38S07T0 brake system diagnosis and repair 2005

How is the parking brake activated on rear wheel disc brakes on vehicles without drum in rotor parkingbrakes?A.. Master Cylinder Fluid Bypass Test Internal Leak Test If no sign of extern

Diagnosis and

Repair

Student Guide

Appropriate service methods and proper repair procedures are essential for the safe, reliable operation of all motor vehicles,

as well as the personal safety of the individual doing the work This manual provides general directions for accomplishing service and repair work with tested, effective techniques Following them will help assure reliability.

There are numerous variations in procedures, techniques, tools and parts for servicing vehicles, as well as in the skill of the individual doing the work This manual cannot possibly anticipate all such variations and provide advice or cautions as to each Accordingly, anyone who departs from instructions provided in this manual must first establish that he compromises neither his personal safety nor the vehicle integrity by his choice of methods, tools or parts.

As you read through the procedures, you will come across NOTES, CAUTIONS, and WARNINGS Each one is there for a specific purpose NOTES give you added information that will help you to complete a particular procedure CAUTIONS are given to prevent you from making an error that could damage the vehicle WARNINGS remind you to be especially careful

in those areas where carelessness can cause personal injury The following list contains some general WARNINGS that you should follow when you work on a vehicle.

• Always wear safety glasses for eye protection.

• Use safety stands whenever a procedure requires you to

be under the vehicle.

• Be sure that the ignition switch is always in the OFF

position, unless otherwise required by the procedure.

• Set the parking brake when working on the vehicle If you

have an automatic transmission, set it in PARK unless

instructed otherwise for a specific service operation If

you have a manual transmission it should be in

RE-VERSE (engine OFF) or NEUTRAL (engine ON) unless

instructed otherwise for a specific service operation.

• Operate the engine only in a well-ventilated area to avoid

the danger of carbon monoxide.

• Keep yourself and your clothing away from moving parts

when the engine is running, especially the fan and belts.

• To prevent serious burns, avoid contact with hot metal parts such as the radiator, exhaust manifold, tail pipe, catalytic converter and muffler.

• Do not smoke while working on the vehicle.

• To avoid injury, always remove rings, watches, loose hanging jewelry, and loose clothing before beginning to work on a vehicle Tie long hair securely behind your head.

• Keep hands and other objects clear of the radiator fan blades Electric cooling fans can start to operate at any time by an increase in underhood temperatures, even though the ignition is in the OFF position Therefore, care should be taken to ensure that the electric cooling fan is completely disconnected when working under the hood.

The recommendations and suggestions contained in this manual are made to assist the dealer in improving his dealership parts and/or service department operations These recommendations and suggestions do not supersede or override the provisions of the Warranty and Policy Manual, and in any cases where there may be a conflict, the provisions of the Warranty and Policy Manual shall govern.

The descriptions, testing procedures, and specifications in this handbook were in effect at the time the handbook was approved for printing Ford Motor Company reserves the right to discontinue models at any time, or change specifications, design, or testing procedures without notice and without incurring obligation Any reference to brand names in this manual

is intended merely as an example of the types of tools, lubricants, materials, etc recommended for use Equivalents, if available, may be used The right is reserved to make changes at any time without notice.

WARNING: Many brake linings contain asbestos fibers When working on brake components, avoid breathing the dust Breathing

the asbestos dust can cause asbestosis and cancer.

Breathing asbestos dust is harmful to your health.

Dust and dirt present on car wheel brake and clutch assemblies may contain asbestos fibers that are hazardous to your health when

5. Provide me with a clear and thorough explanation of the service performed.

6. Call me within a reasonable amount of time after my service visit to ensure that I'm completly satisfied.

7. Be responsive to questions or concerns I bring to your attention.

1. Make it convenient to have my vehicle

serviced at your dealership.

2. The Service Advisor should demonstrate

a genuine concern for my service needs.

3. Fix it right the first time.

4. Complete servicing my vehicle in a timely

and professional manner.

Expectation 3

“Fix It Right The First Time, On Time.”

Both service advisors and technicians are important players when it comes to Expectation

It is our goal to help the technician acquire all of the skills and knowledge necessary to “Fix

It Right The First Time, On Time.” We refer to this as “competency.”

