light JEEP CHEROKEE 1994 Service Owner's Guide

scan tool will be necessary to determine which ABS
component has malfunctioned.
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
electronic components with the DRB II scan tool.
BRAKE WARNING LIGHT DISPLAY
The red brake warning light and the ABS light op-
erate independently. If the red light remains on after
startup or illuminates during a brake stop, refer to
the standard brake system diagnosis section. Either
the parking brakes are applied, or a wheel brake
malfunction has occurred.
ECU DIAGNOSIS
The ECU controls all phases of antilock system op-
eration. It also differentiates between normal and an-
tilock mode braking.
The ECU monitors and processes the signals gen-
erated 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
program. A failure of the self check program will
cause the immediate illumination of the amber warn-
ing 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.
HCU DIAGNOSIS
The HCU pump and motor and solenoid valve body
are serviced 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.
ABS SYSTEM WIRING AND ELECTRICAL CIRCUITS
Location of the ABS fuse (in the fuse panel) is
shown in Figure 1. The engine compartment harness
routing for the ABS components is shown in Figure 2.
ABS FAULT DIAGNOSIS
The fault diagnosis chart provides additional infor-
mation on potential ABS system faults. Use the
chart as a guide when diagnosing a system problem.
Fig. 1 ABS Fuse Location
5 - 4 BRAKESJ

SERVICE BRAKE DIAGNOSIS
INDEX
page page
Component Inspection...................... 8
Diagnosing Parking Brake Problems.......... 10
Diagnosing Service Brake Problems........... 8
Diagnosis Procedures...................... 7
General Information........................ 7Master Cylinder/Power Booster Test.......... 11
Power Booster Check Valve Test............ 11
Power Booster Vacuum Test................ 12
Preliminary Brake Check.................... 7
Road Testing............................ 7
GENERAL INFORMATION
The diagnosis information in this section covers
service brake components which include:
²disc brake calipers
²disc brakeshoes
²drum brake wheel cylinders
²drum brakeshoes and brake drums
²drum brake support plates
²parking brake mechanism
²master cylinder/combination valve
²vacuum power brake booster
²brake pedal and brakelight switch
²brake warning light
DIAGNOSIS PROCEDURES
Service brake diagnosis involves determining if a
problem is related to a mechanical, hydraulic or vac-
uum operated component. A preliminary brake
check, followed by road testing and component in-
spection are needed to determine a problem cause.
Road testing will either verify proper brake opera-
tion or confirm the existence of a problem. Compo-
nent inspection will, in most cases, identify the
actual part responsible for a problem.
The first diagnosis step is the preliminary brake
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 existence of a problem. The final diagnosis
procedure involves road test analysis and a visual in-
spection 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.
(2) Check condition of tires and wheels. Damaged
wheels and worn, damaged, or underinflated tires
can cause pull, shudder, tramp and a condition simi-
lar to grab.
(3) If complaint was based on noise when braking,
check suspension components. Jounce front and rearof vehicle and listen for noise that might be caused
by loose, worn, or damaged suspension or steering
components.
(4) Inspect brake fluid level:
(a) If vehicle has one-piece master cylinder, fluid
level should be to 6 mm (1/4 in.) of reservoir rim. If
vehicle two-piece, removable reservoir, correct level
is to top of indicator rings in reservoir.
(b) On models with ABS brakes, preferred level
is to MAX mark on reservoir. Acceptable level is
between MAX and MIN marks.
(c) Remember that fluid level in the front and
rear reservoir compartments will decrease in pro-
portion to normal lining wear. However, if fluid
level is abnormally low, look for leaks at calipers,
wheel cylinders, brakelines and master cylinder.
(5) Inspect brake fluid condition:
(a) Fluid should be reasonably clear and free of
foreign material.Note that brake fluid tends to
darken over time. This is normal and should
not be mistaken for contamination. If fluid is
clear of foreign material, it is OK.
(b) If fluid is highly discolored, or appears to con-
tain foreign material, drain out a sample with a
clean suction gun. Pour sample in a glass container
and note condition.
(c) If fluid separates into layers, obviously con-
tains oil, or a substance other than brake fluid,
system seals and cups will have to be replaced and
hydraulic system flushed.
(6) 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.
(7) 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 be-
ing loose or for bind condition. Do not road test until
condition is corrected.
