93ZJ-Secc-5-Brakes.pdf

BRAKES 5 - 1

BRAKES

CONTENTS

page

ANTILOCK BRAKE OPERATION ............ 14

ANTILOCK BRAKE SYSTEM DIAGNOSIS ...... 3

ANTILOCK ELECTRONIC COMPONENT

SERVICE ............................. 28

BRAKE ADJUSTMENTS-FLUID LEVEL-BRAKE

BLEEDING ........................... 10

BRAKE PEDAL AND SWITCH SERVICE ...... 48

DISC BRAKE SERVICE ................... 33

DRUM BRAKE SERVICE .................. 41

GENERAL INFORMATION .................. 1

MASTER CYLINDER—HCU—COMBINATION

VALVE—BRAKELINES .................. 21

PARKING BRAKE SERVICE ................ 44

POWER BRAKE BOOSTER SERVICE ........ 26

SERVICE BRAKE COMPONENT DIAGNOSIS . . . 5

SPECIFICATIONS ....................... 50

GENERAL INFORMATION

INDEX

page

Antilock Brake System (ABS) ................ . 1

Brake Fluid/Lubricants/Cleaning Solvents ........ 2

Brake Safety Precautions .................... 2

Service Brake Components .................. 1

SERVICE BRAKE COMPONENTS

The red light alerts the driver if a pressure differen-

tial exists between the front and rear hydraulic sys-

tems. The red light also alerts the driver when the

parking brakes are applied. The light is located in the

instrument cluster.

The amber antilock warning light is also located in

the instrument cluster. The light illuminates only

when an antilock system fault occurs.

WHEEL BRAKE UNITS

Front disc brakes and rear drum brakes are used on

all models. The front disc brakes consist of single

piston calipers and ventilated rotors.

Drum type rear brakes are used on all models.

Brake size is 254 x 44 mm (10.0 x 1.75 in.). The

assemblies are dual shoe, internal expanding units

with a single wheel cylinder. A self adjusting mecha-

nism is used for all applications.

The parking brakes are operated by a hand lever assem-

bly. The lever assembly is connected to the rear brake

trailing shoes by cables. Parking brake adjustment is con-

trolled by a cable tensioner attached to the front cable.

BRAKELINING MATERIAL

Factory installed front and rear brakelining on

Grand Cherokee models, is made from organic mate-

rials combined with metallic particles. The brakelin-

ing material does not contain asbestos.

ANTILOCK BRAKE SYSTEM (ABS)

An antilock brake system (ABS) is standard equipment

on Jeep Grand Cherokee models. The antilock system is an

electronically operated all wheel brake control system. The

system is designed to retard wheel lockup during periods of

high wheel slip when braking.

The antilock electronic control system is separate

from other electrical circuits in the vehicle. A spe-

cially programmed electronic control unit (ECU) is

used to operate the system components.

Antilock system components consist of:

VACUUM/HYDRAULIC COMPONENTS

A vacuum operated, 200 mm (7.8 in.), dual dia-

phragm power brake booster is used on all models. A

center feed, dual reservoir master cylinder and a

combination proportioning valve and pressure differ-

ential switch are used on all models. The proportion-

ing valve is a fixed rate type.

BRAKE WARNING LIGHTS

All models are equipped with two brake warning

lights. A red light is used for the service brake sys-

tem. An amber light is used for the antilock system.

electronic control unit (ECU)

wheel speed sensors and axle shaft tone rings

5 - 2 BRAKES

hydraulic control unit (HCU)

Use Mopar multi-mileage grease to lubricate drum

brake pivot pins and rear brakeshoe contact points on

the support plates. Use GE 661 or Dow 111 silicone

grease, or multi-mileage grease on caliper bushings

and slide pins.

Use fresh brake fluid or Mopar brake cleaner to

clean or flush brake system components. These are

the only cleaning materials recommended.

tandem master cylinder with central valves

vacuum power brake booster

pedal travel sensor

acceleration switch

main relay and pump motor relay

antilock warning light

pump motor sensor

CAUTION: Never use gasoline, kerosene, alcohol,

motor oil, transmission fluid, or any fluid containing

mineral oil to clean the system components. These

fluids damage rubber cups and seals. If system

contamination is suspected, check the fluid for dirt,

discoloration, or separation into distinct layers.

