausts through the proportioning valve in the same manner as when a trailer is attached.

OPERATIONAL TESTS Proper operation of the bobtail proportioning relay valve is tested using two accurately calibrated test gauges.

1. Block the wheels to prevent the vehicle from moving.

2. Drain the reservoirs.

3. Install one tee fitting at the service port, and one tee fitting at one of the delivery ports of the proportioning valve. Then install a test gauge in each fitting.

4. Connect the tractor service and emergency trailer hose couplings to hose couplings that have been plugged, or connect to a trailer.

5. Start the engine and build system pressure to governor cutout. Make four or five full brake applications. Check the fittings installed at the proportioning relay valve for leakage. Tighten as needed.

10. Pull the trailer supply valve out.

11. Slowly apply the brakes, increasing the application pressure to 20 psi. Note that the delivery pressure rises to approximately 5–10 psi and remains constant as the pressure at the service port continues to rise until reaching 20 psi.

12. Release the brakes.

13. Apply the brakes again and slowly increase the service port pressure to approximately 60–70 psi while observing the pressure indicated on the pressure gauge installed at the delivery port. Delivery pressure should rise above the initial application pressure of 5–10 psi when service port pressure rises between 20–30 psi. The proportioned rate of delivery pressure should be approximately 3:1 (as an example, a 70-psi service pressure should give a delivered pressure of 15–25 psi).

14. Fully apply the brakes and note that both test gauges indicate the same pressures.

15. Remove the test gauges and tee fittings from the valve and reinstall the air lines.

6. Stop the engine.

7. With both the trailer air-supply valve and the parking brake valve pushed in, apply, HOLD, then release the service brakes several times at varying application pressures, while noting the reaction of the test gauges installed in the proportioning relay valve. Note that a prompt application occurs, can be held and releases promptly.

8. Check the differential pressure of the proportioning relay valve by applying 10 psi to the service port and noting the pressure indicated on the test gauge installed in the delivery port. Subtract the delivery port pressure from the 10 psi to obtain the differential. The pressure differential should be approximately 4 psi.

Some proportioning valves incorporate a relay piston return spring. When a return spring is used, the pressure differential will be higher.

9. Make and hold a full brake application (100 psi or more) and note that full pressure is delivered to the service brake chambers.

Page 100

LEAKAGE TESTS 1. Start the engine and build air system pressure until governor cutout.

2. Stop the engine.

3. With the trailer air supply valve pushed in, apply a soap-and-water solution to all three of the exhaust ports (two ports in the cover and one port in the body of the valve).

Leakage should not exceed a one-inch bubble in less than three seconds at any of the exhaust ports.

4. Fully apply the brakes, and again apply a soap-and-water solution to the three exhaust ports, and around the cover where it joins the valve body. Leakage should not exceed a one-inch bubble in three seconds at any of the exhaust ports, or at the cover.

Replace the proportioning valve if it fails any of the operational or leakage tests.

DESCRIPTION AND OPERATION PREVENTIVE MAINTENANCE

DESCRIPTION

앫

B, C, D Inspections — Remove any accumulated contaminants from around the valve and visually inspect the exterior of the valve for physical damage or signs of excessive corrosion.

Hose couplings provide a means of connecting and disconnecting the air lines between the tractor and trailer.

앫

B, C, D Inspections — Inspect all air line connections for signs of wear or physical damage. Replace as necessary.

앫

B, C, D Inspections — Test the air line fittings for excessive leakage and tighten or replace as necessary.

앫

B, C, D Inspections — Perform the leakage tests as described above.

앫

D Inspection — Perform the operational tests as described above.

Hose Couplings (Glad Hands) 122

LEAKAGE TESTS Connect the couplings to a dummy coupling that does not have an exhaust port. Pressurize the lines. Apply a soap-and-water solution to the coupling and check for leaks. Leakage should not exceed a one-inch bubble in one second.

If leakage occurs at the joint, replace the packing ring. If leakage occurs elsewhere, replace the coupling.

PREVENTIVE MAINTENANCE A, B, C, D Inspections — Check the couplings for defects that might affect sealing, and repair or replace as necessary.

Brake Chambers 123

Figure 123 — Single-Diaphragm Brake Chamber

Figure 122 — Hose Couplings (Glad Hands)

Page 101

DESCRIPTION AND OPERATION Single-Diaphragm Brake Chambers

124

125

Figure 124 — Multiple-Diaphragm Brake Chamber

DESCRIPTION The brake chamber is a diaphragm-type actuator assembly that converts the energy of air pressure into the mechanical force necessary to push the brake shoes into contact with the drums.

Generally, single-diaphragm brake chambers are used on front axles, while multiple-diaphragm spring brake chambers are used on rear axles.

Figure 125 — Single-Diaphragm Brake Chamber Cutaway

DESCRIPTION The single-diaphragm brake chamber has a pressure side which receives air pressure from the air system, and a non-pressure side which is opened to atmosphere. The diaphragm is held between the pressure and non-pressure plates with either a one-piece or two-piece clamp. The non-pressure plate is vented through holes in the plate. For installations that require the chamber to be weatherproof, venting is accomplished by passages drilled through the mounting bolts.

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DESCRIPTION AND OPERATION Air pressure entering the brake chamber pushes against the diaphragm and moves the push plate and rod assembly forward. Forward motion of the push rod assembly provides the force that pushes the brake shoes against the brake drums.

The greater the pressure applied to the diaphragm, the greater the force applied to the brakes. Conversely, when less pressure is applied to the diaphragm, less force is applied to the brakes.

When pressure is removed from the pressure side of the brake chamber, the force of the push-rod return spring, in combination with the brake-shoe return springs, returns the diaphragm to its released position, thus releasing the brakes.

PREVENTIVE MAINTENANCE A, B, C, D Inspections — Check push rod travel.

Travel should be as short as possible without allowing the brakes to drag. Adjust the slack adjusters, if necessary, to maintain proper push rod travel. Check the alignment of the push rod to slack adjuster from the release to full stroke positions. Make sure there is no binding. Check the angle formed by the slack adjuster arm and the push rod. Angle should not be greater than 90 degrees when the push rod is in the released position. The push rod should also form a 90-degree angle with the flat mounting surface of the brake chamber. Check the tightness of the mounting nuts. Check that all cotter pins are in place. Refer to “BRAKE ADJUSTMENT” on page 196.

OPERATIONAL TESTS 1. Apply the service brakes and observe that the push rods respond quickly, and with no indication of binding.

2. Release the brakes and observe that the push rods return quickly to the released position without binding.

3. Check push rod travel. Refer to “BRAKE ADJUSTMENT” on page 196. Travel should be as short as possible without allowing the brakes to drag.

In addition to the checks described above, perform the following checks: 앫

The breather cap or dust cover must be in place.

앫

Check that the service brake chamber clamping ring is evenly seated and the clamp band bolts are torqued to 25–30 lb-ft.

앫

Visually inspect the exterior surfaces of the brake chamber for signs of damage.

앫

Check that the mounting stud nuts are torqued to 100–115 lb-ft, and make sure that the hardened flat washers are in place.

앫

Check the air line fittings.

LEAKAGE TESTS 1. Make and hold a full service brake application.

2. Apply a soap-and-water solution to the clamping ring(s). If any leakage is detected, tighten the clamping ring only enough to stop the leakage. DO NOT OVERTIGHTEN the ring as this can distort the sealing surface or the ring.

3. Apply a soap-and-water solution to the area around the push rod hole. No leakage is acceptable. If leakage is evident, the diaphragm must be replaced.

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DESCRIPTION AND OPERATION Multiple-Diaphragm Spring Brake Chambers It is extremely important to use a retaining method when working on all spring brake chambers. The spring is under heavy compression and can expand rapidly and with enough force to cause serious personal injury. Methods of retention include an arbor press, safety cage and stud and capscrew arrangement. One of these methods should be used in addition to the precautions recommended by the spring brake chamber manufacturer.

126

OPERATION 127

Figure 126 — Multiple-Diaphragm Spring Brake Chamber Cutaway

DESCRIPTION Multiple-diaphragm spring brake chambers are generally used on rear axle assemblies to actuate the brakes for service, parking and emergency applications. One air chamber applies and releases the service brakes in the same manner as the single-diaphragm brake chamber, and a second air chamber, that contains a powerful compression spring, applies and releases the brakes for parking and emergency situations.

Figure 127 — Spring Brakes Released

Page 104

DESCRIPTION AND OPERATION During normal operation when the parking brake control valve is pushed in, air pressure is applied to the spring section of the brake chamber to cage the compression spring and hold it ready for parking or emergency situations. If air system pressure should drop to 40 psi or less, the compression spring expands and sets the brake shoes against the brake drums.

128

As an emergency backup, the spring brakes apply if air system pressure drops to 40 psi or less.

Proper precautions must be taken when servicing spring brakes. Spring brake chambers contain a very powerful spring that is under compression and could expand suddenly with enough force to cause serious personal injury or death. Spring brake chambers must be mechanically caged before servicing. To avoid serious injury while servicing spring brake chambers, the following precautions must be observed:

앫

Always block the wheels to prevent the vehicle from rolling while servicing the brake system or attempting to manually cage the spring brakes.

앫

If a spring brake chamber shows structural damage, NO attempt to service the unit should be made. The complete chamber should be replaced.

앫

If an uncaged spring brake chamber must be removed from the vehicle, it must be removed and dismantled according to the manufacturer’s recommendations.

앫

NEVER strike any part of the spring brake chamber with a hammer or any other heavy object, as structural damage may result.

앫

DO NOT drop a spring brake chamber, as the spring may forcefully release.

Figure 128 — Service Brakes Applied

Applying the treadle valve directs air pressure to the service portion of the spring brake chamber.

Pressure entering the chamber applies force against the diaphragm and push rod assembly to move the brake shoes into contact with the brake drum.

129

MANUAL RELEASE

Figure 129 — Spring Brakes Applied

Pulling the parking brake control valve out exhausts the pressure from the spring section of the chamber, allowing the compression spring to expand and apply the brakes for positive parking.

DO NOT attempt to mechanically release a spring if the spring brake chamber shows structural damage and/or the safety ears have been removed. (Gold Seal chambers do not have safety ears or clamps.) Attempting to cage the spring or disassembling the chamber may result in the forceful release of the spring chamber and its contents, which could result in serious injury or death.

Page 105

DESCRIPTION AND OPERATION 130

131

Figure 131 — Inserting Release Tool

Figure 130 — Spring Brake Chamber, Manual Release

1. Remove the cover from the center of the chamber to reveal the release tool keyhole.

2. Remove the release tool from the storage pocket found on the side of the chamber.

3. Assemble the washer and nut onto the release tool.

Page 106

4. Insert the release tool, crosspin end first, through the keyhole in the spring chamber and into the push plate. Making sure the crosspin has actually entered the plate, continue inserting until the release tool bottoms out.

DESCRIPTION AND OPERATION 132

133

Figure 132 — Turn Tool 1/4 Turn

5. When satisfied that the release tool is properly engaged, turn the tool 1/4 turn clockwise and pull up to seat into the crosspin slot.

6. Finger-tighten the nut against the washer.

Figure 133 — Tighten Release Tool Nut

7. Using a handwrench, tighten the release nut to manually cage the spring. DO NOT USE AN IMPACT WRENCH. Make sure that the service chamber push rod is retracting while the release nut is being tightened.

8. To ensure that the spring is properly caged, measure the release tool length from the nut to the end of the tool.

The following procedures are used to manually release the spring brakes only if pressure has been exhausted from the spring brake chambers.

If the springs are being manually caged with pressure still present in the chambers, only finger-tighten the release tool nut. Torquing the nut may cause push plate damage, which may result in sudden release of the spring.

Page 107

DESCRIPTION AND OPERATION Anchorlok Standard and Gold Seal Chambers

134

DO NOT overtorque the release tool or damage to the pressure plate may result.

Release nut torque should not exceed the following values: 앫 Cam-type chambers — 35 lb-ft (47 N폷m) maximum Gold Seal and steel chamber models: 앫

30″ chambers: 3.38″ minimum

앫

24″ chambers: 2.92″ minimum

Aluminum chamber models:

Figure 134 — Measure Release Tool Length

Release tool measurement should be as follows.

MGM Chambers 앫

Types 2424 and 3024 chambers: 3.25″

앫

Types 2430 and 3030 chambers: 3.00″

DO NOT exceed the release tool measurement lengths, and DO NOT exceed 50 lb-ft torque on the release nut. Damage may result to the pressure plate, which could prevent further manual release of the spring.

Page 108

앫

36″ chambers: 3.38″ minimum

앫

30″ chambers: 2.72″ minimum

앫

24″ chambers: 2.81″ minimum

앫

16″ chambers: 3.12″ minimum

앫

12″ chambers: 2.38″ minimum

If the dimensions cannot be met at the listed torque values, the spring brake chamber should be considered structurally damaged, and must be removed from the chassis and disassembled according to the chamber manufacturer’s recommendations.

After uncaging the power spring, always return the release tool to the storage pocket so that it is available in the event of an emergency situation.

DESCRIPTION AND OPERATION MGM Stopgard LD-Type Chambers To manually release the MGM Stopgard spring brake, remove the breather cap from the top of the chamber. Turn the release bolt counterclockwise until the power spring is fully caged. While turning the release bolt, observe that the service chamber push rod is retracting into the chamber the same approximate distance the release bolt is extending from the spring chamber.

OPERATIONAL TESTS Service Brakes Operational checks for the service portion of multi-diaphragm spring brake chambers are the same as for single-diaphragm chambers.

Spring Brakes

135

To prevent serious personal injury, perform the following:

앫

Before testing the operation of the spring brakes, block the wheels to prevent the vehicle from rolling when the parking brakes are released.

앫

Actuate the parking brake valve to apply the spring brakes. Note that the spring brakes apply promptly with no evidence of push rod bind.

앫

Release the spring brakes by actuating the parking brake valve and note that the spring brakes fully and promptly release without any push rod bind.

LEAKAGE TESTS 앫

With the spring brakes released, apply a soap-and-water solution around the spring brake chamber clamping ring. If leakage is detected, tighten the clamping ring only enough to stop the leakage. DO NOT exceed the recommended torque of the ring as the sealing surface or the ring could be distorted. Also check for leakage at the air line fittings.

Figure 135 — MGM Stopgard Manual Release

The power spring is manually caged when the release bolt extends from the spring chamber when measured as follows: 앫

Type 24 and 30 chambers: 2.25″ to 2.50″

앫

Type 36 chambers: 2.75″ to 3.00″

DO NOT apply more than 50 lb-ft (68 N폷m) torque to the release bolt.

Page 109

DESCRIPTION AND OPERATION PREVENTIVE MAINTENANCE 앫

A, B, C, D Inspections — Perform the following checks: —

The breather cap or dust cover must be in place.

The arrow on the breather cap installed on MGM brake chambers must point toward the ground. If a breather cap is installed, it must be checked periodically. If dirty or clogged, it must be replaced. On MGM LD-type chambers, remove the breather cap and check that release bolt torque is 50 lb-ft (clockwise).

—

Check that the spring brake chamber clamping ring is evenly seated and the clamp band bolts are torqued to 25–30 lb-ft.

NEVER remove or attempt to remove the spring brake chamber clamping ring without properly caging the spring. Serious personal injury may be the result. Refer to the chamber manufacturer’s service literature for proper disassembly procedures.

—

Check that the service brake chamber clamping ring is evenly seated and the clamp band bolts are torqued to 25–30 lb-ft.

—

Visually inspect the exterior surfaces of the brake chamber for signs of damage.

—

Check that the mounting stud nuts are torqued between 100–115 lb-ft, and make sure that the hardened flatwashers are in place.

—

Check all air line fittings.

Rotochambers 136

Figure 136 — Rotochamber Cutaway

Page 110

DESCRIPTION AND OPERATION DESCRIPTION

Long-Stroke Air Chambers

Rotochambers are generally used on chassis that have heavy-capacity front axle assemblies.

These chambers operate with the same principles as the previously described chambers except that a rolling-type diaphragm is used to move the push rod assembly. This type of diaphragm gives a constant output force throughout the entire chamber stroke.

DESCRIPTION

One end of the diaphragm is clamped to the inside wall of the chamber body by the outer clamp, and the other end is clamped between the diaphragm guide and the inner diaphragm clamp.

Brake application pressure entering the chamber through the inlet port acts upon the diaphragm and moves the diaphragm guide and the diaphragm forward. The diaphragm moves along the inside wall of the chamber body with a smooth rolling motion. The forward motion of the diaphragm and guide moves the push plate and the push rod forward. This moves the slack adjuster and pushes the brake shoes into contact with the brake drums.

When the brake application is released, the force of the diaphragm return spring moves the push rod and plate assembly, along with the diaphragm and diaphragm guide, back into the released position.

OPERATIONAL TESTS

Prior to 1/27/97, type 24 long-stroke brake chambers were standard equipment on 34,000to 44,000-lb rear axle suspensions, with type 30 brake chambers as an available option. After 1/27/97, type 30 brake chambers became the standard chamber on 34,000- to 44,000-lb rear axle suspensions.

The long-stroke concept provides increased stroke for reduced adjustment frequency, improved service chamber power and increased spring force for parking. Smaller chambers may be used while still developing adequate braking force.

There is a difference in diaphragm configuration between the long-stroke and standard chambers.

The diaphragm used in the long-stroke chamber has a depth of 1.53 inches (38.8 mm), while the standard diaphragm has a depth of 1.25 inches (31.8 mm). Stroke length is 2.50 inches (63.5 mm) for a long-stroke chamber and 2.25 inches (57.2 mm) for the standard-stroke chamber.

The standard-stroke diaphragm cannot be installed in the long-stroke chamber. To prevent confusion and/or mismatch of parts, both the diaphragm and housing(s) are identified by prominent markings.

1. Apply the brakes and observe that the push rods move out promptly and without binding.

2. Release the brakes and observe that the push rods return to the released position promptly and without binding.

3. Check push rod travel. Travel should be as short as possible without allowing the brakes to drag. Adjust travel as necessary. Refer to “BRAKE ADJUSTMENT” on page 196.

LEAKAGE TESTS 1. Loosen the rubber boot from around the push rod. Then make and hold a full brake application.

2. Coat the area with a soap-and-water solution. No leakage at this area is permitted. If bubbles are detected, the diaphragm is leaking and must be replaced.

Page 111

DESCRIPTION AND OPERATION 137

Figure 137 — Long-Stroke Chamber Identification

Page 112

DESCRIPTION AND OPERATION AIR DRYERS

DESICCANT-TYPE AIR DRYER 138

Description Air dryers remove moisture and other contaminants from the compressed air before it reaches the supply/service reservoir. The air dryer is installed in the compressor discharge line between the air compressor and the supply/ service reservoir, and is usually mounted to the frame rail behind the cab in an area of airflow while the truck is in motion.

There are two different types of air dryers: 앫

Desiccant Type — uses a replaceable desiccant material to dry the air.

앫

Aftercooler Type — uses heat dissipation to dry the air.

Some air dryers employ a thermostatically controlled heater to prevent air line and valve body freeze-ups when operating in subfreezing temperatures.

Figure 138 — Desiccant-Type Air Dryer

A typical desiccant-type air dryer consists of a desiccant cartridge through which the compressed air passes, and a valve body that contains a sump cavity, check valve, purge valve and the necessary ports for connecting the air dryer to the air system.

Contaminated, moisture-laden compressed air enters the air dryer through the supply port, and dry filtered air exits through the delivery port.

Control pressure from the governor enters the air dryer through the control port. While in operation, the air dryer alternates between two modes of operation: the charge (or drying) cycle and the purge cycle.

Page 113

DESCRIPTION AND OPERATION Charge (Drying) Cycle Compressed air flows through the compressor discharge line and enters the air-dryer supply port. It then flows through a filter (oil separator) where oil, water droplets and other contaminants are initially removed. Once through the filter, the air then flows into the desiccant cartridge where the remaining moisture is removed. Moisture clings to the desiccant material inside the cartridge rather than being absorbed by the desiccant. After flowing through the desiccant material, the dry, filtered compressed air exits the air dryer and flows into the supply reservoir. A small volume of air, however, is diverted into a purge area and is held there until the compressor unloads and the air-dryer purge cycle begins.

is regenerated, and the dryer is ready to begin the next charge cycle. The purge valve remains open until air system pressure drops to governor cut-in, at which point pressure at the control port is exhausted and the purge valve closes.

A one-way check valve prevents reservoir pressure from bleeding through the air dryer during the purge cycle.

AFTERCOOLER-TYPE AIR DRYER 139

The Brakemaster T2000 and the WABCO 1200P air dryers use a separate reservoir to hold the volume of purge air. The ArvinMeritor™ WABCO System Saver 1000, 1200 and 1200E, and the Bendix AD/SP dryers all use pressure from the supply and primary air reservoirs to purge the air dryer.

Purge Cycle When air system pressure reaches governor cutout, air compression stops. Air pressure is directed to the air-dryer control port by the governor, signaling the air dryer to begin the purge cycle. Control pressure received from the governor causes the purge valve assembly to open, which allows the pressurized air inside the dryer to backflush the desiccant bed, filter and sump cavity, and expel moisture and other contaminants from the dryer. At the same time, the volume of air held in the purge cavity (or reservoir) is metered through an orifice, then slowly passes through the desiccant cartridge in the direction opposite of flow during the charge cycle. The purge volume passes through the desiccant cartridge (at a pressure slightly higher than atmospheric) to remove the moisture being held by the desiccant material, then expels it through the purge valve.

The purge cycle should last between 10 and 60 seconds, depending upon air dryer design and the length of time it takes for the purge volume to flow through the desiccant cartridge. After the purge cycle is completed, the desiccant material Page 114

Figure 139 — Aftercooler-Type Air Dryer

An aftercooler-type air dryer uses heat dissipation to cool the air and condense the moisture, rather than a desiccant material.

Compressed air flows through the compressor discharge line and into the air dryer through the supply port. The compressed air circulates around the lower portion of the air dryer, through the exit tube, around the baffles and into the finned portion. It then passes through a wire-mesh filter before exiting through the delivery port.

DESCRIPTION AND OPERATION When the hot, moisture-laden air enters the finned portion of the air dryer, heat dissipates to the outside, causing the moisture in the air to condense and drop to the bottom of the dryer. At governor cutout, pressure is directed to the air dryer unloader valve by the governor. Upon receiving control pressure, the air dryer unloader valve opens and allows the pressurized air contained within the dryer, along with the accumulated moisture and other contaminants, to exhaust through the exhaust port. An internal check valve at the delivery port prevents a loss of system pressure through the air dryer while it is unloading.

Anchorlok “Moisture Lok” Dry Air Tank (Aftercooler Type) 140

Air Dryer Service The following air dryers are used on MACK chassis: 앫

Anchorlok (No longer manufactured as of 11/98)

앫

Bendix

앫

CR Brakemaster

앫

Cyclo-Gard (Aftercooler Type)

앫

Haldex

앫

Midland

앫

ArvinMeritor™ WABCO

The following operational checks and maintenance procedures cover some of the most popular models.

With all air dryer installations, proper routing of compressor discharge line is important. Except for the portion immediately after the compressor, the discharge line should run downhill to the air dryer. Avoid “goosenecks” in the routing and 90-degree elbows in the installation, as moisture could become trapped in these areas where it may freeze and block the compressor discharge line.

Figure 140 — Anchorlok Dry Air Tank Dryer

Page 115

DESCRIPTION AND OPERATION SPECIFICATIONS Manufacturer:

Anchorlok

Model:

DV85/DH85

Type:

Cooler

Maximum Flow Capacity:

36 SCFM

Heater:

12V

Purge Air Source:

Not Applicable

Pressure-Controlled Check Valve for System Purge:

Not Applicable

Purge Signal:

Pneumatic

Additional Valves and Piping for all Compressors Except Holset* Isolation Valve:

Not Required

Additional Valves and Piping for Holset Compressors Isolation Valve:

Not Required

Feedback Line and Check Valve:

Not Required

* Bendix Tu-Flo 1400 not included.

141

OPERATIONAL TESTS 1. Start the engine and build air system pressure to governor cutout.

2. Using a soap-and-water solution, check for leaks at all fittings and repair as required.

3. Apply and release the service brakes (using a minimum of 22 psi application pressure).

Note that the ejector valve expels contaminants.

4. Allow air system pressure to build again to governor cutout. At governor cutout, the line from the unloader port to the air dryer will be charged and contaminants will be forced into the valve cavity.

5. Reduce system pressure to governor cut-in.

Contaminants should be expelled from the air dryer valve.

Figure 141 — Anchorlok Dry Air Tank, Typical Piping Diagram

Page 116

DESCRIPTION AND OPERATION PREVENTIVE MAINTENANCE

The following maintenance should be performed in the spring and fall.

Remove the 1/8-inch pipe plug from the bottom of the air dryer assembly. Start the engine and build system pressure to governor cutout. Reduce system pressure by cycling the treadle valve so that the air compressor cycles between governor cut-in and cutout three or four times. As the compressor is cycling, the accumulated moisture and contaminants are being expelled from the diaphragm area of the valve, ensuring that the line to the ejector valve is clear. Shut the engine off and reinstall the pipe plug when the procedure is complete.

142

The Anchorlok “Moisture Lok” dry air tank is no longer available from the manufacturer. If repair of a dry air tank is not possible, it can be replaced with a Bendix AD-IP air dryer. On chassis equipped with a Bendix Tu-Flo 1400 air compressor and used in bulk tank unloading operations, the Bendix AD-IP may not provide satisfactory performance. In these applications, a WABCO Twin air dryer may be an acceptable alternative.

REPLACING AN ANCHORLOK DRY AIR TANK WITH A BENDIX AD-IP AIR DRYER In November 1998, Anchorlok Corporation discontinued manufacture of the Anchorlok Dry Air Tank. If repair of a defective dry air tank is not possible, it can be replaced with a Bendix AD-IP air dryer.

Dry Air Tank Removal and Reinstallation 1. Apply the parking brakes and block the wheels to prevent the vehicle from moving.

2. Open the reservoir drain valves and completely drain the air system.

3. Disconnect the inlet, outlet and purge control air lines from the dry air tank.

4. Unplug the wire harness from the purge valve heater.

5. Remove the fittings from the inlet, outlet and purge control ports and save the fittings for later reuse.

Figure 142 — Remove Pipe Plug

On chassis equipped with a Holset air compressor, special fittings, valves and a make-up air line are used. These fittings, valves and make-up line must be removed from the Anchorlok dry air tank and retained for possible reuse when connecting the AD-IP dryer.

6. Remove the dry air tank from the frame mounting bracket.

7. Remove the dry air tank frame mounting bracket from the frame rail.

Page 117

DESCRIPTION AND OPERATION 8. Install a new AD-IP air dryer frame mounting bracket, using the existing hardware, or new hardware.

2. Install a new 1/2″ NPTF-to-#10 flared, straight fitting, into the AD-IP air dryer inlet port.

9. Install the AD-IP air dryer to the frame mounting bracket. Use four bolts and four nuts to secure the air dryer to the mounting bracket.

3. Install a 1/4″ NPTF-to-#4 flared, straight fitting, into the AD-IP dryer control port.

Connecting the Air Lines to the Dryer Air line connections for the air dryer are different for Bendix and Holset air compressors.

Depending upon which air compressor is installed on the chassis, connect the air dryer as follows: Connecting the AD-IP Air Dryer Air Lines on a Chassis Equipped with a Bendix Air Compressor 1. Install the 1/2″ NPTF-to-#10 flared, 90-degree elbow fitting, that was removed from the dry air tank discharge port to the AD-IP air dryer discharge port.

4. Connect the Bendix air compressor discharge line into the AD-IP air dryer inlet port and the supply reservoir feed line to the AD-IP outlet port. Refer to the following figure for an illustration of how the air line connections are routed.

In some instances, it may be necessary to fabricate new #10 steel braided cloth lines to properly accommodate the new AD-IP air dryer.

143

Figure 143 — Typical AD-IP Piping with Bendix Air Compressor

Page 118

DESCRIPTION AND OPERATION

The air compressor discharge line should slope continuously downward from the top of the transmission to the air dryer inlet port. There should not be any area of the discharge line that drops below the inlet port. This would create an area where moisture could collect, freeze and eventually block the compressor discharge line.

Connecting the AD-IP Air Dryer Air Lines on a Chassis Equipped with a Holset Air Compressor 1. Install a new, special one-way check valve in the outlet port of the AD-IP air dryer.

2. Install a 1/2″ NPTF special street tee fitting in the AD-IP air dryer inlet port.

3. Install a 1/2″ NPTF straight-to-#12 flared fitting into the female port of the special street tee fitting, directly opposite the male pipe end.

4. Install a 1/2″-to-1/4″ NPTF adapter fitting and the 1/4″ NPTF-to-#4 90-degree elbow fitting in the remaining female port of the special street tee fitting.

5. Install a 1/4″ NPTF-to-#4 flared, straight fitting into the control port of the AD-IP dryer.

6. Connect the Holset air compressor discharge line to the AD-IP inlet port, and connect the purge control line into the air dryer purge port.

The air compressor discharge should slope continuously downward from the top of the transmission to the air dryer inlet port. There should not be any area of the compressor discharge line that drops below the inlet port, as this would create an area where moisture could possibly collect, freeze and eventually block the air compressor discharge line.

7. Connect the supply reservoir feed line to the special one-way check valve installed in the AD-IP air dryer outlet port.

8. Install the #4 make-up air line from the special one-way check valve to the special street tee fitting installed in the air dryer inlet port. One end of this make-up line requires a 90-degree, #4 hose end, to connect either to the one-way check valve, or the special street tee fitting. Positioning of this 90-degree #4 hose end depends upon air line routing. Refer to the following note and illustrations for proper hose routing and fitting orientation.

Routing of the supply reservoir feed line and the make-up line should remain the same as it was for the Anchorlok dry air tank. The supply reservoir feed line may have been routed toward the rear of the chassis and over the frame rail to the supply reservoir. Install the fittings in the air dryer to retain the same air line routing. Refer to the following figure for an illustration of the air line routing configurations and fitting positions.

Page 119

DESCRIPTION AND OPERATION 144

Figure 144 — Typical Piping for AD-IP Air Dryer with Holset Air Compressor

9. After completing the installation, start the engine and allow the air system pressure to build to governor cutout. Stop the engine and check the air dryer installation for air leaks.

Page 120

DESCRIPTION AND OPERATION Bendix AD-9 and AD-9 Soft Seat Air Dryers 145

Figure 145 — Bendix AD-9

SPECIFICATIONS FOR AD-9 Manufacturer:

Bendix

Model:

AD-9 Part No. 26QE377

Type:

Desiccant

Maximum Flow Capacity:

25 SCFM

Heater:

12V or 24V

Purge Air Source:

Internal

Pressure-Controlled Check Valve for System Purge:

Not Applicable

Purge Signal:

Pneumatic

Additional Valves and Piping for All Compressors Except Holset* Isolation Valve:

Not Required

Additional Valves and Piping for Holset Compressors Isolation Valve:

Required

Feedback Line and Check Valve:

Required

* Bendix Tu-Flo 1400 not included.

Page 121

DESCRIPTION AND OPERATION 146

Figure 146 — Bendix AD-9, Typical Piping Diagram

SPECIFICATIONS FOR AD-9 SOFT SEAT Manufacturer:

Bendix

Model:

AD-9 Soft Seat Part No. 26QE384

Type:

Desiccant

Maximum Flow Capacity:

25 SCFM

Heater:

12V or 24V

Purge Air Source:

Internal

Pressure-Controlled Check Valve for System Purge:

Not Applicable

Purge Signal:

Pneumatic

Additional Valves and Piping for All Compressors Except Holset* Isolation Valve:

Not Required

Additional Valves and Piping for Holset Compressors Isolation Valve:

Not Required

Feedback Line and Check Valve:

Required

* Bendix Tu-Flo 1400 not included.