(8) If components inspected look OK, road test the
vehicle.
ROAD TESTING
(1) If amber warning light is illuminated, problem
is with antilock system component. Refer to Antilock
Brake System Diagnosis.
JBRAKES 5 - 7

(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
firm under steady foot pressure. If pedal falls away,
problem is either in vacuum booster or master cylin-
der.
(4) During road test, make normal and firm brake
stops in 25-40 mph range. Note faulty brake opera-
tion such as pull, grab, drag, noise, fade, pedal pul-
sation, etc.
(5) Inspect suspect brake components and refer to
problem diagnosis information for causes of various
brake conditions.
COMPONENT INSPECTION
Fluid leak points and dragging brake units can
usually be located without removing any compo-
nents. The area around a leak point will be wet with
fluid. The components at a dragging brake unit
(wheel, tire, rotor) will be quite warm or hot to the
touch.
Other brake problem conditions will require compo-
nent removal for proper inspection. Raise the vehicle
and remove the necessary wheels for better visual ac-
cess.
During component inspection, pay particular atten-
tion to heavily rusted/corroded brake components
(e.g. rotors, caliper pistons, brake return/holddown
springs, support plates, etc.).
Heavy accumulations of rust may be covering se-
vere damage to a brake component. It is wise to re-
move surface rust in order to accurately determine
the depth of rust penetration and damage. Light sur-
face rust is fairly normal and not a major concern (as
long as it is removed). However, heavy rust buildup,
especially on high mileage vehicles may cover struc-
tural damage to such important components as
brakelines, rotors, support plates, and brake boosters.
Refer to the wheel brake service procedures in this
group for more information.
DIAGNOSING SERVICE BRAKE PROBLEMS
BRAKE WARNING LIGHT OPERATION
The red brake warning light will illuminate under
the following conditions:
²for 2-3 seconds at startup as part of normal bulb
check
²parking brakes applied
²low pedal caused by malfunction in front/rear
brake hydraulic circuit (differential switch valve ac-
tuated)
If the red light remains on after startup, first ver-
ify that the parking brakes are fully released. Then
check pedal action and fluid level. A red light indi-
cates that the valve in the differential pressureswitch has been actuated. If a problem is confirmed,
inspect the hydraulic system and wheel brake compo-
nents.
On models with ABS brakes, the amber warning
light only illuminates when an ABS component has
malfunctioned. The ABS light operates indepen-
dently of the red warning light. Refer to the antilock
brake section for more detailed diagnosis informa-
tion.
PEDAL FALLS AWAY
A brake pedal that falls away under steady foot
pressure is generally the result of a system leak. The
leak point could be at a brakeline, fitting, hose,
wheel cylinder, or caliper. Internal leakage in the
master cylinder caused by worn or damaged piston
cups, may also be the problem cause.
If leakage is severe, fluid will be evident at or
around the leaking component. However internal
leakage in the master cylinder will not be physically
evident. Refer to the cylinder test procedure in this
section.
LOW PEDAL
If a low pedal is experienced, pump the pedal sev-
eral times. If the pedal comes back up, worn lining
and worn rotors or drums are the most likely causes.
However, if the pedal remains low and/or the warn-
ing light illuminates, the problem is in the master
cylinder, wheel cylinders, or calipers.
A decrease in master cylinder fluid level may only
be the result of normal lining wear. Fluid level will
decrease as lining wear occurs. It is a result of the
outward movement of caliper and wheel cylinder pis-
tons to compensate for normal wear.
SPONGY PEDAL
A spongy pedal is most often caused by air in the
system. However, thin drums or substandard brake
lines and hoses will also cause a condition similar to
a spongy pedal. The proper course of action is to
bleed the system, or replace thin drums and suspect
quality brake lines and hoses.
HARD PEDAL OR HIGH PEDAL EFFORT
A hard pedal or high pedal effort may be due to
lining that is water soaked, contaminated, glazed, or
badly worn. The power booster or check valve could
also be faulty. Test the booster and valve as de-
scribed in this section.
BRAKE DRAG
Brake drag occurs when the lining is in constant
contact with the rotor or drum. Drag can occur at
one wheel, all wheels, fronts only, or rears only. It is
a product of incomplete brakeshoe release. Drag can
be minor or severe enough to overheat the linings,
rotors and drums.