Drain and flush the system with new brake fluid if

contamination is suspected.

BRAKE SAFETY PRECAUTIONS

Fig. 1 AntiLock Brake System Basic Layout

WARNING: ALTHOUGH FACTORY INSTALLED

BRAKELINING ON GRAND CHEROKEE MODELS IS

MADE FROM ASBESTOS FREE MATERIALS, SOME

AFTER MARKET BRAKELINING MAY CONTAIN AS-

BESTOS. THIS SHOULD BE TAKEN INTO ACCOUNT

WHEN SERVICING A VEHICLE WITH PRIOR BRAKE

SERVICE. WEAR A RESPIRATOR WHEN CLEANING

BRAKE COMPONENTS AS ASBESTOS FIBERS CAN

BE A HEALTH HAZARD. NEVER CLEAN WHEEL

BRAKE COMPONENTS WITH COMPRESSED AIR.

USE A VACUUM CLEANER SPECIFICALLY DE-

SIGNED FOR REMOVING BRAKE DUST. IF A

VACUUM CLEANER IS NOT AVAILABLE, CLEAN

THE PARTS WITH WATER DAMPENED SHOP RAGS.

DO NOT CREATE DUST BY SANDING BRAKELIN-

ING. DISPOSE OF ALL DUST AND DIRT SUSPECTED

OF CONTAINING ASBESTOS FIBERS IN SEALED

BAGS OR CONTAINERS. FOLLOW ALL RECOM-

MENDED SAFETY PRACTICES PRESCRIBED BY

THE OCCUPATIONAL SAFETY AND HEALTH ADMIN-

ISTRATION (OSHA) AND THE ENVIRONMENTAL

PROTECTION AGENCY (EPA), FOR HANDLING AND

DISPOSAL OF PRODUCTS CONTAINING ASBES-

TOS.

BRAKE FLUID/LUBRICANTS/CLEANING SOLVENTS

Recommended brake fluid is Mopar brake fluid or

equivalent, meeting SAE J1703 and DOT 3 stan-

dards.

BRAKES 5 - 3

ANTILOCK BRAKE SYSTEM DIAGNOSIS

INDEX

page

ABS Fault Diagnosis Chart .................. . 4

ABS Warning Light Display ................. . 3

Antilock Control Unit (ECU) Diagnosis .......... 4

Brake Warning Light Operation ............... . 4

Diagnosis Procedure ...................... . 3

Hydraulic Control Unit (HCU) Diagnosis ......... 4

Loss of Sensor Input ...................... . 3

Operating Sound Levels .................... . 3

Rear Speed Sensor Air Gap .................. 3

Steering Response ....................... . 3

Vehicle Response in Antilock Mode ............ 3

Wheel/Tire Size and Input Signals ............. 3

DIAGNOSIS PROCEDURE

Antilock system diagnosis involves three basic

steps. First is observation of the warning light dis-

play. Second is a visual examination for low fluid

level, leaks, or obvious damage to system components

or wires. The third step involves using the DRB II

scan tool to identify a faulty component.

The visual examination requires a check of reser-

voir fluid level and all system components. Things to

look for are leaks, loose connections, or obvious com-

ponent damage.

The final diagnosis step involves using the DRB II

scan tool to determine the specific circuit or compo-

nent at fault. The tester is connected to the ABS

diagnostic connector in the passenger compartment.

The ABS diagnostic connector is inside the

vehicle. It is located at the forward end of the

console, just above the accelerator pedal and

under the carpet. Access to the connector only

requires that the carpeting be moved aside.

Refer to the DRB II scan tool manual for test proce-

dures. Also refer to the ABS Fault Diagnosis charts at

the end of this section for additional diagnosis infor-

mation.

Initial faults should be cleared and the vehicle road

tested to reset any faults that remain in the system.

Faults can be cleared with the scan tool.

