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CHAPTER 32 DISC BRAKE SYSTEM

FUNDAMENTALS OF

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Automotive Technology Š SA 20 M 12 PL Jo E ne C s H & AP B TE art R let O tL N ea LY r n

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Principles and Practice

Meets 2012 NATEF Automobile Accreditation Standards


Get in gear in

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Change is in the air. As you know, the new National Automotive Technicians Education Foundation (NATEF) Automobile Accreditation Model was approved by the NATEF Trustees and National Institute of Automotive Service Excellence (ASE) Board of Directors. The 2012 NATEF Automobile Accreditation Model and the accompanying 2012 NATEF Automobile Accreditation Task Lists focus on the future of the automotive industry: more preventative maintenance and fewer repairs.

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Dear Educator,

The 2012 NATEF Automobile Accreditation Model is intended to promote clarification of responsibilities by introducing three levels of training: Maintenance & Light Repair (MLR), Auto Service Technology (AST), and Master Auto Service Technology (MAST). By grouping Task Lists by level, the goal is to promote consistency of training across programs and to promote learning through active experience as opposed to learning through passive listening. In addition, the three distinct levels provided by the 2012 NATEF Automobile Accreditation Model provide students with a set list of marketable skills. CDX is using the 2012 NATEF Automobile Accreditation Model and 2012 NATEF Automobile Accreditation Task Lists to develop a complete teaching and learning system: Fundamentals of Automotive Technology: Principles and Practice. Students and instructors will have the tools to build a solid, knowledgeable foundation with world-class automotive content. Cutting-edge digital and online resources expand upon and reinforce this foundation, creating skilled technicians.

Let us help you redefine your automotive courses.


with CDX! The Fundamentals of Automotive Technology: Principles and Practice teaching and learning system will include: n Printed textbook – Fundamentals of Automotive Technology

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will be the first training program that completely and concisely covers the entire 2012 NATEF Automobile Accreditation Task Lists. Presented in an approachable writing style, this highlydeveloped manual will feature an unparalleled level of casebased learning tools, including detailed step-by-step pictorial skill drills.

n eBook/eWorkbook – With the content of Fundamentals of

Automotive Technology at your students’ fingertips, students will be able to take notes, test their knowledge of automotive systems, watch animations and videos, and perfect their understanding of key psychomotor skills. The interactive eWorkbook will hone students’ critical thinking skills and analyze their comprehension of critical content.

n Web Tools – Additional interactive and mobile educational

resources such as a complete audio book in mp3 format, chapter pretests, interactive skill drills, and skill evaluation sheets will be available.

n Learning Management System – With this powerful online

tool, instructors will be able to manage assignments, enjoy automatic grading, and facilitate discussions.

n Test Prep – This dynamic tool will help prepare students for

ASE Certification Tests by providing practice examinations and simulated certification examinations using ASE-style questions and detailed rationales.

n Interactive Course Content – Online modules that cover

the entire scope of the 2012 NATEF Automobile Accreditation Task Lists will be available. The modules will provide anytime, anywhere access for students in a safe and self-paced training environment that will allow students to learn at their own convenience and pace.

n Personalized Adaptive Learning (PAL) – The shift to

competency-based education is driving the need for more sophisticated digital tools. PAL will help educators determine competency.

Contact your CDX Account Manager or visit www.cdxauto.com to get started.


What steps are CDX the 2012 NATEF Automobile

Just remember that the brake lights will stay on if  Fundamentals of Automotive Technology will offer instructors you don’t pull the brake light fuse. (Step 3) and students comprehensive coverage of every NATEF Task in an 5 Remove the brake line or hose from the caliper. Be    engaging and accessible format. careful not to lose the two brake hose copper (or 

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and damage to the caliper housing, and determine any 

aluminum) sealing rings, if equipped. (Step 4)   6 Push the caliper pistons back into their bores     slightly. Use of a small pry bar or C-clamp will   usually force the piston back just far enough so  that the caliper can be removed from the pads  and rotor once the caliper is loose from its mount.  (Step 5)   7 Remove the caliper assembly from its mountings,    willfollowing the service manual procedure. Be careful  this help me in the shop?” Through concrete examples in to avoid dislodging brake dust, which may contain  each chapter, Fundamentals of Automotive Technology gives asbestos. (Step 6)   students a genuine context for the application of the knowledge 8 Inspect the caliper for leaks or damage, including    presented in the chapter. This approach makes it clear how all of the piston dust boot.   this new information will be used in the 7)        shop. 9 Determine any necessary actions. (Step  

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For the last several years, CDX Automotive has been SKILLproducing SKILL DrILL 32-1  :  necessary actions, follow the steps in   Research the procedure for removing the caliper  1 that allow student-directed learning and innovative materials  

hybrid courses. Now we are taking these tools to the next level and adding a printed resource for students. With Fundamentals of  removed, you might want to use a brake pedal  Automotive Technology: Principles and Practice, CDX will offer a holding tool to  slightly apply the brakes and block  complete and learning system. off the  cteaching ompensating ports in the master cylinder. 

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vi BrakeS We have gathered22 a teamsection of outstanding educators from across the country to help create a complete teaching and learning system of the rotors on the vehicle, removal of the rotors for  using CDX’s Know-See-Do-Prove model. In addition to developing replacement, or machining of the rotors off the vehicle.  a gold standard student resource, we are building a wide range of Further, it allows for a thorough inspection of the caliper,  teaching and learning tools that will enable instructors to achieve pads, and rotor to determine the cause of a brake congreater individualcern. To remove the caliper assembly, inspect for leaks  creativity in course design.

in the appropriate service information. Follow  this procedure. The following steps are general  in  nature and should not be substituted for the   manufacturer’s  specifi c  procedure.   2 If the caliper is likely to be reinstalled on the     vehicle or rebuilt and reinstalled, it is good  practice  to loosen the bleeder screws slightly and then   retighten them. Doing so ensures that they are  A Relaxed, Readable Textbook – When writing automotive not seized in place and that they will be able to be  textbooks, authors often forget who their audience really is.  loosened later when bleeding the system. Failure to  Fundamentals of Automotive Technology will create a learning do this now could waste a lot of time later trying to  repair a bleeder screw when it breaks off.   (Step 1)    environment in which students are comfortable with the material If the caliper is being rebuilt or a new caliper will  3 presented. That comfort level translates into better understanding       be installed, it is good practice to fl ush the old  and retention, and ultimately leads to better pass rates. This brake  fl uid from the system at this time, so that old  textbook talks to yourbrake fl students, not at them.  uid will not have to be bled through the  new or newly rebuilt caliper. Also, leave the masClear Application of to Real-World Situations – ter  Material cylinder reservoir level low so that pushing the  istons into their bores will not overfl Students who want tocaliper   enter pthe automotive field are hands-on. ow  the  rinformation eservoir.  (Stepis2)   important to learn. “How They need to know why draining  4 To minimize the amount of brake fl uid         out of the brake lines or hoses when they are 

Students Will Enjoy

SKILL DRILL

  

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appropriate service information. Loosen the bleeder screws slightly and then retighten them.

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technology is constantly TECHNICIAN TIP changing. The content of Fundamentals of Automotive Technology reflects the guidance and Some technicians pinch off the fl exible brake hoses recommendations of an extremely experienced, geographically with vice grip pliers. This should be avoided because it diverse group of authors. crimps the hose, potentially damaging it internally and/ or externally.

Removing and Inspecting Calipers

32-1

Research the procedure for

  removing the caliper in the

Current, State-of-the-Art Content – Automotive

  

2

If the caliper is being rebuilt or

  a new caliper will be installed, it is good practice to flush the old brake fluid from the system at this time.

  

3

Use a brake pedal holding tool to

  slightly apply the brakes and block off the compensating ports in the master cylinder to avoid excess fluid leakage.

Let us help you redefine your automotive courses.

27/06/12 5:24 PM


taking to implement Accreditation Task Lists? Instructors Will Enjoy

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decades of experience in both automotive technology and in the education of future automotive technicians. This textbook is clearly written by one of us, for all of us.

Constant Reinforcement of Concepts – Instructors are concerned about the 2012 NATEF Automobile Accreditation Task List and its impact on their classrooms. Fundamentals of Automotive Technology eases any transition to the new 2012 NATEF Automobile Accreditation Task Lists.

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A Textbook That Reflects the Expertise of its Author Team – The authors are seasoned automotive instructors with

Clear Application of Material to Real-World Situations – Instructors will find countless opportunities

to place their students “in the shop” with case studies, video products that show automotive technicians in action, and critical thinking examination tools. Opportunities to apply knowledge ultimately make students better-equipped automotive technicians. And isn’t that our goal: to teach students how to be great automotive technicians?

Fundamentals is the cornerstone of a complete teaching and learning system consisting of ample resources for both student and faculty. With online resources, students and faculty are able to take practice tests, work on module assignments, and use TestPrep to ensure competency. Instructors will enjoy the updated presentations, test banks, and learning management system. This system provides an outstanding platform for a dynamic learning environment for all students.

Contact your CDX Account Manager or visit www.cdxauto.com to get started.


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NATEF Tasks Brakes

General Brake Systems

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CHAPTER 32

Describe procedure for performing road test to check brake system operation, including an anti-lock brake system (ABS).

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Hydraulic System n

Diagnose poor stopping, pulling or dragging concerns caused by malfunctions in the hydraulic system; determine necessary action.

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Disc Brakes

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Diagnose poor stopping, noise, vibration, pulling, grabbing, dragging or pulsation concerns; determine necessary action.

20

Remove and clean caliper assembly; inspect for leaks and damage/wear to caliper housing; determine necessary action.

20–23

Clean and inspect caliper mounting and slides/pins for proper operation, wear, and damage; determine necessary action.

23–24

Check brake pad wear indicator; determine necessary action.

23–25

Remove, inspect and replace pads and retaining hardware; determine necessary action.

25

Lubricate and reinstall caliper, pads, and related hardware; seat pads and inspect for leaks.

26–28

Retract and readjust caliper piston on an integrated parking brake system.

28–29

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Clean and inspect rotor, measure rotor thickness, thickness variation, and lateral runout; determine necessary action.

30–32

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Remove and reinstall rotor.

32–34

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NATEF Tasks, continued

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Disc Brake System Refinish rotor on vehicle; measure final rotor thickness and compare with specifications.

34–36

Refinish rotor off vehicle; measure final rotor thickness and compare with specifications.

35–38

The applicable Inspect and replace drive axle 2012 wheelAutomobile studs. (NATEF, Drive Axles)

39–41

Accreditation Task List along with the chapter’s Knowledge n Install wheel and torque lug nuts. (NATEF, Drum Brakes) and Skill Objectives are listed at n Describe importance of operating vehicle to burnish/break-in replacement the beginning of each chapter brake pads according tocorresponding manufacturer’s levels recommendations. with the and page references.

Knowledge Objectives

After reading this chapter, you will be able to: 1. Describe the components of the disc brake system. (pp 6–8) 2. Describe how the components of the disc brake system work together during braking operations. (pp 6–7) 3. Describe the advantages and disadvantages of the disc brake system. (pp 7–8) 4. Describe the purpose of disc brake calipers. (pp 8–11) 5. Describe the components of disc brake calipers. (pp 9–11) 6. Describe the purpose of disc brake pads. (pp 11–15) 7. Describe the principle of the coefficient of friction and how it affects brake lining materials. (pp 12–15) 8. Describe the components that are employed to prevent noise in disc brakes. (pp 14–15) 9. Describe the types of wear indicators for disc brakes. (pp 15–16) 10. Describe the purpose of disc brake rotors. (pp 16–17) 11. Describe the types of disc brake rotors. (p 17) 12. Describe how the parking brake system operates in a disc brake system. (pp 18–19) 13. Describe the types of parking brakes in a disc brake system. (pp 18–19) 14. Describe the process of diagnosing issues with a disc brake system. (pp 19–43)

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SECTION VI BRAKES

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After reading this chapter, you will be able to: 1. Remove and inspect the caliper. (pp 20–23) 2. Inspect caliper mountings, slides, and pins. (pp 23–24) 3. Inspect brake pads and wear indicators. (pp 23–25) 4. Check the brake pads. (p 25) 5. Disassemble the caliper. (pp 25–26) 6. Reassemble the caliper. (pp 26–28) 7. Retract and readjust the piston on an integrated parking brake. (pp 28–29) 8. Inspect and measure the disc brake rotor. (pp 30–32) 9. Remove and reinstall the disc brake rotor. (pp 32–34) 10. Refinish the disc brake rotor while it is on the vehicle. (pp 34–36) 11. Refinish the disc brake rotor while it is off the vehicle. (pp 35–38) 12. Inspect and replace wheel studs. (pp 39–41) 13. Install a wheel, torque lug nuts, and make final checks and adjustments. (pp 39–43)

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Skills Objectives

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chapter 32 Disc Brake System

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introduction Strong– No Deflection Heavy Pressure

Moderate Pressure

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Not as Strong– Deflection

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  isc (also spelled disk) brakes are so named because  D they create braking power by forcing fl at friction pads  against the sides of a rotating disc. This disc is also called  a disc brake rotor, or rotor. The vehicle wheels are bolted  to the disc  FIGURE 32-1  . The applied force is created in  the  caliper, which straddles the pads and rotor. Higher  applied forces can be used in disc brakes than in drum  brakes, because the design of the rotor is stronger than  the design of the drum  FIGURE 32-2  . Since heat is generated on the outside surfaces of the rotor, it can be easily  transferred to the atmosphere. Disc brakes are effective at 

FIGURE 32-2 32-2 Disc versus drum brakes.

creating substantial braking power using a fairly simple  design that is relatively easy for technicians to service  and  repair.    

TECHNICIAN TIP

FIGURE 32-1 32-1 Disc brake operation.

he purpose of the disc brake system is to provide an T effective means to slow the vehicle under a variety of conditions in an acceptable distance and manner. The better a braking system can do this, the more likely the vehicle will avoid an accident.