5 - 8 BRAKESJ

Brake drag also has a direct effect on fuel economy.
If undetected, minor brake drag can be misdiagnosed
as an engine or transmission/torque converter prob-
lem.
Minor drag will usually cause slight surface char-
ring of the lining. It can also generate hard spots in
rotors and drums from the overheat/cool down pro-
cess. In most cases, the rotors, drums, wheels and
tires are quite warm to the touch after the vehicle is
stopped.
Severe drag can char the brake lining all the way
through. It can also distort and score rotors and
drums to the point of replacement. The wheels, tires
and brake components will be extremely hot. In se-
vere cases, the lining may generate smoke as it chars
from overheating.
An additional cause of drag involves the use of in-
correct length caliper mounting bolts. Bolts that are
too long can cause a partial apply condition. The cor-
rect caliper bolts have a shank length of 67 mm
(2.637 in.), plus or minus 0.6 mm (0.0236 in.). Refer
to the Disc Brake service section for more detail on
caliper bolt dimensions and identification.
Some common causes of brake drag are:
²loose or damaged wheel bearing
²seized or sticking caliper or wheel cylinder piston
²caliper binding on bushings or slide surfaces
²wrong length caliper mounting bolts (too long)
²loose caliper mounting bracket
²distorted brake drum or shoes
²rear brakeshoes binding on worn/damaged support
plates
²severely rusted/corroded components
²misassembled components.
If brake drag occurs at all wheels, the problem may
be related to a blocked master cylinder compensator
port or faulty power booster (binds-does not release).
The brakelight switch can also be a cause of drag.
An improperly mounted or adjusted brakelight
switch can prevent full brake pedal return. The re-
sult will be the same as if the master cylinder com-
pensator ports are blocked. The brakes would be
partially applied causing drag.
BRAKE FADE
Brake fade is a product of overheating caused by
brake drag. However, overheating and subsequent
fade can also be caused by riding the brake pedal,
making repeated high deceleration stops in a short
time span, or constant braking on steep roads. Refer
to the Brake Drag information in this section for
causes.
PEDAL PULSATION
Pedal pulsation is caused by components that are
loose, or beyond tolerance limits.
Disc brake rotors with excessive lateral runout or
thickness variation, or out of round brake drums arethe primary causes of pulsation. Other causes are
loose wheel bearings or calipers and worn, damaged
tires.
PULL
A front pull condition could be the result of:
²contaminated lining in one caliper
²seized caliper piston
²binding caliper
²wrong caliper mounting bolts (too long)
²loose caliper
²loose or corroded mounting bolts
²improper brakeshoes
²damaged rotor
²incorrect wheel bearing adjustment (at one wheel)
A worn, damaged wheel bearing or suspension
component are further causes of pull. A damaged
front tire (bruised, ply separation) can also cause
pull. Wrong caliper bolts (too long) will cause a par-
tial apply condition and pull if only one caliper is in-
volved.
A common and frequently misdiagnosed pull condi-
tion is where direction of pull changes after a few
stops. The cause is a combination of brake drag fol-
lowed by fade at the dragging brake unit.
As the dragging brake overheats, efficiency is so
reduced that fade occurs. If the opposite brake unit is
still functioning normally, its braking effect is mag-
nified. This causes pull to switch direction in favor of
the brake unit that is functioning normally.
When diagnosing a change in pull condition, re-
member that pull will return to the original direction
if the dragging brake unit is allowed to cool down
(and is not seriously damaged).
REAR BRAKE GRAB
Rear grab (or pull) is usually caused by contami-
nated lining, bent or binding shoes and support
plates, or improperly assembled components. This is
particularly true when only one rear wheel is in-
volved. However, when both rear wheels are affected,
the master cylinder or proportioning valve could be
at fault.
BRAKES DO NOT HOLD AFTER DRIVING
THROUGH DEEP WATER PUDDLES
This condition is generally caused by water soaked
lining. If the lining is only wet, it can be dried by
driving with the brakes lightly applied for a mile or
two. However, if the lining is both wet and dirty, dis-
assembly and cleaning will be necessary.
BRAKE FLUID CONTAMINATION
There are two basic causes of brake fluid contami-
nation. The first involves allowing dirt, debris, or
other liquid materials to enter the cylinder reservoirs
JBRAKES 5 - 9

assembled, they will not function. In addition, since
the adjuster mechanism only works during reverse
stops, it is important that complete stops be made.