OPERATING SOUND LEVELS

The hydraulic control unit pump and solenoid

valves may produce some sound as they cycle on and

off. This is a normal condition and should not be

mistaken for faulty operation. Under most conditions,

pump and solenoid valve operating sounds should not

be audible.

VEHICLE RESPONSE IN ANTILOCK MODE

During antilock braking, the hydraulic control unit

solenoid valves cycle rapidly in response to antilock

electronic control unit inputs.

The driver will experience a slight pulsing sensa-

tion within the vehicle as the solenoids decrease,

hold, or increase pressure as needed. Brake pedal

pulsing will also be noted and is a normal condition

when the solenoids are cycling.

The pulsing sensation occurs as the solenoids cycle

during antilock mode braking. A slight pulse in the

brake pedal may also be noted during the dynamic

self check part of system initialization.

STEERING RESPONSE

A modest amount of steering input is required dur-

ing extremely high deceleration braking, or when

braking on differing traction surfaces. An example of

differing traction surfaces would be when the left side

wheels are on ice and the right side wheels are on dry

pavement.

REAR SPEED SENSOR AIR GAP

The front wheel sensors are fixed and cannot be

adjusted. Only the rear sensor air gap is adjustable.

Air gap must be set with a brass feeler gauge.

Correct air gap is important to proper signal gen-

eration. An air gap that is too large may cause com-

plete loss of sensor input. Or, a gap that is too small

could produce a false input signal, or damaging con-

tact between the sensor and tone ring.

LOSS OF SENSOR INPUT

Sensor malfunctions will most likely be due to loose

connections, damaged sensor wires, incorrect rear

sensor air gap, or a malfunctioning sensor. Additional

causes of sensor faults would be sensor and tone ring

misalignment or damage.

ABS WARNING LIGHT DISPLAY

WHEEL/TIRE SIZE AND INPUT SIGNALS

Antilock system operation is dependant on accurate

signals from the wheel speed sensors. Ideally, the

vehicle wheels and tires should all be the same size

and type. However, the Jeep ABS system is designed

to function with a compact spare tire installed.

ABS LIGHT ILLUMINATES AT STARTUP

The amber antilock light illuminates at startup as

part of the system self check feature. The light illumi-

nates for 2-3 seconds then goes off as part of the

normal self check routine.

5 - 4 BRAKES

ABS LIGHT REMAINS ON AFTER STARTUP

An ABS system fault is indicated when the light

remains on after startup. Diagnosis with the DRB II

scan tool will be necessary to determine which ABS

component has malfunctioned.

gram. A failure of the self check program will cause

the immediate illumination of the amber warning

light. The light will also illuminate if a solenoid or

other system component fails during the dynamic

phase of initialization.

If a system malfunction should occur, do not imme-

diately replace the ECU. A blown system fuse, bad

chassis ground, or loss of feed voltage will each cause

a system malfunction similar to an ECU failure.

Never replace the ECU unless diagnosis with the

DRB II scan tool indicates this is necessary.

ABS LIGHT ILLUMINATES DURING BRAKE STOP

A system fault such as loss of speed sensor signal or

solenoid failure, will cause the amber warning light to

illuminate. The most effective procedure here is to

check for obvious damage first. Then check the elec-

tronic components with the DRB II scan tool.

BRAKE WARNING LIGHT OPERATION

The red brake warning light and the amber ABS

light operate independently. If the red light remains

on after startup or illuminates during a brake stop,

refer to the standard brake system diagnosis section.

HYDRAULIC CONTROL UNIT (HCU) DIAGNOSIS

The HCU pump and motor and solenoid valve body

are services only as an assembly. The HCU assembly

should not be replaced unless a fault has actually

been confirmed. Verify fault conditions with the DRB

II scan tool before proceeding with repair.

ANTILOCK CONTROL UNIT (ECU) DIAGNOSIS

The antilock, electronic control unit (ECU) controls

all phases of antilock system operation. It also differ-

entiates between normal and antilock mode braking.

The ECU monitors and processes the signals gener-

ated from all of the system sensors at all times.