Page 122

DESCRIPTION AND OPERATION 147

Figure 147 — Bendix AD-9 Soft Seat, Typical Piping Diagram

OPERATIONAL AND LEAKAGE TESTS 1. Test the delivery-port check valve assembly by installing an accurately calibrated air-pressure test gauge into the outlet port of the supply reservoir, then by starting the engine and building air system pressure to governor cutout. Observe the reading on the test gauge. A rapid loss of pressure could indicate a failed outlet port check valve.

A failed outlet port check valve can be confirmed as follows: 앫

Shut off the engine.

앫

Drain the air system.

앫

Remove the check valve assembly from the end cover.

앫

Apply air pressure to the inlet port of the check valve.

앫

Apply a soap-and-water solution to the outlet port of the check valve. Leakage should not exceed a one-inch bubble in one second. If leakage exceeds this limit, replace the outlet port check valve.

2. Check for excessive leakage around the purge valve by starting the engine and, with the compressor in the loaded mode (compressing air), by applying a soap-and-water solution to the exhaust port of the purge valve housing assembly.

Observe that leakage does not exceed a one-inch bubble in one second. If leakage exceeds the maximum, service the purge valve assembly.

3. Check that all reservoir draincocks are closed. Then start the engine and build air system pressure to governor cutout. Note that the dryer purges with an audible escape of air. Rapidly cycle the treadle valve until system pressure is reduced to governor cut-in. Note that the air system rebuilds to full system pressure and that the air dryer purges.

Page 123

DESCRIPTION AND OPERATION 4. Check the operation of the safety valve by pulling on the exposed stem found at the bottom of the dryer, while the engine is running and the compressor is in the loaded mode (compressing air). There must be an exhaust of air while the stem is held, and the valve should reseat when the stem is released.

5. Check for leakage at all air lines and fittings leading to and from the air dryer. Check air line integrity.

6. Check the operation of the end cover heater and thermostat assembly during cold weather operations as follows: 앫

앫

Electric Power to the Air Dryer — With the ignition switch in the ON position, use a test light or multi-meter set to measure DC voltage. Test for voltage to the heater and thermostat assembly by unplugging the electrical connector from the dryer and placing the leads of the test light or multi-meter on the two pins of the male connector. If voltage is not present, look for a blown fuse, broken wires or corrosion in the vehicle wiring harness. Also check for a proper ground connection.

Thermostat and Heater Operation — Turn the ignition switch off and cool the end cover assembly to a temperature below 40°F (5°C). Using an ohmmeter, measure the resistance between the electrical pins in the female connector. Resistance should be between 1.5–3.0 ohms for a 12-volt heater assembly, and between 6.8–9.0 ohms for a 24-volt heater assembly.

Page 124

Some early models of the AD-9 air dryer have resistance readings between 1.0–2.5 ohms for the 12-volt heater, and between 4.8–7.2 ohms for the 24-volt heater.

Warm the end cover assembly to a temperature above 90°F (32°C) and again measure the resistance. Resistance should exceed 1000 ohms. If the measured resistance is not within the specified values at both cold and hot measurements, replace the purge valve assembly, which includes the heater and thermostat assembly.

PREVENTIVE MAINTENANCE At every A, B, C, D inspection interval: 1. Check for moisture in the air system by opening the reservoir draincocks (or valves) and checking for the presence of water. If moisture is present, the desiccant may require replacement. However, the following conditions may also contribute to water accumulation in the system and should be considered before replacing the desiccant: 앫

An outside air source, which did not pass through the desiccant bed, was used to charge the air system.

앫

Air usage is exceptionally high and not normal for a highway vehicle. This may be due to accessory air demands or some unusual air requirement that does not allow the compressor to load and unload in a normal fashion. Also check for excessive amounts of air system leakage.

앫

The air dryer was installed in a system that was previously used without an air dryer. The system will most likely be saturated with moisture and requires several weeks of operation to dry out.

앫

Location of the air dryer is too close to the compressor.

앫

In areas where more than a 30-degree range of temperature can occur in a single day, a small amount of moisture is normal and should not be considered an indication that the air dryer is not operating properly.

DESCRIPTION AND OPERATION 2. Small amounts of oil in the system may be normal and should not be considered a reason to replace the desiccant. An oil-stained desiccant can function adequately.

3. Check the mounting bolts for tightness.

Retorque to 270–385 lb-in (31–44 N폷m).

4. Perform the tests as outlined under OPERATIONAL AND LEAKAGE TESTS.

Every 300,000 miles/483 000 km, 10,800 hours or 3 years (whichever occurs first), rebuild the air dryer and replace the desiccant cartridge.

The desiccant cartridge change interval may vary between vehicles. Although a typical desiccant cartridge should last approximately three years, some vehicle applications may require that the cartridge be changed more often, while in other applications, the cartridge may perform adequately for more than three years. In order to take maximum advantage of desiccant life and ensure that replacement occurs only when necessary, it is important that the operational and leakage tests be performed on a regular basis.

Page 125

DESCRIPTION AND OPERATION Bendix AD-IP Air Dryer 148

Figure 148 — Bendix AD-IP Air Dryer

SPECIFICATIONS Manufacturer:

Bendix

Model:

AD-IP

Type:

Desiccant

Maximum Flow Capacity:

25 SCFM

Heater:

12V or 24V

Purge Air Source:

Internal

Pressure-Controlled Check Valve for System Purge:

Not Applicable

Purge Signal:

Pneumatic

Additional Valves and Piping for All Compressors Except Holset* Isolation Valve:

Not Required

Additional Valves and Piping for Holset Compressors Isolation Valve:

Not Required

Feedback Line and Check Valve:

Required

* Bendix Tu-Flo 1400 not included.

Page 126

DESCRIPTION AND OPERATION 149

Figure 149 — Bendix AD-IP, Typical Piping Diagram

OPERATIONAL AND LEAKAGE TESTS 1. Test the delivery-port check valve assembly by installing an accurately calibrated air-pressure test gauge into the outlet port of the supply reservoir, then by starting the engine and building air system pressure to governor cutout. Observe the reading on the test gauge. A rapid loss of pressure could indicate a failed outlet-port check valve.

A failed outlet-port check valve can be confirmed as follows: 앫

Shut off the engine.

앫

Drain the air system to a point below governor cut-in (usually not less than 95 psi).

앫

Bleed residual air pressure from the compressor discharge line by loosening the fitting.

앫

Remove the plug located in the air dryer end cover, adjacent to the air dryer delivery port.

앫

Disconnect the air dryer delivery line and apply compressed air to the air dryer delivery port.

앫

Apply a soap-and-water solution to the opened port from where the plug was removed. Leakage should not exceed a one-inch bubble in one second. If leakage exceeds this limit, replace the outlet-port check valve.

앫

Reconnect all fittings and reinstall the plug.

Page 127

DESCRIPTION AND OPERATION 2. Check for excessive leakage around the purge valve by starting the engine and, with the compressor running in the loaded mode (compressing air), by applying a soap-and-water solution to the purge-valve exhaust port. Observe that leakage does not exceed a one-inch bubble in one second. If leakage exceeds the maximum, service the purge valve assembly.

3. Check that all reservoir draincocks are closed. Then start the engine and build air system pressure to governor cutout. Note that the dryer purges with an audible escape of air. Rapidly cycle the treadle valve until system pressure is reduced to governor cut-in, and note that the air system rebuilds to full system pressure and that the air dryer purges.

PREVENTIVE MAINTENANCE At every A, B, C, D inspection interval: 1. Check for moisture in the air system by opening the reservoir draincocks (or valves) and checking for the presence of water. If moisture is present, the desiccant may require replacement. However, the following conditions may also contribute to water accumulation in the system and should be considered before replacing the desiccant: 앫

An outside air source, which did not pass through the desiccant bed, was used to charge the air system.

앫

Air usage is exceptionally high and not normal for a highway vehicle. This may be due to accessory air demands or some unusual air requirement that does not allow the compressor to load and unload in a normal fashion. Also check for excessive amounts of air system leakage.

앫

The air dryer was installed in a system that was previously used without an air dryer. The system will most likely be saturated with moisture and requires several weeks of operation to dry out.

앫

Location of the air dryer is too close to the compressor.

앫

In areas where more than a 30-degree range of temperature can occur in a single day, a small amount of moisture is normal and should not be considered an indication that the air dryer is not operating properly.

앫

Small amounts of oil in the system may be normal and should not be considered a reason to replace the desiccant. An oil-stained desiccant can function adequately.

4. Check for leakage at all air lines and fittings leading to and from the air dryer. Check air line integrity.

5. Check the operation of the end cover heater and thermostat assembly during cold weather operations as follows: 앫

앫

Electric Power to the Air Dryer — With the ignition switch in the ON position, use a test light or a multi-meter set to DC voltage. Test for voltage to the heater and thermostat assembly by unplugging the electrical connector from the dryer and placing the leads of the test light or multi-meter on the two pins of the male connector. If voltage is not present, look for a blown fuse, broken wires or corrosion in the vehicle wiring harness. Also check for a proper ground connection.

Thermostat and Heater Operation — During cold weather operations, turn the ignition switch off and cool the end cover assembly to a temperature below 40°F (5°C). Using an ohmmeter, measure the resistance between the electrical pins in the female connector. Resistance should be between 1.5–3.0 ohms for a 12-volt heater assembly, and between 6.8–9.0 ohms for a 24-volt heater assembly.

Warm the end cover assembly to a temperature above 90°F (32°C) and again measure the resistance. Resistance should exceed 1000 ohms. If the measured resistance is not within the specified values at both cold and hot measurements, replace the heater and thermostat assembly.

Page 128

DESCRIPTION AND OPERATION 2. Check the mounting bolts for tightness.

Retorque to 270–385 lb-in (31–44 N폷m).

3. Perform the tests as outlined under OPERATIONAL AND LEAKAGE TESTS. Every 300,000 miles/483 000 km, 10,800 hours or 3 years (whichever occurs first), rebuild the air dryer and replace the desiccant cartridge.

The desiccant cartridge change interval may vary between vehicles. Although a typical desiccant cartridge should last approximately three years, some vehicle applications may require that the cartridge be changed more often, while in other applications, the cartridge may perform adequately for more than three years. In order to take maximum advantage of desiccant life and ensure that replacement occurs only when necessary, it is important that the operational and leakage tests be performed on a regular basis.

Page 129

DESCRIPTION AND OPERATION Bendix AD-SP Air Dryer 150

Figure 150 — Bendix AD-SP Air Dryer

SPECIFICATIONS Manufacturer:

Bendix

Model:

AD-SP

Type:

Desiccant

Maximum Flow Capacity:

30 SCFM

Heater:

12V or 24V

Purge Air Source:

Brake System

Pressure-Controlled Check Valve for System Purge:

Required

Purge Signal:

Pneumatic

Additional Valves and Piping for All Compressors Except Holset* Isolation Valve:

Not Required

Additional Valves and Piping for Holset Compressors Isolation Valve:

Not Required

Feedback Line and Check Valve:

Required

* Bendix Tu-Flo 1400 not included.

Page 130

DESCRIPTION AND OPERATION 151

Figure 151 — Bendix AD-SP, Typical Piping Diagram

OPERATIONAL AND LEAKAGE TESTS 1. Check for excessive leakage around the purge valve by starting the engine. With the compressor running in the loaded mode (compressing air), apply a soap-and-water solution to the purge-valve exhaust port and observe that leakage does not exceed a one-inch bubble in five seconds. If leakage exceeds the maximum, service the purge valve assembly.

2. Check for leakage around the desiccant by applying a soap-and-water solution around the desiccant cartridge seal while the engine is running and the compressor is in the loaded mode (compressing air). Observe that no leakage occurs. If leakage is noted, tighten the cartridge with a strap wrench.

Then retest for leakage.

3. Shut off the engine.

4. Install one hose of the dual-needle test gauge in the primary reservoir, and the second hose in the secondary reservoir.

5. Start the engine and build system pressure to governor cutout.

6. When system pressure reaches governor cutout, note that the air dryer purges with an audible escape of air. The purge cycle should last approximately 10–15 seconds.

7. During the purge cycle, observe the dual-needle test gauge and note that the needle indicating primary system pressure indicates 10 psi less than the needle indicating secondary system pressure. 앫

If the test gauge does not indicate a pressure drop during the purge cycle, check the pressure-controlled check valve installed in the primary reservoir and replace as required.

Page 131

DESCRIPTION AND OPERATION 앫

If, during the purge cycle, the test gauge indicates a pressure drop of greater than 15 psi and no other air-operated components are using air, check for and correct any air leaks or other air system malfunctions.

8. With the system pressurized, check for air leaks by applying a soap-and-water solution to all connections and fittings where air pressure is present. Repair any leaks detected.

PRESSURE-CONTROLLED CHECK VALVE TESTS

The pressure-controlled check valve is installed in the primary air reservoir in place of, not in addition to, the one-way check valve. The system will not function properly if there are any additional check valves installed between the air dryer and the primary reservoir.

The pressure-controlled check valve has an arrow embossed on the valve body to indicate the direction of airflow through the valve. The valve is properly installed when the arrow is pointing toward the reservoir. If a malfunction is indicated, always check that the valve is installed properly.

PREVENTIVE MAINTENANCE At every A, B, C, D inspection interval: 1. Check for moisture in the air system by opening the reservoir draincocks (or valves) and checking for the presence of water. If moisture is present, the desiccant may require replacement. However, the following conditions may also contribute to water accumulation in the system and should be considered before replacing the desiccant: 앫

An outside air source, which did not pass through the desiccant bed, was used to charge the air system.

앫

Air usage is exceptionally high and not normal for a highway vehicle. This may be due to accessory air demands or some unusual air requirement that does not allow the compressor to load and unload in a normal fashion. Also check for excessive amounts of air system leakage.

앫

The air dryer was installed in a system that was previously used without an air dryer. The system will most likely be saturated with moisture and requires several weeks of operation to dry out.

앫

Location of the air dryer is too close to the compressor.

앫

In areas where more than a 30-degree range of temperature can occur in a single day, a small amount of moisture is normal and should not be considered an indication that the air dryer is not operating properly.

앫

Small amounts of oil in the system may be normal and should not be considered a reason to replace the desiccant. An oil-stained desiccant can function adequately.

1. Install an accurately calibrated pressure gauge in the primary air reservoir.

2. Start the engine.

3. Open the drain valve on the secondary reservoir and drain system pressure down to 80 psi or lower.

4. Check the test gauge and note that pressure is 95 ±5 psi. 앫

If the test gauge indicates less than 85 psi, check the air system for air leaks. If no significant leakage can be located, replace the pressure-controlled check valve. Then retest.

앫

If the test gauge readings do not change or do not fall below 105 psi, the pressure-controlled check valve may be shutting off at 105 psi or higher.

Replace the valve. Then retest.

Page 132

DESCRIPTION AND OPERATION 2. Check the mounting bolts for tightness.

Retorque to 270–385 lb-in (31–44 N폷m).

3. Perform the tests as outlined under OPERATIONAL AND LEAKAGE TESTS. Every 300,000 miles/483 000 km, 10,800 hours or 3 years (whichever occurs first), rebuild the air dryer and replace the desiccant cartridge.

The desiccant cartridge change interval may vary between vehicles. Although a typical desiccant cartridge should last approximately three years, some vehicle applications may require that the cartridge be changed more often, while in other applications, the cartridge may perform adequately for more than three years. In order to take maximum advantage of desiccant life and ensure that replacement occurs only when necessary, it is important that the operational and leakage tests be performed on a regular basis.

Page 133

DESCRIPTION AND OPERATION CR Brakemaster Models 62 and 68 (Aftercooler Type) 152

Figure 152 — CR Brakemaster Air Dryer

SPECIFICATIONS Manufacturer:

CR Brakemaster

Model:

62/68

Type:

Cooler/Separator

Heater:

12V

Purge Air Source:

Not Applicable

Pressure-Controlled Check Valve for System Purge:

Not Applicable

Purge Signal:

Pneumatic

Additional Valves and Piping for All Compressors Except Holset* Isolation Valve:

Required

Additional Valves and Piping for Holset Compressors Isolation Valve:

Required

Feedback Line and Check Valve:

Required

* Bendix Tu-Flo 1400 not included.

Page 134

DESCRIPTION AND OPERATION 153

Figure 153 — CR Brakemaster Models 62 and 68, Typical Piping Diagram

OPERATIONAL TESTS 1. Check all hoses and fittings for tightness.

2. Start the engine and build system pressure to governor cutout.

3. When reaching governor cutout, check the air dryer exhaust valve and note that it is exhausting a small quantity of air.

4. Make several brake applications until the pressure drops to governor cut-in. When reaching governor cut-in, note that the exhaust valve closes and air is no longer exhausting. The exhaust valve should remain closed while system pressure is building.

5. Shut off the engine.

6. With the system pressurized, check the air dryer fittings for air leaks. Correct as required.

앫

Check that the cooling fins have not been painted.

앫

Check all the air lines at the air dryer to be sure they are not kinked, cracked, broken or abraded.

앫

Start the engine and pressurize the air system.

앫

Allow the compressor to cycle between governor cut-in and cutout several times.

앫

Compare the temperature of the inlet and outlet ports by feeling them with the hand.

The inlet port may be very warm.

The inlet port should be warmer than the outlet port, and the outlet port should be slightly above ambient temperature.

PREVENTIVE MAINTENANCE 앫

Occasionally steam-clean the cooling fins of the air dryer to remove accumulated road grime.

Page 135

DESCRIPTION AND OPERATION CR Brakemaster T2000 and T3000 Air Dryers 154

Figure 154 — CR Brakemaster Turbo 2000

SPECIFICATIONS FOR T2000 AIR DRYER Manufacturer:

CR Brakemaster

Model:

T2000

Type:

Desiccant

Maximum Flow Capacity:

24 SCFM

Heater:

12V or 24V

Purge Air Source:

Separate Purge Tank

Pressure-Controlled Check Valve for System Purge:

Not Applicable

Purge Signal:

Pneumatic

Additional Valves and Piping for All Compressors Including Holset* Isolation Valve:

Not Required

Feedback Line and Check Valve:

Not Required

* Bendix Tu-Flo 1400 not included.

Page 136

DESCRIPTION AND OPERATION 155

Figure 155 — T2000 Typical Piping Diagram

SPECIFICATIONS FOR T3000 AIR DRYER Manufacturer:

CR Brakemaster

Model:

T3000

Type:

Desiccant

Maximum Flow Capacity:

24 SCFM

Heater:

12V or 24V

Purge Air Source:

Internal

Pressure-Controlled Check Valve for System Purge:

Not Applicable

Purge Signal:

Pneumatic

Additional Valves and Piping for All Compressors Including Holset* Isolation Valve:

Not Required

Feedback Line and Check Valve:

Not Required

* Bendix Tu-Flo 1400 not included.

Page 137

DESCRIPTION AND OPERATION Bleed Valve and Check Valve Tests

156

1. Start the engine and build air system pressure to governor cutout and allow the air dryer to exhaust.

2. Stop the engine and listen for exhausting air at the exhaust port. After an initial exhaust, air should continue to exhaust approximately 45–60 seconds. 앫

If no air was exhausted, indicating that a purge cycle did not occur, inspect the bleed valve and repair or replace as required.

앫

If air continued to exhaust after 45–60 seconds passed, test the function of the check valve and repair or replace as necessary.

Unloader Valve Tests — Compressor Unloaded 1. Start the engine, build air system pressure to governor cutout and allow the air dryer to exhaust.

Figure 156 — T3000 Typical Piping Diagram

OPERATIONAL TESTS Air Dryer Pressure Checks 1. With the engine stopped, open the reservoir drain valves and completely drain the air system.

2. Start the engine and build air system pressure to approximately 100 psi. Do not allow the air dryer to exhaust.

3. Stop the engine.

4. With the engine stopped, apply a soap-and-water solution around the joint between the desiccant cartridge and the base plate of the air dryer assembly. If leaks are evident, the desiccant requires replacement.

5. On Turbo 2000 models, use a soap-and-water solution to check for air leaks at the purge reservoir air line connections.

Page 138

2. Cycle the air dryer between the charge and purge cycles several times by rapidly cycling the treadle valve to decrease air pressure below governor cutout. Then allow system pressure to rebuild. 앫

If the dryer fails to unload or the unloader valve sticks, the valve should be replaced.

DESCRIPTION AND OPERATION Unloader Valve Tests — Compressor Loaded

PREVENTIVE MAINTENANCE

1. Start the engine and build system pressure to approximately 100 psi (just before governor cutout). Do not allow the compressor to unload.

At each A, B, C, D inspection interval, check air dryer operation as described above. Also check for moisture in the system by draining the supply tank and checking for the presence of moisture.

2. Stop the engine and listen for leaking air at the exhaust port.

Replace the desiccant cartridge every 2–3 years.

앫

앫

If air is leaking at the exhaust port, remove the air line from the unloader valve nut. If the air leak stops, repairing or replacing the governor is required.

Always replace the desiccant cartridge after rebuilding the air compressor.

If air continues to leak after repairing or replacing the governor, it is necessary to replace the unloader valve.

Page 139

DESCRIPTION AND OPERATION Cyclo-Gard Air Dryer Models 17 and 22

158

157

Figure 158 — Cyclo-Gard Models 17 and 22 Typical Piping Diagram

Figure 157 — Cyclo-Gard Aftercooler Air Dryer

SPECIFICATIONS Manufacturer:

Maradyne Corp.

Model:

17 and 22

Type:

Aftercooler

Maximum Flow Capacity:

Model 17 —20 SCFM Model 22 —40 SCFM

Heater:

12V or 24V

Purge Air Source:

Not Applicable

Pressure-Controlled Check Valve for System Purge:

Not Applicable

Purge Signal:

Pneumatic

Additional Valves and Piping for Bendix* and ArvinMeritor Compressors Isolation Valve: * Bendix Tu-Flo 1400 not included.

Page 140

Not Required

DESCRIPTION AND OPERATION OPERATIONAL TESTS 1. Start the engine and build air system pressure to governor cutout.

2. With air system pressure at governor cutout and the air compressor running unloaded, check that the air dryer discharges. The discharge cycle should last only a few seconds. 앫

If the discharge cycle lasts longer than a few seconds and the dryer is constantly cycling 30–50 seconds apart, inspect the air dryer for a faulty check valve. Repair or replace as necessary.

앫

The air dryer unloader valve should only be opened when pressure is applied from the governor when the compressor is running in the unloaded mode. When the compressor is running in the unloaded mode, the unloader valve maintains 35 psi in the air dryer to prevent a loss of turbcharged air. This minimizes the pumping of low pressure air from an unloaded single-cylinder air compressor. If the unloader valve remains open while the compressor is compressing air, the air system cannot be brought up to normal operating pressure, since air intended for the reservoirs is escaping through the opened unloader valve. If the unloader valve remains open while the compressor is in a compression mode, either the unloader valve or the governor may be faulty. To determine the cause, crack open the control-port air line fitting at the unloader valve cap slightly and note if any air escapes.

The control line from the governor to the air dryer may be pressurized. Use caution when cracking the fitting open.

Escaping air indicates that the control line is pressurized and that the governor is defective. Repair or replace the governor as necessary. If no air escapes from the control line when the fitting is cracked open and the air dryer unloader valve remains open, the valve is faulty and must be replaced.

3. With the engine stopped, check the air dryer function by draining the supply reservoir and checking for the presence of moisture. A high accumulation of moisture in the supply reservoir indicates that the baffle may be damaged and the pressurized air is not being cooled sufficiently.

PREVENTIVE MAINTENANCE At each 200,000 mile/320 000 km interval or every 2 years (whichever occurs first), disassemble, inspect and clean the air dryer.

Check the baffles and other parts for damage.

Remove the wire mesh filter and soak in a suitable nonflammable solvent to remove the accumulation of oil. Be sure to dry the filter before reinstalling.

Unloader Valve Maintenance 1. Block the wheels to prevent the vehicle from moving. Then completely drain the air system.

2. Disconnect the air line from the control port of the air dryer unloader valve.

3. Drain any water that may be in the line.

4. Loosen the unloader valve locknut and unscrew the cap from the body.

5. Remove the piston and dry any water that may be found in the cap.

6. Clean and lubricate the valve with a low temperature grease (Dow 55 or equivalent).

7. Before reassembling the cap-and-piston assembly to the body, depress and release the plunger inside the body. Plunger travel should be approximately 1/4 inch, and the washer should remain flush with the end of the body. If plunger travel is not normal, remove the unloader valve from the body, clean and reinstall.

8. Reassemble the valve cap to the body with the open side of the piston toward the body.

Fully tighten the valve cap to the body. Then tighten the locknut.

Page 141

DESCRIPTION AND OPERATION Winterizing the Air Dryer

Haldex Dry E.S.T. Air Dryer

To prepare the Cyclo-Gard air dryer for winter service, heater function should be checked, and the unloader valve preventive maintenance and function check should be performed (as described above). Test function of the heater as follows:

159

Testing the heater involves lowering the heater temperature below 35°F (2°C).

1. Disconnect and remove the heater from the air dryer.

2. Place the heater in a freezer for one hour.

3. After one hour, remove the heater from the freezer, connect and energize the heater.

The heater should begin to heat, and continue heating until the thermostat reaches 75°F (24°C).

At 75°F (24°C), the thermostat should turn the heater off. If the heater fails the above test, it must be replaced.

Figure 159 — Haldex Dry E.S.T. Air Dryer

SPECIFICATIONS FOR HALDEX DRY E.S.T. AIR DRYER FOR BOTH BENDIX AND HALDEX AIR COMPRESSORS Manufacturer:

Haldex

Model:

Dry E.S.T.

MACK Part Number:

26QE512-Bendix 26QE513-Holset

Type:

Desiccant

Maximum Flow Capacity:

30 SCFM

Heater:

12V or 24V

Purge Air Source:

Brake System

Pressure-Controlled Check Valve for System Purge:

Required

Purge Signal:

Pneumatic

Additional Valves and Piping for All Compressors Excluding Holset* Isolation Valve:

Not Required

Additional Valves and Piping for Holset Compressors Isolation Valve:

Required

Feedback Line and Check Valve:

Required

* Bendix Tu-Flo 1400 not included.

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DESCRIPTION AND OPERATION 160

Figure 160 — Haldex Dry E.S.T., Typical Piping Diagram for Bendix and Holset Air Compressors

SPECIFICATIONS FOR HALDEX DRY E.S.T. AIR DRYER FOR HOLSET HD AIR COMPRESSOR Manufacturer:

Haldex

Model:

Dry E.S.T.

MACK Part Number:

26QE514-Holset HD

Type:

Desiccant

Maximum Flow Capacity:

30 SCFM

Heater:

None

Purge Air Source:

Brake System

Pressure-Controlled Check Valve for System Purge:

Required

Purge Signal:

Pneumatic, Internal

Additional Valves and Piping for Holset HD Compressors Isolation Valve:

Not Required

Feedback Line and Check Valve:

Not Required

Page 143

DESCRIPTION AND OPERATION PREVENTIVE MAINTENANCE

161

At each A, B, C, D inspection interval, perform the operational tests as described above.

ADDITIONAL MAINTENANCE ITEMS Additional air dryer maintenance items are as follows: 앫

Safety Valve — Using a 22-mm wrench, loosen the safety valve. When installing a new valve, check the placement of the O-ring. The valve is set to open at 155 psi.

Tighten the valve to 10 lb-ft (14 N폷m).

앫

Heating Element — The heater is thermostatically controlled and is designed to heat when the temperature is below freezing. If defective, loosen the screw on the heater housing, and remove and replace the heater assembly. Ensure that the O-ring is seated against the aluminum housing.

앫

Check Valve — Using a 32-mm wrench, loosen and remove the check valve.

Replace the spring and seal, reassemble and tighten to 20 lb-ft (28 N폷m).

앫

Regeneration Valve — Using a 32-mm wrench, remove the regeneration valve.

Before installing a new valve, check that the O-rings and check valve are in the proper position. Tighten the valve to 20 lb-ft (28 N폷m). A regeneration valve is not used on vehicles equipped with an external purge tank. On these vehicles, the regeneration valve port is sealed with a plug and O-ring.

앫

Valve Pack — The valve pack is not serviceable. If the valve pack fails, it must be replaced as a unit by loosening the six bolts with a 6-mm hex key and removing the valve. Clean the mounting surface, install a new O-ring and install a new valve pack.

앫

Desiccant Cartridge Replacement — The desiccant cartridge must be replaced yearly.

Figure 161 — Typical Piping Diagram for Holset HD Compressor

OPERATIONAL TESTS 1. Start the engine and build system pressure to governor cutout. When governor cutout is reached, two bursts of air will exhaust from the air dryer purge valve located at the bottom of the dryer. These two short bursts of air will then be followed by a slow flow of air lasting approximately 25 seconds.

2. Cycle the treadle valve to reduce air system pressure to governor cut-in.

3. Allow the air system to rebuild pressure to governor cutout, and again, note if the air dryer purges. The dashboard air pressure gauge should drop approximately 6 psi during the purge cycle.

Page 144

DESCRIPTION AND OPERATION PRESSURE-CONTROLLED CHECK VALVE TESTS

162

The pressure-controlled check valve is usually installed in the primary air reservoir (or it may, however, be installed in the secondary reservoir) in place of, not in addition to, the one-way check valve. The system will not function properly if there are any additional check valves installed between the air dryer and the primary (or secondary) reservoir.

The pressure-controlled check valve has an arrow embossed on the valve body to indicate the direction of airflow through the valve. The valve is properly installed when the arrow is pointing toward the reservoir. If a malfunction is indicated, always check that the valve is installed properly.

1. Install an accurately calibrated pressure gauge in the primary air reservoir.

2. Start the engine.

3. Open the drain valve on the secondary reservoir and drain system pressure down to 80 psi or lower.

4. Check the test gauge and note that pressure is 95 ±5 psi.

Figure 162 — Exploded View of Haldex Dry E.S.T.

앫

If the test gauge indicates less than 85 psi, check the air system for air leaks. If no significant leakage can be located, replace the pressure-controlled check valve, then retest.

앫

If the test gauge readings do not change or do not fall below 105 psi, the pressure-controlled check valve may be shutting off at 105 psi or higher.

Replace the valve, then retest.

Page 145

DESCRIPTION AND OPERATION Midland Pure Air Plus Air Dryer 163

Figure 163 — Midland Pure Air Plus Air Dryer

SPECIFICATIONS Manufacturer:

Midland

Model:

Pure Air Plus

Type:

Desiccant

Maximum Flow Capacity:

24 SCFM

Heater:

12V or 24V

Purge Air Source:

Internal

Pressure-Controlled Check Valve for System Purge:

Not Applicable

Purge Signal:

Pneumatic

Additional Valves and Piping for All Compressors Except Holset* Isolation Valve:

Not Required

Additional Valves and Piping for Holset Compressors Isolation Valve:

Not Required

Feedback Line and Check Valve:

Required

* Bendix Tu-Flo 1400 not included.

Page 146

DESCRIPTION AND OPERATION 164

Figure 164 — Midland Pure Air Plus, Typical Piping Diagram

OPERATIONAL TESTS

앫

1. Start the engine and build air system pressure to 100 psi.

2. Stop the engine.

3. Using a soap-and-water solution, check for air leaks at the air dryer inlet and outlet connections. Repair as required.

