CLARK FORKLIFT BR120 Brake Systems TECHNICAL TRAINING MANUAL

BR120 Brake Systems

TECHNICAL TRAINING Copyrighted Material Intended for CLARK dealers only Do not sell or distribute

Copyrighted Material Intended for CLARK dealers only Do not sell or distribute

Contents About this class......................................................................................................

About safety ...........................................................................................................

Section1. Principles of Braking ........................... ................................................

Newton's Laws............................................................................................

First Law (Inertia Law)..............................................................................

Second Law (Acceleration Law)..................................................................

Third Law (Action and Reaction Law).......................................................

Application of the Braking Principle..........................................................

How Brake Linings, Shoes, Drums and the Road Work Together...........

Basic Objectives in Brake Design..............................................................

BrakeStopping Torque...............................................................................

Shoe Energization ................. .....................................................................

Shoe Leverage.............................................................................................

Lining Characteristics................................................................................

Drum Deflection and Thermal Expansion.................................................

Section2. Methods ofActuating Brakes..............................................................

Hydraulic BrakeActuation.........................................................................

Hydrovac BrakeActuation.........................................................................

Hydraulic Brake Operation........................................................................

Hydrovac Brake Operation.........................................................................

Air BrakeActuation....................................................................................

Section3. Components of the BrakingSystem...... .............................................

Master Cylinder..........................................................................................

Residual Check Valve..... .............................. .................... ...... ....................

Wheel Cylinder............................................................................................

HydraulicInching.......................................................................................

BrakeSelectorValve...................................................................................

BrakeAdjusters..........................................................................................

Hydraulic Brake Tubes and Hose...............................................................

Brake Fluid .................................................... ..... .........................................

Drum andShoe Brakes...............................................................................

Disc Brakes..................................................................................................

Wet Disc Brakes..........................................................................................

Parking Brakes ...................................................... ............................ ..........

Section4. Pre-ServiceBrake Inspection............................ ..................................

BrakeSystemInspection ............................................................................

Brake Pedal Check......................................................................... .............

Brake Lining and DrumInspection...........................................................

Chassis Inspection .......................................... ............................................

Master Cylinder Check...............................................................................

Parking Brake Check........ ...................... ....................................................

Section5. Drum andShoe Maintenance and Repair..........................................

Drum andShoe Replacement or Overhaul................................................

Installing Wheel Cylinders.........................................................................

Checking andShimmingAdjuster Gaps....................................................

Replacing Brake shoes................................................................................

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Brake Systems page I

Resurfacing Drums... ............................... ... .... ........... .......... .... ....... ...... ......

Section 6. Disc Brakes Maintenance and Repairs... ..... .......................................

Inspection.................................................... ........... .................. ............ .......

Replacing brake disc lining................................ .... ....... ....................... ... ...

Replacing brake piston lining.................................................... .... ............

Caliper Replacement. .... ....... .............................................. .........................

Section7. Bleeding the Brake System.................................................................

When to Bleed the System ........ ........................ ......... ......... ............. .... ..... ..

Bleeding Provisions and Objectives...........................................................

Bleeding Problems......................................................... ..... ..... ...................

Three Bleeding Methods ............. ............................................... .................

Bottom Up Bleeding....................................................................................

Manual Bleeding.......................................................................... ...............

Pressure Bleeding.... ..... ............. .... .... ... ...... ........ .... ... ........... .......... ... .... .... .

Brake and Inching Circuit Bleeding..........................................................

Hydraulic Brake Fluid and Bleeding Precautions................... .................

Section8. Component Reconditioning..................................................................

Reconditioning the Master Cylinder..........................................................

Reconditioning the Two Stage Master Cylinder... ...... ................ ...............

Reconditioning the Wheel Cylinders..........................................................

Section9. Genesis Hydraulic Brake Valve...........................................................

Brake Valve Description.............................................................................

Brake Valve Operation...............................................................................

Brake Valve Removal..................................................................................

System Bleeding...................................... ....................................................

Brake Valve Overhaul................................................................................

Section 10. Repairing Wet Disc Brakes................................................................

Checking Brake Pedal Linkage..................................................................

Checking Master Cylinder........................................................................ .

Checking Loss of Transmission Fluid........................................................

Isolating Between the Master Cylinder, Inching, and the Right or Left Brakes.......................................................

Removing the Wheel Axle Assembly..........................................................

Further Isolating Fluid Loss......................................................................

Removing Discs and Drum........................................................................ .

Reassembling the Wheel/Axle Assembly ...................................................

Installing Parking Brake Arm...................................................................

Parking Brake Adjustment ........................................................................

Troubleshooting Guide............................................................................... ©Copyright Clark Material Handling Company 1990.

Revised 1998

Brake System page 2

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About this class

Welcome to class BR-120: Brake Systems.

The purpose of this class is to provide an overview of brake systems as they apply to Clark lift trucks.

This class consists of ten sections:

1.

Principles of Braking

2.

Methods of Actuating Brakes

3.

Components of the Braking System

4.

Pre-Service Brake Inspection

5.

Drum and Shoe Maintenance and Repairs

6.

Disc Brake Maintenance and Repairs

7.

Bleeding the Brake System

8.

Component Reconditioning

9.

Genesis Hydraulic Brake Valve

10.

Wet Disc Brake Service

Each section contains information vital to an overall understanding of the kinds of brakes Clark uses, but at the same time makes no effort to be comprehensive in cover­ ing this complex subject.

It is important to refer to the Service Manuals for each family of bucks, as no two types of Clark lift bucks have completely identical braking systems.

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About safety

The following messages may be used to emphasize important information: Note This message is used when special information, instructions or identification is required relating to procedures, equipment, tools, pressures, capacities and other special data.