Technician’s Role

Acquire the skills and knowledge for competency in your specialty via:

– Web Based Training – Web Based Training

The Benefits

The successful implementation of expectations means:

– Satisfied customers

– Repeat vehicle sales

– Repeat service sales

– Recognition that Ford and Lincoln/Mercury technicians are “the Best in the Business”

Customer Expectations: Service

INTRODUCTION AND PREREQUISITE REVIEW

OBJECTIVES Intro - 1 FORD BRAKES SERVICE TECHNICIAN SPECIALITY TRAINING (STST) CURRICULUM Intro - 2 Curriculum Goals Intro - 2 Brake Systems Diagnosis and Repair Instructor-Led Course Description Intro - 2 Course Objective Intro - 2 Lesson Objectives Intro - 2 Audience Intro - 2 Course Prerequisites Intro - 3 Evaluation Intro - 3 Student Guide Intro - 3 Service Standards Intro - 4 PREREQUISITE REVIEW Prereq - 1

LESSON ONE-MODULE 1:BRAKE SYSTEM DIAGNOSIS AND TESTING

Symptom-to-System-to-Component-to-Cause Diagnostic Procedure 2

Customer Concern 2

Symptom Charts 2

Pinpoint Tests 2

Removal and Installation 2

Disassembly and Assembly 2

Other Component and Subsystem Tests 2

PRELIMINARY BRAKE SYSTEM CHECKS 3

DIAGNOSTIC TESTS 4

External Leak Test 4

Master Cylinder Non-Pressure External Leak Test 4

Air Entrapment Test 5

Master Cylinder Fluid Bypass Test (Internal Leak Test) 5

Master Cylinder Compensating Port Test 6

Hydro-Boost System Inspection 7

Hydro-Boost Functional Check: 7

Accumulator Test: 8

Hydro-Boost Air Bleeding 8

COMMON CUSTOMER CONCERNS 9

Brake Roughness 9

Normal Roughness 9

Red Brake Warning Indicator Always On 16

Brake Warning Indicator Always On Diagnosis 16

Brakes Lock Up (Grabbing) 17

Brakes Lock Up Diagnosis 17

Excessive Brake Pedal Effort 18

Excessive Brake Pedal Effort Diagnosis 18

Brakes Drag 19

Brakes Drag Diagnosis 19

Brake Noise 20

Normal Noise 20

Abnormal Noise 21

Brake Noise Diagnosis 21

Slow or Incomplete Brake Pedal Return 22

Slow or Incomplete Brake Pedal Return Diagnosis 22

LESSON ONE WORKSTATIONS 23

WORKSTATION 1 25

WORKSTATION 2 26

WORKSTATION 3 28

WORKSTATION 4 30

LESSON ONE-MODULE 2:BRAKE SYSTEM SERVICE INTRODUCTION TO BRAKE SYSTEM SERVICE 34

SERVICE PRECAUTIONS 35

BRAKE INSPECTION PROCEDURES 36

HYDRAULIC COMPONENT INSPECTION 36

Brake Master Cylinder Reservoir 37

BRAKE ROTOR INSPECTION 38

Rotor Visual Inspection 38

Rotor Runout 40

Rotor Thickness and Thickness Variation 41

BRAKE DRUM INSPECTION 42

Visual Inspection 42

Drum Diameter 43

Barrel Shape Drums 44

Out-of-Round Drums 44

Eccentric Drums 45

Bell-Mouth 45

Tapered Drum 46

DISC BRAKE PAD SERVICE 47

Disc Brake Pad Replacement 50

DRUM BRAKE INSPECTION AND LINING REPLACEMENT 52

DRUM BRAKE LINING SERVICE 53

Drum Brake Component Disassembly 54

Drum Brake Component Reassembly 55

PARKING BRAKE SERVICE 56

Linkage Inspection and Test 56

Rear Drum Brake Parking Brakes 56

Caliper Integrated Parking Brakes 58

MASTER CYLINDER 62

Bench Bleeding a Master Cylinder 63

Installing a Master Cylinder 63

BRAKE FLUID 64

BRAKE SYSTEM BLEEDING 65

Manual Bleeding 66

Pressure Bleeding 67

Gravity Bleeding 67

Vacuum Bleeding 68

BRAKE LINES AND HOSES 69

Metal Brake Lines 70

Brake Hoses 71

LESSON TWO DEMONSTRATION 1: BRAKE INSPECTION 73

DEMONSTRATION 2: MACHINING 77

BRAKE ROUGHNESS — CAUSES 78

Lateral Runout 78

Disc Thickness Variation 79

Lining Material Transfer 80

Rotor Corrosion 80

BRAKE ROUGHNESS — REPAIR 81

COMMON MACHINING PRACTICES FOR ROTORS 89

COMMON MACHINING PRACTICES FOR DRUMS 89

ROTUNDA PRO-CUT ON-CAR BRAKE LATHE (201-00002) 90

Brake Lathe Set-up 90

Attach Lathe To Mount Adapter 93

Compensate For Lathe Runout 94

Lathe Operation 98

On-Car Lathe Summary 102

LESSON TWO WORKSTATIONS 103

WORKSTATION 1 104

WORKSTATION 2 106

WORKSTATION 3 108

WORKSTATION 4 110

GLOSSARY Glossary - 1

INTRODUCTION

Curriculum Goals

The goals of this curriculum are to provide:

First Time On Time” repairs

Brake Systems Diagnosis and Repair Instructor-Led Course Description

This is the first instructor-led course in the Brakes Curriculum It is a two-day course facilitated by an instructor.This course is designed to provide hands-on opportunities for technicians to learn and improve their skills usingtools and equipment; and to apply knowledge learned in previous curriculum courses