You are the Automotive Technician

a customer comes into the service department. She has been experiencing a pulsating brake pedal and high pitched sqealing during braking on her 2009 Town and Country minivan, which has 41,000 miles on the odometer. after reviewing the vehicle’s service history on your computer, you notice the vehicle has never had any brake service. You advise the customer that you will need to complete a more thorough inspection to determine what is causing the issues. after completing a visual inspection of the brakes, and measurement of the rotor’s thickness and parallelism, you see that the front brake linings have worn down to the wear indicators and the rotors are warped beyond specifi cations. You inform the customer of your fi ndings and recommend that the vehicle needs new front brake pads installed, and the rotors refi nished. You also recommend that the brake fl uid be fl ushed, since the fl uid is beyond the end of its two-year life. 1. What conditions can cause a rotor to become warped? 2. What conditions would require replacement of the rotors rather than just refi nishing them? 3. What are the relatively common maximum specifi cations for rotor runout and thickness variation? Case Studies capture students’ attention and offer an authentic context for students to apply their knowledge.


section vi BrakeS

Purpose and Overview   isc brakes operate on the same principle as all  friction  D brakes. They generate stopping power by applying   friction materials to moving surfaces, thus transforming  the  vehicle’s kinetic energy into heat energy. This is accomplished by disc brake calipers using hydraulic pressure  from the master cylinder to create a mechanical clamping  action, forcing the brake pads onto the surface of the rotor,  creating friction. As the vehicle’s kinetic  energy is transformed into heat energy, the vehicle’s speed  decreases.   

to provide a clamping force on a rotor that is attached to  the wheel hub. This clamping action is designed to stop  the rotation of the rotor and the wheel.    The rotors are free to rotate with the wheels due to  wheel bearings and the hubs that contain them. The  hub can be part of the brake rotor or a separate assembly that the rotor slips over and is bolted to by the lug 

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Disc Brake system

Key Terms are easily identified and   odern passenger vehicles are almost always equipped  M defined with the text. A list of Key with disc brakes on at least the front two wheels, and  Terms concludes each chapter, many manufacturers are using them on all four wheels.  and a comprehensive glossary The primary components of the disc brakes are:  appears at the end n R    otor   of the textbook. n C    aliper   n B    rake  pads   FIGURE 32-3         The  rotors  are the main rotating part of this brake    are the main rotating part of this brake  system. They are durable and resist being damaged by  the high temperatures that occur during braking. In highperformance vehicles, the rotors are made from composite  FIGURE 32-3 32-3 The disc brake system. materials, ceramics, or carbon fi ber; otherwise, they are  usually made of cast iron.   The  caliper  straddles the rotor and houses the disc  brake pads and an activating piston(s). The calipers  use hydraulic pressure from the master cylinder to  apply the brake pads. They are usually bolted to the  steering knuckle or, in the case of a nonsteering axle, to  a suspension component. Calipers need to be inspected  at the same time as the brake pads.  T   he  disc brake pads  are located inside the caliper or  caliper mounting bracket. The pads clamp onto the rotor  to slow or stop the vehicle. The disc brake pad consists  of a friction material bonded or riveted to a steel backing  plate. With this design, the pads will wear out over time  and need to be replaced periodically.  Master cylinder

Disc Brake Operation

  isc brakes can be used on all four wheels of a vehicle,  D or a combination of brake types can be used, with disc  brakes on the front wheels and drum brakes on the rear.  When the brake pedal is depressed, a  pushrod   transfers  the force through a  brake booster  to a hydraulic master  cylinder. The master cylinder converts the pedal force  into hydraulic pressure, which is then transmitted via  brake lines and hoses to one or more pistons at each brake  caliper   FIGURE 32-4  . The pistons operate on friction pads 

Pedal

Secondary Primary piston piston

FIGURE 32-4 32-4 The master cylinder converts the pedal force into hydraulic pressure, which is then transmitted via brake lines and hoses to one or more pistons at each brake caliper.


chapter 32 Disc Brake System

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keeping the wheels on the ground, especially on uneven  road  surfaces.     isc brake pads require much higher application  D pressures to operate than drum brake shoes because  they are not self-energizing. This additional clamping   pressure is created by increasing the diameter of the caliper  pistons. Unfortunately, this means the brake pedal  travel is lengthened to move the additional fl uid being  displaced by the larger caliper pistons. Building in more  pushrod travel would require more room under the dash.  Manufacturers have overcome this problem by equipping  most disc brake systems with a power booster. Because  of the high forces needed to apply a disc brake, using it  as a parking brake is more challenging. Some manufacturers have chosen to design more complicated calipers,  while others have built an auxiliary drum brake assembly  into the center of the rear disc brake rotors to provide  for  parking brake operation. This is referred to as a top  hat  design.  

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nuts    FIGURE 32-5  . On rear-wheel drive vehicles, the rotor  is mounted onto the driving axle or hub and may be held  in place by the wheel. On front-wheel drive vehicles, it can  be mounted on the front hub and wheel bearing assembly.    The brake caliper assembly is normally bolted to  the vehicle axle housing or suspension  FIGURE 32-6  .  In  most cases, the brake is positioned as close as  possible  to the wheel, but there are exceptions. Some high-  performance cars with  independent rear suspension (IRS)  use  inboard disc brakes on the rear wheels. The  calipers are mounted on or next to the differential, which  is directly mounted to the vehicle body. Manufacturers  claim  improved vehicle handling for this design because  it reduces the vehicle’s unsprung weight by taking the  differential assembly and brakes from the suspension and  mounting them to the body. Because the wheels and  axles  are now lighter, the vehicle’s springs can do a better job of 

7

Advantages and Disadvantages

FIGURE 32-5 32-5 The hub and hubless rotors.  

FIGURE 32-6 32-6 Caliper mounting methods.  

  isc brakes have a number of advantages over drum  D brakes. They also have some disadvantages. In most  cases, the advantages outweigh the disadvantages. One  of the biggest advantages is that disc brakes can generate  and transfer greater amounts of heat to the atmosphere;  because most of the friction area of a rotor is exposed  to air, cooling is far more rapid than for a drum brake.  This faster cooling makes them better suited for highperformance driving or heavy-duty vehicles and reduces  the likelihood of brake fade.  A   lso, because of their shape, rotors tend to scrape  off water more effectively. After being driven through  water, disc brakes operate at peak performance almost  immediately. Further, due to their design, disc brakes  are self-adjusting and do not need periodic maintenance  or rely on a self-adjusting mechanism that is prone to  sticking (see the Disc Brake Calipers section). Lastly, in  most cases, disc brakes are also easier to service than  drum brakes.  W   hile disc brakes have a number of benefi ts over  drum brakes, there are some disadvantages. Probably  the most apparent disadvantage is that disc brakes  are much more prone to noise. Their design tends  to create squeals and squeaks, which can be very  annoying. Many a  technician has spent time servicing  perfectly functional disc brakes due to excessive noise  complaints. Another issue is that the rotors warp easier  than in drum brake systems. Since the brake pads are  pressing on each side of the rotor, thickness variations  of as small as 0.0003" (0.0076 mm) can cause brake 


section vi BrakeS

TECHNICIAN TIP

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hile there may appear to be more disadvantages W to disc brakes versus drum brakes, the advantages are generally considered much more critical than the disadvantages. Thus, disc brakes are preferred over drum brakes in most applications.

  ydraulic pressure forces the pistons on both sides of  h the caliper inward, causing the brake pads to come in  contact with the rotor   FIGURE 32-9  . Once the  pad-to-rotor  c  learance is taken up, the hydraulic pressure rises equally  on each side of the caliper, applying both brake pads  equally.     The sliding or fl oating caliper has brake pads located  on each side of the rotor, but all of the pistons are only  on one side, usually the inside of the rotor. Thus, the    ydraulic force is generated on one side of the rotor, but  h the unique design applies equal braking force to both  sides of the rotor. This distribution of force is possible   because the caliper is mounted on pins, or slides, that  allow it to move (fl oat or slide) from side to side as necessary. This movement allows pistons on one side of the  rotor to generate force on both sides of the rotor at the  same time. 

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pedal pulsations, requiring resurfacing or replacement.  The last disadvantage is that since disc brakes are not  self-energizing, they need higher clamping forces, which  requires a power booster. This also makes it harder to  use them as effective  parking brakes.    

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Disc Brake calipers

I  n most applications, the disc brake caliper assembly is  bolted to the vehicle axle housing, or  steering knuckle ,  and clamps the brake pads onto the rotors to slow the   vehicle. There are two main types of calipers:  fixed calipers  and  sliding or floating calipers       FIGURE 32-7  .  Sliding or fl oating calipers are the most common type  used in passenger vehicles because they are easier to  build and are more compact. All calipers are fi tted with  a  bleeder screw  on the top of the piston bore to allow for  the removal of air within the disc brake system as well as  to help in performing routine brake fl uid changes.    F ixed calipers are rigidly bolted in place and   cannot move or slide. This makes their application of   braking forces more precise than fl oating calipers. They  c  ommonly have one to four pistons on each side of  the  rotor  FIGURE 32-8  . When the brakes are applied, 

FIGURE 32-7 32-7 Fixed and sliding/floating calipers.  

FIGURE 32-8 32-8 Fixed calipers with multiple pistons.  

FIGURE 32-9 32-9 Fixed caliper being applied.  


chapter 32 Disc Brake System

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I  n disc brake calipers, the piston is sealed by a stationary  square section sealing ring, also called a  square cut O-ring       FIGURE 32-11  . This O-ring has a square  crosssection and is fi tted in a machined groove in the caliper.  The O-ring is compressed between the piston and 

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caliper housing, creating a positive seal to keep the  high-pressure brake fluid from leaking out. It also  prevents air from  being drawn into the system when a  low-pressure  situation is created in the hydraulic system  when the brake pedal is released quickly.     hen the brakes are applied, the piston moves  W  outward, slightly deforming the O-ring seal   FIGURE 32-12  .  When the brakes are released, the elasticity or fl exibility  of the seal causes it to return to its original shape. This  action of the sealing ring retracts the piston to provide a  small running clearance between the rotor and pads. As  the brake pads wear, the piston needs to move outward  a bit farther than the sealing ring can stretch or fl ex.  The sealing ring is designed to allow the piston to slide  through it in this situation, taking up the extra clearance  and making the disc brakes self-adjusting.   

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  hen the brakes are applied, hydraulic pressure  W f  orces the piston toward the rotor. This takes up any clearance between the brake pad and rotor and starts to push  the pad into the rotor. Since the caliper is free to move  on the pins or slides, it gets pushed away from the rotor,  pulling the outer brake pad into contact with the outside  of the rotor. Once all clearance is taken up on the outer  brake pad, the clamping force will  increase equally on  both brake pads, applying the brakes  FIGURE 32-10  .  

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Text that prepares students for the shop.

TECHNICIAN TIP

S ince the force generated by the O-ring to retract the piston is fairly small, any corrosion or buildup on the piston or bore will cause the piston to stick and not retract. This holds the brakes in the applied position, causing brake drag, overheated brakes, and poor fuel economy. Technicians can identify this situation by using an infrared temperature gun to measure the temperature of each brake rotor after test-driving the vehicle. The temperatures should be approximately the same on each side. If they are not, suspect a stuck or binding caliper.

FIGURE 32-10 32-10 Sliding/floating caliper application.  

A

B

O-ring groove in caliper

FIGURE 32-11 32-11 A. Square cut O-ring and O-ring cut to show square section. B. Square cut O-ring groove in caliper.  


section vi BrakeS

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B

FIGURE 32-12 32-12 A. Square cut O-ring during brake application. B. Square cut O-ring during brake release.  

Highly descriptive and detailed illustrations enable the student to free of pitting or rust; therefore, steel pistons are chrome  visualize automotive systems and plated. This gives the surface a hard, wear-resistant, and  mechanical concepts.

Seal travel Low drag caliper

Seal travel Standard caliper

corrosion-resistant fi nish. Chrome can still rust, but it  is much more corrosion resistant than steel. Another  way manufacturers have dealt with the corrosion issue  is by making pistons out of a  phenolic resin . Pool balls  also are made from phenolic resin, which is very dense  when it hardens and does not corrode or rust, making  for a good sealing surface in brake systems. Although  the phenolic pistons themselves do not corrode, the cast  iron bore of the caliper does corrode and rust and can  therefore cause a phenolic piston to seize in the bore  FIGURE 32-14  .  

FIGURE 32-13 32-13 Low-drag caliper.  

 Some calipers, sometimes called  low-drag calipers ,  are designed to maintain a larger brake pad-to-rotor clearance by retracting the pistons a little bit farther. This  is accomplished by modifying the sealing groove in the  caliper so the outside of the groove is slightly angled   toward the rotor  FIGURE 32-13  . This position allows the  seal to fl ex a bit farther upon brake application and then  retract the piston a greater distance. These systems use a  “quick take-up” or “fast fi ll” master cylinder to maintain  adequate brake pedal reserve height.   T   he primary sealing surface is the outside diameter  of the piston. It is critical that this surface be smooth and 

FIGURE 32-14 32-14 Corroded caliper piston bore.  


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FIGURE 32-16 32-16 Floating caliper guide pins.  

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 Phenolic pistons transfer heat slower than steel    istons   FIGURE 32-15  , which is a good thing because they  p transfer less heat from the brake pad to the brake fl uid.  This helps prevent boiling of the brake fl uid in the caliper  under heavy brake usage. Calipers with phenolic pistons  are therefore less susceptible to brake failure from boiling  brake  fl uid.    There is also a dust boot that seals the surfaces of  the piston and caliper bore from outside dirt and moisture. This seal connects to both the piston and the caliper  and must be expandable to allow the piston to move outward as the brake pads wear. It also must be free from cuts  and holes; otherwise the piston and bore could corrode and  cause the piston to bind in the bore, causing brake drag.  

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chapter 32 Disc Brake System

Caliper Lubrication

  loating calipers are mounted in place by  guide pins F and  bushings       FIGURE 32-16  . The pins allow the  caliper  to move in and out as the brakes are operated and as the  brake pads wear. Since the calipers move on the pins,  the bushings must be lubricated with high-temperature,  w   aterproof disc brake caliper grease when they are   serviced. This will help prevent them from binding or  sticking. Inspecting, cleaning, and lubricating the pins  and pin bores, including any bushings and dust boots,  are important steps in disc brake repair.    Sliding calipers have matching machined surfaces  on the caliper and caliper mount that allow the caliper  to slide in the mount  FIGURE 32-17  . The sliding mount  holds the caliper in position and prevents it from  rotating  when the brakes are applied. The machined mounts allow  the caliper to move side to side as necessary to operate the  brakes or adjust for brake pad wear. The surfaces must be 

FIGURE 32-17 32-17 Sliding caliper.  

cleaned and lubricated with the same  high-temperature,  waterproof grease as the fl oating calipers when the  calipers  are serviced. Sliding calipers are held in place by a spring  steel clip or shim that is bolted to the caliper mount.    