4. Restart the engine and build air system pressure to governor cutout.

5. Upon reaching governor cutout, note that the air-dryer purge valve opens and expels a large volume of air, followed by a slow flow lasting approximately 30 seconds. 앫

앫

If the purge cycle lasts longer than 40 seconds, check for a faulty air dryer one-way check valve or a partially plugged purge orifice.

If air constantly leaks from the purge valve, check for a damaged purge valve seal, foreign particles on the purge valve seat, or a faulty governor.

If the purge cycle does not occur, check for a sticking purge valve, restricted air line between the governor and the air dryer, or a faulty governor.

6. To ensure that the air dryer does not cycle excessively, check for air leaks at the following locations: 앫

Air compressor unloader mechanism

앫

Governor

앫

Drain valve and safety valve at the supply reservoir

앫

All air line connections leading to and from the supply reservoir

PREVENTIVE MAINTENANCE At each A, B, C, D inspection interval, perform the operational checks as described above.

Change the coalescing filter yearly and the desiccant cartridge every 2–3 years.

Page 147

DESCRIPTION AND OPERATION ArvinMeritor™ WABCO System Saver 1000, 1200, 1200E and 1200P 165

Figure 165 — ArvinMeritor™ WABCO System Saver 1200 Series Air Dryer

SPECIFICATIONS FOR SYSTEM SAVER 1000 AND 1200 Manufacturer:

ArvinMeritor™ WABCO

Model:

System Saver 1000 and 1200

Type:

Desiccant

Maximum Flow Capacity:

30 SCFM

Heater:

12V or 24V

Purge Air Source:

Brake System

Pressure-Controlled Check Valve for System Purge:

Required

Purge Signal:

Pneumatic

Additional Valves and Piping for All Compressors Except Holset* Isolation Valve:

Not Required

Additional Valves and Piping for Holset Compressors Isolation Valve:

Required

Feedback Line and Check Valve:

Required

* Bendix Tu-Flo 1400 not included.

Page 148

DESCRIPTION AND OPERATION SPECIFICATIONS FOR SYSTEM SAVER 1200E Manufacturer:

ArvinMeritor™ WABCO

Model:

System Saver 1200E

Type:

Desiccant

Maximum Flow Capacity:

30 SCFM

Heater:

12V or 24V

Purge Air Source:

Brake System

Pressure-Controlled Check Valve for System Purge:

Required

Purge Signal:

Pneumatic

Additional Valves and Piping for Holset Compressors Isolation Valve:

Not Required

Feedback Line and Check Valve:

Integrated into Lower Dryer Housing

SPECIFICATIONS FOR SYSTEM SAVER 1200P Manufacturer:

ArvinMeritor™ WABCO

Model:

System Saver 1200P

Type:

Desiccant

Maximum Flow Capacity:

30 SCFM

Heater:

12V or 24V

Purge Air Source:

Dedicated Purge Reservoir

Pressure-Controlled Check Valve for System Purge:

Not Required

Purge Signal:

Pneumatic

Additional Valves and Piping for Holset Compressors Isolation Valve:

Not Required

Feedback Line and Check Valve:

Integrated into Lower Dryer Housing

Page 149

DESCRIPTION AND OPERATION 166

Figure 166 — System Saver 1000 and 1200, Typical Piping Diagram

Page 150

DESCRIPTION AND OPERATION 167

168

Figure 167 — System Saver 1200E, Typical Piping Diagram

Figure 168 — System Saver 1200P, Typical Piping Diagram

For ArvinMeritor™ WABCO System Saver 1000 air dryers that are not equipped with a pressure-relief valve in the lower air dryer housing, an external pressure-relief valve kit must be installed in the air dryer inlet port.

ArvinMeritor™ WABCO System Saver 1000, 1200 and 1200E air dryers use air pressure from the supply and primary reservoirs to purge moisture from the desiccant bed. The backflow of air is controlled by the air dryer regeneration valve, and begins when governor cutout pressure is reached. The regeneration cycle ends when the regeneration valve senses a 10-psi drop from the initial pressure at which the purge/ regeneration cycle began. When the cycle is complete, pressure in the supply and primary reservoirs will be 10 psi less than governor cutout pressure.

Page 151

DESCRIPTION AND OPERATION

WABCO 1200P air dryers do not use a regeneration valve. The purge air source is supplied from a dedicated purge air reservoir.

On chassis equipped with WABCO System Saver 1000, 1200 and 1200E air dryers, a pressure-controlled check valve replaces the standard check valve in the primary reservoir to allow the backflow of air from the primary reservoir to the supply reservoir, provided system pressure remains within normal governor cut-in and cutout range. A pressure-controlled check valve is not used on chassis equipped with WABCO 1200P air dryers.

Some vehicles use the secondary reservoir as the purge source.

OPERATIONAL TESTS 1. Install an accurately calibrated pressure gauge in the primary air reservoir.

2. Start the engine and build air system pressure to governor cutout.

3. When air system pressure reaches governor cutout, note that the air dryer purges and regeneration is initiated. The purge cycle should last approximately 10–15 seconds.

4. During the purge cycle, note that the pressure gauge installed in the primary reservoir indicates 10 psi less than secondary system pressure, as indicated on the dashboard air gauge. 앫

If the pressure gauge does not indicate a pressure drop during the purge cycle, check the pressure-controlled check valve. Repair or replace as necessary.

앫

If, during the purge cycle, the pressure gauge indicates a pressure drop of 15 psi or more and no other air-operated components are using air, locate and correct any air leaks or other air-system malfunctions.

Page 152

5. With the air system pressurized, check for air leaks by applying a soap-and-water solution to all connections that contain pressurized air. Repair any leaks that are found.

PRESSURE-CONTROLLED CHECK VALVE TESTS — SYSTEM SAVER 1000, 1200 AND 1200E ONLY

The pressure-controlled check valve is usually installed in the primary air reservoir (it may, however, be installed in the secondary reservoir) in place of, not in addition to, the one-way check valve. The system will not function properly if there are any additional check valves installed between the air dryer and the primary reservoir.

The pressure-controlled check valve has an arrow embossed on the valve body to indicate the direction of airflow through the valve. The valve is properly installed when the arrow is pointing toward the reservoir. If a malfunction is indicated, always check that the valve is installed properly.

1. Install an accurately calibrated pressure gauge in the primary air reservoir.

2. Start the engine and build air system pressure to governor cutout, and allow the air compressor to unload.

3. Stop the engine.

4. Open the drain valve on the secondary air reservoir and drain system pressure down to 80 psi or lower.

5. Check the air gauge installed in the primary reservoir and note that pressure is 95 ± 5 psi. 앫

If the test gauge indicates less than 85 psi, check the air system for air leaks. If no significant leaks can be located, replace the pressure-controlled check valve and retest.

앫

If the test gauge reading does not change, or does not fall below 105 psi, the pressure-controlled check valve may be shutting off at 105 psi or higher.

Replace the valve and retest.

DESCRIPTION AND OPERATION PREVENTIVE MAINTENANCE

DESCRIPTION

At each A, B, C, D inspection interval, check air dryer operation as outlined above in the operational tests and pressure-controlled check valve test. Also, check for moisture in the air system by draining the supply reservoir and checking for the presence of moisture.

Isolation (ECON) valves are necessary when the vehicle is equipped with a purge-type air dryer and the air compressor uses turbocharged intake air. The isolation valve prevents a loss of turbo-boost pressure through the air dryer while the compressor is unloaded and the dryer is purging.

Replace the desiccant cartridge every 2–3 years.

Additionally, whenever the air compressor is rebuilt, always replace the desiccant cartridge.

Desiccant cartridge life varies depending on operating conditions, speeds, loads, air system usage and compressor condition.

Isolation (ECON) Valve 169

If the vehicle is equipped with a Holset E-type air compressor, the isolation valve is required to pressurize the air compressor discharge line and hold the exhaust valve closed while the compressor is unloaded.

Some air dryers are equipped with an integral turbo cutoff valve and may be used with a Holset air compressor without an external isolation valve. Air dryers with turbo cutoff valves include: 앫

CR Brakemaster Turbo 2000 and Turbo 3000

앫

Bendix AD-9 with soft seats

앫

Midland Pure Air Plus

앫

Bendix AD-SP

For Bendix AD-9 air dryers, only soft-seat air dryer valves may be used without an isolation valve when used in conjunction with a Holset compressor.

The isolation valve is a pneumatic spool valve that allows the free flow of air through the valve, but blocks the flow when control pressure is applied.

Figure 169 — Isolation Valve

Page 153

DESCRIPTION AND OPERATION 170

Figure 170 — Isolation Valve Airflow

The valve contains an inlet port, outlet port, control port and a reservoir port that in some applications may be plugged. Inside the valve is a valve spool that shifts position when control pressure is applied.

Page 154

With no pressure at the control port, air flows through the inlet port to the outlet and reservoir ports. When control pressure is applied, the valve spool shifts position and seals the outlet port. Air then flows through the inlet and reservoir ports, but not through the outlet port. Air may flow through the inlet and reservoir ports in any direction.

DESCRIPTION AND OPERATION ANTI-LOCK BRAKE SYSTEM (ABS)

Pro-Link 9000 with the proper EPROM, or a personal computer and the appropriate diagnostic software.

System Overview Federal Motor Vehicle Safety Standards require Anti-lock Brake Systems (ABS) on all tractors manufactured 3/1/97 and later, on all trucks and trailers manufactured 3/1/98 and later. Beginning 3/1/01, Federal regulations require that a trailer ABS indicator lamp be provided on all combination vehicles (any vehicle that pulls an air brake equipped trailer) to alert the operator should a malfunction in the trailer ABS occur.

MACK chassis may be equipped with either ArvinMeritor™ WABCO, Eaton, Bendix or Midland systems. The following information is intended only as a general overview of anti-lock brakes. For more specific troubleshooting and repair information, refer to the specific system manufacturer’s service literature. If information concerning the vehicle electrical system is required, refer to the specific wiring diagram for the vehicle. Vehicle wiring diagrams are available on paper or on CD-ROM, and may be ordered through your local MACK dealer.

Introduction Anti-lock Brake Systems (ABS) provide increased stability, safety and better braking performance by preventing wheel lockup when applying the brakes in an emergency situation. The electronically controlled system constantly monitors wheel speed to determine if the wheel is accelerating, freewheeling or approaching wheel lockup. If wheel lockup is detected, a signal is sent to the appropriate ABS modulator valve to either reduce or hold pressure on the brakes.

This self-monitoring system continuously checks all sensors, valves and other electrical components to make sure everything is operating properly. If a problem is detected, a dashboard indicator light illuminates to alert the driver. Faults which may occur are logged into the system and stored for later reference by the service technician, so identifying and correcting problems is made quick and easy. Fault codes may be read either by accessing the diagnostic blink codes, or by installing a suitable diagnostic tool such as the

Signals generated by the wheel speed sensors are transmitted to the ABS Electronic Control Unit (ECU). The ECU processes the information and determines wheel activity. If, during a brake application, the system senses that a particular wheel is entering a lockup situation, the ECU sends a signal to the appropriate modulator valve which activates and reduces air pressure delivered to the air chamber. As wheel speed enters the stable region, the ECU signals the modulator valve to either hold or increase air pressure to that of the driver’s application.

Although the ABS system continuously monitors wheel speed, anti-lock braking takes place only when the system senses a need.

Chassis may also be equipped with optional Automatic Traction Control (ATC). ATC prevents the drive wheels from spinning when starting from a standing position or when accelerating. Chassis using the C-version ECU have two additional ATC solenoid valves and two double check valves. On D-version systems, only one ATC solenoid valve is used. ATC is not available on systems that use the D-Basic version ECU.

For proper ABS/ATC operation with the standard ECU configuration on the ArvinMeritor™ WABCO system, front and rear tire sizes must be within 5% of each other. Exceeding this tire size range without modifying the ECU can cause the indicator lamp to illuminate and the ABS system to deactivate. Percent difference is calculated as follows (where rpm = tire revolutions per mile): % = [rpm steer axle ÷ rpm drive axle − 1] x 100 For tire RPM (revolutions per mile) values, refer to the specific tire manufacturer’s data sheets.

Consult the ABS/ATC system manufacturer if planned use of tire size is different than 5%.

Page 155

DESCRIPTION AND OPERATION Dyno-Testing Vehicles with ATC Option Anti-lock Brake Systems became mandatory on all tractors beginning March 1, 1997 and on all trucks and trailers beginning March 1, 1998. Additionally, the March 1, 1998 Federal regulations established that a constant source of electrical power be provided to trailer ABS when the vehicle ignition key switch is turned on. With this regulation, the center pin of the standard trailer electrical connector became the standardized source of uninterrupted power to trailer ABS. Beginning March 1, 2001, Federal regulations require that for combination vehicles (any vehicle that pulls an air brake equipped trailer), a trailer ABS indicator lamp must be mounted inside the cab to alert the operator should a trailer ABS malfunction occur. This has been accomplished with technology that allows data to be carried over the same line that supplies power to the trailer (power-line carrier). Because the center pin of the trailer electrical connector provides both power and the means of communication between the truck/tractor and trailer anti-lock brake systems, incompatibilities may exist between old and new equipment, in that some trailers (manufactured prior to the trailer ABS regulations) may use the center pin to power certain trailer auxiliary equipment. The possibility exists that this auxiliary equipment may be unexpectedly activated by the truck or tractor electrical systems, resulting in personal injury or damage to equipment.

Caution must be used when connecting the trailer electrical connector to ensure that power at the center trailer connector pin will not unintentionally activate any trailer auxiliary equipment.

Failure to disable the Automatic Traction Control (ATC) system before dynamometer testing could result in serious personal injury and possible damage to the vehicle.

When preparing to run an ATC-equipped vehicle on a chassis dynamometer, ATC must be disabled first. To disable automatic traction control on a C-version system, remove the ABS circuit breakers/fuses, or disconnect the 35-pin ECU harness connector from the ECU. When disconnecting the connector or removing the circuit breakers/fuses, always do so with the ignition switch in the OFF position.

On D-version systems, ATC can be disabled by pressing and holding the ABS diagnostic switch for at least three seconds. When the system configuration code begins to flash, automatic traction control is disabled. The ATC lamp activates and stays on while ATC is disabled.

Removing the ABS circuit breakers/fuses, or disconnecting the 18-pin power connector from the ECU also disables automatic traction control.

On chassis equipped with an electronic dashboard (CV, CX and CH), the ABS diagnostic switch has been eliminated. ATC must be disabled by removing the ABS circuit breakers/ fuses, or disconnecting the 18-pin power connector from the ABS ECU.

For complete chassis wiring diagrams, including diagrams for the ABS chassis connections, consult the specific main wiring diagram for the chassis being serviced.

Page 156

DESCRIPTION AND OPERATION ANTI-LOCK BRAKE SYSTEM COMPONENTS Electronic Control Unit (ECU) The ABS Electronic Control Unit (ECU) is a microcomputer-based controller that receives information from the wheel speed sensors relative to wheel speed. If the ECU detects wheel lockup, a pulsed signal is sent to the appropriate modulator valve to reduce air pressure being delivered to the affected brake chambers. As wheel speed re-enters the stable region, the ECU signals the modulator valve to either hold or increase pressure to that of the driver application.

Do not perform any welding operations on the frame of an ABS-equipped vehicle without first disconnecting the connectors from the ABS electronic control unit. To prevent damaging any sensitive electronic components, all electronic control units should be disconnected. The vehicle batteries should also be disconnected.

Location of the ABS electronic control unit varies by vehicle. Refer to the following illustrations for location of the ECU on various model chassis.

If the vehicle is equipped with optional Automatic Traction Control (ATC) and the ECU detects wheel spin, a pulsed signal is sent to the appropriate ATC valve to apply brake pressure to the brakes of the wheel(s) that is spinning, and also sends a signal to the Vehicle Electronic Control Unit (VECU) to derate engine horsepower. Once wheel spin is no longer detected, application pressure is released, and engine horsepower is returned to normal.

171

Figure 171 — ABS ECU (Bendix Shown) 1. Full ABS Module

2. Basic ABS Module

A. Power Supply — 18-Pin B. Sensors/Modulators — 18-Pin

C. Third Axle — 15-Pin

Page 157

DESCRIPTION AND OPERATION 172

Figure 172 — CXN/CHN/CH/CX/CT/CV/CL Models

Page 158

DESCRIPTION AND OPERATION 173

174

Figure 173 — R Model

Figure 174 — DM Model

On the MR model chassis, the ABS module is located on the center tunnel. To access the module, remove the cover from the tunnel. The engine brake disable relay is located on the electrical equipment panel.

175

Figure 175 — MR Model

Page 159

DESCRIPTION AND OPERATION On the LE model chassis, the ABS module is located under the left side driver’s position, as shown in the illustration below. The engine brake disable relay is located on the electrical equipment panel.

176

The relay is normally closed. However, when the ABS system detects wheel lockup, a signal is sent by the ECU to energize the engine brake disable relay. With the relay energized, the relay contacts move to deactivate the engine brake circuit. When the signal is removed from the relay, the relay de-energizes and the relay contacts move back to their normally closed position, which reactivates the engine brake circuit. Since the engine brake disable relay is connected in series with the clutch switch on V-MAC-equipped vehicles, it is used whether or not the chassis is equipped with an engine brake.

Refer to the following schematic diagrams for the engine brake disable circuits used on non-V-MAC, V-MAC II and V-MAC III chassis.

177

Figure 176 — LE Model

Engine Brake Disable Relay On earlier ABS-equipped chassis that have an engine brake, a relay is required to disable the engine brake circuit in the event the ABS system detects a wheel lockup condition.

On current production models (excluding DM, MR and LE models), the engine communicates with the ABS module via the J1939 data bus. Because of this, the engine brake disable relay has been eliminated on all models except DM, MR and LE models.

Page 160

Figure 177 — Engine Brake Disable Circuit, Mechanical and V-MAC II Engines, Early Production (with ArvinMeritor™ WABCO C-Version ECU)

DESCRIPTION AND OPERATION Location of the engine brake disable relay varies according to vehicle model. Typically, on mechanically governed engines, the relay is mounted on the ABS ECU mounting bracket. On V-MAC II and V-MAC III vehicles, the relay is located on the electrical equipment panel.

178

ABS Relay Panel On early chassis using the ArvinMeritor™ WABCO C-version ECU, an ABS relay panel, which contains the diagonal relays, fuses, etc., is located in the same area as the chassis electrical equipment panel. Location of the relay panel varies with vehicle design. Refer to the operator manual supplied with each vehicle for the location of the electrical equipment panel.

Figure 178 — Engine Brake Disable Circuit, Mechanical and V-MAC II Engines, Later Production (with ArvinMeritor™ WABCO D and D-Basic ECU) 179

An ABS relay panel is not required with the later ArvinMeritor™ WABCO D and D-Basic systems.

All necessary relays, fuses, etc., are an integral part of the ECU.

Tone Wheel The tone wheel is a metal wheel containing 100 teeth and is mounted to the hub of each monitored wheel. The tone wheel turns with the road wheel and provides the sensor with a means of sensing wheel speed.

180

Figure 179 — Engine Brake Disable Circuit, V-MAC III Engines (DM, MR and LE Models)

Figure 180 — Tone Wheel

Page 161

DESCRIPTION AND OPERATION Wheel Speed Sensors

WHEEL SPEED SENSOR ADJUSTMENT

Wheel speed sensors use the principle of induction to generate pulses of alternating current. The sensor contains a permanent magnet and is mounted in close proximity to the tone wheel. As the teeth of the tone wheel pass in front of the sensor, the magnetic field is broken and a pulse of AC voltage is generated.

No air gap adjustment is required for the wheel speed sensors. Sensor adjustment simply involves gently pushing the sensor toward the tone wheel until it bottoms. The sensor self-adjusts after wheel rotation. Do not pry or push a speed sensor with a sharp object.

182

A wheel speed sensor is installed at each monitored wheel. On front axles, the sensors are installed through the steering knuckle. The sensors on the drive axle are mounted in a block attached to the axle housing.

181

Figure 182 — Wheel Speed Sensor Figure 181 — Wheel Speed Sensor

Wheel speed sensor locations are as follows:

Page 162

앫

Steering Axle —The sensor is accessible on the inboard side of the steering knuckle.

앫

Drive Axle — The wheel and drum assembly must be removed to gain access to the sensor.

DESCRIPTION AND OPERATION Modulator (ABS) Valve

184

The modulator valve controls air pressure to each affected brake during anti-lock braking functions.

During normal braking, air pressure passes freely through the ABS valve to the brake chamber.

When anti-lock braking takes place, the modulator valve receives a signal from the ECU, and instantly responds by adjusting air pressure delivered to the brake chambers so that wheel lockup is prevented. The modulator valves are usually mounted to the frame rail or a crossmember, and are connected to the air system between the relay valve (or quick release valve) and the air chamber.

183

Figure 184 — ATC Valve Figure 183 — Modulator (ABS) Valve

ATC Valve On vehicles equipped with automatic traction control, an ATC valve is added to the system that directs air pressure to the modulator valve when the ECU detects wheel spin during acceleration.

The ATC valve is basically an ON/OFF solenoid air valve that, upon receiving an electrical signal from the ECU, opens and allows full reservoir pressure to flow.

On chassis equipped with the C-version ECU and ATC, two ATC valves (one for the left side and one for the right side) and two double check valves are used. When the system detects wheel spin, the ECU sends a signal to the ATC valve on the appropriate side of the vehicle. This signal causes the solenoid to energize and open the valve, allowing the flow of reservoir pressure through the double check valve to the ABS modulator valve. The modulator valve, which also responds to signals received from the ECU, regulates how much pressure is applied to the brake chamber of the spinning wheel. With this system, only one ATC valve and one ABS valve (on the side of the vehicle where the wheels are spinning) will be active.

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DESCRIPTION AND OPERATION 185

186

Figure 185 — Typical ATC Valve Piping, Early Model Chassis

On D-version ECUs, only one ATC valve is used.

If wheel spin is detected, the ECU sends a signal to the ATC valve to energize and allow the flow of reservoir pressure to the control port of the relay valve. The relay valve then allows full application pressure to flow to the modulator valves on both sides of the vehicle. With the D-version system, both modulator valves must activate. On the side of the vehicle where the wheels are not spinning, the modulator valve must activate to block the flow of pressure to the brake chamber. On the side of the vehicle where the wheels are spinning, the modulator valve regulates the amount of pressure to the brake chamber to apply the brakes.

Page 164

Figure 186 — Typical ATC Piping Diagram, Later Models

DESCRIPTION AND OPERATION ABS Indicator Lamp

ATC Indicator Lamp

The ABS indicator lamp is an amber-colored lamp with the ISO symbol for anti-lock. The indicator lamp, which is located on the dashboard, alerts the operator if an ABS malfunction occurs. Beginning March 1, 2001, Federal regulations require that a trailer ABS indicator lamp also be located on the dashboard of a tractor or a truck with a full trailer air connection to alert the operator, should a trailer ABS malfunction occur. Location of the ABS indicator lamps varies by vehicle design. The following illustration shows the various lamps for truck, tractor and trailer ABS.

Similar to the ABS indicator lamp, the ATC indicator lamp is also an amber-colored lamp, located on the dashboard, that illuminates when ATC is active or constantly illuminates if there is a malfunction in the ATC system. Location of the lamp on the dashboard varies depending on the chassis model. On C-version systems, the ATC lamp is used for the diagnostic blink codes.

188

187

Figure 188 — ATC Indicator Lamp

ATC is not available on vehicles that have the ArvinMeritor™ WABCO D-Basic ABS system.

Figure 187 — ABS Indicator Lamps

If the indicator lamp activates and remains on during vehicle operation, an existing ABS fault is indicated.

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DESCRIPTION AND OPERATION Diagnostic Blink Codes Diagnostic blink codes provide the technician with a method of determining failures which may occur with the anti-lock brake system. When a failure occurs, the ABS indicator lamp illuminates and the fault is stored in the ECU memory. These faults may be accessed by the technician as a troubleshooting aid when diagnosing the fault.

The diagnostic blink codes are activated with the ABS diagnostic switch. This switch is generally located next to the vehicle communication port.

189

Once activated, the blink codes are displayed by the blinking ABS indicator lamp. For information on activating the blink code sequence and interpreting blink code diagnostics, refer to the literature for the specific system being serviced.

The ABS diagnostic switch has been eliminated on chassis equipped with an electronic dashboard (CX, CV and CH). ABS diagnostic information is displayed on the odometer/hour meter/fault code screen located on the dashboard B panel, above the speedometer and tachometer.

ABS fault information is displayed as a PID (parameter identifier) code, SID (subsystem identifier) code and MID (message identifier) code. For a complete list of PID, SID and MID codes relating to ABS/ATC, refer to the applicable V-MAC service manual.

BENDIX ABS/ATC DIAGNOSTIC LAMPS

Figure 189 — ABS Diagnostic Switch

On early chassis equipped with the ArvinMeritor™ WABCO C-version ECU, the ABS diagnostic switch is located on the ABS relay panel located near the vehicle electrical equipment panel.

Page 166

On vehicles equipped with Bendix ABS, faults are displayed by the diagnostic lamps (Light Emitting Diodes [LED]) located on the Bendix ABS/ATC controller. These LEDs allow the technician to locate and diagnose faults. For complete information on diagnostics and troubleshooting, refer to the Bendix ABS/ATC service literature.

DESCRIPTION AND OPERATION ABS/ATC Diagnostic Tools

Service support software packages are available from the various anti-lock brake system manufacturers. Contact your nearest MACK dealer for information on software availability.

When troubleshooting ABS/ATC faults, the ABS diagnostic software packages or the Pro-Link 9000 diagnostic tool can be used in place of diagnostic blink code procedures. When using the Pro-Link 9000, operating instructions and illustrations of screen displays can be found in the Pro-Link instruction booklet supplied with the tool.

When using diagnostic software packages from a specific ABS manufacturer, instructions are supplied along with the software.

PRO-LINK 9000 DIAGNOSTIC TOOL

BENDIX ABS/ATC DIAGNOSTIC TOOLS

ABS/ATC diagnostic cartridges are available for the Pro-Link 9000 diagnostic tool. The Pro-Link 9000 and cartridges are available through SPX Kent-Moore Tools. Part numbers for the cartridges are as follows:

For the Bendix ABS/ATC system, the following diagnostic tools are available.

Several ABS/ATC diagnostic tools are available.

ABS/ATC DIAGNOSTIC SOFTWARE

앫

앫

앫

J 38500-404 — ABS Pro-Link cartridge that is compatible for ArvinMeritor™ WABCO C-, D- and D-Basic version ECUs. J 38500-403A — The original diagnostic cartridge No. available for the ArvinMeritor™ WABCO C-version ECU. This cartridge may be updated for D-version ECUs by installing the PROM chip, part No. J 38500-414.

J 38500-1300D — Eaton PCMCIA card version 2.3, covers the Eaton VORAD system, ABS generation 4 and G2S, and Eaton electronically controlled transmissions.

The diagnostic software packages and Pro-Link 9000 are useful for diagnosing system faults with the ABS and ABS/ATC systems. The screens identify faults as existing or stored, and the software tool may also be used to perform component measurement and function tests.

The components that may be tested are: 앫

Vehicle voltages

앫

ABS modulator valves

앫

ATC valves

앫

ABS/ATC lamps

앫

Sensors

앫

Engine datalink

앫

Retarder relay

앫

Retarder datalink

앫

ABS/ATC switches

앫

802108 — Bendix ACOM for Windows® software, a software package that allows expanded diagnostic capabilities using a personal computer.

앫

801869 — Bendix Remote Diagnostic Unit (RDU) is a diagnostic tool that can be used to read codes, clear codes and reconfigure the ABS control unit.

The RDU is a diagnostic tool that plugs into the diagnostic connector and utilizes LEDs to relay diagnostic information to the technician. A small magnet can be used to clear fault codes and reconfigure the module to which the RDU is connected.

The above tools are available by contacting Bendix Commercial Vehicle Systems, LLC.

The above part numbers are Bendix part numbers available from Bendix. These tools are not available through the MACK Parts System or from SPX Kent-Moore.

Page 167

NOTES

Page 168

TROUBLESHOOTING

TROUBLESHOOTING

Page 169

TROUBLESHOOTING TROUBLESHOOTING BRAKE SYSTEM PROBLEMS The following charts summarize some common problems which may be experienced with the dual air brake system.

COMMON BRAKE SYSTEM PROBLEMS Condition No pressure build-up.

Low air pressure warning activates while operating the vehicle.

Air pressure drops rapidly with the engine stopped and the brakes fully applied.

Air system will not retain pressure with the engine stopped and the brakes released.

Page 170

Possible Causes

Correction

1. Restricted compressor discharge line.

1. Inspect for restrictions. Repair or replace.

2. Restricted or faulty one-way check valve or valves.

2. Possible malfunction in the air supply system. Leak check system.

3. Air system leaks.

3. Test air system for leakage.

4. Faulty governor.

4. Test governor. Repair or replace as necessary.

5. Faulty unloader mechanism.

5. Check unloader mechanism. Repair or replace as necessary.

6. Faulty air compressor.

6. Check air compressor. Repair as necessary.

1. Loss of one section of the dual air system.

1. Vehicle may be moved with EXTREME caution to the nearest safe parking area. Leak-check faulty system. Observe both pressure gauges to determine which system is not functioning.

2. Loss of complete air system.

2. Spring brakes will automatically apply when system pressure decreases to 40 psi. The vehicle cannot be moved.

Leak-check system.

3. Faulty governor.

3. Check governor for leakage, and repair or replace as necessary.

4. Compressor malfunction.

4. Repair compressor.

5. Air line leakage.

5. Check for air line leakage. Repair or replace as necessary.

1. Treadle valve leaking.

1. Check treadle valve for leakage and repair or replace as necessary.

2. Brake chamber leakage.

2. Repair or replace leaking brake chamber.

3. Air line hoses, fittings, tubing or components leaking.

3. Leak-check air system and repair or replace components as necessary.

1. Treadle valve leaking.

1. Check treadle valve for leakage and repair or replace as necessary.

2. Air line hoses, fittings, tubing or components leaking.

2. Leak-test air system and repair or replace components as necessary.

3. Spring brake chamber leakage.

3. Check spring brake chambers for leakage and repair or replace as necessary.

TROUBLESHOOTING Condition Air pressure will not rise to normal.

Air system build-up time too slow.

Air pressure rises above normal.

Insufficient braking power.

Brakes apply too slowly.

Possible Causes

Correction

1. Reservoir draincocks opened.

1. Check reservoir draincocks and close if necessary.

2. Excessive leakage from air system components.

2. Leak-check entire system and repair or replace any components found to be leaking.

3. Governor out of adjustment.

3. Check governor setting and make required adjustments if necessary.

4. Defective air pressure gauge.

4. Check air pressure gauge and replace if necessary.

5. Defective air compressor.

5. Check air compressor function.

Repair or replace as necessary.

1. Engine speed too low.

1. Check engine speed and adjust if necessary.

2. Excessive leakage from air system components.

2. Leak-check entire air system and repair or replace any components found to be leaking.

3. Faulty air compressor.

3. Check compressor and repair or replace as necessary.

1. Defective air pressure gauge.

1. Disconnect the pressure gauge and install an accurately calibrated test pressure gauge, and observe pressure. Replace pressure gauge if necessary.

2. Governor out of adjustment or faulty restricted governor signal line.

2. Check governor and adjust or replace if necessary.

3. Restriction in air lines.

3. Check air line for kinks, sharp bends or other restrictions. Replace as required.

1. Low system pressure, excessive leaks or brake application pressure below normal.

1. Leak-check system. Make necessary adjustments and repairs.

2. Brakes out of adjustment, need lubrication or brake shoe relining.

2. Check brake adjustment and adjust if necessary. Check condition of brake components and repair and lubricate as required.