Course Objective

Given the information presented in the Ford Brake Systems Diagnosis and Repair course, the necessary serviceinformation and tools, technicians will be able to perform accurate, timely, cost-effective diagnosis and repair ofbrake systems on Ford Motor Company vehicles

The Ford Brakes Service Technician Speciality Training (STST) Curriculum consists of seven courses related tobrake system diagnosis and service Each course in the curriculum is a “building block” for the next course in thecurriculum

This curriculum is designed for technicians who want to learn the methods and techniques to properly diagnoseand service brake systems and components

FORD BRAKES SERVICE TECHNICIAN SPECIALITY TRAINING (STST) CURRICULUM Courses of The Ford Brakes Service Technician Speciality Training (STST) Curriculum

Course Prerequisites

All students must have completed the first three courses in the curriculum prior to enrolling in this course dents who do not show passing credit in their STARS planners for the previous courses should not be admitted tothis class Their presence will slow down the course flow, as well as monopolize valuable instructor time

Evaluation

Each technician attending this course will be required to pass a combination hands-on/written evaluation This will

be administered on the afternoon of the second day The hands-on evaluation is a pass/fail type

In order to pass the course, you must demonstrate acceptable skills at the evaluated hands-on exercises AND youmust answer at least 80% of the written post test questions correctly

Student Guide

The Student Guide contains the worksheets used at the workstations for each of the two days You must completeeach worksheet

IMPORTANT: Actively participate in exercise reviews This is your opportunity to ask questions and clear up any

areas that you may not fully understand

Service Standards

Mission Statement

All dealership personnel will treat every customer as a potential lifetime purchaser, communicating a professionalimage that embraces honesty and concern for customer wants and needs

Dealer-to-Customer Service Standards

Standard 4

Vehicles Serviced Right on the First Visit:

The technician is the most important player when it comes to Standard 4.

“Fix it Right the First Time, on Time”

Why:

Customers tell us “Fixing It Right the First Time, On Time” is one of the top reasons they would decide to return

to a dealer to buy a vehicle and get their vehicles serviced

Technician Training

It is our goal to help the technician acquire all of the skills and knowledge necessary to “Fix It Right the FirstTime, On Time.” We refer to this as “competency.”

Technician’s Role

The technician’s role is to acquire the skills and knowledge for competency in your specialty via:

NOTES

NOTES

REVIEW

PREREQUISITE REVIEW

Introduction

This course begins with a review of the content covered in the prerequisite web-based courses The review isdesigned to help you recall the key points and basic concepts of these courses Comprehension of these key pointsand concepts is essential to being successful in this course

Directions: Select the best answer for the questions listed on the following pages.

1 Which of the following is an example of kinetic energy?

A A vehicle in motion

B A motionless internal combustion engine

C A vehicle’s braking system

D A starter motor’s magnetic field

2 A braking system stops a vehicle by changing the vehicle’s into

A Kinetic energy, Potential energy

B Kinetic energy, Heat energy

C Potential energy, Heat energy

D Heat energy, Kinetic energy

3 The rate at which a vehicle can convert kinetic energy into heat energy is the:

D All of the above

5 During vehicle braking, weight transfer requires that:

A The rear brakes handle 60-70% of the braking

B The front brakes handle 30-40% of the braking

6 Technician A says that to increase the amount of leverage created by a brake pedal, the connection to themaster cylinder should be placed as close as possible to the pivot point Technician B says that placing theconnection to the master cylinder as close as possible to the pivot point will also increase the amount of brakepedal travel when the brake is applied Who is right?