Disc Brake Pads and Friction Materials

A

B

FIGURE 32-15 32-15 A. Phenolic piston (slow heat transfer) B. Steel piston (fast heat transfer)

  isc brake pads consist of friction material bonded  D or  r iveted onto a steel  b acking plate       FIGURE 32-18  .  Bonded linings  are more common on light-duty  vehicles  since they are less expensive to build and the bonding agent  can fail under the very high temperatures of heavy-duty  use.  Riveted linings  are used on heavier-duty or highperformance vehicles. Metal rivets provide a  mechanical  connection to hold the lining to the backing plate that  is less susceptible to failure under high temperatures.  Since the rivets actually pinch some of the lining between  the rivet head and the backing plate, the linings must  be changed sooner than bonded linings. Otherwise, the 


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FIGURE 32-19 32-19 Brake pad locating lugs.  

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FIGURE 32-18 32-18 Bonded and riveted brake pads.  

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rivet heads would contact the rotor and wear a groove  in the face of the rotor. The backing plate has  lugs   that  correctly position the pad in the caliper assembly and  help the backing plate maintain the proper position to the  rotor  FIGURE 32-19  . Disc brakes are usually designed so  that the thickness of the pads can be checked easily once  the wheel has been removed. Most disc brakes also are   designed to allow the pads to be replaced with a minimum  of  disassembly.     S ome pads have a groove cut into the friction   surface. This groove helps ventilate gases that build up  at the  surface of the friction material under heavy brake   application. It also can help modify the harmonic vibration quality of the friction material to reduce brake squeal.  On some pads, the depth of this groove is set so that as  the pad wears thinner, the remaining groove gets smaller;  when it can no longer be seen, the pad should be replaced.   The composition of the friction material affects brake  operation. Materials that provide good braking with low  pedal pressures tend to lose effi ciency when they get hot,  thus increasing the stopping distance. They also tend to  wear out quicker. Materials that maintain a stable friction coeffi cient over a wide temperature range generally  require higher pedal pressures to provide effi cient braking. They also tend to put added wear on the disc brake  rotor, reducing its useful life  FIGURE 32-20  .  

Brake Friction Materials   riction is the force that acts to prevent two surfaces in  F contact from sliding against each other. The amount of  friction between two surfaces is expressed as a ratio and  is called the coeffi cient of friction. When friction occurs,  the kinetic energy (motion) of the sliding surfaces is converted into thermal energy (heat). Some combinations of  materials, such as a hockey puck on ice, have a very low  coeffi cient of friction. There is very little friction between 

FIGURE 32-20 32-20 Brake rotor wear.  

them and therefore almost no sliding resistance. Rubber  tires against a dry hard road surface have a high coeffi cient of friction, which means they tend to grip and resist   sliding against each other.   Disc brake pads and drum brake linings are made  from materials that have a moderate coeffi cient of friction  TABLE 32-1  . They also must be able to absorb and  TABLE 32-1: Brake Lining Coeffi cient of Friction (Sliding) Materials Involved

Coefficient of Friction—Dry Sliding

rubber and concrete Steel and cast iron Copper and cast iron Brass and cast iron Leather and oak Brake lining (FF rating)

.6–.85 .23 .29 .3 .52 .35–.45


chapter 32 Disc Brake System

applied

Math

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Safety

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Don’t assume that a brake pad doesn’t contain asbestos; AM-17: Charts/Tables/Graphs: The technician can it is still found in some applications. interpret charts, tables, and graphs to determine the manufacturer’s specifications for a given system. algebra (9–12) Safety Tips reinforce safety and n   Ceramic materials—Ceramic fi ber materials and  C3: Draw reasonable conclusions about a situation being injury prevention concepts. modeled. possibly a small amount of copper     r epresentation  The choice of brake lining compound depends on the  a2: Select, apply, and translate among mathematical application. Lighter passenger vehicles generate less heat  representations to solve problems. in the brakes than heavy or high-performance vehicles.  T echnicians regularly apply math concepts to disc Living in a very hilly region of the country, or where there  brake diagnosis and repair. For example, a technician will measure the amount of rotor thickness variation is a lot of stop-and-go traffi c, will put added demands  and runout if there is a brake pedal pulsation problem. on the brake pads. The optimum brake composition for  Let’s say the technician performed these measurements any given vehicle or use is a combination of weighted  and came up with a thickness variation of 0.0025" qualities, including:  (0.064 mm) and a runout of 0.0015" (0.038 mm) on n S    topping  power   the left front rotor. Next the technician looks up the n H    eat  absorption  and  dispersion   manufacturer’s specifi cation chart and found that the maximum allowable thickness variation is 0.0005" n R    esistance  to  fade   (0.013 mm) and the maximum allowable runout is n R    ecovery  speed  from  fade   0.003" (0.076 mm) for the vehicle being worked on. n W    ear  rate   Using the information from the chart, the technician n P    erformance  when  wet   determines that the thickness variation is excessive n O    perating  noise   by 0.002" (0.051 mm) (0.0025" [0.064 mm] – 0.0005" n P    rice     [0.013 mm] = 0.002" [0.051 mm]) and the runout is Ok since it is under the maximum allowable specifi cation.  For instance, owners of small economy vehicles tend  But even so, since the thickness variation is out of to value a longer pad life and minimal operating noise  specifi cations, the rotor will need to be refi nished or rather than resistance to fade in extreme  conditions.  replaced to bring it back within specifi cation.

d   isperse large amounts of heat without their  braking   performance being adversely affected. As the heat in  brake pads and linings builds up, the coeffi cient of friction  capability of the material—and consequently its  stopping power—is reduced. This is called brake fade.  Minimizing or overcoming fade is a major factor in the  design of brakes and the development of brake friction  materials.     Brake friction materials were historically made from  asbestos compounds because of the excellent heat resistance of that material. Now that asbestos has been proven  to be toxic, it is generally banned and is not normally  used. Today, brakes are manufactured from a variety of  different materials, including:  n   Non-asbestos organic (NAO) materials—Organic  materials such as Kevlar and carbon   n   Low-metallic NAO materials—Small amounts of  copper or steel and NOA materials   n   Semimetallic materials—A higher quantity of  steel, copper, and/or brass  

  wners of high-performance cars, however, may  consider  O fade resistance and stopping power at high speeds more  important than noise levels or wear rate.   The Society of Automotive Engineers (SAE) has   a dopted letter codes to rate brake lining materials’  coeffi cient of friction. The rating is written on the  edge of the friction linings and is called the  edge code FIGURE 32-21  . The lower the letter, the less friction the  material has, and the harder the brake pedal must be   applied to achieve a given amount of stopping power.  These code letters represent the following coeffi cients  of friction: n C: ≤ 0.15 n D: 0.15–0.25 n E: 0.25–0.35 n F: 0.35–0.45 n G: 0.045–0.55 n H: > 0.55 n Z: Unclassifi ed  The lining is tested both cool and hot. The rating  is a two letter designation such as “FF.” The first letter is for the cool performance and the second letter is 


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FIGURE 32-21 32-21 Brake lining edge code.  

FIGURE 32-22 32-22 Brake pad shims and guides.  

for the hot performance. For example, FF has a cool   coeffi cient of  friction of 0.35–0.45 and the same coeffi cient of friction at the hot temperature. It also is very  possible that the hot and cold ratings differ from each  other. For example, if the rating is FE, the coeffi cient of  friction reduces as the temperature of the lining heats up.  Notice that the coeffi cient of friction range is quite wide  for each letter designation. Linings with the same letter  ratings may not have the same braking performance as  each other. This means that an EE-rated lining from one  manufacturer is likely to have different braking characteristics than an EE-rated lining from another manufacturer. Always use high-quality brake lining from reliable  companies to help avoid brake issues.    

Anti-Noise Measures

  isc brakes are more prone to annoying brake squealD ing than are drum brakes. Brake squealing is caused  by  vibrations set up between the brake pad and rotor.   Manufacturers have addressed this problem in a number  of ways:  1.  Using softer linings with a higher coeffi     cient of  friction, which are less prone to noise than harder  linings with a lower coeffi cient of friction   2.    Adding  brake pad shims and guides  to the  brake pads, which help cushion the brake pad  and absorb some of the vibration  FIGURE 32-22     3.  Using springs to tightly hold the pads in place to     minimize vibration  FIGURE 32-23     4.  Contouring and grooving the lining material in a     way that minimizes vibration  FIGURE 32-24    

FIGURE 32-23 32-23 Example of brake pad retainers.

FIGURE 32-24 32-24 Brake lining grooves and contouring.


chapter 32 Disc Brake System

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5.    Incorporating  bendable tangs  on the brake pad  backing plate that allow technicians to crimp the  tangs so they are more fi rmly mounted in the   caliper   FIGURE 32-25           

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S ome manufacturers claim that refi nishing their rotors removes enough material from the rotor that it can cause the brakes to squeal due to less mass, which changes the harmonic vibration qualities of the rotor. They recommend replacing the rotors any time the rotors are worn enough to need resurfacing.

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 Technicians also can apply noise-reducing   compounds to the brake pads. One is a type of hightemperature liquid rubber compound that is applied to  the back of the brake pad. When it cures, it stays  fl exible  and absorbs brake pad vibrations and helps reduce  brake noise. Another compound is a specially designed  liquid that is applied directly to the face of the lining  material. This compound helps to modify the lining’s  coeffi cient of friction slightly, making it less likely that  the lining will squeal. Make sure you apply the correct  compound to the correct side of the brake pad.    

applied

Science

AS-36: Sound: The technician can demonstrate an understanding of the role sound plays in identifying various problems in the vehicle. Sound is a series of waves that travel through a gas, liquid, or solid and can often be heard by the human ear. Sound waves are created by vibrating objects, such as a guitar string. Moving objects that are in sliding contact with each other are highly likely to create sound. One example of this is fi ngernails dragging on a chalkboard. The fi ngernails vibrate on the surface of the chalkboard and create sound waves that are then heard by the ear. T echnicians commonly use differences in sound to assist in diagnosing disc brake problems. For example, brake pads that are worn down to the metal backing plate make a deep grinding noise when the brakes are applied. Listening to hear which wheel or wheels the noise is coming from helps identify the source of the problem. In the same way, if the disc brakes are equipped with a scratcher style of brake warning system, the brakes will make a high-pitched screeching noise. Many times this noise will happen when the vehicle is being driven when the brakes are not applied. One way to help determine which side the noise is coming from is by driving the vehicle next to a concrete traffi c wall or building. If the noise is on that side, it will get much louder than when not near the wall.

FIGURE 32-25 32-25 Brake pad bendable tangs.

Wear indicators

S  ome manufacturers provide a means of notifying the  driver that the brake pad linings are worn to their minimum limit. This helps ensure that the brake linings do  not wear down to the point that they cannot properly  perform their job anymore. Excessively thin brake linings  tend to heat up quicker than thicker linings, which can  lead to premature brake fade. Not all manufacturers use a  brake lining wear indicator. In those cases, it is especially  Applied Math, Science, and important to inspect the brakes at regular intervals, usuCommunication boxes identify ally during tire rotations or oil changes.  critical academic concepts that the student must master.

Types These boxes show how to apply

abstract concepts directly to S  ome manufacturers use a mechanically operated wear  everyday activities in the shop. indicator to notify the driver that the brake pads are worn  to their minimum limit. This is achieved by a spring    mounted to the brake pad  FIGURE 32-26  .  steel  scratcher  mounted to the brake pad   Part of the scratcher extends below the brake pad  backing plate at the lining’s minimum wear thickness.  When the friction material wears down far enough, the  scratcher contacts the surface of the rotor and makes a  squealing noise similar to fi ngernails on a chalkboard. This  distinctive noise means the brakes need service right away.  When you replace the brake pads, make sure they come 

TECHNICIAN TIP I n many cases, the scratchers will start to make noise when the brakes are not applied and stop making noise when the brakes are applied, as applying the brakes tends to dampen the vibrations.


section vi BrakeS

made of reinforced carbon, carbon ceramic, or composite  ceramic substances to reduce weight and withstand much  higher temperatures.   Since the rotor surfaces are squeezed between two  brake pads, any unevenness of the rotor surfaces will  cause pulsation of the brakes as the thicker and thinner  portions pass between the brake pads. The rotor surfaces  must be parallel to each other to avoid this situation.   Rotors can fail in two ways: parallelism, which is also  called thickness variation, and lateral runout.   Parallelism is the most critical condition. If the rotor’s thickness  varies  by as little a 0.003" (0.076 mm), the rotor will tend to  push the brake pads outward at any high spots. This tends  to create more pressure on the brake pads and slows the  vehicle down faster at that point. It also pushes up on the  brake pedal as fl uid is being forced back to the master  cylinder. The result is a pulsation of the brake pedal and  a surging of the vehicle while braking, which is usually  more noticeable at lower braking speeds.  Lateral runout , also called warpage, is the side- toside movement of the rotor surfaces as the  rotor turns.  A warped rotor can be within specifi cations for parallelism but out of specifi cation for lateral  runout. Lateral  runout tends to move the caliper pistons in the same  direction as each other, so brake  fl uid is not pushed back  to the master cylinder.  However, the caliper tends to be  moved side to side. This  movement can cause the steering  wheel to shimmy as the warped rotor follows the brake  pads, if the  lateral runout is greater than about 0.003"  (0.076 mm). Also, runout causes the pads to rub on high spots of  the  rotor when the brakes are not being applied, causing   uneven wear and/or the depositing of pad material on  the rotor, which leads to thickness variation concerns.  