3. Mechanical brake component (slack adjusters, push rods, brake cams, etc.) failure.

3. Check brake components and repair as required.

4. Air line restrictions.

4. Check entire air system for kinks in hoses, sharp bends or any other type of restriction. Repair or replace as required.

1. Brakes out of adjustment or in need of lubrication.

1. Check brake adjustment and adjust if necessary. Lubricate components as required.

2. Air line restrictions.

2. Check air lines for kinks, sharp bends or other types of restrictions. Repair or replace as required.

3. Check possible causes under “Air pressure drops quickly with the engine stopped and the brakes applied.”

3. Follow corrections outlined for the possible cause.

Page 171

TROUBLESHOOTING Condition Brakes release too slowly.

Service brakes do not release.

Brakes grab.

Page 172

Possible Causes

Correction

1. Treadle valve not returning to the released position.

1. Check for accumulation of dirt, gravel or other types of debris around the brake treadle. Clean as necessary.

Lubricate the treadle valve roller and hinge pin.

2. Brakes out of adjustment or in need of lubrication.

2. Check brake adjustment and adjust if necessary. Lubricate components as required.

3. Air line restrictions.

3. Check air lines for kinks, sharp bends or other types of restrictions. Repair or replace as required.

4. Exhaust ports of the treadle valve, quick release valves, relay valves, etc., restricted or plugged.

4. Check the operation of the valves and repair or replace as necessary.

1. Broken or weak brake shoe or brake chamber return springs.

1. Check springs and replace as required.

2. Treadle valve not fully released.

2. Check for accumulation of dirt, gravel or other types of debris around the brake treadle. Clean as necessary.

Lubricate the treadle valve hinge pin and roller.

3. Air line restrictions.

3. Check air lines for kinks, sharp bends or other types of restrictions. Repair or replace as necessary.

4. Spring brake chamber leaking.

4. Check spring brake chambers for leakage. Repair or replace as necessary.

1. Grease or oil on brake linings.

1. Determine cause of oil or grease contamination and repair as necessary. Replace grease- or oil-soaked brake linings, and thoroughly clean brake drums (or disc rotors) and any other components that may be involved.

2. Brake drum out-of-round.

2. Check concentricity of the brake drum. Machine within allowable limitations, or replace if necessary.

3. Defective brake valves.

3. Check for faulty valves. Repair or replace as necessary.

4. Brake actuating linkages bind (slack adjusters, push rods, etc.).

4. Check brake actuating components for freedom of movement. Repair or replace as required.

TROUBLESHOOTING Condition Uneven braking performance.

Brakes do not apply.

Possible Causes

Correction

1. Brakes out of adjustment or in need of lubrication.

1. Check brake adjustment and adjust if necessary. Lubricate brake components as required.

2. Grease or oil on brake linings.

2. Determine cause of oil or grease contamination and repair as necessary. Replace grease- or oil-soaked brake linings and thoroughly clean brake drums (or disc rotors) and other components that may be involved.

3. Brake shoe return springs or air-chamber diaphragm return springs broken.

3. Check brake shoe return springs and air chamber springs. Replace as required.

4. Out-of-round brake drum.

4. Measure concentricity of the brake drums. Machine within allowable limits, or replace as required.

5. Leaking air chamber diaphragms.

5. Check for leakage at the air chambers. Repair or replace as required.

1. Restricted or broken air lines.

1. Check air system to locate problem area. Repair or replace as required.

2. Faulty brake treadle valve.

2. Inspect treadle valve. Repair or replace as necessary.

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TROUBLESHOOTING BRAKE NOISE INVESTIGATION Brake systems can produce a variety of noises ranging from insignificant, but irritating sounds to those noises that indicate possibly serious problems.

It is important to recognize which sounds are normal and what problems might be the source of a specific noise. This section deals with the following common and easily identified brake noises, plus possible causes and remedies. 앫

Rattle

앫

Scrape

앫

Grinding

앫

Squeal

Diagnosing a brake noise problem includes the following sequence of steps: 1. Review driver observations relating to the noise complaint.

2. Check the vehicle service history if available.

3. Determine that the braking effectiveness is satisfactory to allow a safe road test of the vehicle.

4. Road-test the vehicle. 앫

Listen for the noise when the brakes are applied and when they are released.

앫

Note the circumstances during which the noise occurs, such as speed, degree of brake application, road surface and weather condition.

앫

Determine the category of the noise which is experienced: rattle, scrape, grinding, squeal, etc.

5. Refer to the following troubleshooting chart for a listing of the noise, the possible cause, and the correction.

Noise

Possible Cause

Correction

RATTLE (disc brakes): Usually occurs when brakes are released.

Rattle at low speed indicates excessive clearance between the brakes pads and the rotor.

Disassemble the brakes and check for loosely mounted pads resulting from worn, damaged or missing parts.

Replace parts as required. During reassembly, be sure that all caliper guide pins, bushings, retaining clips and springs are installed.

SCRAPE: Usually occurs when the brakes are released.

DISC BRAKES: Bent splash shield rubbing against rotor.

DRUM BRAKES: Bent backing shield contacting the drum.

Repair or replace splash shield or backing plate as required.

GRINDING: Usually occurs when brakes are applied.

SLIGHT GRIND: Occurs during low-speed operation on vehicles that are equipped with semi-metallic lining.

Advise the operator that this is a normal sound due to formulation of semi-metallic friction material.

LOUD GRIND: Worn brake linings allowing metal-to-metal contact between the brake shoes and drums (drum brakes) or the pad backing plates to the rotor (disc brakes).

Disassemble brakes as required and inspect the brake shoes or brake pads.

If worn excessively, replace shoes or pads, and inspect the brake drums or rotors. Machine or replace drums or rotors as required.

High frequency vibration of the disc pads inside the calipers or the brake shoes.

Reduce vibrations by minimizing brake pad or brake shoe movement, and by insulating the pads or shoes from other brake parts.

SQUEAL: Usually occurs when brakes are applied.

Page 174

TROUBLESHOOTING DUAL-NEEDLE TEST GAUGE To properly diagnose air system problems, an accurate dual-needle test gauge, such as Kent-Moore J 42206 or Bendix 745-277671, is required.

190

A dual-needle test gauge is actually two pressure gauges contained within a single unit that can be used to test either an individual circuit or two circuits simultaneously. The gauge needles are color-coded to the gauge fittings to make it easier to determine circuit pressures when testing two circuits simultaneously.

A dual-needle test gauge is useful for: 앫

Accurately checking primary and secondary system pressure

앫

Accurately checking supply and delivery pressure at the valves

앫

Checking crack pressure of relay and quick release valves

앫

Checking exhaust timing of two systems

앫

Checking application timing of two separate systems

앫

Checking control versus delivery pressure

앫

Checking steering axle versus drive axle delivery pressure

앫

Checking front rear versus rear rear axle delivery pressure on tandem axles

앫

Checking tractor versus trailer application pressure

Figure 190 — Dual-Needle Test Gauge

Page 175

TROUBLESHOOTING AIR SYSTEM DIAGNOSTIC PROCEDURES When diagnosing chassis air system problems, a logical method of troubleshooting must be followed. The following diagnostic procedures aid in determining which area of the air system (control, supply or delivery) is contributing to the problem.

A dual-needle test gauge, such as Kent-Moore J 42206, Bendix 745-277671 or equivalent, must be used to measure and record the pressure readings obtained when performing the diagnostic procedures. Pressure readings obtained during these tests should be recorded so that a comparison between pressures can be developed. The Chassis Air System Diagnostic Check sheet, Figure 191 and Figure 192, can be used to record and note pressure readings.

The following tests must be performed with the parking brakes released and a system pressure of 110 psi or greater. Service brakes on all axles must be adjusted equally before proceeding.

Refer to “BRAKE ADJUSTMENT” on page 196.

Before beginning, make a thorough inspection of the chassis air system to check for obvious signs of problems such as pinched, rubbing or leaking air lines and fittings, valves exhibiting visible signs of damage, and other such problems.

Before proceeding with the diagnostic procedures, check the chassis for excessive air system leakage as follows: 1. Start the engine and build system pressure to governor cutout.

2. Apply the parking brakes.

3. Observe the dashboard air system pressure gauge and note any drop in primary or secondary system pressure.

4. Fully apply the brake treadle, and again, note any drop in system pressure.

If air system leakage exceeds the limits listed in the chart below, make the necessary repairs before proceeding.

Brakes Released

Brakes Fully Applied

Tractor

4 psi in 2 min.

8 psi in 2 min.

Straight truck

4 psi in 2 min.

8 psi in 2 min.

Tractor with trailer

6 psi in 2 min.

8 psi in 2 min.

Tractor with two trailers

8 psi in 2 min.

10 psi in 2 min.

Vehicle Type

To avoid possible injury due to automatic application of the spring brakes during the test procedures, spring brakes should be mechanically caged.

Measuring Supply Pressure at the Service Brake Relay Valve (If Equipped) 1. Block the wheels to prevent the vehicle from moving. Then release the parking brakes.

2. Completely drain the air system.

3. Connect one of the dual-needle test gauge hoses to the circuit by disconnecting the supply line from the relay valve serving the front rear drive axle, then by installing a suitable tee fitting into the relay valve supply port. Connect the supply line and one of the hoses from the dual-needle test gauge to the tee fitting installed in the relay valve supply port.

4. Start the engine and build air system pressure to governor cutout.

5. Measure and record the supply pressure at the relay valve.

6. Shut off the engine.

7. Completely drain the air system.

8. Disconnect the dual-needle test gauge and the supply line from the tee fitting.

9. Remove the tee fitting from the relay valve supply port. Then reconnect the supply line.

10. Repeat the above procedure for the relay valve serving the rear rear drive axle.

Page 176

TROUBLESHOOTING Measuring Supply Pressure at the Treadle Valve

Measuring Relay Valve Control Pressure Versus Delivery Pressure

1. Block the wheels to prevent the vehicle from moving. Then release the parking brakes.

2. Completely drain the air system.

3. Connect the dual-needle test gauge to the primary and secondary circuits by removing the primary and secondary supply lines from the treadle valve, then by installing suitable tee fittings into the treadle valve supply ports. Connect one portion of the dual-needle test gauge to the tee fitting installed in the primary supply port, and the other portion of the gauge to the tee fitting installed in the secondary supply port.

Reconnect the primary and secondary supply lines to the corresponding tee fittings.

Do not cross the primary and secondary circuits when reconnecting the air lines to the treadle valve.

4. Start the engine and build system pressure to governor cutout.

5. Measure and record the primary and secondary supply pressures.

6. Stop the engine and completely drain the air system.

7. Remove the dual-needle test gauge from the circuits. Then remove the tee fittings from the treadle valve.

8. Reconnect the primary and secondary air lines to the corresponding supply ports in the treadle valve.

When performing the following three tests (measuring relay valve control pressure versus delivery pressure, measuring drive axle delivery pressure versus steering axle delivery pressure, measuring drive axle control pressure versus trailer control pressure [tractors only]), all measurements must be taken by increasing application pressure in 10-psi increments only.

Do not apply and release brakes for each measurement, and do not overapply, then attempt to adjust the application to obtain the desired pressure, as measurements will not be accurate. If pressure is overapplied, release the brakes fully, then reapply to obtain the desired application pressure.

The following tests must be made with the parking brakes released and the air system at 110 psi or greater. To make the following tests more convenient, the dual-needle test gauge hoses should be made long enough to reach inside the cab so the measurements may be taken as the brake treadle application is being made.

1. Disconnect the control line from the relay valve serving the front rear drive axle.

2. Install a suitable tee fitting into the relay valve control port. Then connect the control line and one of the dual-needle test gauge hoses to the tee fitting.

3. Disconnect the delivery line from one of the front rear axle brake chambers.

DO NOT cross the primary and secondary air lines when reconnecting to the treadle valve. The air system will not function properly if these lines are reversed.

4. Install a suitable tee fitting into the brake chamber. Then connect the delivery line and the other hose from the dual-needle test gauge to the tee fitting.

5. Make a steadily increasing treadle valve application in 10-psi increments (from 10 psi to 90 psi), then a full treadle application.

6. Record the pressure readings at each 10-psi application.

7. Release the treadle application.

Page 177

TROUBLESHOOTING 8. Disconnect the control line, delivery line and dual-needle test gauge lines from the tee fittings, and remove the tee fittings from the relay valve and the brake chamber.

9. Reconnect the control line to the relay valve control port and the delivery line to the brake chamber.

10. Repeat the above procedure for the rear rear drive axle.

3. Fabricate a hose that allows the dual-needle test gauge to be connected to the service control glad hand. Connect the hose to the glad hand, and connect the second hose of the dual-needle test gauge.

4. Make a steadily increasing treadle valve application in 10-psi increments (from 10 psi up to 90 psi), then a full treadle application.

5. Record the pressure reading at each 10-psi application.

Measuring Drive Axle Delivery Pressure Versus Steering Axle Delivery Pressure

6. Remove the dual-needle test gauge and the tee fitting from the circuits. Then reconnect the control line to the relay valve control port.

1. Disconnect the delivery line from one of the steering axle brake chambers.

Measuring Drive Axle Delivery Pressure Versus Trailer Axle Delivery Pressure (Tractors Only)

2. Install a tee fitting into the brake chamber.

Then connect the delivery line and one of the hoses from the dual-needle test gauge to the tee fitting.

3. Disconnect the delivery line from one of the rear drive axle service brake chambers.

4. Install a tee fitting into the brake chamber.

Then connect the delivery line and the second hose from the dual-needle test gauge to the tee fitting.

1. Disconnect the delivery line from one of the rear axle service brake chambers.

2. Install a tee fitting into the chamber. Then connect the delivery line and one of the hoses from the dual-needle test gauge to the fitting.

3. Disconnect the delivery line from one of the trailer axle service brake chambers.

5. Make a steadily increasing treadle valve application in 10-psi increments (from 10 psi to 90 psi), then a full treadle application.

4. Install a tee fitting into the chamber. Then connect the delivery line and the other hose from the dual-needle test gauge to the fitting.

6. Record the pressure reading at each 10-psi application.

5. Make a steadily increasing treadle valve application in 10-psi increments (from 10 psi up to 90 psi), then a full treadle application.

7. Disconnect the delivery lines and test gauge lines from the tee fittings in both brake chambers. Then remove the tee fittings.

6. Record the pressure reading at each 10-psi application.

8. Reconnect the delivery lines to both brake chambers.

7. Remove the dual-needle test gauge and the tee fitting from the circuit. Then reconnect the delivery line to the brake chamber.

Measuring Drive Axle Control Pressure Versus Trailer Control Pressure (Tractors Only)

8. Repeat the above procedures for the remaining axles on the trailer.

1. Disconnect the control line from the relay valve serving the rear rear axle.

2. Install a tee fitting into the relay valve control port. Then connect the control line and one hose of the dual-needle test gauge to the tee fitting.

Page 178

In general, pressures obtained during the above tests should equal (or nearly equal) each other. If differences in pressure exist (such as supply versus system, control versus delivery, steering axle versus drive axle, and tractor drive axle control versus trailer control), the cause must be determined and corrected. Inspect the air system for sticking or corroded valves, pinched or restricted air lines, or other such problems.

TROUBLESHOOTING Air System Diagnostic Check 191

Figure 191 — Air System Diagnostic Check (Page 1)

Page 179

TROUBLESHOOTING 192

Figure 192 — Air System Diagnostic Check (Page 2)

Page 180

MAINTENANCE

MAINTENANCE

Page 181

MAINTENANCE AIR SYSTEM MAINTENANCE

앫

Service Tests Regularly scheduled service tests should be performed by the operator of the vehicle to ensure safe, reliable operation of the air brake system. The following checks should provide a general indication of air system performance and isolate any specific problems before a major failure occurs. 앫

앫

Drain Moisture from Reservoirs Daily: Apply the parking brakes and open the reservoir drain valves to drain moisture and other contaminants from the reservoirs.

Open the valves slowly so a channel of air does not develop that would only drain air from the reservoirs and not the accumulation of contaminants. Close the valves as soon as moisture has drained. Do not completely drain the reservoirs.

Completely Drain the Reservoirs Monthly: Block the wheels and release the parking brakes. With the air system fully pressurized, open the reservoir drain valves and allow the reservoirs to drain slowly and completely to remove accumulated moisture and other contaminants from the system.

Open the valves slowly so a channel of air does not develop that would only drain air from the reservoirs and not the accumulation of contaminants. Make sure the spring brakes apply automatically when the air pressure drops to 40 psi.

앫

Stoplight Switch Test: With the pressure entirely exhausted from the system, start the engine and apply the treadle valve. The stop lamps should illuminate before the air pressure gauge on the dash registers 6 psi (41 kPa).

앫

Low-Pressure Indicator Test: With the engine running, allow the system to continue building pressure. The low-pressure warning lamp and buzzer should remain activated until system pressure reaches a minimum of 65 psi or a maximum of 75 psi.

Page 182

Air Pressure Build-Up Test: With the engine running at full governed speed, observe the time it takes for air pressure to build from 50–90 psi. When pressure has reached 90 psi or more, rapidly cycle the treadle valve to reduce pressure below 85 psi, and observe the time it takes for the pressure to rise from 85–100 psi. Time should not exceed 25 seconds.

Build-up time may exceed 25 seconds if the chassis is equipped with increased reservoir capacity. 앫

Governor Setting: With the engine running, observe the pressure at which the governor cuts out. It should cut out when reservoir pressure reaches between 130–135 psi.

Reduce system pressure by rapidly cycling the treadle valve and observe the pressure at which the governor cuts in. Governor cut-in should occur when reservoir pressure drops between 110–115 psi.

For chassis built prior to March 15, 1995, governor cutout is set at 120 ± 5 psi and governor cut-in is set at 100 + 5 psi. 앫

Leakage Test: With the air system fully pressurized and the parking brakes released, pressure drop should be less than 2 psi per minute for a truck, and less than 3 psi per minute for a tractor/trailer combination. With the parking brakes released and a full treadle application, pressure drop should not exceed 3 psi per minute for a truck and 4 psi per minute for a tractor/trailer combination.

If the air system fails any of these tests, the cause must be determined and corrected before the vehicle is operated.

MAINTENANCE Preventive Maintenance Preventive maintenance is the most cost-effective method of maintaining reliable, trouble-free vehicle operation. The air system and all vehicle components require periodic inspections along with specific maintenance procedures to maintain peak system efficiency and prevent mechanical failure.

Refer to the Maintenance and Lubrication Manual, TS494, for complete maintenance schedules along with mileage/time intervals.

The following maintenance procedures are required at the recommended inspection interval:

The MACK Preventive Maintenance Program is arranged in A, B, C and D order: 앫

Schedule A is a light inspection.

앫

Schedule B is a more detailed check.

앫

Schedule C is a heavy inspection and adjustment.

앫

Schedule D is a comprehensive inspection and adjustment.

SYSTEM MAINTENANCE Inspection Schedule

Inspect the air system for leaks by fully pressurizing the system, releasing the parking brakes, and observing any pressure drop as indicated by the dashboard air pressure gauge. Pressure drop should be less than 2 psi per minute for a truck, or less than 3 psi per minute for a tractor/trailer combination. Make a full treadle application and check again for leaks by observing the air pressure gauge. Pressure drop should not exceed 3 psi per minute for a truck or 4 psi per minute for a tractor/trailer combination.

A, B, C, D

With air system fully charged, block the wheels, release the parking brakes, then drain reservoirs slowly and completely. Spring brakes should apply automatically when air pressure decreases to 40 psi (276 kPa).

A, B, C, D

Check alcohol evaporator reservoir level (if so equipped). Add fluid if necessary. (Use only 188 proof methanol alcohol.) Check that the connections are tight.

A, B, C, D

Check the treadle valve pivot pin and plunger for freedom of movement. Lubricate the plunger and make sure the treadle valve is securely mounted and structurally sound. For floor-mounted treadle valves, clean any debris from around the valve.

A, B, C, D

Check air dryer for proper operation. Consult the air dryer manufacturer’s service literature for recommended service intervals and procedures.

B, C, D

Check the condition of all brake hoses. Check for interference and/or chafing.

B, C, D

Check mounting of air reservoirs.

C, D

Perform dual circuit brake test.

C, D

Page 183

MAINTENANCE AIR SYSTEM COMPONENT MAINTENANCE Inspection Schedule Compressor Check for proper operation. Build-up time from 85–100 psi (586–690 kPa) should not exceed 25 seconds (at maximum governed, no-load speed). Rapidly cycle brake treadle valve until reservoir pressure drops below 105 psi (620 kPa). Note and record pressure at which governor cut-in occurs — should be 110–115 psi (100–105 for chassis prior to 3/15/95).

A, B, C, D

Governor cutout should occur when pressure reaches 125–135 psi (861–930 kPa) (115–125 psi [793–862 kPa] for chassis manufactured prior to 3/5/95). Note and record pressure at which governor cutout occurs. Check operation of the low-air pressure indicator lamp and the audible low-air buzzer.

A, B, C, D

Glad Hands Check couplings for defects that may affect sealing. Repair or replace as necessary.

A, B, C, D

Governor Check governor cut-in/cut-out operation, and test for excessive leakage. Replace if necessary.

C, D

Low-Pressure Indicator, Stoplight Switch Check lamps and electrical connections.

B, C, D

Check operation and test for excessive leakage. Replace if necessary.

B, C, D

Trailer Supply Valve, Tractor Parking Brake Control Valve, Parking Control Valve, Trailer Control Valve Check operation and test for excessive leakage. Replace if necessary.

B, C, D

Check Valves, Double Check Valves, Automatic Drain Valve Check operation and test for excessive leakage. Replace if necessary.

B, C, D

Treadle Valve, Quick Release Valve(s), Ratio Valve(s), Pressure Protection Valve, Tractor Protection Valve, Spring Brake Control Valve, Relay Valve(s), Hand Control Valve, Inversion Valve, Bobtail Proportioning Relay Valve Check operation and test for excessive leakage. Replace if necessary.

Page 184

B, C, D

MAINTENANCE Dual-Circuit Brake System Function Test The following dual-circuit brake system function test should be performed at each C and D inspection interval, and after any air system service procedure involving the disconnecting and reconnecting of air lines where the possibility of incorrect reconnection exists, such as at the treadle valve.

1. Block the wheels to prevent the vehicle from moving.

TRACTOR: 앫

The brakes on either the steering axle or the rear drive axle(s) should always apply.

앫

The low-air warning buzzer and warning lamp should activate for at least two of the tests.

Repeat the above procedures for the remaining air reservoirs on the chassis. (Do not include reservoirs for the air starter if the chassis is so equipped.)

2. Start the engine and build air system pressure to governor cutout.

3. Stop the engine.

4. Completely drain one of the air reservoirs.

5. Release the parking brakes, then fully apply and hold the brake treadle.

6. Have an assistant check for proper results by observing movement of the slack adjusters as indicated below.

TRUCK: 앫

The brakes on the rear drive axle(s) should always apply.

앫

The low-air warning buzzer and warning lamp should activate for at least two of the tests.

Page 185

NOTES

Page 186

REPAIR INSTRUCTIONS

REPAIR INSTRUCTIONS

Page 187

REPAIR INSTRUCTIONS ANTI-LOCK BRAKE SYSTEM COMPONENT REMOVAL AND INSTALLATION

Front-Axle Speed Sensor Installation 1. Connect the sensor cable to the chassis harness.

2. Reinstall any fasteners and tie-wraps used to hold the sensor cable in place.

Prevent serious eye injury by always wearing safety glasses when performing vehicle service or maintenance. Drain air system pressure before disconnecting any components, as pressurized air can cause serious personal injury.

Front-Axle Speed Sensor Removal 1. Apply the parking brakes and block the wheels to prevent the vehicle from moving.

2. Remove the sensor from the steering knuckle by grasping the sensor head and using a twisting motion, if necessary, to pull the sensor from the knuckle. DO NOT attempt to remove the sensor by pulling on the sensor cable.

3. Apply lubricant to the sensor spring clip and sensor body. Lubricant must be mineral oil-based, containing molydisulfide, and have excellent anti-corrosion and adhesion characteristics. This lubricant must be capable of continuous function within a temperature range of −40°F to 300°F (−40°C to 150°C). A quantity of approved ArvinMeritor™ WABCO lubricant is included with all replacement sensors.

4. Push the sensor spring clip into the steering knuckle, making sure that the flange stops are on the inboard side of the vehicle.

194

193

Figure 194 — Properly Installed Sensor Spring Clip

5. Push the sensor completely into the sensor spring clip until it contacts the tone wheel.

Figure 193 — Removing Sensor

3. Remove any fasteners and cut any tie-wraps that secure the sensor harness to frame or suspension components.

4. Disconnect the sensor cable from the chassis harness.

5. Remove the sensor spring clip from the steering knuckle.

Page 188

There is no air gap adjustment required for the wheel speed sensors. The sensor self-adjusts during the first wheel rotation.

6. Remove the blocks from under the wheels.

REPAIR INSTRUCTIONS Rear-Axle Speed Sensor Removal 1. Apply the parking brakes and block the wheels to prevent the vehicle from moving.

7. Remove the sensor spring clip from the mounting block.

196

2. On the side of the vehicle from which the sensor must be removed, raise the wheel off the ground and support the axle on jackstands of adequate capacity to support the weight.

DO NOT work on or under a vehicle that is supported only by hydraulic jacks, as they can slip or fail unexpectedly, causing serious personal injury.

3. Back off the slack adjuster to provide clearance between the brake shoes and brake drum. Refer to the information on slack adjusters in “BRAKE ADJUSTMENT” on page 196 for complete instructions.

4. Remove the wheel and tire assembly.

5. Remove the brake drum.

6. Remove the speed sensor from the mounting block by grasping the sensor head and using a twisting motion, if necessary, to pull the sensor. DO NOT attempt to remove the sensor by pulling on the sensor cable.

195

Figure 196 — Removing Sensor Spring Clip

8. Disconnect any fasteners or cut any tie-wraps that secure the sensor to any frame or suspension components.

9. Disconnect the sensor cable from the chassis harness.

Figure 195 — Removing Sensor

Page 189

REPAIR INSTRUCTIONS Rear-Axle Speed Sensor Installation 1. Apply lubricant to the sensor spring clip and the sensor body. Lubricant must be mineral oil-based, containing molydisulfide, and have excellent anti-corrosion and adhesion characteristics. This lubricant must be capable of continuous function within a temperature range of −40°F to 300°F (−40°C to 150°C). A quantity of approved ArvinMeritor™ WABCO lubricant is included with all replacement sensors.

6. Reinstall any fasteners and replace any tie-wraps that secured the sensor cable/ harness.

198

2. With the flange stops on the sensor spring clip facing the inboard side of the chassis, install the spring clip into the sensor mounting block until it stops.

197

Figure 198 — Properly Routed Sensor Cable/Harness

7. Reinstall the brake drum.

8. Adjust the brakes. Refer to “BRAKE ADJUSTMENT” on page 196.

9. Reinstall the wheels and torque the wheel nuts to specification. Refer to the Wheels, Rims and Tires Service Manual, 15-101, or the Maintenance and Lubrication, TS494 manual, for wheel installation procedures and wheel nut torque specifications.

Figure 197 — Sensor Spring Clip Flange Stops

3. Insert the speed sensor into the spring clip and push in completely until contacting the tone wheel.

No air gap adjustment is required for the wheel speed sensors. The sensor self-adjusts during the first wheel rotation.

4. Insert the sensor cable through the hole in the brake spider and housing flange. Then route the cable to the frame rail. Be sure to route the cable in a way that prevents pinching or chafing and allows sufficient movement for suspension travel.

5. Connect the sensor cable to the chassis harness.

Page 190

10. Remove the jackstands and lower the vehicle to the ground. Remove the blocks from under the wheels.

REPAIR INSTRUCTIONS ABS Valve Removal 1. Apply the parking brakes and place blocks under the wheels to prevent the vehicle from moving.

2. Completely drain the air system.

3. Disconnect the harness connector from the ABS valve that is to be removed.

4. Disconnect the air lines from port No. 1 (supply) and port No. 2 (delivery) of the ABS valve.

5. Remove the two mounting bolts and nuts that secure the ABS valve to the frame.

Then remove the valve.

200

199

Figure 199 — ABS Valve

Figure 200 — Removing the ABS Valve

Page 191

REPAIR INSTRUCTIONS ABS Valve Installation

ATC Valve Removal 202

Moisture adversely affects ABS/ATC systems, as well as standard brake systems. Follow accepted installation procedures to prevent moisture contamination when installing air lines and valves. Use thread sealant where applicable.

1. Using the two mounting bolts and nuts, install the ABS valve to the frame. Torque the mounting bolts to 18 lb-ft (24 N폷m).

2. Connect the supply line to port No. 1 of the ABS valve and the delivery line to port No. 2.

201

Figure 202 — ATC Valve Figure 201 — ABS Valve Ports

3. Reconnect the ABS valve wire harness.

4. Test the valve installation as follows: a.

b.

Start the engine and build system pressure to governor cutout. Then shut off the engine.

Apply a soap-and-water solution to the air line connections of the ABS valve and around the valve body, and check for leaks.

c.

Turn the ignition switch to ON position and listen for the modulator valve cycle.

If the valve fails to cycle, check the electrical connection. If the connection is OK, refer to “ANTI-LOCK BRAKE SYSTEM (ABS)” on page 155.

d.

Remove the blocks from under the wheels. Then operate the vehicle and verify that the ABS indicator lamp operates properly.

Page 192

1. Make sure the ignition switch is OFF, apply the parking brakes, and block the wheels to prevent the vehicle from moving.

2. Completely drain the air system.

3. Disconnect the harness from the ATC valve.

4. Disconnect the supply line from port No. 1 and the delivery line from port No. 2 of the ATC valve.

5. Remove the two mounting bolts and nuts that secure the ATC valve to the chassis.

6. Remove the ATC valve.

REPAIR INSTRUCTIONS ATC Valve Installation 1. Using the two mounting bolts and nuts, install the ATC valve to the chassis.

2. Tighten the two mounting bolts to 10 lb-ft (24 N폷m).

3. Connect the supply line to port No. 1 and the delivery line to port No. 2 of the ATC valve.

4. Reconnect the harness connector to the ATC valve.

5. Test the ATC valve as follows: a.

Start the engine and build air system pressure to governor cutout. Then shut off the engine.

b.

Apply the brakes and apply a soap-and-water solution to the air line connections and around the valve body to check for leaks.

c.

Remove the blocks and operate the vehicle to verify that the ABS indicator lamp operates properly.

WHEELBASE CHANGES ON ABS-EQUIPPED VEHICLES Whenever wheelbase changes are made to a chassis equipped with ABS, the ABS components for the rear axle(s) must be moved to correspond with the increase or decrease in wheelbase length. The relationship between the rear suspension and the ABS modulator valve must be kept the same. Additionally, the rear axle service brake relay valve should also be moved so that the same distance between the modulator valve and relay valve is maintained.

REPLACEMENT OF ABS CHASSIS HARNESSES Splicing or repairing of Anti-lock Brake System (ABS) chassis harnesses (cables) is not recommended. On chassis where the ABS harness is damaged, individual universal harnesses are available through the MACK Parts System to replace specific harnesses that are damaged. These cables are supplied with special connectors on one end which are required to attach to the modulator valve, wheel speed sensor cable or Automatic Traction Control (ATC) valve.

Instructions for installing the replacement harnesses are as follows: 1. After identifying the damaged harness, remove the clamps and harness ties that secure the harness in place on the chassis.

Save all clamps for reinstallation after the new harness has been routed in place.