A Technician A

B Technician B

C Both Technician A and B

D Neither Technician A or B

7 Which of the following is a characteristic of a basic hydraulic system?

A Liquid in a confined space will compress

B Pressure applied to a liquid in a confined space will be transferred equally in all directions

C Air in a confined space will not compress

D Pressure applied to a liquid in a confined space will be transferred in the direction of flow

8 In a basic hydraulic system, if a small piston acts upon a larger piston the force of the larger piston will

_ and the distance it will travel will

C It is purple in color and readily absorbs moisture

D It must meet the minimum standards which are set by SAE

10 Which of the following occurs as the amount of moisture in brake fluid increases?

11 A diagonally split braking system refers to a system that is a :

A dual master cylinder system which is divided front and rear

B dual master cylinder system which has each front brake connected to the opposite rear brake

C single master cylinder which is divided from side to side

D None of the above are correct

12 Technician A says that fluid pressure from the master cylinder pressure chamber creates hydraulic pressure toapply the brakes Technician B says that when the brakes are released, the piston cup deflects allowing fluid tomove from the secondary area into the pressure chamber Who is right?

A Technician A

B Technician B

C Both Technician A and B

D Neither Technician A or B

13 Which of the following is true when comparing drum brakes to disc brakes?

A Drum brakes dissipate heat more effectively than disc brakes

B Drum brakes apply braking force slower than disc brakes

C Drum brakes usually weigh less than disc brakes

D Drum brakes disperse water more effectively than disc brakes

14 Which component is used to return the disc brake piston into the caliper bore?

A Piston seal

B Return spring

C Vacuum

D Hydraulic

15 What advantage do internally vented type rotors provide over solid rotors?

A Decreased centrifugal force

B Decreased rotor weight

C Increased heat dissipation

D Increased braking surface

16 How is the parking brake activated on rear wheel disc brakes (on vehicles without drum in rotor parkingbrakes)?

A By placing small balls into the indentations on the operating shaft

B By manually forcing brake fluid into the caliper bore

C By turning the thrust screw through electromotive force

D By moving small balls out of the indentations on the operating shaft

17 Technician A says that on leading-trailing shoe brake systems the leading shoe performs almost all of thebraking Technician B says that leading-trailing type drum brakes have an anchor point at the top of thebacking plate Who is right?

A One-shot adjusting mechanism

B Leading-trailing incremental self-adjuster

C Duo-servo incremental self-adjuster

D Non of the above are correct

21 Under which of the following conditions is a vacuum brake booster vacuum-suspended?

A engine running, brakes applied

B engine running, brakes released

C engine off, brakes applied

D All of the above are correct

22 When the vacuum port is closed and the atmospheric port is open, in what position is the brake booster?

D None of the above are correct

24 Technician A says that the power steering pump provides boost pressure on the hydro-boost system cian B says that the hydro-boost system has an accumulator to provide supplemental brake assist in the event

Techni-of a boost pressure loss Who is right?

A Technician A

B Technician B

C Both Technician A and B

D Neither Technician A or B

25 Which of the following safety warnings must be followed when handling asbestos dust?

A Compressed air and/or brushes must not be used to clean asbestos from brake components

B Asbestos dust must be placed in a sealed and labeled bag for disposal

C A high efficiency cartridge or air line respirator must be worn to avoid breathing asbestos dust

D All of the above answers are correct

NOTES

NOTES

vehicle system, subsystem, or component

BRAKE SYSTEM

DIAGNOSIS AND

TESTING

MODULE 1

DIAGNOSIS AND TESTING

Symptom-to-System-to-Component-to-Cause Diagnostic Procedure

In order to properly diagnose an automotive concern, a logical diagnostic procedure must be used Ford MotorCompany workshop manuals are organized to guide the technician from the customer concern to the cause of theconcern using the symptom-to-system-to-component-to-cause diagnostic procedure

Because brakes wear at different rates based on operating conditions, it is important to follow this strategy all theway down to the cause of a problem You do not want to fix a symptom, such as a worn brake pad, only to over-look the cause, such as a corroded caliper slide pin

