[ Pobierz całość w formacie PDF ]
Z
BRAKES 5 - 1
BRAKES
CONTENTS
page
page
ANTILOCK BRAKE OPERATION ............
ANTILOCK BRAKE SYSTEM DIAGNOSIS ......
ANTILOCK ELECTRONIC COMPONENT
SERVICE .............................
BRAKE ADJUSTMENTS-FLUID LEVEL-BRAKE
BLEEDING ...........................
BRAKE PEDAL AND SWITCH SERVICE ......
DISC BRAKE SERVICE ...................
DRUM BRAKE SERVICE ..................
GENERAL INFORMATION ..................
MASTER CYLINDER—HCU—COMBINATION
VALVE—BRAKELINES ..................
PARKING BRAKE SERVICE ................
POWER BRAKE BOOSTER SERVICE ........
SERVICE BRAKE COMPONENT DIAGNOSIS . . .
SPECIFICATIONS .......................
GENERAL INFORMATION
INDEX
page
page
Antilock Brake System (ABS) ................
Brake Fluid/Lubricants/Cleaning Solvents ........
Brake Safety Precautions ....................
Service Brake Components ..................
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.
²
electronic control unit (ECU)
²
wheel speed sensors and axle shaft tone rings
 5 - 2 BRAKES
Z
²
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.
²
tandem master cylinder with central valves
²
vacuum power brake booster
²
pedal travel sensor
²
acceleration switch
²
main relay and pump motor relay
²
antilock warning light
²
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.
 Z
BRAKES 5 - 3
ANTILOCK BRAKE SYSTEM DIAGNOSIS
INDEX
page
page
ABS Fault Diagnosis Chart ..................
ABS Warning Light Display .................
Antilock Control Unit (ECU) Diagnosis ..........
Brake Warning Light Operation ...............
Diagnosis Procedure ......................
Hydraulic Control Unit (HCU) Diagnosis .........
Loss of Sensor Input ......................
Operating Sound Levels ....................
Rear Speed Sensor Air Gap ..................
Steering Response .......................
Vehicle Response in Antilock Mode ............
Wheel/Tire Size and Input Signals .............
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
Z
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
 Z
BRAKES 5 - 5
SERVICE BRAKE COMPONENT DIAGNOSIS
INDEX
page
page
Component Inspection .....................
Diagnosing Brake Problems .................
Diagnosis Procedures .....................
General Information .......................
Power Brake Booster Check Valve Test .........
Power Brake Booster Vacuum Test .............
GENERAL INFORMATION
The diagnosis information in this section covers the
vehicle service brake components which include:
²
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.
(c) Remember that fluid level in front disc brake
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.
²
disc brakeshoes
²
drum brake wheel cylinders
²
drum brakeshoes and brake drums
²
drum brake support plates
²
parking brake mechanism
²
master cylinder/combination valve
²
vacuum power brake booster
²
brake pedal and brakelight switch
²
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
  [ Pobierz całość w formacie PDF ]