The adjuster mechanism does not operate when roll-
ing stops are made in reverse. The vehicle must be
brought to a complete halt before the adjuster lever
will turn the adjuster screw.
A condition where the parking brakes do not hold,
will most probably be due to a wheel brake compo-
nent.
Items to look for when diagnosing a parking brake
problem, are:
²rear brakeshoe wear
²rear brakedrum wear
²brakedrums machined beyond allowable diameter
(oversize)
²parking brake front cable not secured to lever
²parking brake rear cable seized
²parking brake strut reversed
²parking brake strut not seated in both shoes
²parking brake lever not seated in secondary shoe
²parking brake lever or brakeshoe bind on support
plate
²brakeshoes reversed
²adjuster screws seized
²adjuster screws reversed
²holddown or return springs misassembled or lack
tension
²wheel cylinder pistons seized
Brake drums that are machined oversize are diffi-
cult to identify. If oversize drums are suspected, the
diameter of the braking surface will have to be
checked with an accurate drum gauge. Oversize
drums will cause low brake pedal and lack of park-
ing brake holding ability.
Improper parking brake strut and lever installa-
tion will result in unsatisfactory parking brake oper-
ation. Intermixing the adjuster screws will cause
drag, bind and pull along with poor parking brake
operation.
Parking brake adjustment and parts replacement
procedures are described in the Parking Brake sec-
tion.
MASTER CYLINDER/POWER BOOSTER TEST
(1) Start engine and check booster vacuum hose
connections. Hissing noise indicates vacuum leak.
Correct any vacuum leak before proceeding.
(2) Stop engine and shift transmission into Neu-
tral.
(3) Pump brake pedal until all vacuum reserve in
booster is depleted.
(4) Press and hold brake pedal under light foot
pressure.
(a) If pedal holds firm, proceed to step (5).
(b) If pedal does not hold firm and falls away,
master cylinder is faulty (internal leakage). Over-
haul or replace cylinder.(5) Start engine and note pedal action.
(a) If pedal falls away slightly under light foot
pressure then holds firm, proceed to step (6).
(b) If no pedal action is discernible, power
booster or vacuum check valve is faulty. Install
known good check valve and repeat steps (2)
through (5).
(6) Rebuild booster vacuum reserve as follows: Re-
lease brake pedal. Increase engine speed to 1500
rpm, close throttle and immediately turn off ignition.
(7) Wait a minimum of 90 seconds and try brake
action again. Booster should provide two or more
vacuum assisted pedal applications. If vacuum assist
is not provided, perform booster and check valve vac-
uum tests.
POWER BOOSTER CHECK VALVE TEST
(1) Disconnect vacuum hose from check valve.
(2) Remove check valve and valve seal from
booster (Fig. 1).
(3) Hand operated vacuum pump can be used for
test (Fig. 2).
(4) Apply 15-20 inches vacuum at large end of
check valve (Fig. 1).
(5) Vacuum should hold steady. If gauge on pump
indicates any vacuum loss, valve is faulty and must
be replaced.
Fig. 1 Vacuum Check Valve And Seal (Typical)
Fig. 2 Hand Operated Vacuum Pump (Typical)
JBRAKES 5 - 11

CAUTION: Do not allow the master cylinder to run
out of fluid when bleeding the brakes. An empty
cylinder will allow additional air to be drawn into
the system. Check the cylinder fluid level frequently
and add fluid as needed.
(10) Bleed each wheel brake unit as follows:
(a) Open caliper or wheel cylinder bleed fitting
1/2 to 3/4 turn.
(b) Have helper press and hold brake pedal to
floor.Do not pump brake pedal while bleeding.
Air in system will be compressed into small
bubbles that are distributed throughout hy-
draulic system. This will make a second and
third bleeding operation necessary.
(c) Tighten bleed fitting and have helper release
brake pedal. Continue bleeding operation until
fluid entering bleed container is clear and free of
bubbles.
(d) Repeat bleeding operation at remaining
wheel brake units.
(e) Discard fluid bled into glass container. It
should not be reused.
(11) Check and adjust master cylinder fluid level.
(12) Verify proper brake operation before moving
vehicle.
PRESSURE BLEEDING
The front brake metering valve is located in the
forward end of the combination valve. The valve
stem is accessible from the same end of the valve.