Customer Concern

The first step in the diagnosis of a customer concern is to make sure that the customer concern (symptom) isclearly defined and verified This means that the technician may need to reproduce the concern by operating thevehicle under the same circumstances in which the customer states that the concern occurs This is usually the firststep listed in the Diagnosis and Testing section of the workshop manual Once the concern is verified, the techni-cian can use the Symptom Charts to determine the cause of the concern

In most cases, the Symptom Charts will guide the technician to a pinpoint test that will provide a logical sequence

of subsystem and component tests to help determine the cause of the customer concern

Removal and Installation

Once the cause of the customer concern is determined, the technician may have to replace a component Theproper procedure for component replacement can be found in the Removal and Installation Section

Disassembly and Assembly

Some foundation brake components can be repaired instead of being replaced The proper procedures for nent repair can be found in the Disassembly and Assembly Section

compo-Other Component and Subsystem Tests

The workshop manual cannot include every possible test required to diagnose every possible customer concern.This means that the technician must posses certain knowledge and skills regarding automotive systems in order toproperly diagnose and repair them Ford Motor Company training programs are designed to give you the knowl-edge and skill required to properly diagnose and repair customer concerns

PRELIMINARY BRAKE SYSTEM CHECKS

Proper and consistent inspection of brake systems is crucial to improve your speed and your accuracy in thediagnosis of existing brake problems When a vehicle is brought in with a brake concern there are certain stepsthat should be followed These include:

Know and understand the customers concern – Be sure that the problem that you are going to diagnose is

the one that the customer is concerned with If the customer concern is a noise in the rear of the vehicle, andyou repair a rattle in the front, it is not likely that the customer will be satisfied (even though the rattle in thefront may have needed repairing)

Check brake fluid level and condition – (Be sure to wipe the top of the master cylinder before removing the

cap) This step can give you a good indication of the condition of the hydraulic system Look at the fluid level.Low fluid may indicate a hydraulic leak Because the fluid level in the master cylinder drops as the pistonsmove out to compensate for brake lining wear, low fluid level could indicate excessive wear of the brakelinings Also look for fluid contamination, which may be indicated by discoloration (see Brake Fluid LevelTest) While under the hood check for disconnected vacuum lines (for correct vacuum hose routing refer toGroup 00 in the vehicle's service manual, or to the Vehicle Emission schematic in the engine compartment) Ifthe vehicle has a hydraulic boost system, inspect for kinked or leaking hydraulic lines or a loose drive belt tothe hydraulic pump

Verify the concern by operating the vehicle – This step allows you to verify that a concern exists and

experience the malfunction Occasionally a customer that is unfamiliar with the vehicle will misinterpretnormal operation of the vehicle Also try to determine when the concern occurs (vehicle cold, hot, heavilyloaded, towing a trailer etc.) Inspect all hoses and connections prior to performing the operational check Allunused vacuum connectors should be capped Make sure hoses and their connections are correctly secured and

in good condition with no holes, soft or collapsed areas Check the parking brake for proper operation

Check vehicle repair history, TSB's and OASIS – Determine if the vehicle has a history of brake concerns,

or if any TSB's or OASIS messages pertain to the vehicle's condition

Perform a visual inspection – Place the vehicle on a hoist and check for leaking or damaged brake lines.

Look for steering or suspension problems that may duplicate a brake concern Inspect junction blocks and linefittings for leaks Note if heavy duty trailering devices are installed that may indicate heavy trailering Inspectfor load leveling devices, which if installed, may defeat operation of the height-sensing brake-proportioningvalve Check the condition, adjustment, and tension of the parking brake cable

Remove the wheels and inspect the brake assemblies – This check will let you determine the condition of

the individual brake assemblies Look for leaking calipers and wheel cylinders, worn out pads or shoes, anddamaged drums and rotors Also note excessive corrosion which could prevent smooth operation of the brakesystem

Reading through the above preliminary checks you can see that what you should be looking for are clues to thecause of the concern Many times the results of preliminary checks will point you towards the cause of a brake

Hydraulic leaks can be external or internal When external leaks occur, the system loses pressure External leaksare caused by cracks or breaks in the master cylinder reservoir, loose system connections, damaged seals, orleaking brake lines or hoses The external leak test should be performed if the pedal is low, the BRAKE warninglamp is on, and if the reservoir fluid level is low or empty.