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FIGURE 32-26 32-26 The scratcher brake wear indicator.  

equipped with new scratchers set to the correct depth  so they can function the next time the pads wear down.     Some manufacturers use a warning lamp or warning  message on the dash to alert the driver that the lining is  worn to its minimum thickness. These systems have an  electrical contact installed on the brake pad at the point  of the lining’s minimum wear thickness. When the pad  wears to this minimum thickness, the contact touches  the rotor as the brakes are applied, prompting a warning  light or warning message that tells the driver the disc  brake pads are due for replacement. These contacts can  be manufactured into the pad or they can be clipped onto  the pad. The contacts are normally replaced when the  pads are replaced. Make sure that either the contacts come  with the new pads or order them along with the pads.   

Disc Brake Rotors

  he brake disc or rotor is the main rotating component  T of the disc brake unit. The wheel is bolted to the  rotor  and they rotate together, leading some manufacturers to  integrate the anti-lock brake system (ABS) tone wheel  Technician Tips provide realinto the rotor. Since friction between the rotor and brake  world advice from experienced pads generates great amounts of heat,   rotors must be able  automotive technicians. to withstand high temperatures. The pads are also forced  onto the surface of the rotor with potentially thousands  of pounds of force, so the rotor must be strong and have  a durable surface. The rotors are usually made of cast  iron. To reduce weight, some manufacturers use a twopart rotor with a cast iron disc and a stamped steel center  hat. This style of rotor is called a composite rotor. Some  heavy-duty and/or high-performance vehicles have rotors 

TECHNICIAN TIP

otors can be warped by improperly torquing the lug r nuts. always use a properly calibrated torque wrench (or the proper torque stick if the shop policy allows) to torque the lug nuts to the manufacturer’s specifi ed torque.

  or proper operation, rotors must maintain their  F shape and resist warpage under high heat and pressure conditions. Because of these requirements, they are   usually made of cast iron. On motorcycles, rotors are often  made of stainless steel for cosmetic reasons. Disc brakes  also are equipped with a dust shield to help  protect the  rotor. Dust shields help keep dust, water, and other road  debris away from the inside surface of the rotor. They also 


chapter 32 Disc Brake System

can help direct air fl ow to the rotor to assist with heat  transfer to the atmosphere. Dust shields are commonly  made of stamped sheet metal, but they also can be made  of plastic. Dust shields can become damaged during brake  repair so always inspect them for proper clearance before  installing  the  wheel  assembly.     B

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  otors can be solid or ventilated  FIGURE 32-27  .  Solid R rotors  are less expensive and usually found on smaller   vehicles.  Ventilated rotors  are used to improve heat  transfer to the atmosphere. These passageways are  designed  to use centrifugal force to cause air to fl ow through the  center of the rotor when it is rotating. Ventilated rotors are  used on heavier vehicles or high-performance vehicles.  Some ventilated rotors are directional, meaning they are  designed to force air through the rotor in one direction  only  FIGURE 32-28  . If the rotor is rotated in the wrong  direction, it will not pump air properly and will overheat  easier.   

in

Types of Rotors

FIGURE 32-27 32-27 A. Standard rotors. B. Ventilated rotors.

  isc brake rotors with holes or slots machined into  D their surface dissipate heat quicker  FIGURE 32-29  .  They  also help to remove water quickly from the surface of the  pad in wet driving conditions. Since the pads wipe across  the holes or slots, the surface of the pad is  prevented from  becoming hard and glassy smooth from the friction and  heat of use. However, this scraping action  reduces the  overall life of the brake pad, so these types of  rotors are  generally only used in high-performance or race  vehicles.    Most disc brake rotors are stamped with the manufacturer’s minimum thickness specifi cation   FIGURE 32-30  .  This minimum thickness ensures an adequate amount  of thermal mass for stopping power  FIGURE 32-31  .  When material is removed, there is not as much material  to absorb heat and the rotor heats up faster. The excess  heat can lead to brake fade sooner. Also, when the brake  pads wear, if the thickness of the rotor were below this  minimum, the piston could be pushed out beyond the  edge of the sealing ring, which would cause the brakes  to lose hydraulic pressure and fail. Make sure the rotors  are always above the manufacturer’s minimum thickness  before putting them back in service.     

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Direction of

I f you hear a loud scraping or grinding noise when you test-drive a vehicle after servicing the brakes, check to see if the dust shield is contacting one of the rotors. If so, it can make a lot of loud grinding noises. Since it is thin sheet metal, chances are good that it is bent. It can usually be bent back into shape easily.

rot ati o

TECHNICIAN TIP

FIGURE 32-28 32-28 Directional ventilated rotor.

FIGURE 32-29 32-29 Slotted and drilled rotor.  

17


18

section vi BrakeS

used on some vehicles. The electric motor can pull on a   conventional parking brake cable, or the electric motor  can be mounted on the caliper and directly drive the  caliper piston to apply force to the brake pads. 

Integrated Mechanical Parking Brake Calipers

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FIGURE 32-30 32-30 Rotor with minimum thickness stamped on it.  

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  he integrated parking brake mechanically forces the disc  T brake piston outward, forcing the brake pads to clamp  the rotor when the parking brake is applied   FIGURE 32-32  .  A lever on the back side of the caliper is pulled by the  parking brake cable. The lever converts that motion to  rotary motion on a shaft that enters the rear of the caliper  cylinder. The shaft uses a seal to prevent fl uid leakage from  the bore. The shaft has a coarse thread machined into it,  which threads into a nut assembly inside the caliper piston.  As the shaft is turned by the parking brake lever, the nut  causes the piston to be forced outward, applying the brakes.  Releasing the parking brake cable allows a spring to unwind  the shaft and release the  pressure on the brake pads.   

Top Hat Design Parking Brake

400° F

Rotor-Standard Thickness (At end of moderate hill)

500° F

Rotor-Below Minimum Thickness (At end of moderate hill)

FIGURE 32-31 32-31 Rotor thickness and heat capacity.

Parking Brakes

  arking brakes are designed to hold the vehicle  stationary  P when parked. Manufacturers are required to design the   vehicle so the parking brake will hold the vehicle for a  given  amount of time on a specifi ed grade in both  directions.  The parking brake must be separately  activated from the  service brakes, and the driver must be able to latch it into  the applied position. Parking brakes can be foot operated or hand operated. Since disc brakes  require higher  applied forces to  operate, they are a bit more  diffi cult  to use as parking brakes. However, manufacturers have  overcome this challenge in a couple of ways. 

  he top hat design gets it name from the shape of the  T  rotor. The rotor has a deeper offset than normal, giving the   appearance of a top hat. The offset portion allows room for  a drum surface within the center of the rotor. Drum brake  shoes are mechanically forced outward into contact with the  inside of the brake drum, which locks the wheel. Releasing  the parking brake allows the springs to retract the brake  shoes from contact with the drums.    

Electric Parking Brake

  he electric parking brake uses an electric motor to  T apply the disc brake assemblies. The cable style uses an  electric motor to pull standard parking brake cables,  which apply standard integrated mechanical parking  brake calipers. The electrically integrated caliper style 

Types of Parking Brakes   urrently most parking brakes are mechanically  applied  C by use of a cable and ratcheting lever assembly. Parking  brakes on disc brake units are primarily of two types: an  integrated parking brake caliper and the top hat drum  style. Alternatively, electric parking brakes are being 

FIGURE 32-32 32-32 Integrated parking brake operation.  


chapter 32 Disc Brake System

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is illuminated, the ABS system is deactivated, and you  should not try to activate ABS on a test drive. If the yellow ABS lamp is off, the ABS system should be active and  ready to activate. It is helpful when testing ABS to do so  on a surface with limited traction, such as wet pavement  or a dirt road. When you do apply the brakes fi rmly, ABS  activation can typically be felt as pulsations in the brake  pedal and possibly the steering wheel. The vehicle should  brake quickly while maintaining steering control. In some  cases, a “poor traction” lamp may illuminate, telling you  that the ABS system had to activate. This warning lamp  will usually turn off after several seconds. If the yellow  ABS warning lamp illumines, it typically means that the  vehicle’s PCM has observed a fault in the ABS system and  will need to be checked for DTCs.  Once the customer concern has been verifi ed, you will  hopefully have enough information to know how best to  proceed. This could be as simple as performing a  visual  i  nspection of the brake fl uid level and condition,  removing  the wheels to disassemble and inspect the brake units,  looking up technical service bulletins, or reviewing the  diagnostic troubleshooting chart for the particular sympCurrent state-of-the-art tom in the service information to determine the next step.  automotive technology content  Suspension and steering system faults can appear to  is presented in an engaging and be brake system faults. An example of this is a pulling  comprehensive writing style. condition while braking. If the strut rod bushings on the  Throughout the text, the student suspension are worn, then braking the vehicle will cause  is reminded how the knowledge the wheel to move rearward; at the same time, that will  will be applied in the shop. cause the steering angle to change, causing the wheel to  point in a direction other than straight down the road,  imitating a brake pull.   The braking system on a vehicle must be restored  to its proper operation. Diagnosis of any problem must  identify all issues that would prevent the brakes from  operating normally. Lawyers and technicians have been  known to say, “He who touched the brake system last,  owns it!” What this means is that if there is a problem in  the brake system and you inspected it or worked on it, you  are very likely liable for anything that went wrong with  it. Brake system failures are more likely to lead to vehicle  accidents than failures of most systems. Any  diagnosis and  subsequent repairs need to be thorough and complete.  

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uses an electric motor mounted on the caliper to directly  apply the brakes. Pushing a parking brake button on  the dash causes the motor to either tension the cable or  directly apply the parking brake. Electric parking brakes  also can be integrated with the controller area network  bus ( CAN-bus) system to provide additional features  beyond just holding the vehicle when it is parked. It  can be used to automatically hold the vehicle while it  is stopped on a hill to prevent it from rolling backward  or forward. It also can be automatically released by the  vehicle’s  e lectronic control module (ECM)   when  the throttle is applied for starting to move away from  the stop. It also may work with the vehicle’s proximity  detector when backing up. If the system detects the  vehicle getting too close to an object, the ECM can apply  the electric parking brake to stop the vehicle and prevent  it from striking the object.    

19

Diagnosis

  isc brake diagnosis usually starts with understanding  D the customer’s concern. Communicating directly with  the customer is the best way to do that, but the customer  is not always available. An experienced service advisor  will gather the required information, so you should read  the service advisor’s notes on the repair order carefully  or speak with him or her directly. Once you understand  the customer’s concern, a test-drive is usually needed  to verify the accuracy of the concern. This is a good   opportunity to test the brakes under a variety of conditions. Replicating the customer concern is important  in order to address the situation that the customer is  experiencing.   During the test-drive, fi nd a safe place to operate the  brakes at a variety of speeds with a variety of brake pedal  pressures, especially trying to mimic the conditions the  customer described. It is may be necessary to go on a test  drive with the customer driving, allowing him or her to  operate the vehicle in the way that makes the problem  evident and point out the particular situation he or she is  experiencing. Also, it is good to have the customer along  in case the problem does not occur, in which case he or  she won’t think you don’t believe them or are ignoring  the issue.  If there is a concern related to the anti-lock brake  system (ABS) that requires a test drive, extreme caution  is required so that an accident doesn’t happen. Since ABS  operates only during extreme braking or poor traction  conditions, you run the risk of being rear-ended by a  vehicle behind you or losing control of the vehicle if you  apply the brakes hard enough to activate the ABS. So  make sure the vehicle is being tested away from all other  traffi c. Remember that if the yellow ABS warning lamp 

TECHNICIAN TIP ne way to help identify if a problem is coming from O the front or rear brakes is to test-drive the vehicle in a safe place at a relatively low speed and lightly apply the parking brake. If the condition is still present, the problem is with the rear brakes, since the parking brakes are usually on the rear wheels. If the condition is not present, the problem is likely with the front brakes.


section vi BrakeS

Removing and Inspecting Calipers   emoving the caliper is necessary for replacing the brake  R pads on most vehicles. It also allows access for  machining 

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 The tools that are used to diagnose and repair brake   systems  include:  n Brake lining thickness gauges —Used  to  measure  the thickness of the brake lining   n Brake wash station —Used to clean drum and  disc brake dust   n C     aliper piston pliers —Used to grip caliper   pistons when removing them   n D     isc brake rotor micrometer —Used to measure  the thickness and parallelism of a rotor   n D     ial indicator —Used to measure the lateral   runout (side to side) of the rotor   n P     arking brake cable pliers —Used to install   parking  brake  cables   n C     aliper piston retracting tool —Used to retract  caliper pistons with integrated parking brakes   n C     -clamp —Used to push pistons back into the  caliper bore on non-integrated parking brakes   n O     ff-car brake lathe —Used to machine drums  and rotors that are off the vehicle   n O     n-car brake lathe —Used to machine rotors that  are on the vehicle   n C     aliper dust boot seal driver set —Consists  of  a driver and a variety of adapters used to install  various sizes of dust boot seals  FIGURE 32-33        

system and the  manufacturer’s diagnostic procedure for  the condition. Perform any diagnostic tests to identify the  cause of the condition. This could be a visual inspection  or any other prescribed test, such as a power booster test.  It could also involve a  detailed testing sequence, such as  testing the proportioning and metering valves. Once you  have identifi ed the cause of the fault, determine the action  that will rectify the fault. 