2. Begin the installation by attaching the replacement harness to the modulator valve, wheel speed sensor or ATC valve, depending on which harness is being replaced.

3. Carefully route the new cable following the same path as the old cable. Clamp and tie the cable in place.

4. After the replacement cable has been routed and clamped in place, cut and install new Deutsch terminals on the cable. Refer to Figure 203 for the correct terminal pin positions in the bulkhead connector.

Cutting and splicing the ABS wire harnesses is not recommended or approved by Mack Trucks, Inc. When wheelbase changes are made, extension harnesses for the modulator valves and wheel speed sensors are available through the MACK Parts System. Use these extension harnesses, rather than attempting to cut and splice existing harnesses.

Page 193

REPAIR INSTRUCTIONS 203

Figure 203 — Harness Connector Pin Configuration for Bulkhead Connectors

Page 194

REPAIR INSTRUCTIONS 5. Connect the harness to the bulkhead connector and make sure the protective boot is properly installed.

6. If an incorrect connection is made when installing a wheel speed sensor or ATC valve harness, a fault code will be displayed when the ignition switch is turned ON. If an ABS modulator valve is replaced, however, use the appropriate diagnostic tools (ArvinMeritor™ WABCO or Bendix) to test ABS modulator valve functionality before returning the vehicle to service.

Page 195

REPAIR INSTRUCTIONS BRAKE ADJUSTMENT Manual and Automatic Slack Adjusters DESCRIPTION Slack adjusters are used on cam or disc brake systems to convert the linear force applied by the air chambers into the rotary force (torque) necessary to bring the brake shoes (or pads) into contact with the brake drums (or rotors). The slack adjuster is installed over the splines of the S-cam (powershaft on disc brakes) and secured to the air chamber push rod with a clevis.

Slack adjusters are either manual or automatic.

Manual slack adjusters require periodic adjustment to maintain proper brake shoe-to-drum clearance and air chamber stroke.

Automatic slack adjusters adjust automatically during normal service brake applications to compensate for normal brake lining wear and maintain proper stroke and brake shoe-to-drum clearance. All slack adjusters operate on a worm shaft and gear principle.

204

Figure 204 — Manual and Automatic Slack Adjusters

Page 196

REPAIR INSTRUCTIONS 205

Automatic slack adjusters, which are designed to maintain proper brake chamber push rod travel and compensate for brake lining wear during normal use, have been required on all air brake-equipped vehicles since October 1994.

Manual adjustment of an automatic slack adjuster should never be performed except when performing brake or wheel service (such as backing off the brake shoes for wheel removal, brake shoe relining/replacing, brake drum reconditioning, etc.). When push rod travel exceeds specifications (Maximum Allowable Stroke as given in table on page 204) on a vehicle equipped with automatic slack adjusters, a mechanical problem with the slack adjuster, brake components or improper installation of the slack adjuster are indicated.

Figure 205 — Incorrect Adjustment 206

In general, manually adjusting an automatic slack adjuster to bring push rod travel back within specifications is masking a mechanical problem, not repairing it. Additionally, routine adjustment of most automatic slack adjusters will likely result in premature wear of the adjuster. If automatic slack adjusters are found to be out of adjustment, it is recommended that the vehicle be taken to the nearest repair facility as soon as possible to have the problem investigated and corrected.

Figure 206 — Correct Adjustment

Slack Adjuster Maintenance PRELIMINARY SLACK ADJUSTER CHECKS (MANUAL AND AUTOMATIC) Perform the following service tests: 1. Apply the brakes and check that the slack adjusters rotate freely and without binding.

2. Release the brakes and check that the slack adjusters return to the released position freely and without binding.

3. With the brakes released, check that the angle formed by the slack adjuster arm and the push rod is greater than 90 degrees.

5. Measure the push rod stroke. Stroke should be as short as possible without allowing the brakes to drag. Refer to “Adjusting Stroke” on page 204 for measurement procedures.

Automatic slack adjusters are designed to compensate for brake lining wear and maintain proper air chamber stroke by automatically adjusting during normal brake applications.

Automatic slack adjusters should never require manual adjustments while in service. However, periodic measurements should be made as part of routine brake system maintenance to ensure proper slack adjuster operation.

4. With the brakes applied, check that the angle formed by the slack adjuster and the push rod is 90 degrees. The angle formed by the push rod and the flat surface of the brake chamber should also form a 90-degree angle.

Page 197

REPAIR INSTRUCTIONS The only time automatic slack adjusters should be adjusted is during installation or removal, or after backing off the adjusters to provide clearance when removing the brake drums for brake service. If an automatic slack adjuster cannot maintain proper air chamber stroke, it must be removed and repaired, or replaced as necessary.

AUTOMATIC SLACK ADJUSTERS Haldex Automatic Slack Adjusters 208

Maintaining proper brake adjustment cannot be accomplished by the slack adjuster alone. Other brake system components have a direct bearing on the proper operation of the slack adjusters.

Therefore, it is necessary to inspect the following components before assuming that an automatic slack adjuster is at fault: 앫

Air Chambers — Check that the air chambers are securely mounted and that proper alignment is maintained to avoid interference between the chamber push rod and the chamber housing.

앫

Camshafts — Check the camshaft bushings for wear. A worn camshaft bushing increases push rod travel.

207

Figure 208 — Haldex Slack Adjuster Cutaway

Inspect the slack adjuster for the following: 1. Inspect the slack adjuster mounting bracket for damage and make sure it is tight.

2. Check that the control arm is in the full release position.

3. Check the slack adjuster for damage.

Figure 207 — Camshaft

앫

Wheel Bearing Adjustment — Proper wheel bearing adjustment is necessary to maintain proper alignment between the brake drums and the brake shoes. Wheel bearing end play must be maintained between 0.001–0.005 inch (0.025–0.13 mm). Refer to Master Manual section 15-701, Wheel Bearings Service Manual, for wheel bearing adjustment procedures.

Page 198

4. Check the de-adjustment torque of the one-way clutch by placing a torque wrench on the manual adjusting nut and turning counterclockwise. If the nut turns at a torque less than 13 lb-ft (18 N폷m), the one-way clutch is slipping, making it necessary to replace the slack adjuster. (When backing off the adjusting nut, a ratcheting sound should be heard.)

REPAIR INSTRUCTIONS Check slack adjuster operation as follows:

210

1. Block the wheels to prevent the vehicle from moving.

2. Release the spring brakes.

3. Check that the push rods are fully retracted.

209

Figure 210 — Checking Slack Adjuster Operation

Figure 209 — Backing Off Slack Adjuster

4. Create an excessive clearance between the brake shoes and the brake drum by turning the manual adjusting nut counterclockwise.

(When backing off the adjusting nut, a ratcheting sound should be heard.)

5. Fully apply, then release the service brakes.

During release, observe if the manual adjusting nut rotates. (It may be easier to detect rotation by placing a wrench on the adjusting nut.) The rotating adjusting nut indicates that the slack adjuster is automatically adjusting to compensate for the excessive clearance between the brake shoes and brake drum. On each subsequent brake application and release, the amount of adjustment should be reduced until the desired clearance is obtained.

6. With the brakes released, check that the angle formed by the slack adjuster arm and the push rod is greater than 90 degrees.

Page 199

REPAIR INSTRUCTIONS ArvinMeritor™ Automatic Slack Adjusters 211

2. Inspect the slack adjuster boots for damage.

If damage is evident, install a new boot after first inspecting the condition of the grease inside the slack adjuster. If the grease is dry or contaminated, or if the slack adjuster pawl or actuator is dry or worn, the slack adjuster must be removed, disassembled and repaired.

3. Check for heavy corrosion or contamination around the splines and retainer ring. Clean the area as necessary. Also check for excessive movement between the slack adjuster and the S-cam (or powershaft on disc brakes). Repair or replace worn or damaged parts.

212

Figure 211 — ArvinMeritor™ Automatic Slack Adjuster Cutaway

Inspect the slack adjuster for the following: 1. Check the in-service free stroke and the adjusted chamber stroke. Refer to “ARVINMERITOR™ AUTOMATIC SLACK ADJUSTERS” on page 205 for measurement procedures.

Page 200

Figure 212 — Splined Shaft

REPAIR INSTRUCTIONS Bendix Automatic Slack Adjusters

Check slack adjuster operation as follows:

213

1. Block the wheels to prevent the vehicle from moving. Release the parking brakes.

2. Apply and release the service brakes several times and observe that the slack adjusters and external components move freely and without binding.

3. Check the brake chamber stroke. Refer to “Adjusting Stroke” on page 204 for measurement procedures.

Figure 213 — Bendix Automatic Slack Adjuster Cutaway

Inspect the slack adjuster for the following: 앫

Test the adjusting mechanism torque by inserting a 3/8-inch square drive torque wrench into the adjusting crank socket and turning in the opposite direction of the arrow stamped on the face of the housing. If the torque required to back off the crank is greater than 50 lb-ft (68 N폷m), replace the slack adjuster.

앫

If the brakes do not fully release when the chamber push rod is fully retracted and the measured stroke for a full service brake application is less than 1-1/4 inches, the slack adjuster may be overadjusting and should be removed and replaced.

앫

If the measured push rod stroke is greater than 1-1/4 inches and the brakes do not completely release when the brake chamber air is exhausted, a problem with the service brakes is indicated and must be identified and corrected.

앫

If the measured push rod stroke exceeds the recommended maximum operating stroke, the slack adjuster may be underadjusting. Check the linkages for physical damage or excessive wear, and replace as necessary. If no damage to the linkage is evident, check the brake assemblies for excessive camshaft movement, cracked or broken brake chamber brackets, or oversized drums. Repair or replace as necessary. If none of the above conditions exist, replace the slack adjuster.

Page 201

REPAIR INSTRUCTIONS GUNITE AUTOMATIC SLACK ADJUSTERS 214

4. Check the adjusting mechanism torque by using a torque wrench and a 7/16″ socket to turn the adjusting hex counterclockwise.

Note the amount of torque it took to rotate the adjusting hex counterclockwise.

If the adjusting hex did not rotate clockwise when the brakes were applied and released during step 3, or if less than 15 lb-ft (20 N폷m) of torque was required to rotate the adjusting hex counterclockwise, the slack adjuster must be replaced.

If the adjusting hex rotated clockwise when the brakes were applied and released, and a torque greater than 15 lb-ft (20 N폷m) was required to turn the adjusting hex counterclockwise, the slack adjuster is functioning properly.

5. Readjust the brakes.

Figure 214 — Gunite Automatic Slack Adjuster 1. Boot 2. Grease Fitting

3. Adjusting Hex

Inspect the slack adjuster for the following: 앫

Check the slack adjuster housing for structural damage, and also check for a worn clevis, clevis bushing and a torn or cut boot. Replace as required.

Check slack adjuster operation as follows: 1. Using a 7/16″ box wrench on the adjusting hex, turn the hex counterclockwise 3/4 turn.

A ratcheting sound should be heard when the adjusting hex is rotated counterclockwise.

2. Make a chalk mark on the adjusting hex.

3. Apply and release the service brakes several times while watching the adjusting hex. The hex should rotate clockwise during this test.

The adjustment is intentionally made in small increments, so it will take several brake applications to bring the slack adjuster back within stroke specifications.

Page 202

REPAIR INSTRUCTIONS Slack Adjuster Lubrication Lubricate the slack adjusters at each scheduled chassis lubrication interval. Apply a sufficient amount of grease to the fitting to completely fill the slack adjuster body cavity.

215

Figure 215 — Slack Adjuster Lubrication Points

Page 203

REPAIR INSTRUCTIONS Adjusting Stroke

217

MEASURING PUSH ROD TRAVEL 1. With the brakes released, measure the distance between the flat surface of the brake chamber to the center of the push rod clevis pin.

216

Figure 217 — Measuring Distance “B” Figure 216 — Measuring Distance “A”

2. Make and hold a full brake treadle application.

4. Subtract the measurement made with the brakes released from the measurement made with the brakes applied. The difference is the stroke.

3. With the brakes applied, again measure the distance between the flat surface of the brake chamber to the center of the push rod clevis pin.

5. Compare the stroke measurement with the maximum allowable stroke shown in the last column of the following table.

Effective Diaphragm Area (Square Inches)

Overall Diameter (Inches)

Maximum Allowable Stroke (Inches [mm])

9

5-1/4

1-3/8 [35]

12...

12

5-11/16

1-3/8 [35]

16...

16

6-3/8

1-3/4 [44]

20...

20

6-13/16

1-3/4 [44]

24...

24

7-1/4

1-3/4 [44]

24L...

24

7-1/4

2 [51]

30...

30

8-1/8

2 [51]

36...

36

9

2-1/4 [57]

24...

24

7-1/32

1-7/8 [48]

Type Clamp and Stamped Ring Type

Rotochambers

9...

Manual slack adjusters must be adjusted whenever the actual push rod applied stroke exceeds the maximum allowable stroke. With automatic slack adjusters, investigate and correct the probable cause if actual push rod applied stroke exceeds the maximum allowable stroke.

Do not attempt to operate an automatic slack adjuster as a manual adjuster.

Page 204

Proper brake adjustment must be maintained for the safe operation of the truck.

REPAIR INSTRUCTIONS After proper adjustment, apply the brakes.

Block the wheels that remain on the ground.

Raise the axle to be adjusted and support on safety stands. 앫

Support the front axle under the axle housing or the center of the axle.

앫

Support the rear axle under the lower spring trunnion.

Release the parking brake while adjusting the brakes.

MANUAL SLACK ADJUSTERS 218

All wheels must be on the ground before the brakes are applied.

The slack adjuster arm and brake chamber push rod should form a 90-degree angle. The brake chamber push rod should also form a 90-degree angle with the flat mounting surface of the brake chamber. All slack adjusters on the vehicle must be at the same angle.

ARVINMERITOR™ AUTOMATIC SLACK ADJUSTERS The brakes must be readjusted after any operation involving the removal and reinstallation of the slack adjusters, or if the adjustment has been backed off for any reason. DO NOT rely on automatic slack adjusters to take up excess initial clearance.

Slack Adjuster Free Stroke

Figure 218 — Manual Slack Adjuster

Position the wrench over the adjusting screw and depress the adjusting lock sleeve BEFORE attempting to turn the adjusting screw. With the brake chamber push rod in the released position, turn the adjusting screw until the brake linings are against the brake drum. Back off the adjusting screw 1/4 turn or until the wheel rotates freely (a light drag may still be felt when rotating the wheel). When the adjustment is complete, be sure the locking sleeve is returned to its locked position by allowing the sleeve to engage the hex head of the adjusting screw.

Because of different applications and slack adjuster mounting, always make sure the adjusting screw is being turned in the proper direction to adjust the brakes.

Spring brake chambers must be manually caged, and there must not be any air pressure in the service portion of the chambers before measuring free stroke.

Make sure the spring brakes are uncaged before returning the vehicle to service.

Pawls on old-style ArvinMeritor™ automatic slack adjusters must be removed when manually adjusting the brakes or damage to the pawl teeth may result. New-style pawls are spring-loaded and need only be pried out 1/32 inch to disengage. The pawl automatically re-engages when the pry bar is removed.

Page 205

REPAIR INSTRUCTIONS Setting Free Stroke

220

Before attempting to turn the manual adjusting nut, remove or disengage the pawl.

219

Figure 219 — Setting Free Stroke

Set the stroke to its approximate length and set the lining-to-drum (or brake pad-to-rotor) clearance as follows: Turn the manual adjusting nut clockwise until the brake linings contact the drum or disc rotor. Then: 앫

Turn the nut 1/2 turn counterclockwise for drum brakes.

앫

Turn the nut 3/4 turn counterclockwise for disc brakes.

Measuring Free Stroke 1. Measure the distance from the bottom flat surface of the air chamber to the center of the large clevis pin.

2. Using a pry bar inserted in the clevis between the large and small clevis pins, move the slack adjuster until the brake linings contact the brake drum (or disc rotor).

3. Again measure the distance from the bottom flat surface of the air chamber to the center of the large clevis pin.

Page 206

Figure 220 — Measuring Free Stroke

The difference between the two measurements is the free stroke. 앫

Drum brake free stroke = 1/2–5/8 inch (12.7–15.9 mm)

앫

Disc brake free stroke = 3/4–7/8 inch (19.1–22.2 mm)

Adjusting Free Stroke Adjust the free stroke by turning the adjusting nut in 1/8-turn increments.

Before attempting to turn the manual adjusting nut, remove or disengage the pawl.

REPAIR INSTRUCTIONS 1. Block the wheels to prevent the vehicle from moving. Then release the parking brakes.

221

2. Turn the manual adjusting nut until the brake linings contact the brake drum.

222

Figure 221 — Adjusting Free Stroke

앫

Turning the nut clockwise lengthens stroke length.

앫

Turning the nut counterclockwise shortens stroke length.

After properly setting the free stroke, verify the correct installation of the slack adjuster or proper operation of the brakes by checking the adjusted stroke.

Refer to “Adjusting Stroke” on page 204 for measurement procedures.

When measuring adjusted stroke, the applied pressure must be between 80 and 90 psi. If the vehicle is not equipped with an application gauge, pressurize the reservoirs to 100 psi. A full brake application with a reservoir pressure of 100 psi gives an application pressure of 80 to 90 psi at the air chambers.

After properly setting the chamber stroke, reinstall the pawl assembly, and torque the capscrew to 15–20 lb-ft (20–27 N폷m).

HALDEX AUTOMATIC SLACK ADJUSTERS The brakes must be readjusted after any operation involving the removal and reinstallation of the slack adjusters, or if the adjustment has been backed off for any reason. DO NOT rely on automatic slack adjusters to take up excess initial clearance.

Figure 222 — Haldex Slack Adjuster

3. Back off the adjusting nut 1/2 turn.

A minimum torque of 13 lb-ft (17.6 N폷m) is required to overcome the one-way clutch. A ratcheting sound should occur while the adjusting nut is being turned counterclockwise.

4. After properly setting the slack adjuster, measure the adjusted stroke. Refer to “Adjusting Stroke” on page 204 for measurement procedures.

Page 207

REPAIR INSTRUCTIONS BENDIX AUTOMATIC SLACK ADJUSTERS

GUNITE AUTOMATIC SLACK ADJUSTERS

The brakes must be readjusted after any operation involving the removal and reinstallation of the slack adjusters, or if the adjustment has been backed off for any reason. DO NOT rely on automatic slack adjusters to take up excess initial clearance.

The brakes must be readjusted after any operation involving the removal and reinstallation of the slack adjuster, or if the adjustment has been backed off for any reason. DO NOT rely on automatic slack adjusters to take up excess initial clearances.

1. Block the wheels to prevent the vehicle from rolling. Release the parking brakes and raise the wheel to be adjusted off the ground so it spins freely.

1. Block the wheels to prevent the vehicle from rolling, and then release the parking brakes.

2. Insert a 3/8-inch square drive ratchet into the adjusting crank socket.

3. While spinning the wheel, turn the adjusting crank in the direction indicated by the arrow stamped on the face of the housing until wheel rotation stops.

4. Back off the adjustment 3/4 turn in the opposite direction, or until the wheel spins freely.

Considerable torque, as much as 50 lb-ft (67.8 N폷m), is required to back off the manual adjustment.

2. Turn the adjusting hex extension clockwise until the brake linings contact the brake drum.

3. Back off the slack adjuster by turning the adjusting hex counterclockwise approximately 1/2 turn.

Approximately 25–30 lb-ft (34–41 N폷m) of torque will be required to back off the slack adjuster.

When rotating the adjusting hex counterclockwise, a ratcheting should be heard.

This is normal.

223

5. After properly setting the slack adjuster, measure the adjusted stroke. Refer to “Adjusting Stroke” on page 204 for measurement procedures.

Figure 223 — Slack Adjuster Adjusting Hex

Page 208

REPAIR INSTRUCTIONS 4. After backing off the slack adjuster, measure the stroke by measuring the distance between the face of the air chamber and the center of the large clevis pin with the brakes released and applied (refer to “Adjusting Stroke” on page 204).

5. Measure free stroke. Free stroke is the amount of movement of the slack adjuster required to move the brake shoes against the brake drum. Free stroke is measured as follows: a.

With the brakes released, measure the distance from the face of the brake chamber and the center of the large clevis pin.

b.

Using a large screwdriver or pry bar as a lever, move the slack adjuster until the brake shoes contact the brake drum. With the brake shoes in contact with the brake drum, again measure the distance between the face of the brake chamber and the center of the large clevis pin.

Free stroke should be 3/8″–5/8″ (9.53–15.88 mm). If free stroke is within specifications, but the applied stroke is too long, check the brakes for problems such as missing or worn components, cracked brake drums or improper lining to drum contact.

If free stroke is greater than specifications, perform the tests outlined in the section “Slack Adjuster Maintenance” on page 197.

If free stroke is less than 3/8″ (9.53 mm), dragging brakes can occur.

Recheck the brake adjustment procedure.

224

Figure 224 — Measuring Free Stroke

Page 209

REPAIR INSTRUCTIONS BRAKE SYSTEM OVERHAUL Asbestos Fibers Danger

Exposure to airborne asbestos dust particles poses a potential health hazard. Proper precautions must be taken and proper equipment must be used by technicians who perform brake service to minimize the risk of asbestos exposure and personal injury.

The lining material used on many brake shoe assemblies may contain asbestos. Exposure to asbestos poses a potential hazard for technicians who perform brake service or handle brake lining material. It is essential, therefore, that technicians realize the potential hazards that exist, and know the precautions that can be taken to minimize the hazards.

Exposure to airborne asbestos fibers can cause serious, and perhaps fatal, diseases such as: 앫

Asbestosis — a chronic lung disease

앫

Cancer — usually lung cancer

앫

Mesothelioma — a cancer of the chest or abdominal cavities

Symptoms of the above diseases are not usually seen for 15 to 20 years or more after initial asbestos exposure. Additionally, the risk of lung cancer among asbestos workers who smoke is greater than among non-smokers.

Areas where brake service work is performed should be separate from other service areas.

OSHA requires posting the following notice at the entrance to areas where asbestos levels exceed the recommended maximum of 0.2 fibers per cubic centimeter of air (as an 8-hour time weighted average), or 1.0 fiber per cubic centimeter of air (averaged over a 30-minute sampling period).

“CANCER AND LUNG DISEASE HAZARD: AUTHORIZED PERSONNEL ONLY. RESPIRATORS AND PROTECTIVE CLOTHING ARE REQUIRED IN THIS AREA.”

Page 210

Technicians who perform brake service work, which also includes wheel removal and reinstallation, must wear an air-purifying respirator with high-efficiency filters that is approved by NIOSH or MSHA for asbestos dust.

Disposable dust masks are no longer approved by OSHA. OSHA recommends using the enclosed cell systems, which are equipped with high-efficiency (HEPA) filters, while performing brake system service. This type of system totally encloses the brake assembly. Access to the brake assembly is gained through sleeves attached to the enclosed cell. Compressed air is blown into the enclosure to clean the brake assembly. A dust-trapping vacuum removes dirty air.

If an enclosed cell system is not available, brake service must be performed carefully in the open.

Before removing any parts, vacuum the drums, backing plates and other related assemblies with a vacuum cleaner designed to trap asbestos fibers. The vacuum cleaner must be equipped with a HEPA filter, and dirt and dust in the cleaner must be disposed of in a manner that prevents dust exposure. Any dirt remaining on the brake assemblies must be removed with a solvent-soaked rag which is wrung out nearly dry.

During disassembly, gently place parts on the floor to minimize the creation of airborne dust.

DO NOT use compressed air to clean dust from the brake assemblies.

Grinding, filing or machining brake linings exposes the technician to asbestos dust at its highest level. In addition to wearing an approved respirator, exhaust ventilation must also be provided so exposure to asbestos dust is maintained below OSHA standards.

REPAIR INSTRUCTIONS Work areas should be kept clean by vacuuming with an industrial vacuum cleaner equipped with HEPA filters or by wet wiping. Dry sweeping or compressed air should NEVER be used. Waste containing asbestos should be sealed in containers, such as sealed trash bags, labeled and disposed of as required by EPA and OSHA regulations. Respirators should be used when emptying vacuum cleaners and handling asbestos waste.

Workers should wash before eating, drinking or smoking, and should shower after work and not wear work clothes home. Asbestos fibers should be removed from work clothing by vacuuming before laundering. Attempting to remove asbestos fibers by shaking clothing should be avoided.

Wheel Removal

Before performing any maintenance involving the removal of the wheel assemblies, take the following precautions: 앫

Block the wheels that remain on the ground to prevent the vehicle from moving.

앫

Raise the axle from which the wheel assembly is to be removed, and support with jackstands of adequate capacity.

앫

When servicing rear brakes, manually cage the spring brakes. Apply the parking brakes when servicing front brakes.

Non-Asbestos Fibers Danger Brake linings manufactured most recently no longer contain asbestos fibers. In place of asbestos, these linings contain a variety of ingredients including glass fibers, mineral wool, aramid fibers, ceramic fibers and carbon fibers.

At present, OSHA does not regulate these non-asbestos fibers except as a nuisance dust, and medical experts do not agree as to the possible long-term risks of working with and inhaling them. Some experts, however, feel that long-term exposure to some of these fibers can cause diseases of the lung which include pneumoconiosis, fibrosis and cancer. It is, therefore, recommended that technicians who service brake systems use caution to avoid creating and breathing dust when working on brakes that contain non-asbestos fibers, and that the same precautions be used as when working on brakes that contain asbestos fibers.

Before attempting to remove the wheel and brake drum assembly, back off the slack adjuster to obtain sufficient clearance between the brake linings and drum.

225

Figure 225 — Backing Off the Slack Adjuster

Page 211

REPAIR INSTRUCTIONS Refer to “Manual and Automatic Slack Adjusters” on page 196.

226

On chassis equipped with spoke wheels, or stud-located disc wheels, having inboard-mounted cast brake drums, it is necessary to disassemble the hub assembly in order to remove the brake drums. Wheel bearing removal for the various axle assemblies that may be encountered, along with related service and maintenance information, is covered in the Wheel Bearings Service Manual, 15-701.

Brake drums can be removed from chassis having disc wheels (either hub-piloted or stud-located) without disassembling the hub. For detailed information concerning wheel removal, along with all related service procedures, refer to the Wheels, Rims and Tires Service Manual, 15-101, in the Master Manual.

Drum/Rotor Inspection The friction surface of the brake drums, or rotors, indicates brake system performance. Examine the drums or rotors during a brake system overhaul, or any time they are removed.

CRACKED DRUMS Deep cracks through the entire wall of the brake drum indicate excessive heating and cooling.

Repeated cracking may mean that the drums (or the entire brake system) are inadequate for the particular application, or may indicate driver abuse if the drums and system are correctly rated for the application. Replace cracked drums immediately.

Figure 226 — Cracked Drum Surface

HEAT-CHECKED DRUMS Heat checking appears as fine hairline cracks.

This is a normal condition caused by the constant heating and cooling of the braking surfaces.

Thoroughly inspect the drums to be sure that deep cracks have not developed.

227

Figure 227 — Heat-Checked Drums

Page 212

REPAIR INSTRUCTIONS OVERSIZED DRUMS

229

This condition is indicated by uneven brake lining wear. Replace the brake drums and brake shoes when the drum diameter measurements exceed allowable limits.

228

Figure 229 — Out-of-Round Drums

GREASE-STAINED DRUMS

Figure 228 — Oversized Drums

Grease stains appear on a brake drum as spots of discoloration on the braking surface. Also, the entire brake assembly will most likely be splattered with oil or grease. Grease staining may be caused by improper brake cam lubrication, leaking wheel bearing seals, etc. Repair any oil or grease leakage and clean the brake assembly before reassembling. Replace the brake linings if they are soaked with oil or grease.

230

OUT-OF-ROUND DRUMS Variations in drum diameter, when measured at different points on the braking surface, indicate an out-of-round drum. This condition is also evidenced as uneven brake lining wear on one side of the brake shoe. To restore concentricity, the drum may be machined within allowable limits. If the drums are beyond allowable limits, they must be replaced. Do not machine a brake drum in excess of .080 inch over the dimension cast into the drum.

Figure 230 — Grease-Stained Drums

Page 213

REPAIR INSTRUCTIONS HOT SPOTS

232

Hot spots appear on the drum as slightly raised, dark-colored spots. They may cut grooves into the lining material or cause uneven lining wear.

Hot spots result when high energy created on the surface of the drum changes the characteristics of the metal. Machining may remove the spots, but if not, the drum must be replaced. Hot spotting can be avoided by using brake linings that wear quickly enough to seat uniformly against the brake drum friction surface. Using intermittent high-pressure brake applications rather than low-pressure dragging applications helps the linings break in without forming damaging hot spots on the drum.

231

Figure 232 — Scored Drum

POLISHED DRUMS A polished drum is identified by a mirror-like glaze on the braking surface. The glaze can be removed with 80-grit emery cloth. If the problem persists, check the brake lining material for proper friction rating. If the brake lining material is glazed, consider an alternate lining material.

233

Figure 231 — Hot Spots

SCORED DRUMS The braking surface of a drum that is scored has a rough appearance as compared to one that is properly surfaced. A scored drum reduces the life of the brake linings. If scoring is severe, the drum may be machined as long as it can be resurfaced within allowable limits. If the scoring is not excessive and the inside diameter of the drum is within specifications, the drum may be reused.

Replace the brake linings and inspect the entire braking system for excessive amounts of abrasive material which may be entering the brake system.

Figure 233 — Polished Drum

Page 214

REPAIR INSTRUCTIONS EXCESSIVE WEAR

BLUE DRUMS

Excessive wear along the edges of the brake shoe contact area, or in areas coinciding with the brake lining rivet holes, may be caused by abrasive material that has collected inside the drum. If dust shields are installed, remove the lower shield to allow any abrasive material to exit from inside the brake system. If, however, excessive abrasive material collects inside the system and dust shields are not used, install shields to prevent abrasive materials from entering. Check the brake drums for severe scoring, and replace if necessary.

Brake drums with a bluish color on the braking surface, severely worn brake lining material, and/ or deformed brake components indicate that excessive heat is being generated. Excessive heat is usually caused by dragging brakes or severe overloading. Inspect the system for problems that will not allow the brakes to release fully, such as:

234

앫

Incorrect slack adjuster positioning

앫

Spring brakes not released completely

앫

Weak or broken return springs

앫

Air system problems

235

Figure 234 — Excessive Wear Figure 235 — Blue Drum

Page 215

REPAIR INSTRUCTIONS Cam Brake Shoe Removal EATON CAM BRAKES (EB AND ES MODELS) 236

Figure 236 — Eaton Brake

Page 216

REPAIR INSTRUCTIONS Eaton EB-165-5D, 6D, 7D, EB-180-7R and ES-165-7D 1. On model ES-165-7D, pry roller retainer coiled loop out of both shoe web holes as shown below. Then pivot the roller retainer to swing loops clear of shoe webs.

2. Using an adjustable wrench, screwdriver or similar lever, lift the upper shoe to stretch the return spring. Then remove the upper cam roller and pin.

238

EB model brake assemblies do not have roller retainers.

237

Figure 238 — Removing Cam Roller

Remove roller and roller retainer as a unit on ES-165-7D brake assembly.

3. Repeat the previous procedures to remove the lower cam roller and pin.

4. Push the cam end of both shoes toward the cam, and unhook the brake shoe return spring. Remove and discard the spring.

Figure 237 — Removing Roller Retainer

Page 217

REPAIR INSTRUCTIONS 239

240

Figure 239 — Removing Brake Shoe Return Spring

To remove the brake shoe return spring on an ES-165-7D brake assembly, position a lever or suitable tool with a notch to engage the spring rod, as shown in Figure 240. Apply downward force to stretch the spring, allowing removal of the upper spring hook. Remove and discard the spring.