possible external leak exists

may be washed away

Master Cylinder Non-Pressure External Leak Test

If the reservoir empties, but there is no external pressure leak, the problem may be an external leak from themaster cylinder Brake fluid loss can be caused by:

External Leak Test

Common External Leak Points

Air Entrapment Test

A low pedal, bottoming pedal, or a pedal that feels spongy may indicate the presence of air trapped in the lic system

hydrau-CAUTION: This test may cause brake fluid bubbling or spraying out of the master cylinder Cover the master cylinder reservoirs with clear plastic wrap or another suitable cover to keep brake fluid off the paint.

A geyser or a squirt in either reservoir indicates that air has been trapped in the system Pumping the brakescompresses the air; when the brake is released, the compressed air pushes the brake fluid back through the lines,causing the fluid to squirt The remedy for this condition is to bleed the affected system(s) If the squirt onlyoccurs in one reservoir, the other system does not need to be bled

Another possible cause of the squirt or geyser is an out-of-adjustment condition on the rear brake If the pedal islow, check the adjustment of the rear brakes

Master Cylinder Fluid Bypass Test (Internal Leak Test)

If no sign of external leakage exists, but the brake warning lamp comes ON while the brakes are being applied, themaster cylinder may be bypassing fluid (losing pressure internally) Perform the following test to determine ifbrake fluid is bypassing the master cylinder piston cups:

full

released, the brake fluid is bypassing the pistons The fluid level rising in one reservoir and falling in the other

as the brake pedal is applied can also indicates that fluid is bypassing the piston cups

leakage exists, the brake fluid is bypassing the master cylinder piston cups

Master Cylinder Compensator Port Test

The master cylinder compensating port test is used to check for open compensating ports in the master cylinder.This test should be performed if you suspect that the brake master cylinder is failing to return to the fully releasedposition, leaving the brakes partially applied The symptoms of a vehicle with partially applied brakes includeoverheating and premature lining wear Perform the following test to determine if the master cylinder compensat-ing ports are open:

appear in the reservoirs as the brakes are applied

6.35 mm (1/4 in) and pull the master cylinder away from the power booster Hold the master cylinder in thisposition and repeat the previous step

Typical Hydro-Boost Master Cylinder (2002 F-250 Shown)

Before testing hydro-boost components, check the engine and power steering for proper operation If brake

application and steering require excessive effort, the cause is likely related to power steering fluid pressure anddelivery

Perform the following preliminary checks before testing the Hydro-Boost system:

flush and refill the system before proceeding

wheel from stop-to-stop while you look for leaks The high pressure developed should force fluid from smallleaks Possible leak points are lines and hoses, power steering pump, steering gear, or the hydro-boost unit.Repair all leaks

Hydro-Boost System Inspection

Accumulator Test:

applica-tions

Hydro-Boost Air Bleeding

If a hydro-boost or power steering component is removed for service, the power steering hydraulic system must bebled of air Air can also enter the system if the fluid level drops below the minimum specified level in the reservoir.When checking power steering fluid, look for signs of air Aerated fluid looks milky

5 minutes

stabilizes at the full mark

minutes

Hydro-boost Unit on Bench

Hydro-Boost System Inspection (Continued)

COMMON CUSTOMER CONCERNS

anti-lock brake system (ABS)

Abnormal Roughness

Abnormal brake roughness may be caused by:

Brake Roughness Diagnosis

To find the source of brake roughness, perform the following checks:

WARNING: FORD MOTOR COMPANY ADVISES TO ALWAYS DETERMINE IF BRAKE

OPERATION IS ADEQUATE PRIOR TO OPERATING THE VEHICLE PRIOR TO DRIVING A CUSTOMER'S VEHICLE ON A ROAD TEST EVALUATION, THE BRAKES SHOULD BE

TESTED AT A LOW SPEED TO VERIFY THE VEHICLE IS SAFE TO DRIVE ON A PUBLIC ROAD OBSERVE ALL TRAFFIC LAWS, SPEED LIMITS AND LOCAL ROAD CONDITIONS.

