Jeep Wrangler TJ. Manual — part 251
ADJUSTMENT WITH ADJUSTING TOOL
(1) Be sure parking brake lever is fully released.
(2) Raise vehicle so rear wheels can be rotated
freely.
(3) Remove plug from each access hole in brake
support plates.
(4) Loosen parking brake cable adjustment nut
until there is slack in front cable.
(5) Insert adjusting tool through support plate
access hole and engage tool in teeth of adjusting
screw star wheel (Fig. 35).
(6) Rotate adjuster screw star wheel (move tool
handle upward) until slight drag can be felt when
wheel is rotated.
(7) Push and hold adjuster lever away from star
wheel with thin screwdriver.
(8) Back off adjuster screw star wheel until brake
drag is eliminated.
(9) Repeat adjustment at opposite wheel. Be sure
adjustment is equal at both wheels.
(10) Install support plate access hole plugs.
(11) Adjust parking brake cable and lower vehicle.
(12) Drive vehicle and make one forward stop fol-
lowed by one reverse stop. Repeat procedure 8-10
times to operate automatic adjusters and equalize
adjustment.
NOTE: Bring vehicle to complete standstill at each
stop. Incomplete, rolling stops will not activate
automatic adjusters.
FLUID
DIAGNOSIS AND TESTING - BRAKE FLUID
CONTAMINATION
Indications of fluid contamination are swollen or
deteriorated rubber parts.
Swollen rubber parts indicate the presence of
petroleum in the brake fluid.
To test for contamination, put a small amount of
drained brake fluid in clear glass jar. If fluid sepa-
rates into layers, there is mineral oil or other fluid
contamination of the brake fluid.
If brake fluid is contaminated, drain and thor-
oughly flush system. Replace master cylinder, propor-
tioning valve, caliper seals, wheel cylinder seals,
Antilock Brakes hydraulic unit and all hydraulic
fluid hoses.
STANDARD PROCEDURE - BRAKE FLUID
LEVEL
Always clean the master cylinder reservoir and
caps before checking fluid level. If not cleaned, dirt
could enter the fluid.
The fluid fill level is indicated on the side of the
master cylinder reservoir (Fig. 36).
The correct fluid level is to the FULL indicator on
the side of the reservoir. If necessary, add fluid to the
proper level.
SPECIFICATIONS
BRAKE FLUID
The brake fluid used in this vehicle must conform
to DOT 3 specifications and SAE J1703 standards.
No other type of brake fluid is recommended or
approved for usage in the vehicle brake system. Use
Fig. 35 Brake Adjustment
1 - STAR WHEEL
2 - LEVER
3 - BRAKE SHOE WEB
4 - SCREWDRIVER
5 - ADJUSTING TOOL
6 - ADJUSTER SPRING
Fig. 36 Master Cylinder Fluid
1 - INDICATOR
2 - RESERVOIR
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BRAKES - BASE
5 - 21
DRUM (Continued)
only Mopar brake fluid or an equivalent from a
tightly sealed container.
CAUTION: Never use reclaimed brake fluid or fluid
from an container which has been left open. An
open container of brake fluid will absorb moisture
from the air and contaminate the fluid.
CAUTION: Never use any type of a petroleum-based
fluid in the brake hydraulic system. Use of such
type fluids will result in seal damage of the vehicle
brake hydraulic system causing a failure of the
vehicle brake system. Petroleum based fluids would
be items such as engine oil, transmission fluid,
power steering fluid, etc.
FLUID RESERVOIR
REMOVAL
(1) Remove reservoir cap and empty fluid into
drain container.
(2) Remove pins that retain reservoir to master
cylinder. Use hammer and pin punch to remove pins
(Fig. 37).
(3) Clamp cylinder body in vise with brass protec-
tive jaws.
(4) Loosen reservoir from grommets with pry tool
(Fig. 38).
(5) Remove reservoir by rocking it to one side and
pulling free of grommets (Fig. 39).
(6) Remove old grommets from cylinder body (Fig.
40).
Fig. 37 Reservoir Retaining Pins
1 - PIN PUNCH
2 - RESERVOIR
3 - BODY
4 - ROLL PINS
Fig. 38 Loosening Reservoir
1 - PRY TOOL
2 - RESERVOIR
3 - GROMMET
4 - MASTER CYLINDER BODY
Fig. 39 Reservoir Removal
1 - RESERVOIR
2 - GROMMETS
Fig. 40 Grommet Removal
1 - MASTER CYLINDER BODY
2 - GROMMETS
5 - 22
BRAKES - BASE
TJ
FLUID (Continued)
INSTALLATION
CAUTION: Do not use any type of tool to install the
grommets. Tools may cut, or tear the grommets cre-
ating a leak problem after installation. Install the
grommets using finger pressure only.
(1) Lubricate new grommets with clean brake fluid
and Install new grommets in cylinder body (Fig. 41).