Figure 240 — Removing Brake Shoe Return Spring: ES165-D, L, F Models

5. Rotate both brake shoes around the anchor pin. Then lift the shoes off the pins to remove.

241

Figure 241 — Removing Brake Shoes

Page 218

REPAIR INSTRUCTIONS Eaton EB-150-4L and ES-150-4L Cam Brakes 1. Using a large screwdriver, adjustable wrench or other suitable tool as a lever, lift the upper brake shoe to stretch the return spring. Then remove the cam roller.

4. Rotate lower shoe downward and rotate to allow disengagement of the shoe retaining spring from the lower shoe web (refer to Figure 243).

243

2. Repeat step 1 to remove the lower cam roller.

3. Stretch the shoe return spring and unhook it from the upper shoe web (refer to Figure 242).

242

Figure 243 — Removing Lower Brake Shoe

5. Rotate upper shoe upward and remove shoe and shoe retaining spring.

Figure 242 — Removing Brake Shoe Return Spring

Page 219

REPAIR INSTRUCTIONS ARVINMERITOR™ HEAVY-DUTY “P” BRAKES 244

Figure 244 — ArvinMeritor™ “P” Brake

ArvinMeritor™ “P” cam brakes have removable anchor pins and shoes with closed-end anchor pin openings.

245

Anchor pin arrangements may be different on older and newer style brakes. Some arrangements may have more parts, but disassembly and reassembly procedures are all the same.

1. Remove the anchor pin snap rings, washers, retainers, felt seals, anchor pin lock bolts and other parts as necessary.

Anchor pin lock bolts on some brakes may be safety wired, making it necessary to cut the safety wire.

Figure 245 — Removing Lock Rings, Retainers, Felts

Page 220

REPAIR INSTRUCTIONS 2. Using a brass drift, remove the upper and lower anchor pin.

246

3. Rotate the upper brake shoe around the cam roller, release the return spring and remove the brake shoe.

247

Figure 246 — Removing Anchor Pin Figure 247 — Removing Upper and Lower Brake Shoes

4. Using a brass drift, remove the lower anchor pin. Then remove the brake shoe.

Page 221

REPAIR INSTRUCTIONS ARVINMERITOR™ 16.5-INCH “Q” AND “Q-PLUS” BRAKES 248

Figure 248 — ArvinMeritor™ “Q” Brake

ArvinMeritor™ “Q” and “Q-Plus” brakes have removable anchor pins and bushings and shoes with open-end anchor pin openings.

249

1. Push the lower brake shoe downward. Pull the roller retaining clip to disconnect. Then remove the cam roller.

Figure 249 — Disconnecting Cam Roller Retainers

Page 222

REPAIR INSTRUCTIONS 2. Lift the upper brake shoe. Then disconnect and remove the cam roller.

3. Lift the lower brake shoe to release tension on the brake return spring. Then remove the spring.

250

Cam Brake Component Inspection The following topics provide information concerning items of importance to look for when performing a brake system overhaul. This information pertains to both Eaton and ArvinMeritor™ brake systems, and is general in nature. If more specific information is needed, consult the service publications for the particular brake system being serviced.

ANCHOR PINS Clean all dirt and rust from the anchor pins and inspect. Replace the pins if worn.

The anchor pin on an Eaton brake system is part of the brake spider assembly. If anchor pin replacement is necessary, the complete spider assembly must be replaced.

BRAKE SHOE SPRINGS Figure 250 — Removing Return Spring

4. Rotate the lower shoe backward (about 180 degrees) to relieve the tension on the brake shoe retaining springs. Then remove the springs and shoes.

Brake return springs and retaining springs must be replaced at each brake relining.

252

251

Figure 252 — Brake Shoe Springs

Figure 251 — Removing Brake Shoes

Page 223

REPAIR INSTRUCTIONS BACKING PLATE/DUST SHIELD Clean and inspect the backing plate/dust shield, if equipped. Replace if bent or twisted.

253

ArvinMeritor™ Brake Spiders Tighten the brake spider attachment bolts to the torque listed in the following table.

255

Figure 253 — Backing Plate/Dust Shield

BRAKE SPIDERS Clean and inspect the brake spider assembly.

Visually check for cracks around the attachment bolt holes and around the cam area. Replace the spider if defective.

254

Figure 255 — ArvinMeritor™ Spider Bolt Size 7/16″-20

Torque 60–75 lb-ft (81–102 N폷m)

1/2″-20

85–115 lb-ft (115–156 N폷m)

9/16″-18

130–165 lb-ft (176–224 N폷m)

5/8″-18

180–230 lb-ft (224–312 N폷m)

Eaton Brake Spiders Check the anchor pin. If the pin is loose or grooved more than 0.031 inch (0.79 mm) below the original surface, the spider assembly must be replaced.

Figure 254 — Brake Spiders (Eaton Spider Shown)

Page 224

REPAIR INSTRUCTIONS EB-150-4L and ES-150-4L Brake Spiders

257

Tighten the anchor pin reinforcement plate attaching nuts to 35–40 lb-ft (47–53 N폷m).

256

Figure 257 — Torque Anchor Pin Retaining Nut

On the right-hand brakes, the anchor pin retaining nut has right-hand threads. On the left-hand brakes, the retaining nut has left-hand threads. Make sure to turn the nut in the proper direction when checking retaining nut torque.

Figure 256 — Torque Reinforcement Plate Nuts

Tighten the anchor pin retaining nut to 475–525 lb-ft (644–712 N폷m).

If the anchor pin turns while retaining nut torque is being checked, the spider assembly must be replaced.

Page 225

REPAIR INSTRUCTIONS CAMSHAFT INSPECTION

259

Check the spline end of the camshaft for cracks, signs of wear or deformed splines. Replace as necessary.

258

Figure 258 — Camshaft

Check the camshaft bushing journals for wear and signs of corrosion. Replace the camshaft if visible signs of wear are evident or roughness is felt in the journal areas.

Inspect the S-cam for cracking, flat spots or brinelling. Replace as necessary.

Using the following procedures, check the camshaft radial play: 1. Mount a suitable dial indicator with the plunger referencing the S-cam at the roller contact area.

2. Zero the dial indicator.

3. Move the camhead radially, back and forth and note the maximum reading on the dial indicator. 앫

Eaton Maximum Radial Play — 0.020 inch (0.51 mm)

앫

ArvinMeritor™ Maximum Radial Play — 0.030 inch (0.76 mm)

Page 226

Figure 259 — Checking Camshaft Radial Play

If radial play exceeds these maximum specifications, install new camshaft bushings in the brake spider, and then recheck play. If radial play is still excessive, replace the camshaft.

REPAIR INSTRUCTIONS CAM ROLLERS AND BUSHINGS

BRAKE SHOE/LINING INSPECTION

Clean any dirt and rust from the cam rollers, pins and bushings. Replace if worn.

When the brake shoes are removed, inspect for cracks or broken welds on the table or web, loose rivets or elongated rivet holes, and distorted or twisted table. Replace as necessary.

260

262

Figure 260 — Cam Roller

AIR CHAMBER BRACKET INSPECTION Check for a bent, broken or cracked arm and cracked welds (refer to Figure 261). Replace bracket if any abnormalities are evident.

261

Figure 262 — Inspecting Anchor Pin and Roller Recesses (Eaton Shoe Shown)

Check the anchor pin and cam roller recesses (or holes) in the shoe webs for elongation or signs of wear. Replace if diameter exceeds specifications.

Refer to the table below.

Figure 261 — Inspecting Air Chamber Bracket

Check mounting studs (or bolts) for looseness, damaged threads or a bent condition. Replace mounting stud if any of these conditions are evident.

Eaton Brakes All EB

Roller End 0.836 inch

Anchor Pin End 1.400 inch

ArvinMeritor™ Brakes — 16.5-inch shoes only. Anchor pin holes must not exceed 1.009-inch diameter.

Check the lining material for cracks or contamination. Replace as necessary. Replace the linings if they are worn to less than 3/16-inch (4.5-mm) thickness at any point, or within 1/16 inch (1.5 mm) from the rivet heads at any point.

Page 227

REPAIR INSTRUCTIONS

To maintain balanced braking on the vehicle and to minimize the risk of accidents due to brake mismatch, all brakes should be relined at the same time. If complete replacement is not necessary, be sure that all the linings on each side of one axle are replaced at the same time.

Check the brake shoe span and web measurements as shown in Figure 263. Replace any shoes that exceed the specifications.

263

Figure 263 — Checking Shoe Span and Web Measurements

BRAKE LINING MATERIAL FRICTION COEFFICIENT Brake linings must be of the correct material and friction coefficient for the specific application.

Additionally, the same type of lining should be used on each wheel of the same axle.

Linings must be handled carefully to prevent the surface from being contaminated with grease, oil and other foreign material.

Page 228

Brake linings have a code consisting of two letters that designate the friction coefficient of the lining material. The first letter represents the normal coefficient of friction, and the second letter represents the hot coefficient of friction.

Code Letter

Coefficient of Friction

C

Not over 0.15

D

Over 0.15, but not over 0.25

E

Over 0.25, but not over 0.35

F

Over 0.35, but not over 0.45

G

Over 0.45, but not over 0.55

H

Over 0.55

REPAIR INSTRUCTIONS For example, a lining with a normal friction coefficient of 0.37 and a hot coefficient of friction of 0.48 would be coded “FG.”

Cam Brake Shoe Installation

When brake linings are being replaced, make sure that the new linings have the same friction coefficient as the original.

Make sure all components are serviceable.

Choose linings of the proper size and proper friction rating for a specific application. Use the same type of lining for each wheel on the same axle. Handle brake linings carefully to prevent the surface from being contaminated with grease, oil and other foreign material.

EATON BRAKES — EB-150-4L AND ES-150-4L 1. Apply a thin film of grease to the cam roller and anchor pin recesses of each shoe web.

Use only high-temperature waterproof grease conforming to NLGI grade 1.

265

264

Figure 265 — Lubricating Cam Roller and Anchor Pin Recesses Figure 264 — Friction Coefficient Markings

2. Position the upper shoe on the anchor pin.

Then rotate the shoe downward toward the S-cam until the shoe is held in place by the shoe hold-down spring.

3. Hook one end of a new shoe-retaining spring into the hole in the upper shoe web so that the coil lays across the anchor pin.

4. Hook the opposite end of the shoe-retaining spring into the hole of the lower shoe web.

5. Stretch the shoe-retaining spring to allow the lower shoe to be positioned against the anchor pin.

Page 229

REPAIR INSTRUCTIONS 2. DO NOT lubricate:

266

앫

Cam head surfaces. For efficient operation, these surfaces must be free of oil, grease and other contaminants.

앫

Anchor pin recess — single anchor pin brake shoes.

3. Hook the ends of two new retainer springs into the holes in both shoe tables. Spring hooks must be pointing out.

4. Position the upper and lower shoes around the anchor pin. Refer to Figure 267.

267

Figure 266 — Installing Lower Brake Shoe

6. Rotate the lower shoe into position until the shoe is retained in place by the shoe hold-down spring.

7. Hook one end of a new brake shoe return spring in the hole in the lower shoe web.

8. Using a screwdriver, stretch the shoe return spring and hook it into the hole in the upper shoe web.

9. Using an adjustable wrench, screwdriver or similar tool as a lever, pry the upper shoe to stretch the return spring. Then insert a new cam roller on the upper shoe web.

10. Install a new cam roller at the lower shoe web in the same manner.

EATON BRAKES — EB-165-5D, 6D, 7D/ EB-180-7R AND ES-165-7D

Figure 267 — Installing Upper and Lower Brake Shoes

1. Lubricate the following:

5. Install a new shoe return spring.

앫

Shoe roller recess — one-piece roller

앫

Roller ID — two-piece roller On ES-165-7D brakes, a lever may be required to assist in hooking the shoe return spring.

Use only high-temperature waterproof grease conforming to NLGI grade 1.

Page 230

REPAIR INSTRUCTIONS 268

270

Figure 268 — Hooking Brake Shoe Return Spring

Figure 270 — Installing Cam Roller

6. For ES-165-7D only, assemble the roller retainer on the ends of the roller as shown.

269

If drums are oversized or have been resurfaced, oversize rollers must be used.

Oversize rollers are not available for EB-180 brakes.

For identification purposes, the last three digits of the part number are stamped on the roller as shown in Figure 271.

271

Figure 269 — Installing Roller Retainer

7. Using a large screwdriver, adjustable wrench or similar tool as a lever, pry the lower brake shoe upward to allow the new roller and pin (or roller and retainer) into the lower shoe web.

Figure 271 — Cam Roller Identification

Page 231

REPAIR INSTRUCTIONS Roller part numbers are as follows: 074, 234, 523, 524, 525, 526.

EB-165 brakes Standard roller — 074 1.75-inch oversize — 525 1.87-inch oversize — 526 ES-165-7D brakes Standard roller — 234 1.38-inch oversize — 523 1.50-inch oversize — 524

272

8. Recommended procedure for using oversized rollers is as follows: 앫

If drum inside diameter measures between 16.500 and 16.530 inches (16.5-inch brakes), use standard-size rollers.

앫

If drum inside diameter measures between 16.531 and 16.562 inches (16.5-inch brakes), install standard-size roller. Then when brake linings are approximately half worn, replace roller with oversized roller as follows: EB-165 brakes — 525 roller (1.75-inch diameter) ES-165-7D brakes — 523 roller (1.38-inch diameter) 앫

If drum inside diameter measures between 16.563 and 16.619 inches, install standard size roller. Then, when brake linings are approximately half worn, replace roller with oversized roller as follows: EB-165 brakes — 526 roller (1.87-inch diameter) ES-165-7D brakes — 524 roller (1.50-inch diameter) DO NOT use drums with ID measuring 16.620 inches and larger.

9. For ES-165-7D brakes, position assembly in roller recess as shown in Figure 272. Then squeeze retainer loops and swing into position so that the loops snap into the web holes. Verify that both retainer loops engage the web holes before proceeding.

Page 232

Figure 272 — Installing Roller Retainer

10. Repeat process for upper shoe.

EB model brakes do not use a roller retainer.

REPAIR INSTRUCTIONS ARVINMERITOR™ HEAVY-DUTY “P” BRAKES 1. Install upper and lower brake shoes, cam rollers and brake shoe return springs.

2. Install the anchor pins. Be sure to align the flats on the anchor pins with the locking bolt holes on the brake spider.

274

273

Figure 274 — Installing Anchor Pins Figure 273 — Installing Upper and Lower Brake Shoes

Differences may be encountered in anchor pin arrangements. Assembly is still the same.

Page 233

REPAIR INSTRUCTIONS 3. Install the felts, felt retainers and lock rings on both sides of each anchor pin.

277

275

Figure 277 — Lock-Wiring Anchor Pin Locking Bolts Figure 275 — Anchor Pin Retaining Parts

ARVINMERITOR™ “Q” AND “Q-PLUS” BRAKES

4. Install the anchor pin lock bolts and torque to 19–27 lb-ft (85–120 N폷m).

276

DO NOT intermix standard “Q” and “Q-Plus” brake components. “Q” and “Q-Plus” components are marked for easy identification so brake system components are not intermixed. DO NOT use “Q-Plus” brake shoes with a standard “Q” brake camshaft, as the possibility of camshaft rollover exists under certain operating conditions, which results in a non-operating brake and increased stopping distances. Also, the brake drum may not fit over the “Q-Plus” brake shoes if the shoes are used with a standard “Q” brake camshaft. The following illustration shows how to identify the differences between “Q” and “Q-Plus” components.

Figure 276 — Installing Anchor Pin Lock Bolt

5. Lock-wire the anchor pin locking bolts.

Page 234

REPAIR INSTRUCTIONS 278

Figure 278 — “Q” and “Q-Plus” Brake Component Identification

Page 235

REPAIR INSTRUCTIONS

Later production 16.5″ x 5″ and 6″ front “Q” brakes now use a standard “Q-Plus” camshaft and offset-center bar return spring rather than the hammerclaw-style camshaft and straight-center bar return spring. (Refer to Figure 279.)

279

The new offset-center bar brake-shoe return spring can be used with the hammerclaw design “Q” camshaft.

1. Position the anchor pin recess of the upper shoe over the anchor pin of the brake spider.

Then rotate the shoe down until resting against the S-cam.

2. Position the lower brake shoe against the anchor pin and install two new brake shoe retaining springs.

281

Figure 279 — New Style 280

Figure 280 — Previously Used Style Figure 281 — Installing Lower Brake Shoe

DO NOT use the straight-center bar brake-shoe return spring with the “Q-Plus” camshaft. This spring can interfere with the camshaft and affect braking performance, resulting in serious personal injury.

Page 236

REPAIR INSTRUCTIONS 3. Rotate the lower shoe forward and install a new brake-shoe return spring.

282

Install the new offset-center bar return spring with the open end of the spring hooks toward the camshaft as shown in Figure 283.

Figure 282 — Installing Inner and Outer Retaining Springs

Page 237

REPAIR INSTRUCTIONS 283

Figure 283 — Return Spring Installation

Page 238

REPAIR INSTRUCTIONS 4. Pull each brake shoe away from the S-cam to allow enough clearance for installing the cam roller and retainers. Squeeze the retainer ears together so that they fit between the brake shoe webs.

5. Push the retainer into the brake shoe until the ears lock into the holes in the shoe webs.

284

For chassis equipped with ArvinMeritor™ disc brakes, refer to the ArvinMeritor™ service literature covering disc brake overhaul.

Figure 284 — Installing Cam Roller

Page 239

REPAIR INSTRUCTIONS AIR SYSTEM CONTAMINANT REMOVAL Should the air system become contaminated with oil, dirt or other types of debris, the following contaminant removal procedures should be used to protect the air system from additional damage.

When removing contaminants from the air system, do not use chemicals or other types of cleaning agents that damage the rubber O-rings in the valves.

8. Repeat the above procedures for the remaining air reservoirs.

9. Blow compressed air backward through the one-way check valves until the valves are free of contamination.

10. Remove the dual check valve and blow clean shop air through the valve until clean.

11. Blow air backward through the air lines connecting the supply reservoir with the service reservoirs until free of contamination.

12. Remove the primary and secondary supply lines from the treadle valve and blow air backward through the line (from the treadle valve toward the reservoir) until free of contamination.

The following contaminant removal procedures require a source of clean, dry compressed air.

1. Apply the parking brakes. Block the wheels to prevent the vehicle from moving. Then completely drain the air system.

2. Disconnect the discharge line from the air compressor and air dryer.

3. Using clean, dry compressed air, blow through the discharge line in the opposite direction from normal air flow (from the air dryer toward the compressor) until the line is clean. Inspect the discharge line for carbon build-up. Since a build-up of carbon in the discharge would be extremely difficult to remove, the existing discharge line should be replaced, preferably with a new steel-braided Teflon line.

4. Disassemble the air dryer and service according to the manufacturer’s recommendation.

5. Disconnect all the air lines from the supply reservoir, and remove all check valves.

Install plugs into the open reservoir ports, but leave the reservoir inlet port opened.

6. Fabricate an air line with a pressure regulating valve that can be installed into the reservoir inlet port and connected to the shop air source.

7. Open the reservoir draincock, install the fabricated air line and regulating valve to the reservoir inlet port, connect to the shop air source, and set the pressure to 5–8 psi.

Allow the air to flow through the tank for at least 30 minutes.

Page 240

If no oil or other contaminants are found in these lines (from the treadle valve to the reservoirs), the cleaning procedure is complete. If, however, contamination is present, check the treadle valve by removing the lower housing of the valve. If contamination is found in this location, all remaining valves (dashboard push/pull valves, tractor protection valves, dual check valves, etc.) must be checked for contamination and replaced as necessary. Additionally, all interconnecting lines must be cleaned of contamination.

13. Inspect the brake chamber diaphragms for contamination by removing them from the chassis and disassembling.

Spring brake chambers must be manually caged before removing from the chassis and disassembling. Consult the information on brake chambers in “Brake Chambers” on page 101, as well as the specific chamber manufacturer’s service literature before proceeding.

REPAIR INSTRUCTIONS 14. Determine and correct the source of contamination as follows: 앫

Excessive oil contamination — repair or replace the air compressor.

앫

Excessive dirt contamination — inspect air compressor intake source for damage or a malfunctioning filter.

15. Reconnect all air lines and reinstall all check valves, dual check valves and other components that were removed during these cleaning procedures.

high pressure is not available to force the volume of air necessary to set the brake shoes against the drums.

An unbalanced air brake system may be caused by air line restrictions, sticking valves due to dirt or corrosion, etc. Therefore, it is necessary to recognize the importance of balanced brakes, and that the brake system must be maintained as a unit.

Testing for Balanced Brakes

16. Remove and check the safety valve from the supply reservoir, and clean or replace as required.

To determine if the brakes are balanced, perform the following test.

17. Before putting the chassis back into service, perform a complete air and brake system evaluation to ensure proper brake function.

Perform the dual-circuit brake system function test (see “Dual-Circuit Brake System Function Test” on page 185) to verify that the primary and secondary air circuits are connected correctly and functioning properly.

EQUIPMENT NECESSARY

BALANCED AIR BRAKES ON TRACTOR/TRAILER COMBINATIONS On tractor/trailer combinations, the term “balanced brakes” means that each brake assembly on the unit applies an equal amount of force in proportion to the load each axle is carrying. Just as proper load distribution ensures that each axle of the unit is carrying weight in proportion to its Gross Axle Weight Rating (GAWR), adjusting the brakes so that they are “balanced,” ensures that each brake does its proper portion of the total brake application. In addition, all the brakes on the unit should apply simultaneously and should release simultaneously.

Although there is between 95–100 psi available, most brake applications are made with an application pressure of approximately 20 psi or less. A difference of 4–5 psi application pressure between axles may not be significant when application pressure exceeds 60 psi, but it becomes extremely critical when application pressure is between 15–20 psi. It is also important to remember that application time is increased at lower pressures because a head of

앫

A dual-needle test gauge such as Kent-Moore J 42206, Bendix 745-277671, or equivalent

앫

Two air line hoses of the same length (approximately 25–30 feet) equipped with suitable fittings to connect to the dual-needle test gauge and the air system

앫

Two tee fittings

PROCEDURES 1. Disconnect the delivery line from one of the rear axle service brake chambers. Then install the tee fitting into the brake chamber port.

2. Connect one of the fabricated air lines to the tee fitting. This air line should be long enough to reach to the center of the trailer.

3. Reconnect the delivery line to the tee fitting.

4. Disconnect the delivery line from one of the trailer service brake chambers. Then install a tee fitting into the brake chamber port.

5. Connect the second fabricated air line to the tee fitting. This air line should also be long enough to reach to the center of the trailer.

6. Reconnect the delivery line to the tee fitting.

7. Connect the two fabricated air lines to the dual-needle test gauge.

8. Have an assistant slowly make a brake treadle valve application, and observe the pressure indicated by both needles of the dual-needle test gauge.

Page 241

REPAIR INSTRUCTIONS 9. Observe the reaction of the gauge needles as the assistant releases the brake application.

As the brake treadle application is increased, the pressure, as indicated by both needles of the dual-needle test gauge, should build equally and the maximum application pressure (at a full treadle application) should be at least 80 psi. The build-up of pressure and exhaust should be visibly equal between application pressures of 20 and 80 psi. Failure to show equal pressure readings indicates an unbalanced air system, and the cause must be determined and corrected for the tractor/trailer combination to function properly.

After making any necessary corrections and disconnecting the test equipment, test the performance of the brakes while operating the vehicle on the road. With the vehicle fully loaded, make several brake applications to bring the brake drums up to normal operating temperature.

앫

Check the brake chambers for broken return springs, diaphragms or missing or damaged dust boots. Repair or replace as necessary.

COLORED PLASTIC AIR LINES Colored plastic air lines are used on CXN, CHN, CX and CH model chassis. Green, red, blue, brown, orange, yellow, purple, black and gray lines are used, with green designating primary air circuits and red designating secondary air circuits. The remaining colors designate the various supply, dual air and accessory control circuits.

Colored air lines have always been used for the transmission shift circuits at the shifter. For a description of the transmission shifter air line color coding, refer to the applicable transmission service manual.

If an unbalanced braking condition is still evident, check the brake system as follows: It is acceptable to replace a colored plastic air line with a black plastic line.

Refer to “BRAKE SYSTEM OVERHAUL” on page 210 for complete brake system overhaul procedures. 앫

Remove all wheels from both the tractor and trailer. Then examine the drums for signs of heat checking, scoring, wear and eccentricity. Eccentricity should not exceed 0.010 inch. Replace or recondition the brake drums as necessary.

앫

Check the condition of the brake linings and the tightness of the linings on the shoes.

Replace as necessary.

앫

Check the brake shoe return springs for equal tension. Replace as necessary.

앫

With the return springs detached, check the brake shoes for freedom of movement on the anchor pins.

앫

Check the camshafts, bushings, cam followers and wear plates. Repair or replace as necessary.

앫

Check the slack adjusters for binding or slippage on the camshaft. Repair or replace as necessary.

Page 242

REPAIR INSTRUCTIONS The following chart outlines the various air line colors, line sizes and circuit descriptions:

Color Blue

Circuit Identification No. 101

Line Size Inside Diameter

Designation

Circuit Description

0.750″

No. 12

Compressor to Supply Reservoir — 32 cu. ft./min.

425 L/min.

0.625″

No. 10

Compressor to Supply Reservoir — 12 and 15 cu. ft./min 340 L/min.

Blue

143

0.500″

No. 8

Trailer Service Line

Blue

174

0.250″

No. 4

Governor to Compressor (on chassis with bulkhead-mounted governors, line Nos. 174 and 228 are one line)

Blue

228

0.250″

No. 4

Air Compressor Unloader Port to Automatic Drain Valve Control Port (May be Separate Valve or Part of Air Dryer Assembly)

Red

NA

0.250″

No. 4

VTG Oil Coalescing Air Filter, from Shut-Off Valve (at Pressure Protection Valve) to Filter; from Filter to VTG Control Valve

Red

107

0.625″

No. 8

Supply, Secondary Reservoir to Treadle Valve

Red

110

0.188″

No. 3

Secondary Reservoir to Low Pressure Indicator and Air Gauge

Red

128

0.500″

No. 8

Secondary Reservoir to Double Check Valve or Parking Control Valve with Double Check Valve

0.375″

No. 6

Secondary Reservoir to Double Check Valve or Parking Control Valve with Double Check Valve

Red

140

0.375″

No. 6

Trailer Emergency Line

Red

188

0.500″

No. 8

Front Axle Quick Release Valve Delivery to Right Front Brake Chamber

Red

189

0.500″

No. 8

Front Axle Quick Release Valve Delivery to Left Front Brake Chamber

Red

190

0.375″

No. 6

Treadle Valve Delivery or Front Axle Quick Release Valve Delivery to Spring Brake Control Valve (Control)

Red

199

0.500″

No. 8

Treadle Valve Delivery (Secondary) to Front Axle Quick Release Valve (Supply)

0.375″

No. 6

Treadle Valve Delivery (Secondary) to Front Axle Quick Release Valve (Supply)

Red

250

0.250″

No. 4

Air Suspension Height Control Valve Supply

Red

251

0.250″

No. 4

Height Control Valve to Air Spring

Red

293

0.500″

No. 8

Treadle Valve (Secondary) to Trailer Service Double Check Valve or Tractor Protection Valve with Double Check Valve

Red

295

0.250″

No. 4

Pressure Protection Valve to Console Manifold

Red

330

0.375″

No. 6

Secondary Reservoir to Parking Control Valve with Double Check Valve

Red

371

0.500″

No. 8

Front Axle Quick Release Valve Delivery to Left-Hand ABS Modulator Valve Supply (Port 1)

Red

372

0.500″

No. 8

Front Axle Quick Release Valve Delivery to Right-Hand ABS Modulator Valve Supply (Port 1)

Red

373

0.500″

No. 8

Left-Hand ABS Modulator Valve Delivery (Port 2) to Front Axle Brake Chamber

Page 243

REPAIR INSTRUCTIONS Color

Circuit Identification No.

Line Size Inside Diameter

Designation

Circuit Description

Red

374

0.500″

No. 8

Right-Hand ABS Modulator Valve Delivery (Port 2) to Front Axle Brake Chamber

Red

390

0.500″

No. 8

Treadle Valve Delivery to Front-Rear Axle Relay Valve (Control)

Red

393

0.500″

No. 8

Secondary Reservoir to Front-Rear Axle Relay Valve (Supply)

Red

437

0.375″

No. 6

Front Axle Quick Release Valve (or Spring Brake Control Valve Control Port) to Rear Axle Service Brake Relay Valve Control Port (Secondary Control)

Green

112

0.625″

No. 10

Supply, Primary Reservoir to Treadle Valve

Green

114

0.188″

No. 3

Primary Reservoir to Low Pressure Indicator and Air Gauge

Green

129

0.500″

No. 8

Primary Air Reservoir to Double Check Valve or Parking Control Valve with Double Check Valve

0.375″

No. 6

Primary Air Reservoir to Double Check Valve or Parking Control Valve with Double Check Valve

Green

134

0.375″

No. 6

Supply, Primary or Secondary Reservoir to Hand Control Valve

Green

155

0.250″

No. 4

Primary Reservoir to Front-Rear Axle Relay Valve (Supply)

Green

182

0.375″

No. 6

Application, Brake Valve Delivery (Primary) to Front Rear Axle Service Relay Valve

Green

184

0.375″

No. 6

Primary Reservoir to Spring Brake Control Valve (Res. 1 Port)

Green

185

0.625″

No. 10

Supply, Primary Reservoir to Front Rear Axle Service Relay Valve

Green

200

0.375″

No. 6

Service Relay Valve Delivery to Spring Brake Double Check Valve (Inlet) (Anti-compound)

Green

292

0.625″

No. 10

Treadle Valve (Primary) to Trailer Service Double Check Valve or Tractor Protection Valve with Double Check Valve

0.500″

No. 8

Treadle Valve (Primary) to Trailer Service Double Check Valve or Tractor Protection Valve with Double Check Valve

Green

296

0.500″

No. 8

Primary Reservoir to Primary Extension Reservoir

Green

331

0.375″

No. 6

Primary Reservoir to Parking Control Valve with Double Check Valve

Green

375

0.625″

No. 10

Service Brake Relay Valve Delivery to Left-Hand ABS Modulator Valve (Supply, Port 1) or ATC Double Check Valve

Green

376

0.625″

No. 10

Service Brake Relay Valve Delivery to Right-Hand ABS Modulator Valve (Supply, Port 1) or ATC Double Check Valve

Green

377

0.625″

No. 10

Left-Hand ABS Modulator Valve Delivery (Port 2) to Rear-Rear Axle Service Brake Chamber

Green

378

0.625″

No. 10

Right-Hand ABS Modulator Valve Delivery (Port 2) to Rear-Rear Axle Service Brake Chamber

Green

381

0.625″

No. 10

Primary Reservoir to Service Brake Relay Valve Supply (Central Relay 6x4 with 30-30 Chambers)

Page 244

REPAIR INSTRUCTIONS Color

Circuit Identification No.