The ECU program includes a self check routine that

tests each of the system components. The self check

occurs during both phases of the initialization pro-

ABS FAULT DIAGNOSIS CHART

The diagnosis chart describes potential antilock sys-

tem fault conditions. The most probable cause for

each fault condition is also provided. The causes of a

fault condition are listed in order of probability start-

ing with the most likely cause of a fault.

Use the chart as a guide to repair after initial

diagnosis with the DRB II scan tool.

POTENTIAL ABS FAULT CONDITIONS AND CAUSES

BRAKES 5 - 5

SERVICE BRAKE COMPONENT DIAGNOSIS

INDEX

page

Component Inspection ..................... . 6

Diagnosing Brake Problems ................. . 6

Diagnosis Procedures ..................... . 5

General Information ....................... . 5

Power Brake Booster Check Valve Test ......... 8

Power Brake Booster Vacuum Test ............. 9

GENERAL INFORMATION

The diagnosis information in this section covers the

vehicle service brake components which include:

disc brake calipers

vehicle and listen for noise that might be caused by

loose, worn, or damaged suspension or steering compo-

nents.

(4) Inspect brake fluid level and condition.

(a) Fluid level should be at the MAX level indica-

tor mark on master cylinder reservoir.

(b) Check fluid condition. Fluid should be reason-

ably clear and free of foreign material. Note that

brake fluid tends to darken over time. This is

normal and should not be mistaken for con-

tamination. If fluid is reasonably clear and

free of foreign material, it is OK.

reservoir will decrease slightly as normal brakelin-

ing wear occurs. However, if fluid level is abnor-

mally low, look for leaks at calipers, wheel cylin-

ders, brakelines and master cylinder.

(d) If fluid is highly discolored, or appears to

contain foreign material, drain out a sample with a

clean suction gun. Pour sample in a glass container

and note condition.

(e) If fluid separates into layers, or obviously con-

tains oil or substance other than brake fluid, sys-

tem seals and cups will have to be replaced and

hydraulic system flushed.

(5) Check parking brake operation. Verify free

movement and full release of cables and foot pedal or

hand lever. Also note if vehicle was being operated

with parking brake partially applied.

(6) Check brake pedal operation. Verify that pedal

does not bind and has adequate free play. If pedal

lacks free play, check pedal and power booster for

being loose or for bind condition. Do not road test

until condition is corrected.

(7) If components checked appear OK, road test the

vehicle.

disc brakeshoes

drum brake wheel cylinders

drum brakeshoes and brake drums

drum brake support plates

parking brake mechanism

master cylinder/combination valve

vacuum power brake booster

brake pedal and brakelight switch

brake warning light

DIAGNOSIS PROCEDURES

Service brake component diagnosis involves deter-

mining if the problem is related to a mechanical,

hydraulic or vacuum operated part. A preliminary

check, road testing and component inspection are

needed to determine a problem cause.

Road testing will either verify proper brake opera-

tion or confirm the existence of a problem. Component

inspection will, in most cases, identify the actual part

causing a problem.

The first diagnosis step is the preliminary check.

This involves inspecting fluid level, parking brake

action, wheel and tire condition, checking for obvious

leaks or component damage and testing brake pedal

response. A road test will confirm or deny the exist-

ence of a problem. The final diagnosis procedure in-

volves road test analysis and a visual inspection of

brake components.

PRELIMINARY BRAKE CHECK

(1) If amber antilock light is illuminated, refer to

Antilock Brake System Diagnosis. However, if red

warning light is illuminated, or if neither warning

light is illuminated, continue with diagnosis outlined

in this section.

(2) Check condition of tires and wheels. Damaged

wheels and worn, damaged, or underinflated tires can

cause pull, shudder, tramp and a condition similar to

grab.

(3) If complaint was based on noise when braking,

check suspension components. Jounce front and rear of

ROAD TESTING

(1) If amber warning light is illuminated, problem

is with antilock system component. Refer to Antilock

Brake System Diagnosis.

(2) If red warning light is illuminated, or if neither

warning light is illuminated, make several stops and

note pedal action and brake response.

(3) Check brake pedal response with transmission

in Neutral and engine running. Pedal should remain

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