Use finger pressure to install and seat grommets.
(2) Start reservoir in grommets. Then rock reser-
voir back and forth while pressing downward to seat
it in grommets.
(3) Install pins that retain reservoir to cylinder
body.
(4) Fill and bleed master cylinder on bench before
installation in vehicle.
MASTER CYLINDER
DESCRIPTION
The master cylinder has a removable nylon reser-
voir. The cylinder body is made of aluminum and
contains a primary and secondary piston assembly.
The cylinder body including the piston assemblies
are not serviceable. If diagnosis indicates an internal
problem with the cylinder body, it must be replaced
as an assembly. The reservoir and grommets are the
only replaceable parts on the master cylinder.
OPERATION
The master cylinder bore contains a primary and
secondary
piston.
The
primary
piston
supplies
hydraulic pressure to the front brakes. The secondary
piston supplies hydraulic pressure to the rear brakes.
The master cylinder reservoir stores reserve brake
fluid for the hydraulic brake circuits.
DIAGNOSIS AND TESTING - MASTER
CYLINDER/POWER BOOSTER
(1) Start engine and check booster vacuum hose
connections. A 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. The pedal should hold firm, if the pedal
falls away master cylinder is faulty (internal leak-
age).
(5) Start engine and note pedal action. It should
fall away slightly under light foot pressure then hold
firm. If no pedal action is discernible, power booster,
vacuum supply, or vacuum check valve is faulty. Pro-
ceed to the POWER BOOSTER VACUUM TEST.
(6) If the POWER BOOSTER VACUUM TEST
passes, rebuild booster vacuum reserve as follows:
Release brake pedal. Increase engine speed to 1500
rpm, close the throttle and immediately turn off igni-
tion to stop engine.
(7) Wait a minimum of 90 seconds and try brake
action again. Booster should provide two or more vac-
uum assisted pedal applications. If vacuum assist is
not provided, booster is faulty.
POWER BOOSTER VACUUM TEST
(1) Connect vacuum gauge to booster check valve
with short length of hose and T-fitting (Fig. 42).
(2) Start and run engine at curb idle speed for one
minute.
(3) Observe the vacuum supply. If vacuum supply
is not adequate, repair vacuum supply.
(4) Clamp hose shut between vacuum source and
check valve.
(5) Stop engine and observe vacuum gauge.
(6) If vacuum drops more than one inch HG (33
millibars) within 15 seconds, booster diaphragm or
check valve is faulty.
POWER BOOSTER CHECK VALVE TEST
(1) Disconnect vacuum hose from check valve.
(2) Remove check valve and valve seal from
booster.
(3) Use a hand operated vacuum pump for test.
(4) Apply 15-20 inches vacuum at large end of
check valve (Fig. 43).
(5) Vacuum should hold steady. If gauge on pump
indicates vacuum loss, check valve is faulty and
should be replaced.
Fig. 41 Grommet Installation
1 - WORK NEW GROMMETS INTO PLACE USING FINGER
PRESSURE ONLY
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BRAKES - BASE
5 - 23
FLUID RESERVOIR (Continued)
STANDARD PROCEDURE - MASTER CYLINDER
BLEEDING
A new master cylinder should be bled before instal-
lation on the vehicle. Required bleeding tools include
bleed tubes and a wood dowel to stroke the pistons.
Bleed tubes can be fabricated from brake line.
(1) Mount master cylinder in vise.
(2) Attach bleed tubes to cylinder outlet ports.
Then position each tube end into the reservoir (Fig.
44).
(3) Fill reservoir with fresh brake fluid.
(4) Press cylinder pistons inward with wood dowel.
Then release pistons and allow them to return under
spring pressure. Continue bleeding operations until
air bubbles are no longer visible in fluid.
REMOVAL
(1) Remove evaporative canister.
(2) Disconnect brake lines to master cylinder and
combination valve (Fig. 45).
(3) Remove combination valve bracket mounting
nuts and remove valve.
(4) Remove master cylinder mounting nuts and
remove master cylinder.
(5) Remove cylinder cover and drain fluid.
Fig. 42 Typical Booster Vacuum Test Connections
1 - TEE FITTING
2 - SHORT CONNECTING HOSE
3 - CHECK VALVE
4 - CHECK VALVE HOSE
5 - CLAMP TOOL
6 - INTAKE MANIFOLD
7 - VACUUM GAUGE
Fig. 43 Vacuum Check Valve And Seal
1 - BOOSTER CHECK VALVE
2 - APPLY TEST VACUUM HERE
3 - VALVE SEAL
Fig. 44 Master Cylinder Bleeding
1 - BLEEDING TUBES
2 - RESERVOIR
Fig. 45 Master
1 - COMBINATION VALVE
2 - MASTER CYLINDER
5 - 24
BRAKES - BASE
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MASTER CYLINDER (Continued)
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