The stem must be either pressed inward, or held out-
ward slightly in order to bleed the front brakes.
(1) Fill bleeder tank if necessary.
(2) Purge air from bleeder tank and lines before
proceeding.(3) Wipe master cylinder cover clean.
(4) Remove master cylinder cover and install pres-
sure hose adapter in place of cover. A suitable
adapter will usually be available from tank manufac-
turer.
(5) Connect bleeder tank pressure hose to adapter.
(6) Bleed master cylinder first. Then bleed rear
brakes as described in manual bleeding procedure.
(7) Bleed front brakes as described in manual
bleeding procedure. Have helper hold metering valve
open by pressing valve stem inward slightly. Amount
of valve stem movement needed to hold valve open is
quite modest. Do not use excessive force.
(8) Remove pressure bleeding equipment and top
off master cylinder reservoir.
BRAKE BLEEDINGÐXJ/YJ WITH ABS BRAKES
A different bleeding method is required for the
ABS system. It is basically a three step process
consisting of: A conventional manual brake
bleed. A second bleed using the DRB II, fol-
lowed by a repeat of the conventional manual
bleed procedure. Recommended ABS bleeding
procedure is as follows:
(1) Clean master cylinder reservoir caps and reser-
voir exterior. Dirt, foreign material on the caps and
reservoir must not be allowed to enter reservoir.
(2) Fill reservoir with Mopar brake fluid, or equiv-
alent quality fluid meeting SAE 1703 and DOT 3
standards.
(3) Recommended bleeding sequence is:
²master cylinder
²HCU valve body (at fluid lines)
²right rear wheel
²left rear wheel
²right front wheel
²left front wheel.
(4) Attach bleed hose to caliper or wheel cylinder
bleed fitting. Immerse end of bleed hose in glass con-
tainer partially filled with brake fluid. Be sure hose
end is submerged in fluid (Fig. 7).
(5) Bleed each wheel brake unit as follows:
(a) Have helper apply and hold brake pedal.
(b) Open bleed screw 1/2 turn. Close bleed screw
when brake pedal contacts floorpan.Do not pump
brake pedal at any time while bleeding. This
compresses air into small bubbles which are
distributed throughout system. Additional
bleeding operations will then be necessary to
remove all trapped air from the system.
(c) Repeat bleeding operation 5-7 more times at
each rear wheel brake unit.
(d) Continue bleeding until fluid entering glass
container is free of air bubbles. Check reservoir
fluid level frequently and add fluid if necessary.
(e) Repeat bleeding procedures at front wheels.
Fig. 7 Typical Bleed Hose And Fluid Container
5 - 14 BRAKESJ

STANDARD MASTER CYLINDER
INDEX
page page
General Service Information................ 20
Master Cylinder Installation................. 20Master Cylinder Overhaul.................. 20
Master Cylinder Removal.................. 20
GENERAL SERVICE INFORMATION
The service information in this section covers the
standard (non-ABS) master cylinder only. The center
feed master cylinder used with the ABS system is
covered in the antilock brake component service sec-
tion.
MASTER CYLINDER REMOVAL
(1) Disconnect brake lines at master cylinder.
(2) Remove cylinder mounting nuts and remove
master cylinder.
(3) Remove cylinder cover and drain fluid.
MASTER CYLINDER INSTALLATION
(1) Bleed master cylinder on bench before installa-
tion. Refer to overhaul assembly procedure in this
section for bleeding method.
(2) Install cylinder on brake booster studs and in-
stall cylinder attaching nuts. Tighten nuts to 21 NIm
(15 ft. lbs.).
(3) Connect brakelines to cylinder.
(4) Fill and bleed brake system.
MASTER CYLINDER OVERHAUL
CYLINDER DISASSEMBLY
(1) Remove cylinder cover and drain fluid.
(2) Examine cylinder cover seal. Discard seal if
torn or distorted.
(3) Clamp cylinder in vise (Fig. 1).
(4) Press primary piston inward with wood dowel
or phillips screwdriver and remove snap ring (Fig. 2).
(5) Remove and discard primary piston (Fig. 3).
Piston is serviced only as an assembly.
(6) Remove secondary piston (Fig. 4). Apply air
pressure through rear outlet port to ease piston out
of bore. Cover small ports at bottom of rear reservoir
with towel to prevent air leakage.
(7) Discard secondary piston. Do not disassemble
piston as components are only serviced as assembly.
CLEANING AND INSPECTION
Clean the cylinder with Mopar brake cleaning sol-
vent or clean brake fluid. Remove cleaning residue
with compressed air.
Inspect the cylinder bore. A light discoloration of
the bore surface is normal and acceptable but only if
the surface is in good condition.Replace the cylinder if the bore is scored, corroded,
or pitted.Do not hone the cylinder bore in an at-
tempt to restore the surface. Replace the cylin-
der if the bore is corroded or if doubt exists
about cylinder bore condition.
Fig. 1 Cylinder Mounted In Vise
Fig. 2 Removing/Installing Piston Snap Ring
5 - 20 BRAKESJ

DISC BRAKES
INDEX
page page
Caliper Assembly........................ 29
Caliper Cleaning and Inspection............. 28
Caliper Disassembly...................... 27
Caliper Installation........................ 30
Caliper Operation and Wear Compensation..... 24
Caliper Removal......................... 27
Disc Brake Rotor Refinishing................ 32
Disc Brake Rotor Runout................... 31Disc Brake Rotor Thickness................ 31
Disc Brake Rotor Thickness Variation......... 31
Disc Brakeshoe Installation................. 26
Disc Brakeshoe Removal.................. 25
General Information....................... 24
Rotor Installation......................... 30
Rotor Removal.......................... 30
Wheel Nut Tightening..................... 32
GENERAL INFORMATION
1994 Jeep XJ/YJ models are equipped with single
piston, floating-type disc brake calipers. Ventilated,
cast rotors are used for all applications.
The disc brake calipers are supported in mounting
arms that are an integral part of the steering
knuckle. The calipers slide on mounting bolts that
also attach the calipers to the steering knuckle.
CALIPER OPERATION AND WEAR COMPENSATION
Caliper Operation
The significant feature of single piston caliper op-
eration is that the calipers are free to slide laterally
on the mounting bolts. It is the freedom of lateral
movement that allows continous compensation for
lining wear.
A simplified cross section of a single piston caliper
is shown in Figure 1. The illustration graphically
portrays the forces at work when the brakes are ap-
plied.
Upon brake application, fluid pressure exerted
against the caliper piston increases greatly. Of equal
importance, is the fact that this fluid pressure is ex-
erted equally and in all directions. What this means,
is that pressure in the caliper bore, will be exactly
the same as pressure on the piston. In other words,
pressure against piston and caliper bore will be
equal.
Fluid pressure applied to the piston is transmitted
directly to the inboard brakeshoe. This forces the
shoe lining against the inner surface of the disc
brake rotor (Fig. 1).
At the same time, fluid pressure within the piston
bore, forces the caliper to slide inward on the mount-
ing bolts. This action brings the outboard brakeshoe
lining into contact with the outer surface of the disc
brake rotor (Fig. 1).
In summary, fluid pressure acting simultaneously
on both piston and caliper, produces a strong clamp-
ing action. When sufficient force is applied, friction
will stop the rotors from turning and bring the vehi-
cle to a stop.Brakeshoe Wear Compensation
Application and release of the brake pedal gener-
ates only a very slight movement of the caliper and
piston. Upon release of the pedal, the caliper and pis-
ton return to a rest position. The brakeshoes do not
retract an appreciable distance from the rotor. In
fact, clearance is usually at, or close to zero. The rea-
sons for this are to keep road debris from getting be-
tween the rotor and lining and in wiping the rotor
surface clear each revolution.
The caliper piston seal controls the amount of pis-
ton extension needed to compensate for normal lining
wear.
During brake application, the seal is deflected out-
ward by fluid pressure and piston movement (Fig. 2).
When the brakes (and fluid pressure) are released,
the seal relaxes and retracts the piston.
The amount of piston retraction is determined by
brakelining wear. Generally, the amount is just
Fig. 1 Disc Brake Caliper Operation
5 - 24 BRAKESJ

(9) Remove inboard shoe. Grasp ends of shoe and
tilt shoe outward to release springs from caliper pis-
ton (Fig. 8). Then remove shoe from caliper.
(10) Support caliper on box, mechanics stool, or se-
cure it to nearby suspension part with wire.Do not
allow brake hose to support caliper weight.
(11) Wipe caliper off with shop rags or towels.Do
not use compressed air. Compressed air can un-
seat dust boot and force dirt into piston bore.
(12) Inspect condition of caliper piston dust boot
(Fig. 9). Overhaul caliper if there is evidence of leak-
age past piston and dust boot. Then inspect caliper
bushings and boots (Fig. 9). Replace boots if torn or
cut. If bushings or boots are damaged, replace them.
DISC BRAKESHOE INSTALLATION
(1) Clean brakeshoe mounting ledge slide surfaces
of steering knuckle with wire brush. Then apply
light coat of Mopar multi-mileage grease to slide sur-
faces (Fig. 10).
(2) Lubricate caliper mounting bolts and bushings
(Fig. 10). Use GE 661 or Dow 111 silicone grease.(3) Keep new or original brakeshoes in sets.Do
not interchange them.
(4) Install inboard shoe in caliper (Fig. 11). Be
sure shoe retaining springs are fully seated in caliper
piston.
(5) Install outboard shoe in caliper (Fig. 12). Start
one end of shoe in caliper. Rotate shoe downward and
into place until shoe locating lugs and shoe spring
are seated.
(6) Verify that locating lugs on outboard shoe are
seated in caliper (Fig. 6).
(7) Install caliper. Position notches at lower end of
brakeshoes on bottom mounting ledge (Fig. 13). Then
install caliper over rotor and seat upper ends of
brakeshoes on top mounting ledge (Fig. 11).
CAUTION: Before securing the caliper, be sure the
caliper brake hose is not twisted, kinked or touch-
ing any chassis components. Also be sure the hose
is clear of all suspension and steering components.
Loosen and reposition the hose if necessary.
Fig. 7 Removing Outboard Brakeshoe
Fig. 8 Removing Inboard Brakeshoe
Fig. 9 Caliper Dust Boots And Bushing Locations
Fig. 10 Caliper Lubrication Points
5 - 26 BRAKESJ

Do not hone the caliper piston bore. Replace the cal-
iper if the bore exhibits any of the aforementioned
conditions.
Inspect the caliper piston. The piston is made from
a phenolic resin (plastic material) and should be
smooth and clean. Replace the piston if cracked,
chipped, or scored. Do not attempt to restore a
scored, or corroded piston surface by sanding or pol-
ishing. The piston must be replaced if damaged.
CAUTION: Never interchange phenolic resin and
steel caliper pistons. The seals, seal grooves, cali-
per bores and piston tolerances are different for
resin and steel pistons. Do not intermix these com-
ponents.
Inspect the caliper mounting bolt bushings and
boots. Replace the boots if cut or torn. Clean and lu-
bricate the bushings with GE 661 or Dow 111 sili-
cone grease if necessary.
Inspect condition of the caliper mounting bolts. Re-
place the bolts if corroded, rusted, or worn. Do not re-
use the bolts if unsure of their condition.
Length of the caliper mounting bolts is also ex-
tremely important.
Use the replacement bolts specified in the parts
catalog at all times. Do not use substitute bolts.
Bolts that are too long will partially apply the in-
board brakeshoe causing drag and pull. Refer to the
caliper and brakeshoe installation procedures for ser-
vice details and bolt dimensions.
CALIPER ASSEMBLY
(1) Coat caliper piston bore, new piston seal and
piston with clean, fresh brake fluid.
(2) Lubricate caliper bushings and interior of bush-
ing boots with GE 661, Dow 111, or Permatex Dielec-
tric silicone grease.
(3) Install bushing boots in caliper first. Then in-
sert bushing into boot and push bushing into place
(Fig. 20).(4) Install new piston seal in caliper bore. Press
seal into seal groove with finger (Fig. 21).
(5) Install dust boot on caliper piston (Fig. 22).
Slide boot over piston and seat boot in piston groove.
(6) Start caliper piston in bore by hand (Fig. 23).
Use a turn and push motion to work piston into seal.
Once piston is started in seal, press pistononly part
wayinto bore.
(7) Apply light coat of GE 661, Dow 111, or Per-
matex silicone grease to indicated areas (circumfer-
Fig. 20 Installing Bushings And Boots
Fig. 21 Installing Piston Seal
Fig. 22 Installing Dust Boot On Piston
Fig. 23 Installing Caliper Piston
JBRAKES 5 - 29