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TABLE 32-2: Common Brake Issues Concern

Fault

Poor stopping

• Power booster not operating properly • Internal master cylinder leak; air in the hydraulic system • Metering valve or proportioning valve blocking fl uid fl ow • Improperly adjusted drum brakes • Improper friction lining material • Contaminated linings

Noise

• • • •

Vibration

• Improper friction lining material • rotor surface fi nish not correct • Foreign object (mud, rocks, etc.) in the rotor • Warped rotor • aBS operating

Pulling

• • • • • •

Plugged or restricted brake hose Stuck caliper piston Seized caliper guide pins Contaminated lining Lining worn down to metal air in the hydraulic system

Grabbing

• • • •

Contaminated lining Stuck caliper piston Internal master cylinder leak Misadjusted drum brakes

Dragging

• Stuck caliper piston • Seized caliper guide pins • Misadjusted master cylinder pushrod length • Binding brake pedal • Plugged or restricted brake line or hose

Pulsation

• Warped rotors • rotor parallelism • aBS operation

Diagnosing Disc Brakes

  o diagnose poor stopping, noise, vibration, pulling,  T grabbing, dragging, or pulsation concerns and determine  any necessary actions, follow the steps outlined in the  Tables organize information so remainder of this chapter. While braking concerns are  students can quickly locate and generally easier to diagnose than most of the other sysretain critical information. tems on the vehicle, the large variety of conditions listed  makes it imperative that you have a good understanding  of disc brake and hydraulic theory. It also helps to use  all of your senses to assist you in identifying the location  of the fault. As a reminder,  TABLE 32-2    lists some of the  common faults to consider for each concern.    Verify the customer concern by operating the vehicle  if safe to do so. Depending on the concern, it may be as  simple as stepping on the brake pedal without moving  the vehicle and feeling the pedal sink to the fl oor, or  it could require a more detailed test-drive to observe  the fault the customer is describing. Regardless of the  condition, it is almost always good practice to research  any technical service bulletins (TSBs) for the particular  situation. If no related TSBs are found, research the  service information to familiarize yourself with the 

Friction lining material too hard Lining worn down to metal Worn caliper slides/guide pins Component-specifi c noises


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FIGURE 32-33 32-33 A. Brake lining thickness gauges. B. Brake wash station. C. Caliper piston pliers. D. Disc brake rotor micrometer. E. Dial indicator. F. Parking brake cable tool. G. Caliper piston retracting tool. H. Off-car brake lathe. I. On-car brake lathe. J. Caliper dust boot seal driver set.

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of the rotors on the vehicle, removal of the rotors for   removed, you might want to use a brake pedal  replacement, or machining of the rotors off the vehicle.  holding tool to  slightly apply the brakes and block  Further, it allows for a thorough inspection of the caliper,  off the  compensating ports in the master cylinder.  pads, and rotor to determine the cause of a brake conJust remember that the brake lights will stay on if  cern. To remove the caliper assembly, inspect for leaks  you don’t pull the brake light fuse. (Step 3) and damage to the caliper housing, and determine any  5 Remove the brake line or hose from the caliper. Be    necessary actions, follow the steps in  SKILL SKILL DrILL 32-1  :  careful not to lose the two brake hose copper (or  Research the procedure for removing the caliper  aluminum) sealing rings, if equipped. (Step 4)   1   in the appropriate service information. Follow  6 Push the caliper pistons back into their bores    this procedure. The following steps are general   slightly. Use of a small pry bar or C-clamp will  in  nature and should not be substituted for the   usually force the piston back just far enough so    anufacturer’s  specifi c  procedure.   m that the caliper can be removed from the pads  and rotor once the caliper is loose from its mount.  2 If the caliper is likely to be reinstalled on the     vehicle or rebuilt and reinstalled, it is good  practice  (Step 5)   to loosen the bleeder screws slightly and then  7 Remove the caliper assembly from its mountings,     retighten them. Doing so ensures that they are  following the service manual procedure. Be careful  not seized in place and that they will be able to be  to avoid dislodging brake dust, which may contain  l  oosened later when bleeding the system. Failure to  asbestos. (Step 6)   do this now could waste a lot of time later trying to  8 Inspect the caliper for leaks or damage, including    1)    repair a bleeder screw when it breaks off.  (Step 1) the piston dust boot.   If the caliper is being rebuilt or a new caliper will  Determine any necessary actions. (Step 7)        Determine any necessary actions.        “Know-See-Do-Prove” The icon is tied to CDX’s unique and   be installed, it is good practice to fl ush the old  proven instructional methodology. The color-coding within the brake  fl uid from the system at this time, so that old  icon is designed to act as a roadmap. Green represents Know brake fl uid will not have to be bled through the  and indicates where basic principles and concepts are presented. new or newly rebuilt caliper. Also, leave the masRed represents See and indicates where skills are presented. Blue ter  cylinder reservoir level low so that pushing the  represents Do, and indicates that practical skill-building exercises Some technicians pinch off the fl exible brake hoses caliper  pistons into their bores will not overfl ow  with vice grip pliers. This should be avoided because it and tasksheets are available for students in the associated tasksheet the  reservoir.  (Step 2)    crimps the hose, potentially damaging it internally and/ manual. Purple represents Prove, and indicates where To minimize the amount of brake fl   uid   d raining  or externally. students can assess what they have learned.       out of the brake lines or hoses when they are 

SKILL DRILL

  

1

Research the procedure for

  removing the caliper in the

Removing and Inspecting Calipers

32-1

appropriate service information. Loosen the bleeder screws slightly and then retighten them.

  

2

If the caliper is being rebuilt or

  a new caliper will be installed, it is good practice to flush the old brake fluid from the system at this time.

  

3

Use a brake pedal holding tool to

  slightly apply the brakes and block off the compensating ports in the master cylinder to avoid excess fluid leakage.


chapter 32 Disc Brake System

32-1 Removing and Inspecting Calipers, continued

  

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SKILL DRILL

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4

Remove the brake line or hose from the caliper. Be careful not to lose the sealing rings.

7

  damage, including the piston dust

5

Push the caliper pistons back into their bores slightly.

6

Remove the caliper assembly from its mountings.

Inspect the caliper for leaks or

boot. Determine any necessary actions.

Inspecting Caliper Mountings, Slides, and Pins

  he caliper mountings and slides/pins are placed under  T heavy loads and forces. They also operate in harsh  environments. It is common that they experience wear  over time. They can also corrode and bind up. Clean  caliper mountings and slides/pins thoroughly, and inspect  them closely.   To clean and inspect caliper mountings and slides/ pins for operation, wear, and damage and to determine  any necessary actions, follow the steps in  SKILL SKILL DrILL 32-2  :  Clean the caliper mountings and slides/pins using      1   equipment/procedures for dealing with asbestos/ hazardous dust. Once the dust is taken care of, you 

   

   

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3

may need to use a brake cleaning solvent to clean  the components further. (Step 1)   Inspect the caliper mountings and slides/pins for    signs of wear and damage. Also look for stripped  threads on the pins or caliper.   Determine any necessary actions. (Step 2)        

Inspecting Brake Pads and Wear Indicators   he wear indicator system could be a scratcher type or  T a sensor type. It is also very possible that the vehicle  does not incorporate any type of wear indicator system.  Checking this system usually consists of verifying that the  sensor or scratcher is not contacting or nearly contacting 


section vi BrakeS

24

the brake rotor. Some manufacturers require that the  s  ensor be grounded with a test lead and that the brake  pad warning lamp or warning message come on.    o check the operation of the brake pad wear  T indicator system and determine any necessary actions,  SKILL DrILL 32-3  :  follow the steps in  SKILL

1

2

Research the service information to determine    the type of wear indicator system utilized and the    rocedure to test it.   p Check that it is not contacting or nearly contact  ing the rotor. It is also good practice to measure  the brake pad lining thickness and compare it to 

32-2 Inspecting Caliper Mountings, Slides, and Pins

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SKILL DRILL

   

   

1

Clean the caliper mountings and slides/pins using equipment/ procedures for dealing with asbestos/hazardous dust.

SKILL DRILL

  

1

2

32-3

Determine the type of wear

  indicator system utilized. Check

that it is not contacting or nearly contacting the rotor.

Inspect the caliper mountings and slides/pins for wear and damage. Determine any necessary actions.

  

Inspecting Brake Pads and Wear Indicators

2

If the system is a sensor style,

  test the system to verify that the

system is operational. Determine any necessary actions.


chapter 32 Disc Brake System

Checking Brake Pads

Disassembling Calipers   alipers are disassembled and cleaned for a couple of  C reasons. The fi rst is to diagnose a brake system  concern  related to one or more calipers. For example, if the  vehicle  has a brake pull, it could be caused by a  sticking caliper  piston. Disassembling the caliper will allow you to verify  whether that is the case or not. They also need to be  disassembled and cleaned if they are going to be rebuilt.  Some shops rebuild the calipers themselves, but most  shops just replace them with rebuilt calipers if necessary.  Disc brake calipers are usually side specifi c, meaning they  are designed to be installed on a particular side of the  vehicle. Failure to install them on the correct side usually  results in the bleeder screws being on the bottom of the  caliper cylinder. This will prevent air from being bled  from the caliper and result in a very spongy brake pedal. 

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  emoving the brake pads is the most thorough way to  R inspect the brake pads. During a routine maintenance   inspection where there are no customer concerns  regarding  the brakes, a simple measurement of the lining thickness  is usually adequate. But if there are customer concerns  with the brakes, it may be necessary to remove the pads  for a more detailed inspection. This could show cracks  in the lining or other defects that wouldn’t be otherwise  seen from the outside. It also allows for a more thorough  inspection of the retaining hardware. Also pay attention  to the way the brake pads come off, as some pads have  slight differences (such as locating nipples) that make it  easy to install them incorrectly. To remove, inspect, and  replace pads and retaining hardware and to determine  any necessary actions, follow the steps in  SKILL SKILL DrILL 32-4  :  Remove the pads and retaining hardware. If      1   necessary, clean the parts with the appropriate  equipment or cleaner.    Inspect all pads, retaining hardware, and anti-noise      2   shims for wear or damage. Problems could include  cracked linings and worn or missing retaining  hardware or shims. (Step 1)  

4

Measure the remaining brake pad thickness and    compare to specifi cations. Inspect the pads to see  if they are wearing evenly. If not, it could indicate a  caliper or caliper mounting issue.   Determine any necessary actions. (Step 2)         

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the manufacturer’s minimum specifi cations. If the  brake pads are near the end of their useful life, it  would be good practice to inform the customer  and recommend replacement of the pads. (Step 1) If the system is a sensor style, test the system to    verify that the system is operational.   Determine any necessary actions. (Step 2)        

SKILL DRILL

  

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TECHNICIAN TIP

ecause you have the rotor exposed, skip ahead to B the sections on inspecting and servicing rotors, and complete the tasks listed there. This will save you time and effort. Pick up here once you are done with the rotor.

32-4 Checking Brake Pads

Remove the pads and retaining

  hardware. Inspect all pads,

retaining hardware, and anti-noise shims for wear or damage.

  

2

25

Measure the remaining brake pad

  thickness and compare to specifi-

cations. Determine any necessary action(s).


section vi BrakeS

SKILL DRILL

  

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pick tools, such as dental picks, and then wiping  out the groove with a rag. (Step 2)    Inspect each of the parts for damage, rust, and    wear. Also check the caliper pin bores or bushings  for wear or damage. (Step 3)   Measure the caliper bore-to-piston clearance with    a feeler gauge and compare to specifi cations, if  available.   Determine any necessary actions. (Step 4)         

  eassembling the caliper requires patience and attention  R to detail. Ensure that the sealing ring groove is spotless  and that the O-ring gets seated fully in the groove. Use 

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  o disassemble and clean the caliper assembly;  T  inspect parts for wear, rust, scoring, and damage; and  replace the seal, boot, and damaged or worn parts, follow  the steps in  SKILL SKILL DrILL 32-5  :  1 Disassemble the caliper, following the service manual    procedure. If this involves using compressed air to  remove the piston, be very careful, as the piston can  pop out with great force, enough to break fi nger bones  or pinch fi ngers off. Always use an approved cushion  between the caliper  piston and caliper housing. Keep  your fi ngers away from the area. (Step 1)   2 Clean all of the caliper parts according to the     service manual procedure. Make sure the sealing  ring groove is completely clean. This can be performed by scraping the groove with a variety of 

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32-5 Disassembling Calipers

Disassemble the caliper, following

  the service manual procedure.

  

2

Clean all of the caliper parts

  following the service manual procedure.

  

3

Inspect each of the parts for

  damage, rust, and wear.

Skill Drills provide written stepby-step explanations and visual summaries of important skills and procedures. This format enhances student comprehension of complex procedures.

4

Measure the caliper bore-to-piston clearance with a feeler gauge and compare to specifications. Determine any necessary actions.


CHAPTER 32 Disc Brake System

TECHNICIAN TIP

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In some cases, the piston cannot be removed with compressed air due to the piston being seized in the bore. If this happens, reinstall the calipers on the vehicle without the pads, bleed the brakes, and use the brake pedal to force the stuck piston out of the caliper. You may have to block any nonseized pistons so they don’t pop out; that way, just the seized piston gets pushed out.

Reassemble the caliper assembly, following the manufacturer’s procedure. Lubricate the sealing

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clean brake fluid or approved caliper piston assembly lube on the piston and sealing ring prior to installing it. Also check the service manual to see when the piston dust boot needs to be installed. Some calipers require the dust boot to be installed in the caliper before installing the piston. In this case, a special technique using air pressure to “balloon” the dust boot is required so the piston can slip inside it. Ask your supervisor to demonstrate this technique. To reassemble, lubricate, and reinstall the caliper, pads, and related hardware; seat pads; and inspect for leaks, follow the steps in SKILL DRILL 32-6 : 1 Make sure the rotor has been properly installed on the hub/spindle and that the hub mating surface is free of rust or dirt. (Step 1)

SKILL DRILL

32-6

27

Reassembling Calipers

1

Make sure the rotor has been properly installed on the hub/ spindle and the hub surface is free of rust or dirt.

2

Reassemble the caliper assembly, following the manufacturer’s procedure.

3

Assemble the pads, hardware, and caliper on the caliper mountings using the specified lubricant.

4

Reinstall the brake line fittings using two new copper washers (if equipped).

5

Tighten the brake line fitting and caliper bolts to the proper torque. Bleed the brakes following the manufacturer’s procedure.

6

Seat the pads by applying the brake pedal several times, not allowing the pedal to go all the way to the floor.


SECTION VI BRAKES

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32-6

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4

5 6

7

If the brake pedal is spongy, you will need to bleed the brakes of any remaining trapped air in the system.