Line Size Inside Diameter

Designation

Circuit Description

Green

433

0.375″

No. 6

Treadle Valve Delivery (Primary) to Traction Control Solenoid (Port 3)

Green

434

0.375″

No. 6

ATC Valve (Delivery, Port 2) to Rear Axle Service Brake Relay Valve

Black

NA

0.375″

No. 6

Purge Line from Air Dryer to Purge Tank

Black

103

0.500″

No. 8

Supply Reservoir to Primary Reservoir

Black

119

0.500″

No. 8

Supply, Primary or Secondary Reservoir Double Check Valve to Relay Valve

Black

156

0.250″

No. 4

Air Horn Supply

Black

201

0.375″

No. 6

Spring Brake Double Check Valve Delivery to Rear-Rear Axle Frame Tee

Black

261

0.250″

No. 4

Control, Air Suspension Application Valve

Black

262

0.375″

No. 6

Supply Line to Air Suspension Height Control Assembly

0.250″

No. 4

Supply Line to Air Suspension Height Control Assembly

Black

268

0.375″

No. 6

Supply to Transmission Shift Valve

Black

310

0.250″

No. 4

Secondary Air Supply to Air Suspension Seat(s)

Black

435

0.250″

No. 4

Interwheel Differential Lock Control Solenoid to Front Rear Axle Differential Lock Port

Brown

139

0.375″

No. 6

Tractor Emergency, Trailer Supply Valve Delivery to Tractor Protection Valve

Brown

151

0.375″

No. 6

Supply, Primary or Secondary Reservoir Double Check Valve to Parking Brake Control Valve

Brown

436

0.250″

No. 4

Interwheel Differential Lock Control Solenoid to Rear-Rear Axle Differential Lock Port

Yellow

130

0.250″

No. 4

Supply Reservoir to Governor Reserve Port

Yellow

136

0.375″

No. 6

Valve Exhaust

Yellow

259

0.250″

No. 4

Fifth Wheel Air Control Switch Delivery

Orange

152

0.250″

No. 4

Supply, Tractor Parking Brake Delivery to Spring Brake Control Valve (Excluding Four-Wheel Tractors)

0.375″

No. 6

Supply, Tractor Parking Brake Delivery to Spring Brake Control Valve (Excluding Four-Wheel Tractors)

Orange

154

0.250″

No. 4

Spring Brake Control Valve Delivery to Relay Valve Service (Excluding Four-Wheel Tractors)

Orange

178

0.375″

No. 6

Tractor Parking Brake Delivery to Spring Brake Double Check Valve (Inlet) (Domestic Tractors Only)

Gray

135

0.375″

No. 6

Hand Control Valve Delivery to Double Check Valve or Tractor Protection Valve with Double Check Valve

Gray

160

0.250″

No. 4

Power Divider Lock-Out Valve Delivery

Purple

425

0.250″

No. 4

From Air Suspension Pilot Valve (N. O. Port) to Air Gauge

Page 245

REPAIR INSTRUCTIONS AIR LINE HOSE — INSTALLATION Flexible air line hose may eventually fail.

However, by following proper installation, clamping and routing procedures, hose life can be maximized. Also, when selecting an air line hose, make sure that the hose is the same diameter as the hose being replaced. Replacing an air line hose with a different size hose may affect brake timing.

Avoid Twisting — Hoses are imprinted with a layline along the length of the hose to help determine if the hose is twisted. The hose is twisted if the layline spirals around the hose.

Swivel fittings make it possible to install a hose without a twist. When installing a hose, install one fitting so that the layline is visible when the fitting is tight. While the other fitting is still loose, the hose may be rotated as needed until the layline follows the hose routing without spiraling around the hose. Similarly, elbow fittings can be aligned to avoid hose twist.

285

Avoid Excessive Torque on Fittings — Unlike pipe threads, swivel fittings do not depend on thread compression to seal. DO NOT overtighten a swivel fitting, as this will damage the fitting or sealing surfaces.

An air line should be installed as follows: 1. Tighten male pipe ends of hose assemblies first, then tighten the swivel fittings.

2. Whenever possible, install any adapters needed in accessories (as a bench procedure) first.

3. Use an adjustable or open end wrench to install air hose assemblies. DO NOT use pipe wrenches as they will mar the fittings and damage the plating material.

4. DO NOT use pipe thread-sealing compound on swivel-nut hose fittings. Thread sealant should only be used on pipe threads.

5. When installing male-end fittings, use the nipple hex, not the socket hex, to tighten the fitting. Refer to Figure 286.

286

Figure 285 — Twisted and Straight Laylines

Figure 286 — Tightening Male-End Fittings

Page 246

REPAIR INSTRUCTIONS Air Fittings — Quick Disconnect Quick connect style (push-to-connect) air fittings may be used for various applications in the chassis air system. The following guidelines for fitting disassembly and assembly will greatly reduce the possibility of an air leak.

3. With the collet depressed, pull the tubing from the fitting.

289

287

Figure 289 — Remove Tube

FITTING ASSEMBLY GUIDELINES Figure 287 — Push-to-Connect Fitting Cross-Sectional View

FITTING DISASSEMBLY

1. When installing a fitting, install hand-tight, then make final adjustments with a wrench on the hex or flats of the fitting body. Do not use a wrench near the tubing entry or collet head of the fitting.

290

1. Ensure that all pressure has been exhausted from the line before disassembling.

2. Using either the Weatherhead Tube Release tool (Weatherhead part No. 1800TRK) or fingers, depress the collet head to release the grip on the tubing.

288

Figure 290 — Proper Fitting Installation

Figure 288 — Depress Collet

Page 247

REPAIR INSTRUCTIONS 2. When preparing the tube for installation, a square (90-degree), clean cut edge is recommended. An angled cut up to 15 degrees, however, is acceptable.

291

3. Install the tubing straight into the fitting until a solid stop is felt. The tubing grip and seal (on the O-ring) is then accomplished.

Always protect against contaminants in cartridges and fittings during assembly.

293

Figure 291 — Clean, Square Cut Tubing Edge Figure 293 — Insert Tube

Use a tubing cutter (Weatherhead part No. T919 or equivalent) to ensure a good clean cut. Dull knives, side-cutters or other types of cutting tools may not ensure a good, clean cut. Burrs, oval tubing and contamination can damage seals and other air system components.

292

DO NOT use detergent, soap and water, or similar types of solutions as a lubricant when installing the tube.

4. After the tube is fully inserted, gently tug on the tubing to ensure that it is secure in the fitting.

294

Figure 292 — Use a Tubing Cutter for Proper Cut Edges

Figure 294 — Ensure Tubing is Secure

Page 248

REPAIR INSTRUCTIONS 5. Check the completed installation. Allow the tube ample room for a gradual bend. Severe bends can collapse the tubing, resulting in line blockage, flow restrictions and an eventual air leak.

295

Air Lines — Routing A leading cause of flexible air line leakage is routing. Hoses that are too long, too short, twisted, have sharp bends or that rub against other components will eventually leak.

The following basic rules apply when installing and routing flexible air line: 앫

A flexible air line should be routed in a straight line or should follow the contours of the equipment to which it is clamped.

296

Figure 295 — Inspect Final Installation

6. Start the engine and allow the air system to build pressure to governor cut-out. Stop the engine. Then, using soap and water solution, check the installation for leaks.

Figure 296 — Flexible Air Line Following Contour of Equipment

앫

Pairs of flexible air line should be routed together and parallel.

297

Figure 297 — Air Line Pairs Routed Parallel

Page 249

REPAIR INSTRUCTIONS 앫

A flexible air line should be routed and clamped to prevent contact with points of abrasion. When clamping air lines, use clamps that are suitably sized for the diameter of hose. Clamps that are too large allow the hose to move in the clamp, and clamps that are too small may pinch the hose.

앫

A flexible air line must be routed and adequately clamped to avoid contact with sharp edges. Clamps should be installed so that the air line is properly supported to prevent drooping and contacting a sharp edge.

299

298

Figure 299 — Clamps Provide Proper Support Figure 298 — Route and Clamp Line to Prevent Abrasion

Page 250

REPAIR INSTRUCTIONS 앫

Route flexible air line to avoid moving parts.

If necessary, use a stand-off bracket to clamp the line away from a moving part.

앫

300

DO NOT crisscross flexible air lines. The “sawing” action between crisscrossed hoses eventually causes the line to leak. Use suitable clamps to keep the crisscrossed hoses apart.

301

Figure 300 — Route to Avoid Moving Parts Figure 301 — Properly Clamp Crisscrossed Lines

When routing a flexible air line between components in relative motion, leaks due to abrasion and/or less than optimal bend radius may occur. To minimize possible air leakage, the following guidelines are recommended:

Page 251

REPAIR INSTRUCTIONS 앫

Sufficient line length must be provided to allow for movement.

앫

Fittings must not be part of the flexible portion of the hose assembly. To minimize twisting, the hose should bend in the same plane of motion as the boss to which it is connected.

앫

Flexible air line that is bent in two planes should be clamped at the point where the line changes planes. In effect, this divides the line into two assemblies. DO NOT use nylon tubing in these types of applications.

303

302

Figure 303 — Clamp Line Where Planes Change Figure 302 — Install Line to Bend in Same Plane of Motion

When an air line is routed close to a high heat source (e.g., exhaust pipe, exhaust manifold or radiator), the following minimum clearances must be maintained: 앫

Braided hose — 4 inches

앫

Plastic, nylon or rubber line — 6 inches

The above clearances may be reduced if an appropriate heat shield is used.

Page 252

REPAIR INSTRUCTIONS Air Lines — Clamping

앫

To minimize the occurrence of air leakage, the following clamp installation procedures are recommended:

306

앫

If the clamp fastener must be installed perpendicular to the ground, provide full-length support for the clamp.

When installing a clamp, install the fastener parallel to the ground with the clamp suspended from the fastener and the clamp well backed.

304

Figure 306 — Provide Proper Clamp Support

앫

When installing two clamps on one fastener, install the upper clamp first, then suspend the second clamp.

307

Figure 304 — Preferred Clamp Installation

앫

DO NOT install the clamp fastener perpendicular to the ground. The weight of the clamped line may cause the clamp to bend and the line to move.

305

Figure 307 — Installing Two Clamps on One Fastener

Avoid installations where the clamp will not be adequately supported.

Figure 305 — Avoid Installation Where Fastener is Perpendicular to Ground

Page 253

REPAIR INSTRUCTIONS 앫

308

Inverted clamps may be used if the clamp material is of adequate strength to support the load and resist bending.

310

Figure 310 — Inverted Clamp Installation

앫

Figure 308 — Avoid Inadequate Clamp Support

앫

If an installation requires that the clamp mounting legs be bent, make sure the clamp material is of adequate strength to support the load and resist further bending.

311

When clamping multiple hoses, provide a backing of 0.25 inch minimum past the mounting legs of the clamp.

309

Figure 311 — Bent Clamp Leg Installation

CLAMPS

Figure 309 — Proper Backing for Multiple-Hose Clamp Installations

Page 254

Rubber-covered metal-band clamps of suitable size for the hose being clamped should be used for primary support. DO NOT use a clamp that is too large for the diameter of the hose, because the hose may rub against the clamp and result in an air leak.

REPAIR INSTRUCTIONS TIE WRAPS Nylon tie wraps should be used for bundling air lines together, when necessary, between primary supporting clamps. Do not use tie wraps for primary support of hose lines unless button-head

tie wraps are used. Additional information concerning button-head tie wraps can be found in the section “BUTTON-HEAD TIE WRAPS” on page 256.

312

Figure 312 — Metal Clamps for Primary Support, Tie Wraps for Bundling

Page 255

REPAIR INSTRUCTIONS Nylon tie wraps may be used for primary support when clamping additional hoses to metal clamped hoses as long as the number and size of the additional hose(s) are not greater than the

metal clamped hoses. When installing tie wraps, they should be snug, but not so tight as to collapse or cut the hose. Always trim the ends of the tie wraps.

313

Figure 313 — Use Tie Wraps for Primary Support of Additional Hose(s)

BUTTON-HEAD TIE WRAPS

앫

The cutoff should be flush with the button-head, leaving no burrs or sharp edges. If these special tools are not available, or if the tie wrap was originally installed on a stand-off bracket and clearance for using the tensioning tool is insufficient, tension the tie wrap by hand, then cut off the excess with a diagonal cutter (or similar tool). The tie wrap should be tight, but not so tight that it collapses or pinches the line.

앫

For bundled air line installations, the lines should be secure within the bundle and without excessive clearance. Refer to the following illustration.

Button-head tie wraps were used in certain applications for primary support of air lines at MACK assembly plants. If it becomes necessary to cut this type of tie wrap to install a new air line, install a new button-head tie wrap as follows: 앫

Install the tie wrap through the frame hole and around the air line(s).

앫

Tighten the wrap by hand until snug, then use Panduit tool No. GS4H or Snap-on tool No. YA317 to properly tension and cut off the excess end of the tie-wrap.

Page 256

REPAIR INSTRUCTIONS TIE WRAPS WITH FRICTION CLIPS

314

앫

When using tie wraps with friction clips, install the tie wrap through the slots in the clip and around the air lines.

앫

Tighten the tie wrap by hand until snug, then trim the excess. DO NOT leave sharp edges on the cut end of the tie wrap.

앫

For this type of installation, the air lines must be adequately supported as shown below.

315

Figure 315 — Proper Installation Figure 314 — Installing Button-Head Tie Wraps

Page 257

REPAIR INSTRUCTIONS 앫

DO NOT use tie wraps with friction clips in installations where side loads may be applied because the clip and air lines may be forced off the frame. DO NOT allow the weight of the air lines to hang from the friction clip.

Air Lines — Minimum Allowable Radius For rigid air lines, minimum bending radius recommendations are as follows:

316

RIGID AIR LINES Minimum Bending Radius Bent by Hand

Bent with Bending Tool

1/4″

1″

9/16″

3/8″

2″

1″

1/2″

3″

1-1/2″

5/8″

4″

2″

3/4″

6″

2-1/2″

Tubing OD

For flexible air lines, minimum bending radius recommendations are as follows: FLEXIBLE AIR LINES

Figure 316 — Improper Installations

Page 258

Minimum Bending Radius

Hose Size

Hose ID

Hose OD

No. 4

3/16″

0.52″

3/4″

No. 6

5/16″

0.68″

1-1/4″

No. 8

13/32″

0.77″

1-3/4″

No. 10

1/2″

0.92″

2-1/4″

SCHEMATIC & ROUTING DIAGRAMS

SCHEMATIC & ROUTING DIAGRAMS

Page 259

SCHEMATIC & ROUTING DIAGRAMS AIR SYSTEM BASIC CHASSIS AND CAB PIPING DIAGRAMS

317

The basic piping diagrams that follow do not represent customer-specified valves or options.

! ! # ! % "

! %

! "

" " $ $ ! ! % ! % ! % ! % " % " %

! % " %

% ! % ! ! ! ! % ! $ !

Figure 317 — Full Trailer Connection — CTP Series Truck 1. Tractor Protection Valve 2. Double Check Valve 3. Bulkhead Manifold (Connections Outside Cab) 4. Treadle Valve 5. Bulkhead Manifold (Connections Inside Cab) 6. Park Brake Module 7. Hand Control Valve

Page 260

8. Supply Reservoir 9. Secondary Reservoir 10. One-Way Check Valve 11. Primary Reservoir 12. Spring Brake Modulating Relay Valve 13. Tractor Protection Relay Valve

SCHEMATIC & ROUTING DIAGRAMS 318

! # ! ! " " ! # ! % "

! % ! "

" " $ $ ! ! % ! % ! % ! % " % " %

! % " %

% ! % ! ! ! ! % ! $ !

Figure 318 — Full Trailer Connection with Dual Function Hand Control Valve 1. Tractor Protection Valve 2. Double Check Valve 3. Bulkhead Manifold (Connections Outside Cab) 4. Treadle Valve 5. Bulkhead Manifold (Connections Inside Cab) 6. Park Brake Module 7. Hand Control Valve

8. Supply Reservoir 9. Secondary Reservoir 10. One-Way Check Valve 11. Primary Reservoir 12. Spring Brake Modulating Relay Valve 13. Tractor Protection Relay Valve 14. Inversion Valve

Page 261

SCHEMATIC & ROUTING DIAGRAMS 319

" ! ! " # % " ! ! " % " #" !" "' $ " !

!

!

! ! ! !

!

" ! !! ! "

! "

$ $ " ! & & #!" ! !# ! ' !# ' !# ' !# ' " $ '

" ! !# ' $ '

' # " ! ' # " # # " !# ' # " & #!"

Figure 319 — CTP Series Truck with 4S/4M ABS/ATC and Hand Control Valve without MACK Road Stability Advantage (RSA) 1. Front Axle Brake Chamber 2. Treadle Valve 3. Anti-Lock Brake System (ABS) Modulator Valve 4. Quick Release Valve 5. Pressure Protection Valve 6. Park Brake Module 7. Hand Control Valve 8. Supply Reservoir 9. Secondary Reservoir 10. One-Way Check Valve 11. Primary Reservoir 12. Air Solenoid Valve Pack

Page 262

13. Spring Brake Modulating Relay Valve 14. Rear Axle Brake Chamber 15. Frame Fitting 16. Rear Axle Service Brake Relay Valve 17. Automatic Traction Control Valve (ATC) 18. Double Check Valve 19. Bulkhead Manifold (Connections Inside Cab) 20. Bulkhead Manifold (Connections Outside Cab) 21. Bulkhead Manifold 22. Stop Lamp Switch 23. Pressure Regulator, Air-Operated Clutch Assist 24. Cylinder, Air-Operated Clutch Assist

SCHEMATIC & ROUTING DIAGRAMS 320

! ! " $ ! ! $ ! " ! ! $ ! "! ! !& # !

! !

! " & " ! #

!

# # ! % % " ! " & " & " & " & ! # & ! ! # &

! " & # &

& " ! & " ! " " ! " & " ! % " !

Figure 320 — CTP Series Truck with 4S/4M ABS/ATC with Full Trailer Connection without MACK Road Stability Advantage (RSA) 1. Front Axle Brake Chamber 2. Treadle Valve 3. Anti-Lock Brake System (ABS) Modulator Valve 4. Quick Release Valve 5. Pressure Protection Valve 6. Park Brake Module 7. Hand Control Valve 8. Supply Reservoir 9. Secondary Reservoir 10. One-Way Check Valve 11. Primary Reservoir 12. Air Solenoid Valve Pack 13. Spring Brake Modulating Relay Valve

14. Rear Axle Brake Chamber 15. Frame Fitting 16. Rear Axle Service Brake Relay Valve 17. Automatic Traction Control Valve (ATC) 18. Double Check Valve 19. Bulkhead Manifold (Connections Inside Cab) 20. Bulkhead Manifold (Connections Outside Cab) 21. Bulkhead Manifold 22. Stop Lamp Switch 23. Air Regulator, Air-Operated Clutch Assist 24. Cylinder, Air-Operated Clutch Assist 25. Tractor Protection Valve 26. Tractor Protection Relay Valve

Page 263

SCHEMATIC & ROUTING DIAGRAMS 321

! ! " $ ! ! $ ! " ! ! " " ! ! # # $ ! "! ! !& # !

! !

! " & " ! #

!

# # ! % % " ! " & " & " & " & ! # & ! ! # &

! " & # &

& " ! & " ! " " ! " & " ! % " !

Figure 321 — CTP Series Truck with 4S/4M ABS/ATC with Full Trailer Connection and Dual Function Hand Control Valve without MACK Road Stability Advantage (RSA) 1. Front Axle Brake Chamber 2. Treadle Valve 3. Anti-Lock Brake System (ABS) Modulator Valve 4. Quick Release Valve 5. Pressure Protection Valve 6. Park Brake Module 7. Hand Control Valve 8. Supply Reservoir 9. Secondary Reservoir 10. One-Way Check Valve 11. Primary Reservoir 12. Air Solenoid Valve Pack 13. Spring Brake Modulating Relay Valve 14. Rear Axle Brake Chamber

Page 264

15. Frame Fitting 16. Rear Axle Service Brake Relay Valve 17. Automatic Traction Control Valve (ATC) 18. Double Check Valve 19. Bulkhead Manifold (Connections Inside Cab) 20. Bulkhead Manifold (Connections Outside Cab) 21. Bulkhead Manifold 22. Stop Lamp Switch 23. Air Regulator, Air-Operated Clutch Assist 24. Cylinder, Air-Operated Clutch Assist 25. Tractor Protection Valve 26. Tractor Protection Relay Valve 27. Inversion Valve

SCHEMATIC & ROUTING DIAGRAMS CXN, CHN, CT Series Truck with 4S/4M ABS/ATC 322

Figure 322 — CXN, CHN, CT Series Truck with 4S/4M ABS/ATC

Page 265

SCHEMATIC & ROUTING DIAGRAMS CXN, CHN, CT Series Truck with 4S/4M ABS/ATC with Full Trailer Connection 323

Figure 323 — CXN, CHN, CT Series Truck with 4S/4M ABS/ATC with Full Trailer Connection

Page 266

SCHEMATIC & ROUTING DIAGRAMS CXN, CHN, CT Series Truck with 4S/4M ABS/ATC with Full Trailer Connection and Dual Function Hand Control Valve 324

Figure 324 — CXN, CHN, CT Series Truck with 4S/4M ABS/ATC with Full Trailer Connection and Dual Function Hand Control Valve

Page 267

SCHEMATIC & ROUTING DIAGRAMS CXN, CHN, CT Series Tractor with 4S/4M ABS/ATC 325

Figure 325 — CXN, CHN, CT Series Tractor with 4S/4M ABS/ATC

Page 268

SCHEMATIC & ROUTING DIAGRAMS CV Series Truck with 4S/4M ABS/ATC (January 1, 2004 and Later) 326

Figure 326 — CV Series Truck with 4S/4M ABS/ATC (January 1, 2004 and Later)

Page 269

SCHEMATIC & ROUTING DIAGRAMS CV Series Truck with 4S/4M ABS/ATC with Full Trailer Connection (January 1, 2004 and Later) 327

Figure 327 — CV Series Truck with 4S/4M ABS/ATC with Full Trailer Connection (January 1, 2004 and Later)

Page 270

SCHEMATIC & ROUTING DIAGRAMS CV Series Truck with 4S/4M ABS/ATC with Full Trailer Connection and Dual Function Hand Control Valve (January 1, 2004 and Later) 328

Figure 328 — CV Series Truck with 4S/4M ABS/ATC with Full Trailer Connection and Dual Function Hand Control Valve (January 1, 2004 and Later)

Page 271

SCHEMATIC & ROUTING DIAGRAMS CV Series Truck with 4S/4M ABS/ATC (Prior to January 1, 2004) 329

Figure 329 — CV Series Truck with 4S/4M ABS/ATC (Prior to January 1, 2004)

Page 272

SCHEMATIC & ROUTING DIAGRAMS CV Series Truck with 4S/4M ABS/ATC with Full Trailer Connection (Prior to January 1, 2004) 330

Figure 330 — CV Series Truck with 4S/4M ABS/ATC with Full Trailer Connection (Prior to January 1, 2004)

Page 273

SCHEMATIC & ROUTING DIAGRAMS CV Series Truck with 4S/4M ABS/ATC with Full Trailer Connection and Dual Function Hand Control Valve (Prior to January 1, 2004) 331

Figure 331 — CV Series Truck with 4S/4M ABS/ATC with Full Trailer Connection and Dual Function Hand Control Valve (Prior to January 1, 2004)

Page 274

SCHEMATIC & ROUTING DIAGRAMS CV Series Tractor with 4S/4M ABS/ATC 332

Figure 332 — CV Series Tractor with 4S/4M ABS/ATC

Page 275

SCHEMATIC & ROUTING DIAGRAMS CH/CL Series Truck with 4S/4M ABS/ATC 333

Figure 333 — CH/CL Series Truck with 4S/4M ABS/ATC

Page 276

SCHEMATIC & ROUTING DIAGRAMS CH/CL Series Truck without ABS/ATC with Full Trailer Connection 334

Figure 334 — CH/CL Series Truck without ABS/ATC with Full Trailer Connection

Page 277

SCHEMATIC & ROUTING DIAGRAMS CH/CL Series Truck with 4S/4M ABS/ATC and Full Trailer Connection 335

Figure 335 — CH/CL Series Truck with 4S/4M ABS/ATC and Full Trailer Connection

Page 278

SCHEMATIC & ROUTING DIAGRAMS CH/CL Series Truck with 4S/4M ABS/ATC and Full Trailer Connection with Dual Function Hand Control Valve 336

Figure 336 — CH/CL Series Truck with 4S/4M ABS/ATC and Full Trailer Connection with Dual Function Hand Control Valve

Page 279

SCHEMATIC & ROUTING DIAGRAMS CH/CL Series Tractor without ABS/ATC 337

Figure 337 — CH/CL Series Tractor without ABS/ATC

Page 280

SCHEMATIC & ROUTING DIAGRAMS CH/CL Series Tractor with 4S/4M ABS/ATC ArvinMeritor™ WABCO “C” Version ECU 338

Figure 338 — CH/CL Series Tractor with 4S/4M ABS/ATC ArvinMeritor™ WABCO “C” Version ECU

Page 281

SCHEMATIC & ROUTING DIAGRAMS CH/CL/CX Series Tractor with 4S/4M ABS/ATC 339

Figure 339 — CH/CL/CX Series Tractor with 4S/4M ABS/ATC

Page 282

SCHEMATIC & ROUTING DIAGRAMS R Series Truck without ABS/ATC 340

Figure 340 — R Series Truck without ABS/ATC

Page 283

SCHEMATIC & ROUTING DIAGRAMS R Series Truck with 4S/4M ABS/ATC 341

Figure 341 — R Series Truck with 4S/4M ABS/ATC

Page 284

SCHEMATIC & ROUTING DIAGRAMS R Series Truck without ABS/ATC with Full Trailer Connection 342

Figure 342 — R Series Truck without ABS/ATC with Full Trailer Connection

Page 285

SCHEMATIC & ROUTING DIAGRAMS R Series Truck with 4S/4M ABS/ATC with Full Trailer Connection 343

Figure 343 — R Series Truck with 4S/4M ABS/ATC with Full Trailer Connection

Page 286

SCHEMATIC & ROUTING DIAGRAMS R Series Tractor without ABS/ATC 344

Figure 344 — R Series Tractor without ABS/ATC

Page 287

SCHEMATIC & ROUTING DIAGRAMS R Series Tractor with 4S/4M ABS/ATC 345

Figure 345 — R Series Tractor with 4S/4M ABS/ATC

Page 288

SCHEMATIC & ROUTING DIAGRAMS R Series Truck with 4S/4M ABS/ATC with Full Trailer Connection and Dual Function Hand Control Valve 346

Figure 346 — R Series Truck with 4S/4M ABS/ATC with Full Trailer Connection and Dual Function Hand Control Valve

Page 289

SCHEMATIC & ROUTING DIAGRAMS DM, DMM Series Truck without ABS/ATC with Full Trailer Connection 347

Figure 347 — DM, DMM Series Truck without ABS/ATC with Full Trailer Connection

Page 290

SCHEMATIC & ROUTING DIAGRAMS DM, DMM Series Truck with 4S/4M ABS/ATC with Full Trailer Connection 348

Figure 348 — DM, DMM Series Truck with 4S/4M ABS/ATC with Full Trailer Connection

Page 291

SCHEMATIC & ROUTING DIAGRAMS MR Series Truck without ABS/ATC 349

Figure 349 — MR Series Truck without ABS/ATC

Page 292

SCHEMATIC & ROUTING DIAGRAMS MR Series Truck with 4S/4M ABS/ATC 350

Figure 350 — MR Series Truck with 4S/4M ABS/ATC

Page 293

SCHEMATIC & ROUTING DIAGRAMS MR Series Truck without ABS/ATC with Full Trailer Connection 351

Figure 351 — MR Series Truck without ABS/ATC with Full Trailer Connection

Page 294

SCHEMATIC & ROUTING DIAGRAMS MR Series Truck with 4S/4M ABS/ATC with Full Trailer Connection 352

Figure 352 — MR Series Truck with 4S/4M ABS/ATC with Full Trailer Connection

Page 295

SCHEMATIC & ROUTING DIAGRAMS MR Series Tractor without ABS/ATC 353

Figure 353 — MR Series Tractor without ABS/ATC

Page 296

SCHEMATIC & ROUTING DIAGRAMS MR Series Tractor with 4S/4M ABS/ATC 354

Figure 354 — MR Series Tractor with 4S/4M ABS/ATC

Page 297

SCHEMATIC & ROUTING DIAGRAMS LE Series Truck without ABS/ATC without Work Brake 355

Figure 355 — LE Series Truck without ABS/ATC without Work Brake

Page 298

SCHEMATIC & ROUTING DIAGRAMS LE Series Truck with 4S/4M ABS/ATC without Work Brake 356

Figure 356 — LE Series Truck with 4S/4M ABS/ATC without Work Brake

Page 299

SCHEMATIC & ROUTING DIAGRAMS LE Series Truck without ABS/ATC and with Work Brake 357

Figure 357 — LE Series Truck without ABS/ATC and with Work Brake

Page 300

SCHEMATIC & ROUTING DIAGRAMS LE Series Truck with 4S/4M ABS/ATC with Work Brake 358

Figure 358 — LE Series Truck with 4S/4M ABS/ATC with Work Brake

Page 301

SCHEMATIC & ROUTING DIAGRAMS Liftable Axle Air Brake Piping — One Tag or One Pusher 359

Figure 359 — Liftable Axle Air Brake Piping — One Tag or One Pusher 1. Primary Supply Pressure (from Primary Reservoir) 2. Primary Expansion Reservoir 3. One Way Check Valve 4. Rear Axle Service Brake Relay Valve 5. Primary Supply Pressure

Page 302

6. ATC Valve (if Equipped) 7. Primary Control Pressure (from Treadle Valve) 8. Quick Release Valve (if Required) 9. Liftable Axle Service Brake Relay Valve R-12 10. Tag or Pusher Axle Brake Chamber

SCHEMATIC & ROUTING DIAGRAMS Liftable Axle Air Brake Piping — Two Pusher Axles 360

Figure 360 — Liftable Axle Air Brake Piping — Two Pusher Axles 1. Primary Supply Pressure (from Primary Reservoir) 2. Primary Expansion Reservoir 3. One Way Check Valve 4. Rear Axle Service Brake Relay Valve 5. Primary Supply Pressure

6. ATC Valve (if Equipped) 7. Quick Release Valve (if Required) 8. Primary Control Pressure (from Treadle Valve) 9. Pusher Axle Service Brake Relay Valve R-12 (Part No. 8235-9732980360 or 745-103009) 10. Pusher Axle Brake Chamber

Page 303

SCHEMATIC & ROUTING DIAGRAMS Liftable Axle Air Brake Piping — One Tag and One Pusher Axle 361

Figure 361 — Liftable Axle Air Brake Piping — One Tag and One Pusher Axle 1. Primary Supply Pressure (from Primary Reservoir) 2. Primary Expansion Reservoir 3. One Way Check Valve 4. Service Brake Relay Valve 5. ATC Valve (if Equipped) 6. Primary Control Pressure (from Treadle Valve)

Page 304

7. Quick Release Valve (if Required) 8. Pusher Axle Service Brake Relay Valve R-12 9. Pusher Axle Brake Chamber 10. Tag Axle Service Brake Relay Valve R-12 11. Tag Axle Brake Chamber 12. Secondary Reservoir

SCHEMATIC & ROUTING DIAGRAMS Liftable Axle Air Brake Piping — Two Pusher Axles and One Tag Axle 362

Figure 362 — Liftable Axle Air Brake Piping — Two Pusher Axles and One Tag Axle 1. Primary Supply Pressure (from Primary Reservoir) 2. Primary Expansion Reservoir 3. One Way Check Valve (MACK Part No. 63AX3805) 4. Rear Axle Service Brake Relay Valve 5. Delivery Pressure to Rear 6. Primary Supply Pressure 7. ATC Valve (if Equipped)

8. Quick Release Valve (if Required) 9. Primary Control Pressure (from Treadle Valve) 10. Pusher Axle Brake Chambers 11. Pusher Axle Service Brake Relay Valve R-12 (Part No. 8235-9732980360 or 745-103009) 12. Tag Axle Service Brake Relay Valve R-12 (Part No. 8235-9732980360 or 745-103009) 13. Tag Axle Brake Chamber

Page 305

SCHEMATIC & ROUTING DIAGRAMS Rear Axle Relay Valve Configuration 363

Figure 363 — Rear Axle Relay Valve Configuration (Prior to Introduction of ABS/ATC) 4 x 2 Chassis

Page 306

SCHEMATIC & ROUTING DIAGRAMS 364

Figure 364 — Rear Axle Relay Valve Configuration (Prior to Introduction of ABS/ATC) 4 x 2 Chassis

Page 307

SCHEMATIC & ROUTING DIAGRAMS 365

Figure 365 — Rear Axle Relay Valve Configuration (Prior to Introduction of ABS/ATC) 4 x 2 Chassis

Page 308

SCHEMATIC & ROUTING DIAGRAMS 366

Figure 366 — Rear Axle Relay Valve Configuration (Prior to Introduction of ABS/ATC) 6 x 4 Chassis for CAM and Disc Brakes

Page 309

SCHEMATIC & ROUTING DIAGRAMS Bendix TU-FLO Piping 367

Figure 367 — TU-FLO 1400 Compressor with Remote-Mounted Governor and with Remote-Mounted Governor and Air Dryer

Page 310

SCHEMATIC & ROUTING DIAGRAMS Cab Manifold Piping 368

Figure 368 — CH/CL/CX Bulkhead Manifold (Aluminum) Cab Exterior (Engine Side)

Page 311

SCHEMATIC & ROUTING DIAGRAMS 369

Figure 369 — CH/CL/CX Bulkhead Manifold (Aluminum) Cab Interior

Page 312

SCHEMATIC & ROUTING DIAGRAMS 370

Figure 370 — Aluminum Bulkhead (Aluminum) Cab Interior (CL with Vendor Engines)

Page 313

SCHEMATIC & ROUTING DIAGRAMS 371

Figure 371 — CH/CL Bulkhead-Mounted Air Manifold (Aluminum) Straight Truck — One Park Brake Valve — Cab Interior Piping

Page 314

SCHEMATIC & ROUTING DIAGRAMS 372

Figure 372 — CH/CL Bulkhead-Mounted Air Manifold (Aluminum) Truck — (One Park Brake Valve and Rear Service Cab Interior Piping)

Page 315

SCHEMATIC & ROUTING DIAGRAMS 373

Figure 373 — CH/CL Bulkhead-Mounted Air Manifold (Aluminum) Truck — Two Valve Park Brake and Full Trailer Connection Cab Interior Piping

Page 316

SCHEMATIC & ROUTING DIAGRAMS 374

Figure 374 — CH/CL Bulkhead-Mounted Air Manifold (Aluminum) Truck — Three Valve Park Brake and Full Trailer Connection Cab Interior Piping

Page 317

SCHEMATIC & ROUTING DIAGRAMS 375

Figure 375 — CH/CL Bulkhead-Mounted Air Manifold (Aluminum) Tractor — Two Valve Park Brake (Early Production Models) Cab Interior Piping

Page 318

SCHEMATIC & ROUTING DIAGRAMS 376

Figure 376 — CH/CL Bulkhead-Mounted Air Manifold (Aluminum) Tractor — Two Valve Park Brake (Later Production Models CH and CL up to 12/95) Cab Interior Piping

Page 319

SCHEMATIC & ROUTING DIAGRAMS 377

Figure 377 — CH/CL Bulkhead-Mounted Air Manifold (Aluminum) Tractor — Three Valve Park Brake Cab Interior Piping up to 12/95

Page 320

SCHEMATIC & ROUTING DIAGRAMS 378

Figure 378 — CXN/CHN/CX/CH/CL/CV/CT Bulkhead-Mounted Air Manifold (Plastic) Straight Truck with One Park Brake Valve and Rear Service — Cab Interior Piping

Page 321

SCHEMATIC & ROUTING DIAGRAMS 379

Figure 379 — CXN/CHN/CX/CH/CL/CV/CT Bulkhead-Mounted Air Manifold (Plastic) Straight Truck — Cab Exterior (Engine Side) Piping (January 1, 2004 and Later)

Page 322

SCHEMATIC & ROUTING DIAGRAMS 380

Figure 380 — CH/CL/CX Bulkhead-Mounted Air Manifold (Aluminum) Tractor — Cab Exterior Piping

Page 323

SCHEMATIC & ROUTING DIAGRAMS 381

Figure 381 — CH/CL/CX Bulkhead-Mounted Air Manifold (Aluminum) Tractor with Bobtail Proportioning — Cab Exterior Piping

Page 324

SCHEMATIC & ROUTING DIAGRAMS 382

Figure 382 — CH/CL Bulkhead-Mounted Air Manifold (Aluminum) Straight Truck — Cab Exterior Piping

Page 325

SCHEMATIC & ROUTING DIAGRAMS 383

Figure 383 — CH/CL Bulkhead-Mounted Air Manifold (Aluminum) Truck with Rear Service — Cab Exterior Piping

Page 326

SCHEMATIC & ROUTING DIAGRAMS 384

Figure 384 — CH/CL Bulkhead-Mounted Air Manifold (Aluminum) Truck with Full Trailer Connection — Cab Exterior Piping

Page 327

SCHEMATIC & ROUTING DIAGRAMS 385

Figure 385 — CXN/CHN/CH/CX/CL/CV/CT Bulkhead-Mounted Manifold (Plastic with Push-to-Connect Connections) 386

Figure 386 — CXN/CHN/CH/CX/CL/CV/CT Bulkhead-Mounted Manifold (Plastic with Push-to-Connect Connections) — Cab Interior Pass-Through Connections

Page 328

SCHEMATIC & ROUTING DIAGRAMS 387

Figure 387 — CXN/CHN/CX/CH/CL/CV/CT Bulkhead-Mounted Air Manifold (Plastic) Tractor with Two Valve Park Brake Control — Cab Interior Piping

Page 329

SCHEMATIC & ROUTING DIAGRAMS 388

Figure 388 — CXN/CHN/CX/CH/CL/CV Bulkhead-Mounted Air Manifold (Plastic) Straight Truck with One Park Brake Valve and Rear Service — Cab Interior Piping (Prior to January 1, 2004)

Page 330

SCHEMATIC & ROUTING DIAGRAMS 389

Figure 389 — CH/CX/CL Bulkhead-Mounted Air Manifold (Aluminum) Tractor — Two Valve Park Brake (CH and CL Models After 12/95, and All CX) — Cab Interior Piping

Page 331

SCHEMATIC & ROUTING DIAGRAMS 390

Figure 390 — CXN/CHN/CX/CH/CL/CV/CT Bulkhead-Mounted Air Manifold (Plastic) Tractor — Cab Exterior (Engine-Side) Piping

Page 332

SCHEMATIC & ROUTING DIAGRAMS 391

Figure 391 — CXN/CHN/CX/CH/CL/CV/CT Bulkhead-Mounted Air Manifold (Plastic) Tractor with Bobtail Proportioning — Cab Exterior (Engine Side) Piping

Page 333

SCHEMATIC & ROUTING DIAGRAMS 392

Figure 392 — CXN/CHN/CX/CH/CL/CV Bulkhead-Mounted Air Manifold (Plastic) Straight Truck — Cab Exterior (Engine Side) Piping (Prior to January 1, 2004)

Page 334

SCHEMATIC & ROUTING DIAGRAMS 393

Figure 393 — CXN/CHN/CX/CH/CL/CV Bulkhead-Mounted Air Manifold (Plastic) Straight Truck with Rear Service — Cab Exterior (Engine Side) Piping (Prior to January 1, 2004)

Page 335

SCHEMATIC & ROUTING DIAGRAMS 394

Figure 394 — CXN/CHN/CX/CH/CL/CV Bulkhead-Mounted Air Manifold (Plastic) Straight Truck with Full Trailer Connection — Cab Exterior (Engine Side) Piping (Prior to January 1, 2004)

Page 336

SCHEMATIC & ROUTING DIAGRAMS 395

Figure 395 — CXN/CHN/CX/CH/CL/CV/CT Bulkhead-Mounted Air Manifold (Plastic) Straight Truck — Cab Exterior (Engine Side) Piping (January 1, 2004 and Later)

Page 337

SCHEMATIC & ROUTING DIAGRAMS 396

Figure 396 — CXN/CHN/CX/CH/CL/CV/CT Bulkhead-Mounted Air Manifold (Plastic) Straight Truck with Rear Service — Cab Exterior (Engine Side) Piping (January 1, 2004 and Later)

Page 338

SCHEMATIC & ROUTING DIAGRAMS 397

Figure 397 — CXN/CHN/CX/CH/CL/CV/CT Bulkhead-Mounted Air Mainfold (Plastic) Straight Truck with Full Trailer Connection — Cab Exterior (Engine Side) Piping (January 1, 2004 and Later)

Page 339

SCHEMATIC & ROUTING DIAGRAMS 398

Figure 398 — DM/DMM Cab Interior Piping

Page 340

SCHEMATIC & ROUTING DIAGRAMS 399

Figure 399 — DM/DMM Frame Rail Manifold, Truck without Hand Control Valve and without Trailer Connection

Page 341

SCHEMATIC & ROUTING DIAGRAMS 400

Figure 400 — DM/DMM Frame Rail Manifold, Truck with Hand Control Valve for Rear Service Brake Application without Trailer Connection

Page 342

SCHEMATIC & ROUTING DIAGRAMS 401

Figure 401 — DM/DMM Frame Rail Manifold, Truck without Hand Control Valve and with Trailer Connection

Page 343

SCHEMATIC & ROUTING DIAGRAMS 402

Figure 402 — DM/DMM Frame Rail Manifold, Truck with Hand Control Valve and with Trailer Connection

Page 344

SCHEMATIC & ROUTING DIAGRAMS 403

Figure 403 — DM/DMM Frame Rail Manifold, Dual Function Trailer Brakes and Tractor Rear Service Brakes with Hand Control Valve and with Trailer Connection

Page 345

SCHEMATIC & ROUTING DIAGRAMS 404

Figure 404 — R Series Cab Interior Piping

Page 346

SCHEMATIC & ROUTING DIAGRAMS 405

Figure 405 — MR Series Cab Piping

Page 347

SCHEMATIC & ROUTING DIAGRAMS 406

Figure 406 — CX and CH (After January 2000), CXN, CHN, CV, CT and CL Dashboard Air Switch Piping

Page 348

SCHEMATIC & ROUTING DIAGRAMS 407

Figure 407 — Bulkhead-Mounted Air Manifold Location and CX/CH/CL Console Manifold

Page 349

SCHEMATIC & ROUTING DIAGRAMS 408

Figure 408 — DM/DMM Frame Rail Manifold (Located on Left-Hand Side of Chassis, Under Cab, Mounted on Top Frame Flange)

Page 350

SPECIAL TOOLS & EQUIPMENT

SPECIAL TOOLS & EQUIPMENT

Page 351

SPECIAL TOOLS & EQUIPMENT SPECIAL TOOLS The following is a list of special tools that can be used for air and brake system service.

TOOL LIST Tool No.

Tool Name

J 42206

Dual-Needle Pressure Gauge

J 34520-A

Volt/Ohm Meter Kit

J 38500-1

Pro-Link 9000 Diagnostic Reader

J 38500-404

Pro-Link Cartridge for ArvinMeritor™ C-/D-Version ABS Systems

J 38500-403A

Pro-Link Cartridge for ArvinMeritor™ C-Version ABS System

J 38500-1300D

PCMCIA Card for Eaton VORAD Systems

J 24407

30–250 lb-ft Torque Wrench

J 23775-01

100–600 lb-ft Torque Wrench

5004893

AlliedSignal Diagnostic Communication Interface (DCI) for Bendix Systems

5004892

AlliedSignal “ACOM for Windows” Software used with PC

5004894

AlliedSignal DCI Tool and Software Package

1800TRK

Weatherhead Quick-Connect Tube Release Tool

T919

Weatherhead Tubing Cutter

GS4H

Panduit Tie-Wrap Tool

YA317

Snap-On Tie-Wrap Tool

1538-54000100

Norgren Fitting Release Tool

Page 352

INDEX

INDEX

Page 353

INDEX A

B

ABOUT THIS MANUAL . . . . . . . . . . . . . . . . . . .5 ABS INDICATOR LAMP . . . . . . . . . . . . . . . .165 ABS RELAY PANEL . . . . . . . . . . . . . . . . . . .161 ABS VALVE INSTALLATION . . . . . . . . . . . .192 ABS VALVE REMOVAL . . . . . . . . . . . . . . . .191 ABS/ATC DIAGNOSTIC TOOLS . . . . . . . . . .167 ADJUSTING STROKE . . . . . . . . . . . . . . . . . .204 ADVISORY LABELS . . . . . . . . . . . . . . . . . . . . .2 AIR COMPRESSOR . . . . . . . . . . . . . . . . . . . .32 AIR COMPRESSOR AND RESERVOIRS . . . . .8 AIR DRYER SERVICE . . . . . . . . . . . . . . . . .115 AIR DRYERS . . . . . . . . . . . . . . . . . . . . . . . . .113 AIR FITTINGS — QUICK DISCONNECT . . .247 AIR LINE HOSE — INSTALLATION . . . . . . .246 AIR LINES — CLAMPING . . . . . . . . . . . . . . .253 AIR LINES — MINIMUM ALLOWABLE RADIUS . . . . . . . . . . . . . . . . . . . . . . . . . .258 AIR LINES — ROUTING . . . . . . . . . . . . . . . .249 AIR RESERVOIR . . . . . . . . . . . . . . . . . . . . . . .27 AIR SYSTEM BASIC CHASSIS AND CAB PIPING DIAGRAMS . . . . . . . . . . . . . . . .260 AIR SYSTEM COMPONENTS . . . . . . . . . . . .27 AIR SYSTEM CONTAMINANT REMOVAL . . . . . . . . . . . . . . . . . . . . . . . .240 AIR SYSTEM DIAGNOSTIC CHECK . . . . . .179 AIR SYSTEM DIAGNOSTIC PROCEDURES . . . . . . . . . . . . . . . . . . . .176 AIR SYSTEM MAINTENANCE . . . . . . . . . . .182 AIR SYSTEM OVERVIEW . . . . . . . . . . . . . . . . .8 AIR SYSTEM SAFETY FEATURES . . . . . . . .15 AIR SYSTEM THEORY OF OPERATION . . . .11 ANCHORLOK “MOISTURE LOK” DRY AIR TANK (AFTERCOOLER TYPE) . . . . . . . .115 ANTI-COMPOUNDING CIRCUITS . . . . . . . . .22 ANTI-LOCK BRAKE SYSTEM (ABS) . . . . . .155 ANTI-LOCK BRAKE SYSTEM COMPONENT REMOVAL AND INSTALLATION . . . . . .188 ANTI-LOCK BRAKE SYSTEM COMPONENTS . . . . . . . . . . . . . . . . . . . .157 APPLICATION VALVE (TREADLE VALVE) . . .9 APPLYING THE SERVICE BRAKES . . . . . . .13 ARVINMERITOR™ WABCO SYSTEM SAVER 1000, 1200, 1200E AND 1200P . . . . . . .148 ASBESTOS FIBERS DANGER . . . . . . . . . . .210 ATC INDICATOR LAMP . . . . . . . . . . . . . . . .165 ATC VALVE . . . . . . . . . . . . . . . . . . . . . . . . . .163 ATC VALVE INSTALLATION . . . . . . . . . . . .193 ATC VALVE REMOVAL . . . . . . . . . . . . . . . .192 AUTOMATIC DRAIN VALVE . . . . . . . . . . . . . .30

BALANCED AIR BRAKES ON TRACTOR/ TRAILER COMBINATIONS . . . . . . . . . . 241 BENDIX AD-9 AND AD-9 SOFT SEAT AIR DRYERS . . . . . . . . . . . . . . . . . . . . . . . . . 121 BENDIX AD-IP AIR DRYER . . . . . . . . . . . . . 126 BENDIX AD-SP AIR DRYER . . . . . . . . . . . . 130 BENDIX TU-FLO PIPING . . . . . . . . . . . . . . . 310 BOBTAIL PROPORTIONING RELAY VALVE . . . . . . . . . . . . . . . . . . . . . . . . . . . . 94 BRAKE ADJUSTMENT . . . . . . . . . . . . . . . . . 196 BRAKE CHAMBERS . . . . . . . . . . . . . . . . 10, 101 BRAKE NOISE INVESTIGATION . . . . . . . . . 174 BRAKE SYSTEM OVERHAUL . . . . . . . . . . . 210

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C CAB MANIFOLD PIPING . . . . . . . . . . . . . . . 311 CAM BRAKE COMPONENT INSPECTION . 223 CAM BRAKE SHOE INSTALLATION . . . . . . 229 CAM BRAKE SHOE REMOVAL . . . . . . . . . . 216 CH/CL SERIES TRACTOR WITH 4S/4M ABS/ATC ARVINMERITOR™ WABCO “C” VERSION ECU . . . . . . . . . . . . . . . . . 281 CH/CL SERIES TRACTOR WITHOUT ABS/ATC . . . . . . . . . . . . . . . . . . . . . . . . . 280 CH/CL SERIES TRUCK WITH 4S/4M ABS/ATC . . . . . . . . . . . . . . . . . . . . . . . . . 276 CH/CL SERIES TRUCK WITH 4S/4M ABS/ATC AND FULL TRAILER CONNECTION . . . . . . . . . . . . . . . . . . . . 278 CH/CL SERIES TRUCK WITH 4S/4M ABS/ATC AND FULL TRAILER CONNECTION WITH DUAL FUNCTION HAND CONTROL VALVE . . . . . . . . . . . . . . . . . . . . . . . . . . . 279 CH/CL SERIES TRUCK WITHOUT ABS/ATC WITH FULL TRAILER CONNECTION . . . . . . . . . . . . . . . . . . . . 277 CH/CL/CX SERIES TRACTOR WITH 4S/4M ABS/ATC . . . . . . . . . . . . . . . . . . . 282 CR BRAKEMASTER MODELS 62 AND 68 (AFTERCOOLER TYPE) . . . . . . . . . . . . . 134 CR BRAKEMASTER T2000 AND T3000 AIR DRYERS . . . . . . . . . . . . . . . . . . . . . . . . . 136 CV SERIES TRACTOR WITH 4S/4M ABS/ATC . . . . . . . . . . . . . . . . . . . . . . . . . 275 CV SERIES TRUCK WITH 4S/4M ABS/ATC (JANUARY 1, 2004 AND LATER) . . . . . . 269 CV SERIES TRUCK WITH 4S/4M ABS/ATC (PRIOR TO JANUARY 1, 2004) . . . . . . . 272

INDEX CV SERIES TRUCK WITH 4S/4M ABS/ATC WITH FULL TRAILER CONNECTION (JANUARY 1, 2004 AND LATER) . . . . . .270 CV SERIES TRUCK WITH 4S/4M ABS/ATC WITH FULL TRAILER CONNECTION (PRIOR TO JANUARY 1, 2004) . . . . . . .273 CV SERIES TRUCK WITH 4S/4M ABS/ATC WITH FULL TRAILER CONNECTION AND DUAL FUNCTION HAND CONTROL VALVE (JANUARY 1, 2004 AND LATER) . . . . . . . . . . . . . . . . . . . . . . . . . .271 CV SERIES TRUCK WITH 4S/4M ABS/ATC WITH FULL TRAILER CONNECTION AND DUAL FUNCTION HAND CONTROL VALVE (PRIOR TO JANUARY 1, 2004) . . . . . . . . . . . . . . . . .274 CXN, CHN, CT SERIES TRACTOR WITH 4S/4M ABS/ATC . . . . . . . . . . . . . . . . . . .268 CXN, CHN, CT SERIES TRUCK WITH 4S/4M ABS/ATC . . . . . . . . . . . . . . . . . . .265 CXN, CHN, CT SERIES TRUCK WITH 4S/4M ABS/ATC WITH FULL TRAILER CONNECTION . . . . . . . . . . . . . . . . . . . . .266 CXN, CHN, CT SERIES TRUCK WITH 4S/4M ABS/ATC WITH FULL TRAILER CONNECTION AND DUAL FUNCTION HAND CONTROL VALVE . . . . . . . . . . . .267 CYCLO-GARD AIR DRYER MODELS 17 AND 22 . . . . . . . . . . . . . . . . . . . . . . . . . .140 D DASH-MOUNTED PRESSURE GAUGES . . . .9 DESCRIPTION . . . . . . . . . . . . . . . . . . . . . . .113 DIAGNOSTIC BLINK CODES . . . . . . . . . . . .166 DM, DMM SERIES TRUCK WITH 4S/4M ABS/ATC WITH FULL TRAILER CONNECTION . . . . . . . . . . . . . . . . . . . . .291 DM, DMM SERIES TRUCK WITHOUT ABS/ATC WITH FULL TRAILER CONNECTION . . . . . . . . . . . . . . . . . . . . .290 DOUBLE CHECK VALVES . . . . . . . . . . . .16, 38 DRAIN VALVES . . . . . . . . . . . . . . . . . . . . . . . .30 DRUM/ROTOR INSPECTION . . . . . . . . . . . .212 DUAL-CIRCUIT BRAKE SYSTEM FUNCTION TEST . . . . . . . . . . . . . . . . . .185 DUAL-NEEDLE TEST GAUGE . . . . . . . . . . .175 DYNO-TESTING VEHICLES WITH ATC OPTION . . . . . . . . . . . . . . . . . . . . . . . . . .156

E ELECTRONIC CONTROL UNIT (ECU) . . . . 157 ENGINE BRAKE DISABLE RELAY . . . . . . . 160 EXPLANATION OF NUMERICAL CODE . . . . . 4 F FRONT-AXLE SPEED SENSOR INSTALLATION . . . . . . . . . . . . . . . . . . . . 188 FRONT-AXLE SPEED SENSOR REMOVAL . . . . . . . . . . . . . . . . . . . . . . . . 188 G GOVERNOR . . . . . . . . . . . . . . . . . . . . . . . . . . 34 H HALDEX DRY E.S.T. AIR DRYER . . . . . . . . 142 HAND CONTROL VALVE (TROLLEY VALVE) . . . . . . . . . . . . . . . . . . . . . . . . . . . 65 HOSE COUPLINGS (GLAD HANDS) . . . . . . 101 I NTRODUCTION . . . . . . . . . . . . . . . . . . . . . . 155 INVERSION VALVE . . . . . . . . . . . . . . . . . . . . 87 ISOLATION (ECON) VALVE . . . . . . . . . . . . . 153 L LE SERIES TRUCK WITH 4S/4M ABS/ATC WITH WORK BRAKE . . . . . . . . . . . . . . . 301 LE SERIES TRUCK WITH 4S/4M ABS/ATC WITHOUT WORK BRAKE . . . . . . . . . . . 299 LE SERIES TRUCK WITHOUT ABS/ATC AND WITH WORK BRAKE . . . . . . . . . . . . . . . 300 LE SERIES TRUCK WITHOUT ABS/ATC WITHOUT WORK BRAKE . . . . . . . . . . . 298 LIFTABLE AXLE AIR BRAKE PIPING — ONE TAG AND ONE PUSHER AXLE . . . 304 LIFTABLE AXLE AIR BRAKE PIPING — ONE TAG OR ONE PUSHER . . . . . . . . . 302 LIFTABLE AXLE AIR BRAKE PIPING — TWO PUSHER AXLES . . . . . . . . . . . . . . 303 LIFTABLE AXLE AIR BRAKE PIPING — TWO PUSHER AXLES AND ONE TAG AXLE . . . . . . . . . . . . . . . . . . . . . . . . . . . . 305 LONG-STROKE AIR CHAMBERS . . . . . . . . 111 LOW-PRESSURE INDICATOR SWITCH . . . . 36 LOW-PRESSURE WARNING . . . . . . . . . . . . . 15

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INDEX M

Q

MANUAL AND AUTOMATIC SLACK ADJUSTERS . . . . . . . . . . . . . . . . . . . . . .196 MEASURING DRIVE AXLE CONTROL PRESSURE VERSUS TRAILER CONTROL PRESSURE (TRACTORS ONLY) . . . . . . . . . . . . . . . . . . . . . . . . . . .178 MEASURING DRIVE AXLE DELIVERY PRESSURE VERSUS STEERING AXLE DELIVERY PRESSURE . . . . . . . . . . . . .178 MEASURING DRIVE AXLE DELIVERY PRESSURE VERSUS TRAILER AXLE DELIVERY PRESSURE (TRACTORS ONLY) . . . . . . . . . . . . . . . . . . . . . . . . . . .178 MEASURING RELAY VALVE CONTROL PRESSURE VERSUS DELIVERY PRESSURE . . . . . . . . . . . . . . . . . . . . . . .177 MEASURING SUPPLY PRESSURE AT THE SERVICE BRAKE RELAY VALVE (IF EQUIPPED) . . . . . . . . . . . . . . . . . . . . . . .176 MEASURING SUPPLY PRESSURE AT THE TREADLE VALVE . . . . . . . . . . . . . . . . . .177 MIDLAND PURE AIR PLUS AIR DRYER . . .146 MODULATOR (ABS) VALVE . . . . . . . . . . . . .163 MR SERIES TRACTOR WITH 4S/4M ABS/ATC . . . . . . . . . . . . . . . . . . . . . . . . .297 MR SERIES TRACTOR WITHOUT ABS/ATC . . . . . . . . . . . . . . . . . . . . . . . . .296 MR SERIES TRUCK WITH 4S/4M ABS/ATC . . . . . . . . . . . . . . . . . . . . . . . . .293 MR SERIES TRUCK WITH 4S/4M ABS/ATC WITH FULL TRAILER CONNECTION . . . . . . . . . . . . . . . . . . . . .295 MR SERIES TRUCK WITHOUT ABS/ATC . . . . . . . . . . . . . . . . . . . . . . . . .292 MR SERIES TRUCK WITHOUT ABS/ATC WITH FULL TRAILER CONNECTION . . .294 MULTIPLE-DIAPHRAGM SPRING BRAKE CHAMBERS . . . . . . . . . . . . . . . . . . . . . .104

QUICK RELEASE VALVE . . . . . . . . . . . . . . . . 82

N NON-ASBESTOS FIBERS DANGER . . . . . .211 P PARK BRAKE CONTROL MODULE . . . . . . . .46 PRESSURE PROTECTION VALVE . . . . . . . .39 PREVENTIVE MAINTENANCE . . . . . . . . . . .183 PUSH/PULL-TYPE PARK BRAKE CONTROL VALVES . . . . . . . . . . . . . . . . .54

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R R SERIES TRACTOR WITH 4S/4M ABS/ATC . . . . . . . . . . . . . . . . . . . . . . . . . 288 R SERIES TRACTOR WITHOUT ABS/ATC . . . . . . . . . . . . . . . . . . . . . . . . . 287 R SERIES TRUCK WITH 4S/4M ABS/ATC . . . . . . . . . . . . . . . . . . . . . . . . . 284 R SERIES TRUCK WITH 4S/4M ABS/ATC WITH FULL TRAILER CONNECTION . . . . . . . . . . . . . . . . . . . . 286 R SERIES TRUCK WITH 4S/4M ABS/ATC WITH FULL TRAILER CONNECTION AND DUAL FUNCTION HAND CONTROL VALVE . . . . . . . . . . . . . . . . . 289 R SERIES TRUCK WITHOUT ABS/ATC . . . 283 R SERIES TRUCK WITHOUT ABS/ATC WITH FULL TRAILER CONNECTION . . . . . . . . . . . . . . . . . . . . 285 REAR AXLE RELAY VALVE CONFIGURATION . . . . . . . . . . . . . . . . . 306 REAR-AXLE SPEED SENSOR INSTALLATION . . . . . . . . . . . . . . . . . . . . 190 REAR-AXLE SPEED SENSOR REMOVAL . . . . . . . . . . . . . . . . . . . . . . . . 189 REDUNDANT SIGNAL RELAY VALVE . . . . . 20 RELAY VALVES . . . . . . . . . . . . . . . . . . . . . . . 88 RELEASING THE SERVICE BRAKES . . . . . . 14 REPLACEMENT OF ABS CHASSIS HARNESSES . . . . . . . . . . . . . . . . . . . . . 193 ROTOCHAMBERS . . . . . . . . . . . . . . . . . . . . 110 S SAFETY INFORMATION . . . . . . . . . . . . . . . . . 2 SERVICE PROCEDURES AND TOOL USAGE . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 SERVICE TESTS . . . . . . . . . . . . . . . . . . . . . 182 SINGLE CHECK VALVES . . . . . . . . . . . . . . . . 15 SINGLE CHECK VALVES . . . . . . . . . . . . . . . . 37 SINGLE PARK BRAKE CONTROL VALVE WITH DOUBLE CHECK VALVE . . . . . . . . 51 SINGLE-DIAPHRAGM BRAKE CHAMBERS . . . . . . . . . . . . . . . . . . . . . . 102 SLACK ADJUSTER LUBRICATION . . . . . . . 203 SLACK ADJUSTER MAINTENANCE . . . . . . 197 SPECIAL TOOLS . . . . . . . . . . . . . . . . . . . . . 352 SPRING BRAKE CONTROL VALVE . . . . . . . 74 SPRING BRAKE CONTROL VALVE (LE AND MR MODELS) . . . . . . . . . . . . . . . . . . 19

INDEX SPRING BRAKE MODULATING RELAY VALVE . . . . . . . . . . . . . . . . . . . . . . . . .17, 67 STOPLIGHT SWITCH . . . . . . . . . . . . . . . . . . .40 SYSTEM OVERVIEW . . . . . . . . . . . . . . . . . .155 SYSTEM PRESSURIZED WITH PARKING BRAKES APPLIED . . . . . . . . . . . . . . . . . .11 SYSTEM PRESSURIZED WITH PARKING BRAKES RELEASED . . . . . . . . . . . . . . . .12

TRACTOR PROTECTION VALVE — MR AND DM MODELS WITH FULL TRAILER CONNECTION . . . . . . . . . . . . . . . . . . . . . 59 TRACTOR PROTECTION VALVE . . . . . . . . . 26 TRAILER AIR SUPPLY VALVE . . . . . . . . . . . 56 TREADLE VALVE . . . . . . . . . . . . . . . . . . . . . . 42 TROUBLESHOOTING BRAKE SYSTEM PROBLEMS . . . . . . . . . . . . . . . . . . . . . . . 170

T

W

TESTING FOR BALANCED BRAKES . . . . . .241 TONE WHEEL . . . . . . . . . . . . . . . . . . . . . . . .161 TRACTOR — REAR BRAKE PROPORTIONING/FRONT AXLE RATIO VALVES . . . . . . . . . . . . . . . . . . . . .83 TRACTOR PROTECTION MANIFOLD — CXN/CHN/CH/CL/CX/CV/CT MODELS . . . . . . . . . . . . . . . . . . . . . . . . . .62

WHEEL REMOVAL . . . . . . . . . . . . . . . . . . . . 211 WHEEL SPEED SENSORS . . . . . . . . . . . . . 162 WHEELBASE CHANGES ON ABS-EQUIPPED VEHICLES . . . . . . . . . . 193

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NOTES

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AIR AND BRAKE SYSTEM SERVICE MANUAL PRINTED IN U.S.A. 16-104

© MACK TRUCKS, INC. 2007