Important This message is used when special precautions should be taken to ensure a correct action or to avoid damage to or malfunction of the truck or a component.

CAUTION This message is used as a reminder of safety practices which can result in personal injury if proper precautions are not taken.

WARNING This message is used when a hazard exists which can result in injury or death if proper precautions are not taken.

DANGER

This message is used when an extreme hazard exists which will result in death or serious injury if proper precautions are not taken.

Before atempting any service work, carefully read and understand the specific maintenance procedures located in the service manual. Follow all service safety instructions when repairing the lift truck.

Brake System page 4

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Section 1. Principles of Braking

This section of the manual briefly explains braking principles and operation, beginning with the most basic information about force, motion, resistance, and friction, and mov­ ing to a description of brake functions, objectives in brake design, and development of stopping torque.

Newton's Laws

In order to deal with braking problems you need some understanding of the laws of motion.

These laws, formulated by Sir Isaac Newton, are as follows: First Law (Inertia Law) Every body continues in a state of rest, or in uniform motion in a straight line, unless it is compelled by a force or forces to change its state of rest or motion.

Second Law (Acceleration Law) Change of motion is proportional to the force applied, and takes place along the straight line in which the force acts.

Third Law (Action and Reaction Law) To every action there is always an equal reaction; that is, if a force acts to change the state of motion of a body, the body offers a resistance equal and opposite to the force.

Newton's first law, then, defines what is commonly referred to as "inertia" or "momen­ tum. " For example, if a truck is traveling at a certain speed in a straight line on a level surface, and the propulsion power is suddenly removed, it will continue to move at that certain speed until some force causes it to slow down. Inertia causes it to continue.

Any or all of the following forces could cause it to slow down: 1. Rolling resistance 2. Friction in the rotating components; or body friction, which is energy used up in causing stiuctures to flex 3. Air resistance 4. Grades or slopes (although in this case we already stated that the truck is on a level surface) 5. Applied braking to the wheels If none of these five elements were present, the truck would continue at that certain speed indefinitely aft er power was removed. That is, it would never slow down.

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Brake Systems page 5

Application of the Braking Principle

Brakes rob motion from the wheels of the speeding vehicle by developing a controlled friction to convert the vehicle's kinetic energy, (energy of motion), into heat. This heat is dissipated into the surrounding air as rapidly as possible; thus cooling also takes place during non-braking intervals.

Even though effective braking is applied to the brake drums, remember that the only contact between the vehicle tires and the road is a rolling fr iction. It is this friction which actually brakes and stops the vehicle. Should the brakes overcome rolling fric­ tion to lock any wheel on the vehicle, the braking, (heat), must be produced by the small skid area of the tire. More time is required to stop the vehicle, control is lost, and tire wear increases.

The shortest possible stop is thus influenced by the road's coefficient of friction, which is approximately 60 % on dry concrete, less on asphalt, still less on gravel, and quite low on ice.

This maximum brake retarding effect of the road is one of the forces which determines the amount of deceleration, often called the "K" factor, which simply means that a given road can only tolerate a combination of retarding forces up to "K" percent of the weight being stopped. A 0.60 "K" stop (60 pounds retarding force per 100 pounds of weight) is the approximate limit of present highways. Tire cliameter is also a factor, since leverage between the brake and wheel is reduced by increases in the rolling raclius.

Therefore, the amount of brake torque capacity (stopping power) needed depends primarily upon gross vehicle weight, tire size, and the desired "K" factor.

Excess brake torque capacity would not improve performance and could make braking unduly sensitive, reducing control during normal easy stops on slippery surfaces.

CAUTION "Ricling the Brake" can result in overheating and other problems.

How Brake Shoes, Drums, and the Road Work Together

Clark uses three basic types of service brakes on its trucks, Drum and Shoe, Disc, and Wet-Disc or Oil-Cooled brakes.

Braking is caused by the ch-ag of a brake shoe against a drum to stop the wheel rotat­ ing. The modern lift truck is equipped for braking purposes with a brake drum or clisc.

The brake shoes, which contact the brake drum, are faced with a brake lining, which is made from a special friction material. The geometrically designed shoes provide lever­ age, and on modern drum-type brakes, are mounted internally to drag on the protected inner surface of the drum. This design actually makes use of vehicle movement to assist the braking process.

Brake System page 6

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The brake shoe arrangement, known as the "foundation brake," must be controlled with some form of "brake actuating system" rather than a simple linkage. In hydraulic brakes, the shoes are forced against the drum by pistons under fluid pressure, and to assist or supplement manual operation, the system may include a vacuum, hydraulic, or compressed air-operated power unit.

Cam operated brake shoes are actuated mechanically, and in modern usage are found on heavy trucks and trailers equipped with straight air.

Disc brakes are generally controlled hydraulically, with or without power assistance.

On even a comparatively light lift truck, modern brakes develop from 300 to 400 horse­ power in order to stop the truck in as little as one-sixth the distance required by the engine to accelerate to the highest speed.

Note

A Hydrovac system, as in any power brake system, is designed to reduce the pedal effort when stopping the truck.

Wheel Cylflder

Upp«Re Spring

Brake Shoe

pper Return pring

Ill

�

Guide Spring

Brake Shoe

Cross-Strut

Backing Plate

uide Spring

Lower Return Spring

Drum and Shoe Brake used on most current Clark Lift Trucks

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Adaptor

Caliper 0-Ring

DlskUnlng

Piston Piston Lining Diak

Rivet

Disc Brake Assembly used on the H200 series Transmission

Wet-disc Brake Assembly used on the HR600 series Tranmission Brake System page 8

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