8

Inspect the system for any brake fluid leaks, no matter how small.

ring, piston, and any other moving parts. Be careful to not pinch, twist, or cut the sealing ring and dust boot. (Step 2) Assemble the pads, hardware, and caliper on the caliper mountings using the specified lubricant. (Step 3) Reinstall the brake line fittings using two new copper washers (if equipped). Place one between the brake line fitting and the head of the banjo bolt and the other between the brake line fitting and the caliper. (Step 4) Tighten the brake line fitting and the caliper mounting bolt(s) to the proper torque. Bleed the brakes following the manufacturer’s procedure. See the brake bleeding skill drills in the Hydraulics and Power Brakes chapter for more information. (Step 5) Seat the pads by applying the brake pedal several times. It is a good idea to place your left foot under the brake pedal so that when applying the pedal with your right foot, the pedal does not push the master cylinder pistons farther into the master cylinder bore, which could dislodge sludge or cut the lips of the master cylinder primary seals. Applying the brake will force the brake caliper pistons to adjust to the proper clearance for proper

8

9

brake application. You may need to start the vehicle to enable the power booster to help you fully apply the brakes, especially if the vehicle is equipped with integrated parking brake calipers. (Step 6) If the brake pedal is spongy, you will need to bleed the brakes of any remaining trapped air in the system. (Step 7) If the brake pedal is firm and does not sink over time, there could still be a small leak that would cause a future brake failure. Inspect the system for any brake fluid leaks, no matter how small; if found, inform your supervisor/instructor. (Step 8)

Retracting and Readjusting Pistons on an Integrated Parking Brake Retracting the caliper piston on an integrated parking brake system is different than on a standard caliper. Since the integrated parking brake system uses a threaded shaft to force the piston outward from the caliper bore, it cannot just be retracted with a C-clamp. The piston will need to be screwed back in on the threaded shaft to retract it into the bore. This is accomplished by using a tool that mates to slots, grooves, or holes in the outer face of the piston. The tool is then turned by hand or wrench to screw the piston back into the bore. Be careful to not tear the piston dust boot during this operation.


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ratchet and tool need to be held tightly against  the piston so it does not slip. There are other  more application-specifi c tools that use the caliper  housing to keep the tool from slipping out of the  holes in the piston. This style works the best if you  have access to one. (Step 1)   Install the tool and turn it in the direction that    causes the piston to retract. (Step 2)   Continue turning until the piston is lightly seated    at the bottom of its bore. (Step 3)   Make sure the dust boot is seated properly in its    grooves. (Step 4)      

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 To retract the caliper piston on an integrated parking  brake system, follow the steps in  SKILL SKILL DrILL 32-7  :  Research the procedure for retracting the caliper      1   piston on an integrated parking brake system in  the appropriate service information, paying close  attention to which direction the piston needs to be  turned.   Select the proper adapter or tool to match the      2   caliper piston. There are several types of tools that      work. One is a multisided cube with a variety of  projections of varying confi gurations on each  side. This cube fi ts on the end of a ratchet. The     

SKILL DRILL

1

  

Research the procedure for

  retracting the caliper piston. Select the proper adapter or tool to match the caliper piston.

  

4

Make sure the dust boot is seated

  properly in its grooves.

Retracting and Readjusting Pistons on an Integrated Parking Brake

32-7

  

2

Install the tool and turn it in the

  direction that causes the piston to retract.

29

  

3

Continue turning until the piston is

  lightly seated at the bottom of its bore.


section vi BrakeS

3 4 5

If you have not already done so, remove the caliper    assembly, brake pads, and any hardware following  the manufacturer’s procedure.   Clean the rotor with approved asbestos removal    equipment. (Step 1)   Inspect the rotor for hard spots or hot spots,     scoring, cracks, and damage. (Step 2)   Measure the rotor thickness at the deepest groove    or thinnest part of the rotor and compare to  specifi cations. If it is under the allowed size, it will  need to be replaced. If it needs to be  machined  and it is above the minimum thickness, check  to see how badly it is scored. Remember that   removing 0.015" (0.38 mm) on each side of the  rotor results in the thickness being reduced by  0.030" (0.76 mm). Many rotors only start with  0.060" (1.52 mm) of machinable material when  they are new. (Step 3)   Measure the thickness of the rotor in a  minimum    of fi ve to eight places around face of the  rotor.    Calculate the maximum thickness variation  by subtracting the minimum thickness from  the   maximum thickness and compare it to   specifi cations.  (Step 4)  

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  he rotor thickness, lateral runout, and thickness  T variation must be within specifications for the rotor  to function properly. Rotors that are too thin cannot  handle as much heat and will experience brake fade  sooner than thicker rotors will. They also may cause  the piston to be pushed out of the caliper bore far  enough that the sealing ring no longer seals the piston.  This would lead to a lack of braking action on at least  half of the system.   E xcessive thickness variation will cause brake   pedal pulsation and the vehicle to have a surging  feeling  while coming to a stop. Excessive lateral runout tends  to cause the steering wheel to shimmy. It also can cause  an excessive thickness variation problem due to the  high spot of the rotor continuously hitting the brake  pad while driving down the road. This constant rubbing on the high spot of the rotor will wear it slightly,  leading to excessive thickness variation across the face  of the rotor.  T   o clean, inspect, and measure rotor thickness, lateral  runout, and thickness variation and to determine any  necessary action(s), follow the steps in  SKILL SKILL DrILL 32-8  :  Research the procedure and specifi  cations for  1   i nspecting the rotor in the service information.  

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Inspecting and Measuring Disc Brake Rotors

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Inspecting and Measuring Disc Brake Rotors

32-8

Research the procedure and

  specifications for inspecting the

rotor. If you have not already done so, remove the caliper assembly, brake pads, and any hardware. Clean the rotor with approved asbestos removal equipment.

6

  

2

Inspect the rotor for hard spots

  or hot spots, scoring, cracks, and damage.

  

3

Measure the rotor thickness at the

  deepest groove or thinnest part of the rotor.


chapter 32 Disc Brake System

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Inspecting and Measuring Disc Brake Rotors, continued

  

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4

Measure the thickness of the

  rotor in a minimum of five to

eight places around the face of the rotor. Calculate the maximum thickness variation.

7

7

8

  

5

Set up a dial indicator to measure

  lateral runout. Rotate the rotor

and find the lowest spot on the rotor, then zero the dial indicator.

  

6

Slowly rotate the rotor to find

  the highest spot on the rotor.

Read the dial indicator showing maximum runout.

Keep turning the rotor to make sure the dial indicator does not read below zero. If it does, rezero the dial caliper on the lowest spot. Keep turning the rotor to find the highest spot and reread the dial indicator. Compare all of your readings to the specifications and determine if the rotor is fit for service, is machinable, or needs to be replaced.

Set up a dial indicator to measure lateral runout.  Rotate the rotor and fi nd the lowest spot on the  rotor, then zero the dial indicator. (Step 5) Slowly rotate the rotor to fi nd the highest spot  on the rotor. Read the dial indicator showing   maximum  runout.  (Step 6)

9

10

Keep turning the rotor to make sure the dial    indicator does not read below zero. If it does,  rezero the dial caliper on the lowest spot.   Keep turning the rotor to fi nd the highest spot and  reread the dial indicator.  


section vi BrakeS

Removing and Reinstalling Rotors

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  emoving the rotor is usually required when the rotor  R needs to be replaced because it is under the specifi ed  minimum thickness or would be after machining. It  also would need to be removed to be refi nished on an  off-car brake lathe or to service the wheel bearings or  axle shaft. Also, hubless rotors that are being machined  with an on-car brake lathe need to be removed to clean  off the rust and dirt accumulated between the rotor  and the hub.    otors are designed to be mounted in one of two  R ways: hub style or hubless style. The hub style has the  wheel bearing hub cast into the rotor. This style  generally  requires disassembly of the wheel bearing hub to remove  the rotor from the vehicle. The hubless style uses a wheel  bearing hub separate from the rotor, with the rotor held  onto the hub by the wheel studs and lug nuts. Some hubs  also use small screws to hold the rotor on the hub whenever the wheel is removed from the vehicle.  Removing  hubless rotors is generally easier than removing hub-style  rotors, although some manufacturers design their rotors  to unbolt from the rear side of the bearing hub. In these  applications, the wheel bearing hub must be removed  before the rotor can be removed from the hub. 

 To remove and reinstall the rotor, follow the steps in  SKILL DrILL 32-9  :  1 Research the procedure for removing and reinstall  ing the brake rotor in the appropriate service information.   2 If you have not already done so, remove the caliper    assembly, brake pads, and any hardware, following  the manufacturer’s procedure.   3 If the caliper mount straddles the rotor, remove it    according to the specifi ed procedure. This is usually accomplished by removing bolts behind the  rotor. (Step 1)   , fi rst mark  4 To remove the hubless-style rotor    the rotor for reinstallation in the correct position.  A permanent marker, crayon, or center punch can  be used to do this. (Step 2)   5 If there are screws or speed nuts holding the rotor    to the hub, remove them following the specifi ed  manufacturer procedure. (Step 3)   6 Remove the rotor from the hub. (Step 4)     7  To remove the hub-style rotor , remove the wheel  bearing locking mechanism (cotter pin, lock nut,  or peened washer). (Step 5)   8 Remove the wheel bearing adjusting nut, thrust    washer, and outer bearing. (Step 6)   9 If the rear bearing must be removed for service or     replacement of the rotor, use the  following  procedure  to remove the inner bearing and grease seal.  

g

Compare all of your readings to the specifi cations,  and determine if the rotor is fi t for service, is   machinable, or needs to be replaced. (Step 7)

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SKILL DRILL

  

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32-9

Research the procedure for

  removing and reinstalling the

brake rotor. If you have not already done so, remove the caliper assembly, brake pads, and any hardware. If the caliper mount straddles the rotor, remove it.

  

Removing and Reinstalling Rotors

2

To remove the hubless-style

  rotor, mark the rotor for proper reinstallation.

  

3

If there are screws or speed nuts

  holding the rotor to the hub, remove them.


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Removing and Reinstalling Rotors, continued

  

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Remove the rotor from the hub.

5

  

To remove the hub-style

  

6

  rotor, remove the wheel bearing

  

locking mechanism.

7

Follow the steps of the inner

  bearing and grease seal removal

procedure if the rear bearing must be removed.

If the rotor uses small screws to

   10   hold the rotor to the hub, reinstall those and tighten to the proper torque.

  

8

To reinstall a hubless-style

  rotor, clean all mounting surfaces

on the hub and rotor and remove any burrs.

Spin the rotor to ensure it spins

   11   true and does not contact any other

components such as the dust shield.

Remove the wheel bearing adjust-

  ing nut, thrust washer, and outer bearing.

9

  

Slip the rotor over the wheel

  studs.

Be sure to properly lock the

   12   adjustment nut in place once adjustment is completed.

33


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Removing and Reinstalling Rotors, continued

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Spin the rotor to ensure it spins

   13   true and does not contact any other

components such as the dust shield.

n n n

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   einstall the adjusting nut onto the spindle about  R fi ve  turns.     Grasp the rotor on the top and bottom, and push  it toward the center of the vehicle.     Hold slight downward pressure as you fi rmly pull  the rotor toward yourself. This should cause the  adjusting nut to catch the wheel bearing and to  pull it and the seal out of the rear of the hub.     The grease seal will need to be replaced with a  new  one.     Now would be a good time to perform any   other  rotor-related tasks such as inspecting and   measuring a rotor, refi nishing a rotor, and  servicing  wheel bearings. Perform those tasks and return  here to reinstall the rotor.     If a new rotor is being installed, make sure to  clean off any anticorrosion coating it was shipped  with. Follow the rotor manufacturer’s procedure  to  remove this coating. (Step 7)  

To reinstall a hubless-style rotor  , fi rst clean    all mounting surfaces on the hub and rotor and   remove any burrs. (Step 8)   11 Slip the rotor over the wheel studs. (Step 9)     If the rotor uses small screws to hold the rotor to      12   the hub, reinstall those and tighten to the proper  torque.  torque. (Step 10)   Finally, spin the rotor to ensure it spins true and      13   does not contact any other components such as the  dust shield. (Step 11)   To reinstall a hub-style rotor , follow the wheel       14   bearing service skill drill in the Wheel Bearings  10

chapter to pack, install, and adjust the wheel  bearings.  bearings. (Step 12)   15 Be sure to properly lock the adjustment nut in    place once the adjustment is completed.  place once the adjustment is completed. (Step 13) 16 Finally, spin the rotor to ensure it spins true and    does not contact any other components such as the  dust shield. (Step 14)      

Refinishing Rotors on Vehicle

  otors need to be refi nished when they have excessive  R runout, thickness variation, or grooving. A brake lathe  refi nishes the rotor surfaces by removing metal and  truing  the surfaces. If the grooving or surface defects are too  great, the rotor may require the removal of too much  metal to satisfactorily refi nish the surfaces. The rotor  thickness should always be remeasured once the refi nishing is complete to ensure it is above the manufacturer’s  minimum thickness.   Rotors can be refi nished while on the vehicle or off  the vehicle. On-vehicle refi nishing is preferred by most  manufacturers (those who allow refinishing of their   rotors) because it minimizes runout issues between the  hub and rotor. Since the rotor is being machined as it is  mounted on the vehicle, it is being refi nished true to the  hub and other brake components. This minimizes any  lateral runout issues. To refi nish a rotor while it is on the  vehicle and to measure fi nal rotor thickness, follow the  steps on  SKILL SKILL DRILL 32-10  :  1 Research the brake lathe manufacturer’s procedure    for properly refi nishing the rotor. Follow those  guidelines  completely.  


chapter 32 Disc Brake System

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overload the lathe, as well as make the rotors much  thinner. (Step 4)   9 Install the anti-chatter device, if specifi ed. This will    help give an acceptable fi nish on the rotor surfaces.  5) (Step 5)   10 Engage the automatic feed and watch for proper    machining action. (Step 6)   11 If necessary, repeat this step until all damaged     surface areas have been removed on both sides of  the rotor. (Step 7)   12 If necessary, perform a fi nish cut on the rotor. Many    newer machines use an elliptical motion to give a  nondirectional fi nish, so a fi nish cut is not needed.   13 Remeasure the rotor thickness to determine if the    rotor is above minimum thickness specifi cations.  (Step 8)   14 If you had to adjust the wheel bearings in Step 3,    readjust the bearings so they have the specifi ed  end play or preload. (Step 9)      

in

If working on a hubless-style rotor, remove the  r  otor and clean any dirt, rust, and debris from the  mating surfaces of the rotor and hub.   If working on a hub-style rotor, measure the wheel  bearing end play. If excessive, adjust the bearings  so there is no end play. Just remember to readjust  them properly when the refi nishing process is  complete.   Mount the on-car brake lathe to the rotor. (Step 1) Perform the runout compensation on the brake  lathe. Some brake lathes require manual compensation, while other machines can perform this as  part of their features. Follow the lathe manufacturer’s procedure. (Step 2) Adjust the cutting bits and cut off any lip at the  edge of the rotor. (Step 3) Make sure the cutting bits will not contact the  rotor  face, and move the cutting head toward the inner  diameter of the rotor face.   Set the cutting bits to the proper cutting depth  for machining. This is usually between 0.004  and 0.015 of an inch. Too little removal tends to   overheat the edge of the cutting bit. Too much can 

2

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SKILL DRILL

  

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32-10

Research the brake lathe

  manufacturer’s procedure for

properly refinishing the rotor. Mount the on-car brake lathe to the rotor after cleaning the rust and dirt from between the rotor and hub or adjusting the wheel bearing so there is no end play.

  

2

Refinishing Rotors off Vehicle

 Refi nishing a rotor while it is off the vehicle is a bit different than on-vehicle refi nishing. The major difference 

Refinishing Hubless Rotors on Vehicle

Perform the runout calibration on

  the brake lathe.

35

  

3

Adjust the cutting bits and cut off

  any lip at the edge of the rotor.


section vi BrakeS

36

32-10

Refinishing Hubless Rotors on Vehicle, continued

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4

  

Make sure the cutting bits will not

  contact the rotor face, and move

5

  

the cutting head toward the inner diameter of the rotor face. Set the cutting bits to the proper cutting depth for machining.

  

7

If necessary, perform a finish cut

  on the rotor.

  

8

Install the anti-chatter device, if

  specified.

  

6

Engage the automatic feed and

  watch for proper machining

action. If necessary, repeat this step until all damaged surface areas have been removed on both sides of the rotor.

Remeasure the rotor thickness

  to determine if the rotor is above

minimum thickness specifications.

is in the setup. Hub-style and hubless-style rotors each  require their own way of being mounted on the brake  lathe. Most hub-style rotors use the  bearing races  to drive  and center the rotor on the lathe spindle. Thus, bearing  adapters of the proper size need to be selected and used  (see the Wheel Bearings chapter). The spindle nut then  clamps the rotor onto the spindle through these bearing  adapters and races. Hubless rotors are centered using a  spring-loaded centering cone to align the rotor’s centering  hole with the spindle. Clam shell clamps are then used  on each side of the rotor to clamp it to the lathe spindle.  Composite rotors use a special adapter which drives the  rotor from the center hole and, at the same time, clamps  it fi rmly between solid plates. 

  o refinish a rotor while it is off the vehicle and  T measure final rotor thickness, follow the steps in  SKILL DRILL 32-11  :  1 Research the brake lathe manufacturer’s procedure    for properly refi nishing the rotor. Follow those  guidelines  completely.   mounting  2 Clean nicks, burrs, or debris from the     surfaces of the rotor including the centering hole,  if used. Since the rotor is clamped to the lathe  spindle, all of the surfaces on the rotor that contact  the lathe components must be free of nicks, burrs,  and rust; therefore, they must be cleaned prior to  mounting the rotor on the lathe. This is especially  true of a hubless-style rotor. (Step 1)  


chapter 32 Disc Brake System 3 4

7 8 9

Set the cutting bits to the proper cutting depth for    machining the ridge. (Step 5)   By hand, move the cutting head outward toward    the ridge. Slowly remove the ridge. (Step 6)   Once the ridge is removed, run the cutting head all    the way in to the inner face of the rotor. (Step 7)   Set the cutting bits to the proper cutting depth for    machining the rotor face. (Step 8)  

SKILL DRILL

  

32-11

1

Research the brake lathe manu-

  facturer’s procedure for properly

  

Refinishing Rotors off Vehicle

4

Position the cutting head about

  one-quarter the way in from the outer diameter of the rotor.

  

Mount the rotor. Check that the

2

  rotor is running true on the lathe.

5

  cutting depth for machining the

refinishing the rotor. Clean nicks, burrs, or debris from the mounting surfaces of the rotor including the centering hole.

  

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Mount the rotor onto the lathe. Check that the    rotor is running true on the lathe. (Step 2)   Install the anti-chatter band or anti-chatter pucks    on the rotor. (Step 3)   Make sure the cutting bits will not contact the     rotor face, and move the cutting head in about  one-quarter the way from the outer diameter of the  rotor face. Turn on the lathe. (Step 4)  

Set the cutting bits to the proper ridge.

37

  

  

Install the anti-chatter band or

3

  anti-chatter pucks on the rotor.

6

  outward toward the ridge. Slowly

By hand, move the cutting head remove the ridge.


section vi BrakeS

38

Engage the automatic feed on “fast” cut and watch    for proper machining action. Some machines are  called a “single-cut” or “single-pass” lathe and offer  only one cutting speed. (Step 9)   11 If necessary, repeat Step 10 until all damaged surface    areas have been removed on both sides of the rotor.   12 If necessary, perform a fi nish cut on the rotor. This    is usually done on “slow” speed. (Step 10)  

Use sandpaper or a drill with a sanding pad to give    the rotor faces a nondirectional fi nish. (Step 11)   14 Remeasure the rotor thickness to determine if the    rotor is above minimum thickness specifi cations.  (Step 12)   15 Wash the machined rotor in a hot soapy water    solution or parts washing cabinet to remove any  metal particles, and dry. (Step 13)       13

  

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7

Once the ridge is removed, run

  the cutting head all the way in to the inner face of the rotor.

If necessary, perform a finish cut

   10   on the rotor. This is usually done on “slow” speed.

  

8

Set the cutting bits to the proper

  cutting depth for machining the rotor face.

Remeasure the rotor thick-

   11   ness to determine if the rotor is above minimum thickness specifications.

  

9

Engage the automatic feed on “fast”

  cut and watch for proper machining action. If necessary, repeat this step until all damaged surface areas have been removed on both sides of the rotor. Some single-cut machines only have one cutting speed.

Use sandpaper or a drill with a

   12   sanding pad to give the rotor faces a nondirectional finish.


CHAPTER 32 Disc Brake System

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Determine if the stud can be removed with the flange on or off the vehicle. (Step 1) To perform the drawing-in method, first position the flange so the stud has clearance on the back side to be removed. (Step 2) Remove any damaged studs with a hammer. Be careful not to damage any of the surfaces on the flange and hub, including the wheel speed sensor and tone ring. (Step 3) Insert the stud in the hole in the flange and rotate it so that all of the flutes on the stud line up with the notches in the flange. (Step 4) Place enough heavy duty washers over the stud to prevent the lug nut from bottoming out on the threads. (Step 5) Place the lug nut onto the stud, flat side in. Tighten it until the stud bottoms out in the flange. Inspect the threads on the stud and lug nut to make sure they did not get damaged. (Step 6) To perform the hydraulic press method, first remove the hub and wheel flange from the vehicle following the manufacturer’s procedure. (Step 7) Use the press to push out any damaged lug studs. (Step 8) Insert the new lug stud into the wheel flange hole. Line up the flutes on the stud with the notches in the flange. (Step 9) Support the hub and flange so the press is pushing the stud straight into the flange. (Step 10) Push the stud in until it bottoms out in the flange. (Step 11) To complete the drawing-in method and the hydraulic press method, verify that each stud is fully seated in the flange. (Step 12) Reinstall the hub and flange on the vehicle if they were removed. (Step 13)

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Wheel studs need to be replaced when they have been damaged or broken off due to improper installation or normal wear and tear. Wheel studs can be damaged by being overtightened and stretched. Look for a neckeddown or thinned-out section of the stud, which is most likely to happen within the threaded area of the stud. Stretched studs need to be replaced. Studs can also have their threads damaged by cross-threading or seizing of the lug nut on the stud. It is best to replace the stud and nut if this occurs. Lastly, wheel studs may even break off if they are overtightened beyond their stretch point. It is always a good idea to consider replacing all of the studs on a wheel (and maybe the ones on the other wheels also) if one stud is broken off, as it is likely that all of the others have been weakened. Some vehicles are designed to allow for the removal and replacement of the wheel studs while the hub and wheel flange are still installed on the vehicle. The manufacturer may have provided a recessed spot in the steering knuckle where the studs have enough clearance to be removed; thus, the flange needs to be positioned in that particular position. Other vehicles do not have enough clearance on the back side for the stud to be removed; thus, the hub and flange must be removed from the vehicle. There are two primary methods of replacing lug studs: the drawing-in method and the hydraulic press method. The drawing-in method uses the lug nut to draw in the wheel stud. It is accomplished by inserting the new stud into the wheel stud hole in the flange, installing enough heavy-duty washers over the stud to allow the lug nut to draw the wheel stud into the flange when tightened. The lug nut is placed flat side in, on the stud, and tightened. Make sure that as the stud is pulled in the lug nut does not run out of threads on the stud. If it does, remove the nut and add washers. Keep tightening the lug nut until the wheel stud bottoms out in the flange. Verify that the head of the stud is fully seated in the flange. The hydraulic press method uses a press to force the wheel stud into the flange until it bottoms out. This method requires the hub and flange to be removed from the vehicle. Make sure the flange is positioned and supported properly on the press table. Sometimes it is best to use a short piece of pipe (a bit longer than the wheel stud) to support the flange while the stud is being pressed in. Once the stud is installed, verify that it is fully seated in the flange. To inspect and replace wheel studs, follow the steps in SKILL DRILL 32-12 : 1 Inspect the wheel studs and lug nuts for damage. Look for signs of stretched studs, cross-threaded lug nuts, and broken-off studs.

2

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Inspecting and Replacing Wheel Studs

39

7 8 9

10 11

12 13 14

15

Installing Wheels, Torquing Lug Nuts, and Making Final Checks This step, while fairly simple, can result in problems if it is not done properly. Overtightening the lug nuts can cause the wheel studs to break either immediately, or worse, after the vehicle has been driven for a period of time. Overtightening also can cause warpage of the rotors, which results in the need to refinish or replace them. Undertightening can lead to loosening of the lug nuts and result in the wheel working its way off the vehicle. This can cause the driver to lose control of the vehicle and potentially result in an accident. Lug nuts should be tightened to the


section vi BrakeS

40

must  match the mating surface of the wheel. Always check  that these surfaces match.   When installing lug nuts, the weight should be off  the vehicle so that the wheel is off the ground or is barely  touching the ground. The lug nuts should easily center  the wheel on the hub. This is especially  important on  aluminum wheels that use a fl at lug nut seating surface.  The lug nuts can dig into the sides of the lug nut holes 

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proper torque, in the specifi ed sequence. All manufacturers  specify the sequences for each of their vehicles. The torque  pattern is usually in some form of a star or cross.   Be careful which way you install the lug nuts. Many  wheels use a tapered hole that matches the tapered end  of the lug nut and centers the wheel on the wheel fl ange.  Other wheels use a fl at surface that matches fl at surfaces  on the lug nuts. But no matter what, the lug nut surface 

Inspecting and Replacing Wheel Studs

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32-12

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SKILL DRILL

1

  

Inspect the wheel studs and lug

  nuts for damage. Look for signs of

2

   

  

stretched studs, cross-threaded lug nuts, and broken-off studs. Determine if the stud can be removed with the flange on or off the vehicle.

4

Insert the stud in the hole in the

  flange and rotate it so that all of

the flutes on the stud line up with the notches in the flange.

To perform the drawing-in

  method, position the flange so

3

  

  

the stud has clearance on the back side to be removed.

5

Place enough heavy-duty washers

  over the stud to prevent the lug nut from bottoming out on the threads.

Remove any damaged studs

  with a hammer. Be careful not to

  

damage any of the surfaces on the flange and hub, including the wheel speed sensor and tone ring.

6

Place the lug nut onto the stud,

  flat side in. Tighten it until the stud bottoms out in the flange. Inspect the threads on the stud and lug nut to make sure they did not get damaged.


chapter 32 Disc Brake System

32-12

Inspecting and Replacing Wheel Studs, continued

   

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SKILL DRILL

7

To perform the hydraulic

  press method, remove the hub

and wheel flange from the vehicle following the manufacturer’s procedure.

Support the hub and flange so the

   10   press is pushing the stud straight into the flange.

Reinstall the hub and flange on the

   13   vehicle if it was removed.

  

8

Use the press to push out any

  damaged lug studs.

Push the stud in until it bottoms

   11   out in the flange.

  

9

Insert the new lug stud into the

  wheel flange hole. Line up the

flutes on the stud with the notches in the flange.

To complete the drawing-in

   12   method and the hydraulic press method, verify that each stud is fully seated in the flange.

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SECTION VI BRAKES

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There is some controversy regarding the use of a lubricant or antiseize on wheel studs and lug nuts. Since the purpose of a lubricant or antiseize is to prevent the components from sticking, CDX errs on the side of not using those products, for fear of the lug nuts coming loose. Also, the torque given for the lug nuts is dry (no lubricant) so torquing them to specifications would lead to overtorquing. At the same time, in areas of the country prone to rust, it is understandable why some want to put a very light amount of antiseize only on the threads of the wheel stud, being careful not to get any on the contact seat of the wheel and lug nut. Doing so would prevent rust from building up on the threads. However, the lug nut torque would need to be reduced due to the lubricant. CDX prefers to install lug nuts dry and avoid this issue altogether. Many shops have their customers sign on the repair order that they will return and the wheel torque will be rechecked after 50 to 500 miles of driving to make sure the wheels have not loosened.

process of transferring pad material onto the rotor evenly, as well as cooking off the resins that are used to bind the friction material together in the pad. Burnishing results in long, quiet brake life, which results in satisfied customers. For burnishing to happen properly, the rotor and pad material need to be heated slowly and evenly. This is done by making a specified number of stops from a specified speed, with the appropriate wait times between stops. In some cases, brake lining manufacturers want you to perform a series of stops at light to moderate brake application. Other manufacturers specify a series of moderate to heavy stops. Always check the manufacturer’s procedure to burnish the brakes once the brake job is complete. This process will help avoid the dreaded disc brake squeal. To install the wheel, torque lug nuts, and make final checks and adjustments, follow the steps in SKILL DRILL 32-13 : 1 Start the lug nuts on the wheel studs. Make sure the lug nut surface matches the wheel hole. The lug nuts should be able to be turned by finger. (Step 1) 2 Carefully run all of the lug nuts down so they are seated in the wheel. Make sure the wheel is centered on the hub. (Step 2) 3 Lower the vehicle so the tires are partially on the ground to keep them from turning while tightening the lug nuts. (Step 3) 4 Use a torque wrench to tighten each lug nut to the proper torque in the proper sequence. (Step 4)

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and cause the wheel to not center properly. Once the lug nuts are against the wheel, work the wheel onto the lug nut shafts. Then you can torque them down properly. Once the lug nuts are torqued properly and the brake system checked, it is time for a test drive to verify proper brake operation, and to burnish the new brake pads and rotor surfaces. Burnishing, also called bedding in, is the

SKILL DRILL

1

32-13

Start the lug nuts on the wheel studs, being careful to match up the surfaces.

2

Installing Wheels, Torquing Lug Nuts, and Making Final Checks

Carefully run all of the lug nuts down so they are seated in the wheel.

3

Lower the vehicle so the tires are partially on the ground to keep them from turning while tightening the lug nuts.


CHAPTER 32 Disc Brake System

32-13

Installing Wheels, Torquing Lug Nuts, and Making Final Checks, continued

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SKILL DRILL

43

5

6

4

Use a torque wrench to tighten each lug nut to the proper torque in the proper sequence.

7

Check the brake fluid level in the master cylinder reservoir. Start the vehicle and check the brake pedal for proper feel and height. Check the parking brake for proper operation. Also inspect the system for any brake fluid leaks and loose or missing fasteners.

5

Once all of the lug nuts have been torqued, go around them again, this time in a circular pattern to ensure that you did not miss any in the previous pattern.

Once all of the lug nuts have been torqued, go around them again, this time in a circular pattern to ensure that you did not miss any in the previous pattern. (Step 5) If the vehicle was equipped with hubcaps and valve stem caps, reinstall them. (Step 6)

7 8

6

If the vehicle was equipped with hubcaps and valve stem caps, reinstall them.

Check the brake fluid level in the master cylinder reservoir. Start the vehicle and check the brake pedal for proper feel and height. Check the parking brake for proper operation. Also inspect the system for any brake fluid leaks and loose or missing fasteners. (Step 7)


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section vi BrakeS

Wrap-up

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 Disc brakes create braking power by forcing fl at  friction pads against the outer faces of a rotor.  The vehicle’s kinetic energy is transformed into  heat energy by the disc brake components, which  slow the vehicle when applied.  Disc brake assemblies consist of a caliper, brake  pads, and a rotor.  Caliper pistons use hydraulic pressure to create a  clamping force of the brake pads to the faces of the  rotor.  Disc brake pads require much higher application  pressures to operate than drum brake shoes,  Summarizes chapter content because they are not self-energizing. in a comprehensive  Advantages of disc brakes over drum brakes: more  bulleted list. effective at transferring heat to the atmosphere,  self-adjusting, resistant to water fade, and easier to  service.  Disadvantages of disc brakes compared to drum  brakes: more prone to noise, more prone to pedal  pulsations due to warpage, and more diffi cult to  use as an emergency brake.  Disc brake calipers come in two main styles: fi xed  and fl oating/sliding.

 In disc brake calipers, the piston is sealed by a  square cut O-ring.  Floating/sliding calipers require clean and  lubricated pins, bushings, or guides for proper  operation.  Brake pad lining is either riveted or bonded to the  pad backing plate.  Brake pad lining is available in a variety of materials  with varying amounts of coeffi cient of friction.  Brake pads may use shims, spacers, guides, and  bendable tangs to help minimize squealing.  Brake pad wear indicators, if used, can be of the  mechanical or electronic type.  Rotors rotate with the wheels and are usually made  of durable cast iron with friction surfaces that run  true and parallel.  Brake rotors can be solid or ventilated.  Disc brake parking brakes can be of the integrated  caliper style, top hat drum style, electric pull-cable  style, and the integrated electric motor caliper style.  Diagnosing brake faults requires good information  from the customer, an adequate test-drive when  possible, and a good understanding of brake  theory.

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Ready for Review


chapter 32 Disc Brake System

Key Terms

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drawing-in method A  method  for  replacing  wheel  studs that uses the lug nut to draw the wheel stud into  backing plate A metal plate to which the brake lining  the hub or flange. is fixed. edge code A  code  printed  on  the  edge  of  a  friction  bendable tangs Small  tabs  on  the  brake  pad  back lining that describes its coefficient of friction. ing plate that are crimped on to the caliper, creating a  electronic control module (ECM) A  computer  that   secure fit and reducing noise. receives  signals  from  input  sensors,  compares  that  bearing races Hardened metal surfaces that roller or ball   information  with  preloaded  software,  and  sends  an  bearings fit into when a bearing is properly  assembled.  appropriate command signal to output devices; used to  bleeder screw A  screw  that  allows  air  and  brake  manage the anti-lock brake system (ABS).   uid to be bled out of a hydraulic brake system when  fixed caliper A type of brake caliper bolted firmly to  fl it  is  loosened  and  seals  the  brake  fluid  in  when  it  is  the steering knuckle or axle housing, having at least one  t  ightened. piston on both sides of the rotor. bonded linings Brake linings that are essentially glued  guide pins Pins that allow the caliper to move in and  to  the  brake  pad  backing  plate;  more  common  on  out as the brakes operate and as the brake pads wear.  light-duty vehicles. hydraulic press method A method for replacing wheel  brake booster A  vacuum  or  hydraulically  operated  studs that uses a press to force the wheel stud into the  d   evice that increases the driver’s braking effort. flange until it bottoms out. brake lining thickness gauge A tool used to measure  independent rear suspension (IRS) A type of suspenthe thickness of the brake lining. sion system where each rear wheel is capable of moving  sion system where each pieces  of of  metal metal  independently of the other. brake pad shims and guides Small   Small pieces independently of the that  cushion  the  brake  pad  and  absorb absorb Provides some  of of a the the  some list of key termsrunout Also  and lateral called  warpage,  the  side-to-side  runout Also  vibration, helping to cut down on unwanted noise. unwanted noise. from the definitions chapter. movement of the rotor surfaces as the rotor turns. movement of the rotor brake wash station A  piece  of  equipment equipment  designed designed  low-drag caliper A  caliper  designed  to  maintain  a  caliper caliper A to  safely  clean  brake  dust  from  drum drum  and and  disc disc  brake brake  larger  larger brake  brake pad-to-rotor  pad-to-rotor clearance  by  retracting  the   components. pistons farther than normal. farther than bushing An  insert  with  an  inner  bearing  surface  that  lug A  flange  that  is  shaped  to  assist  with  aligning  is fitted into a hole in an object, allowing the object to  o  bjects on other objects. rotate or slide on a pin or shaft. off-car brake lathe A tool used to machine (refinish)  caliper A hydraulic device that uses pressure from the  drums  and  rotors  after  they  have  been  removed  from  master cylinder to apply the brake pads against the  rotor. the vehicle. caliper dust boot seal driver set A set of drivers used  on-car brake lathe A  tool used to machine (refinish)  to install metal-backed caliper dust boot seals. rotors while they are still attached to the vehicle. caliper piston pliers A tool used to grip caliper  pistons  parallelism Also  called  thickness  variation;  both  surwhile removing them. faces  of  the  rotor  should  be  perfectly  parallel  to  each  caliper piston retracting tool A  tool  used  to  retract  other so that brake pulsations do not occur. caliper pistons on integrated parking brake systems. parking brake cable pliers A tool used to install parkC-clamp A  tool  used  to  push  pistons  back  into  the  ing brake cables. c  aliper bore on non-integrated parking brakes. phenolic resin A material used to create some brake pisdial indicator Tool used to measure the lateral runout  tons that is very resistant to corrosion and heat  transfer. of the rotor. pushrod (braking system) A mechanism used to transdisc brake pads Brake  pads  that  consist  of  a  friction  mit force from the brake pedal to the master cylinder. material  bonded  or  riveted  to  a  steel  backing  plate;  riveted linings Brake linings riveted to the brake pad   designed to wear out over time. backing  plate  with  metal  rivets  and  used  on  heavierdisc brake rotor micrometer A  specially  designed  duty or high-performance vehicles.  micrometer used to measure the thickness of a rotor. rotor The main rotating part of a disc brake system.


section vi BrakeS

g

steering knuckle A  device  that  connects  the  front  wheel to the suspension; pivots on the top and bottom,  thus allowing the front wheels to turn. ventilated rotor A  type  of  brake  rotor  with  passages  between the rotor surfaces that are used to improve heat  transfer to the atmosphere. wheel studs Threaded fasteners that are pressed into  the wheel hub flange and used to bolt the wheel onto  the vehicle.

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scratcher A  thin,  spring  steel  wear  indicator  that  is  fixed to the backing plate of the brake pad; it emits a  high-pitched squeal when the brakes are applied if the  brake pads have become too thin. sliding or floating caliper A  type  of  brake  caliper  that only has piston(s) on the inboard side of the rotor.  The  caliper  is  free  to  slide  or  float,  thus  pulling  the   outboard brake pad into the rotor when braking force  is applied. solid rotor A type of brake rotor made of solid metal. square cut O-ring An  O-ring  with  a  square  cross-  section  that  is  used  to  seal  the  pistons  in  disc  brake  c  alipers.

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chapter 32 Disc Brake System

1. Tech A says that disc brakes operate on the princi-

spring-steel brake pad wear indicator. Tech B says  that  some  vehicles  are  equipped  with  an  electric  brake pad wear sensor that activates a warning on  the dash. Who is correct? a. Tech A b. Tech B c. Both A and B d. Neither A nor B 8. Tech  A  says  that  rotors  should  be  measured  for  thickness  variation.  Tech  B  says  that  rotors   should  be  measured  for  lateral  runout.  Who  is  correct? a. Tech A Familiarize students with the b. Tech B format of the ASE certification c. Both A and B and Bexamination and test students’ d. Neither A nor B A norunderstanding B of content. 9. Tech  A  says says  that that  brake brake  pedal pedal  pulsation pulsation  can can  be be  caused by a rotor that is too thin. Tech B says that  rotor that is too thin. Tech B says that brake  pedal  pulsation pulsation  can can  occur occur  when when  activating activating  the ABS. Who is correct? a. Tech A b. Tech B c. Both A and B d. Neither A nor B 10. Tech  A  says  that  a  micrometer  is  used  to  measure  rotor  thickness  variation.  Tech  B  says  that  a  m   icrometer is used to measure rotor lateral runout.  Who is correct? a. Tech A b. Tech B c. Both A and B d. Neither A nor B

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ple of friction. Tech B says that disc brakes operate  on the principle of regeneration. Who is correct? a. Tech A b. Tech B c. Both A and B d. Neither A nor B 2. Tech  A  says  that  some  vehicles  use  fixed  calipers.  Tech B says that some vehicles use sliding /floating  calipers. Who is correct? a. Tech A b. Tech B c. Both A and B d. Neither A nor B 3. Tech A says that disc brakes require higher application pressures than drum brakes. Tech B says that  disc brakes are self-energizing. Who is correct? a. Tech A b. Tech B c. Both A and B d. Neither A nor B 4. Tech  A  says  that  fixed  calipers  use  one  or  more  pistons only on one side of the rotor. Tech B says  that sliding /fixed calipers use one or more pistons  on both sides of the rotor. Who is correct? a. Tech A b. Tech B c. Both A and B d. Neither A nor B 5. Tech A says that calipers use a round section O-ring  to seal each piston. Tech B says that calipers use a  square  section O-ring to  seal each  piston.  Who  is  correct? a. Tech A b. Tech B c. Both A and B d. Neither A nor B 6. Tech A says that brake fade is when the brake pedal  is  soft  and  spongy.  Tech  B  says  that  brake  fade  is  when the wheels skid during a panic stop. Who is  correct? a. Tech A b. Tech B c. Both A and B d. Neither A nor B

47

7. Tech A says that some vehicles are equipped with a 

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ASE-Type Questions

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STEERING AND SUSPENSION 27 Servicing Wheels 28 Servicing Steering Systems 29 Servicing Suspension Systems

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Automotive Technology

MANUAL TRANSMISSION 22 Manual Transmission/Transaxle Principles 23 Clutch System 24 Manual Transmissions/Transaxles 25 Drive Train Components 26 Basic Drive Layouts

in

FUNDAMENTALS OF

Principles and Practice

SAFETY AND FOUNDATION 1 Careers in Automotive Technology 2 Introduction to Automotive Technology 3 Introduction to Automotive Safety 4 Personal Safety 5 Vehicle, Customer, and Service Information 6 Tools and Equipment 7 Vehicle Protection and Jack and Lift Safety 8 Vehicle Maintenance Inspection 9 Communication ENGINE REPAIR 10 Engine Mechanical Testing 11 Engine Removal and Replacement 12 Cylinder Head Components 13 Engine Block Components 14 Engine Machining 15 Engine Assembly

AUTOMATIC TRANSMISSION 16 Automatic Transmission Fundamentals 17 Hydraulic Fundamentals 18 Hydraulically Controlled Transmission 19 Electronically Controlled Transmission 20 Servicing the Automatic Transmission 21 Hybrid and CVT Transmissions

BRAKES 30 Principles of Braking 31 Hydraulics and Power Brakes 32 Disc Brake System 33 Drum Brake System 34 Wheel Bearings 35 Electronic Brake Control ELECTRIC 36 Principles of Electrical Systems 37 Meter Usage and Circuit Diagnosis 38 Batteries, Starting, and Charging Systems 39 Lighting Systems 40 Body Electric System HVAC 41 Principles of Heating and Air-Conditioning Systems 42 Heating and Air-Conditioning Systems and Servicing 43 Electronic Climate Control ENGINE PERFORMANCE 44 Motive Power Types - SI Engines 45 Engine Lubrication 46 Engine Cooling 47 Ignition Systems Overview 48 Gasoline Fuel Systems 49 On-Board Diagnostics 50 Induction and Exhaust 51 Emission Control 52 Alternate Fuel Systems DIESEL ENGINES 53 Compression-Ignition Engines 54 Diesel Fuel Systems

Source Code:SAFATbr

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Jones & Bartlett Learning CDX Automotive Sample Chapter 32  

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