Select a road test route:

road which changes braking performance

This road test procedure should be followed because a concern may not be evident on a brake system that is cool,but is very apparent when the brake system is warm

1 Accelerate the vehicle to highway speed

2 When safe, shift to neutral to check for wheel or driveline imbalance Let the vehicle coast without applyingthe brake and note any vibrations in the steering wheel or seat

3 Warm the brakes to normal operating temperature

4 Lightly apply the brake pedal and slow the vehicle from highway speed to 30 mph

Brake Roughness Diagnosis (continued)

5 If no brake roughness is experienced, repeat the procedure three times

which can be mistaken for brake roughness

CAUTION: Do not perform the following procedure on vehicles equipped with push-to-release

parking brake systems unless equipped with a manual release handle During application of parking brakes the brake lamps do not activate.

CAUTION: Do not perform the following procedure on vehicles equipped with rear disc brakes that utilize drum brake shoes inside the rotor hat to engage the parking brake This can severely damage the parking brake Applying the parking brake on this type of system does not test the rear service brakes and may cause the rear wheels to lockup on some vehicles.

NOTE: Isolation of brake roughness to the front or rear brakes will reduce repeat repairs.

6 If brake roughness was experienced, bring the vehicle back to the speed at which roughness occurs and lightlyapply the parking brake one time with the release activated to prevent rear wheel lock up

if the runout is caused by the rotor or the hub, and repair as necessary

NOTE: This procedure requires the use of a micrometer that can measure in 0.01mm or 0.001 in increments.

Brake Pedal Low or Feels Spongy

A brake pedal is considered to be spongy when the pedal does not provide a firm, even feel as the driver appliesthe brakes A spongy brake pedal may be caused by:

Brake Pedal Low or Feels Spongy Diagnosis

To find the source of a spongy brake pedal, perform the following tests:

points

Pedal Eases Down Slowly

A pedal that eases down slowly towards the floor, as firm even pressure is applied, indicates that the system islosing pressure

A pedal that eases down toward the floor may be caused by:

Pedal Eases Down Slowly Diagnosis

To diagnose a pedal eases down slowly concern, perform the following tests:

a possible leaking outlet/dump valve in the ABS EHCU

Pedal Goes Down Fast/Excessive Pedal Travel

WARNING: IF THE BRAKE PEDAL GOES DOWN FAST, IT MAY INDICATE AN EXTREME PRESSURE LOSS IN THE BRAKE HYDRAULIC SYSTEM OR BRAKE SHOES OR CALIPERS THAT ARE SEVERELY OUT OF ADJUSTMENT CHECK FOR PROPER OPERATION OF THE VEHICLE BRAKES BEFORE OPERATING THE VEHICLE.

A pedal that goes down too fast could be caused by:

runout or worn bearings

Pedal Goes Down Fast/Excessive Pedal Travel Diagnosis

To find the cause of a pedal that goes down fast, perform the following tests:

this book

a possible leaking outlet/dump valve in the ABS EHCU

Brakes Pull or Drift

If the vehicle does not travel in a straight line when the brakes are applied, it indicates uneven braking at one ormore wheels

Brake pull or drift can be caused by:

Brake pull or drift can also be caused by the following non-brake concerns:

Brakes Pull or Drift Diagnosis

To find the cause of brake pull or drift, perform the following tests:

WARNING: IF THE BRAKE WARNING INDICATOR IS ALWAYS ON, A SEVERE BRAKE CONCERN MAY EXIST CHECK FOR PROPER OPERATION OF THE VEHICLE BRAKES BEFORE OPERATING THE VEHICLE.

The indicator could be illuminated by:

Brake Warning Indicator Always On Diagnosis

To determine the cause of an illuminated brake warning indicator, perform the following checks:

Red Brake Warning Indicator Always On

Illuminated Red Brake Warning Indicator Lamp

Brakes Lock Up (Grabbing)

An anti-lock brake system (ABS) prevents the wheels from locking up If the customer states that the brakes lock

up and the vehicle is equipped with ABS, it is possible that the anti-lock brakes are not operating properly

Brake lock up may be caused by:

Brakes Lock Up Diagnosis

To determine the cause of grabbing brakes, perform the following tests:

Excessive Brake Pedal Effort

Excessive brake pedal effort is characterized by a very stiff brake pedal and increased stopping distances

Excessive brake pedal effort can be caused by:

lines, a faulty booster check valve, low engine vacuum, or a faulty vacuum pump (diesel engines)

accessory belt, or a faulty power steering pump

Excessive Brake Pedal Effort Diagnosis

To determine the cause of excessive brake pedal effort, perform the following tests: