front JEEP CHEROKEE 1994 Service Manual PDF

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

BRAKE BLEEDINGÐBRAKE FLUID AND LEVELÐBRAKELINES AND HOSES
INDEX
page page
Brake BleedingÐXJ/YJ with ABS Brakes....... 14
Brake BleedingÐXJ/YJ with Standard Brakes . . . 13
Brake Fluid Contamination.................. 13
Brake Fluid Level........................ 13Brakeline Charts......................... 15
Brakelines and Hoses..................... 15
Combination Valve....................... 15
Recommended Brake Fluid................. 13
RECOMMENDED BRAKE FLUID
The only brake fluid recommended for Jeep vehi-
cles with standard or antilock brakes, is Mopar brake
fluid, or an equivalent fluid meeting SAE J1703 and
DOT 3 standards.
Use new brake fluid only to top off the master
cylinder or refill the system. Never use re-
claimed fluid, fluid not meeting the SAE/DOT
standards or fluid from an unsealed container.
Do not use fluid from any container that has
been left open for any length of time. Fluid in
open containers can absorb moisture.
BRAKE FLUID LEVEL
Always clean the master cylinder and cover before
checking fluid level. If not cleaned, dirt from the
cover could enter the fluid. Also check the cover seal
and replace it if torn or distorted.
Correct fluid level is to within 6 mm (1/4 in.) of the
reservoir rim, or to the fill mark on models with a
plastic reservoir. Refer to the Antilock Brake section
for fluid levels on models equipped with ABS brakes.
BRAKE FLUID CONTAMINATION
Oil in the fluid will cause brake system rubber
seals to soften and swell. The seals may also become
porous and begin to deteriorate.
If fluid contamination is suspected, drain off a sam-
ple from the master cylinder. A suction gun or simi-
lar device can be used for this purpose.
Empty the drained fluid into a glass container.
Contaminants in the fluid will cause the fluid to sep-
arate into distinct layers. If contamination has oc-
curred, the system rubber seals, hoses and cups must
be replaced and the system thoroughly flushed with
clean brake fluid.
BRAKE BLEEDINGÐXJ/YJ WITH STANDARD
BRAKES
Use Mopar DOT 3 brake fluid, or an equivalent
meeting SAE/DOT standards J1703-F and DOT 3, to
fill and bleed the system.
On standard brake models, bleeding can be per-
formed either manually or with pressure equipment.
However, if pressure equipment is used, it will be
necessary to hold the front brake metering valveopen in order to bleed the front brakes. The valve
can be held open with a tension clip tool or by hand.
It will also be necessary that a suitable size pressure
tank hose adapter be available for use on the master
cylinder.
MANUAL BLEEDING PROCEDURE
(1) If master cylinder has been overhauled or a
new cylinder will be installed, bleed cylinder on
bench before installation. This shortens time needed
to bleed system and ensures proper cylinder opera-
tion.
(2) Wipe master cylinder reservoir and cap clean
with shop towels.
(3) Remove cover and fill master cylinder reservoir
with Mopar, or equivalent DOT 3 brake fluid.
(4) Open all caliper and wheel cylinder bleed
screws.
(5) Close bleed screws after fluid begins flowing
from each bleed screw.
(6) Top off master cylinder reservoir again.
(7) Use following bleed sequence:
²master cylinder
²right rear
²left rear
²right front
²left front
(8) Observe following brake bleeding precautions:
²Do not pump brake pedal at any time while bleed-
ing. Air in system will be compressed into small bub-
bles that are distributed throughout hydraulic
system. This will make a second and third bleeding
operation necessary.
²Bleed only one wheel brake unit at a time and use
a bleed hose to bleed each wheel brake unit (Fig. 7).
²Attach one end of bleed hose to bleed screw and in-
sert opposite end in glass container partially filled
with brake fluid (Fig. 7). Glass container makes it
easier to see air bubbles as they exit the bleed hose.
²Be sure end of bleed hose is immersed in fluid. Im-
mersing hose end in fluid prevents air from being
drawn back into cylinder and brakeline.
(9) Bleed master cylinder first. Have helper oper-
ate brake pedal while bleeding each master cylinder
fluid outlet line.
JBRAKES 5 - 13

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

CAUTION: Do not allow the master cylinder reser-
voir to run dry while bleeding the brakes. Running
dry will allow air to re-enter the system making a
second bleeding operation necessary.
(6) Perform ``Bleed Brake'' procedure with DRB II
scan tool. Procedure is described in DRB II software
information and diagnostic manual.
(a) Connect DRB II scan tool to diagnostic con-
nector.
(b) Run Bleed Brake procedure as described in
tester manual.
(7) Repeat conventional bleeding procedure out-
lined in steps (1) through (8).
(8) Top off master cylinder fluid level if necessary.
(9) Verify proper brake operation.
BRAKELINES AND HOSES
Metal brakelines and rubber brake hoses should be
inspected periodically and replaced if damaged.
Rubber brake hoses should be replaced if cut,
cracked, swollen, or leaking. Rubber hoses must be
replaced. They are not repairable parts.
When installing new, or original brakelines andhoses, lubricate the fitting threads with brake fluid
before connection.
The steel brakelines should be checked every time
the vehicle is in for normal maintainence. This is im-
portant on high mileage vehicles. It is even more im-
portant when a vehicle is operated in areas where
salt is used regularly on the road surface during win-
ter.
Heavily rusted/corroded brake rotors, drums, sup-
port plates, and brakelines should be cleaned and
carefully inspected. Heavy rust buildup can hide se-
vere damge to a component. Severely rusted parts
should be replaced if you are unsure about their con-
dition.
COMBINATION VALVE
The combination valve is not a serviceable part.
The valve must be replaced if a malfunction occurs.
BRAKELINE CHARTS
Brakeline charts are provided in illustration Fig-
ures 1 through 8. The illustrations show typical
brakeline routing, hose connections and component
position.
Fig. 1 Front Brakeline Routing (XJ With ABS Brakes)
JBRAKES 5 - 15

Fig. 2 Front Brakeline Routing (YJ With ABS Brakes)
Fig. 3 Brakeline Routing (YJ With Standard Brakes)
5 - 16 BRAKESJ

Fig. 6 Rear Brakeline Routing (YJ With ABS Brakes)
Fig. 7 Front Brakeline Routing (Right Hand Drive XJ With ABS Brakes)
5 - 18 BRAKESJ

Fig. 8 Front Brake Hose Attachment (Right Hand Drive XJ With ABS Brakes)
JBRAKES 5 - 19

POWER BRAKE BOOSTER
INDEX
page page
Power Brake Booster Installation............. 23
Power Brake Booster Operation............. 22Power Brake Booster Removal.............. 22
Service Information....................... 22
SERVICE INFORMATION
The power brake booster is not a serviceable com-
ponent. If a booster malfunction occurs, the booster
must be replaced as an assembly. The booster (Figs.
1 and 2), is attached to the dash panel and pedal sup-
port.
POWER BRAKE BOOSTER OPERATION
Booster Components
The booster assembly consists of a housing divided
into separate chambers by an internal diaphragm.The outer edge of the diaphragm is attached to the
booster housing. The diaphragm is in turn, connected
to the booster push rod.
Two push rods are used to operate the booster. One
push rod connects the booster to the brake pedal. The
second push rod (at the forward end of the housing),
strokes the master cylinder pistons. The rear push
rod is connected to the two diaphragms in the booster
housing.
The atmospheric inlet valve is opened and closed
by the push rod connected to the brake pedal. The
booster vacuum supply is through a hose attached to
a fitting on the intake manifold. The hose is con-
nected to a vacuum check valve in the booster hous-
ing. The check valve is a one-way device that
prevents vacuum leak back.
How Brake Boost Is Generated
Power assist is generated by utilizing the pressure
differential between normal atmospheric pressure
and a vacuum. The vacuum needed for booster oper-
ation is taken directly from the engine intake mani-
fold. The entry point for atmospheric pressure is
through an inlet valve at the rear of the housing.
The forward portion of the booster housing (area in
front of the two diaphragms), is exposed to manifold
vacuum. The rear portion (area behind the dia-
phragms), is exposed to normal atmospheric pressure
of 101.3 kilopascals (14.7 pounds/square in.).
Pressing the brake pedal causes the rear push rod
to open the inlet valve. This exposes the area behind
the diaphragm to atmospheric pressure. The result-
ing force applied to the diaphragm is what provides
the extra apply pressure for power assist.
POWER BRAKE BOOSTER REMOVAL
(1) Loosen but do not remove nuts attaching mas-
ter cylinder to booster (Fig. 3).
(2) Remove instrument panel lower trim cover.
(3) Remove retaining clip attaching booster push
rod to brake pedal (Fig. 4).
(4) Remove bolts/nuts attaching booster to dash
panel.
(5) In engine compartment, loosen vacuum hose
clamp and disconnect vacuum hose from booster
check valve (Fig. 5).
(6) Remove master cylinder attaching nuts and re-
move cylinder from mounting studs on booster.
Fig. 1 Power Brake Booster (XJ)
Fig. 2 Power Brake Booster (YJ)
5 - 22 BRAKESJ

enough to maintain contact between the piston and
inboard brakeshoe. Brakelining running clearance at
the rotor, will be held between zero and a maximum
of 0.12 mm (0.005 in.).
DISC BRAKESHOE REMOVAL
(1) Raise vehicle and remove front wheels.
(2) Drain small amount of fluid from master cylin-
der front brake reservoir with suction gun.
(3) Bottom caliper piston in bore with C-clamp. Po-
sition clamp screw on outboard brakeshoe and clamp
frame on rear of caliper. Typical C-clamp attachment
is shown in Figure 3.Do not allow clamp screw to
bear directly on outboard shoe retainer spring.
Use wood or metal spacer between shoe and
clamp screw if necessary.
(4) Remove caliper mounting bolts (Fig. 4).If
brakeshoes are being removed to correct a pull
or drag condition, verify length of caliper bolts
as they may be incorrect length. Refer to bolt in-
formation in brakeshoe installation procedure.
(5) Tilt top of caliper outward. Use pry tool if nec-
essary (Fig. 5).
(6) Lift caliper off steering knuckle (Fig. 6).
(7)If original brakeshoes will be used, keep
them in sets (left and right); they are not inter-
changeable.(8) Remove outboard shoe. Press one end of shoe
inward to disengage shoe lug. Then rotate shoe up-
ward until retainer spring clears caliper. Press oppo-
site end of shoe inward to disengage shoe lug and
rotate shoe up and out of caliper (Fig. 7).
Fig. 2 Lining Wear Compensation By Piston Seal
Fig. 3 Bottoming Caliper Piston With C-Clamp
Fig. 4 Removing/Installing Caliper Mounting Bolts
Fig. 5 Tilting Caliper Outward
Fig. 6 Caliper Removal
JBRAKES 5 - 25

(8) Install and tighten caliper mounting bolts to
10-20 Nzm (7-15 ft. lbs.) torque.
CAUTION: If new caliper bolts are being installed,
or if the original reason for repair was a drag/pull
condition, check caliper bolt length before proceed-
ing. If the bolts have a shank length greater than
67.6 mm (2.66 in.), they will contact the inboard
brakeshoe causing a partial apply condition. Refer
to Figure 14 for required caliper bolt length.
(9) Install wheels. Tighten lug nuts to 102 Nzm (75
ft. lbs.) torque.
(10) Pump brake pedal until caliper pistons and
brakeshoes are seated.
(11) Top off brake fluid level if necessary. Use Mo-
par brake fluid or equivalent meeting SAE J1703
and DOT 3 standards only.
CALIPER REMOVAL
(1) Raise vehicle and remove front wheels.
(2) Remove caliper mounting bolts (Fig. 4).(3) Rotate caliper rearward by hand or with pry
tool (Fig. 5). Then rotate caliper and brakeshoes off
mounting ledges.
(4) Remove caliper hose fitting bolt and disconnect
front brake hose at caliper. Discard fitting bolt wash-
ers. They are not reusable and should be replaced.
(5) Remove caliper from vehicle.
CALIPER DISASSEMBLY
(1) Remove brakeshoes from caliper.
(2) Pad interior of caliper with minimum, 2.54 cm
(1 in.) thickness of shop towels or rags (Fig. 15). Tow-
els are needed to protect caliper piston during re-
moval.
(3) Remove caliper piston withshort burstsof low
pressure compressed air. Direct air through fluid in-
let port and ease piston out of bore (Fig. 16).
Fig. 11 Installing Inboard Brakeshoe
Fig. 12 Installing Outboard Brakeshoe
Fig. 13 Caliper Installation
Fig. 14 Caliper Mounting Bolt Dimensions
JBRAKES 5 - 27