Content .. 44 45 46 47 ..

Jeep XJ. Manual - part 46

Trac-lok

Tools—8140

Trac-lok

Tools—6960

Pinion Gauge Block—8540

Arbor Discs—8541

Pinion Gauge Set

3 - 134

8 1/4 REAR AXLE

SPECIAL TOOLS (Continued)

BRAKES

TABLE OF CONTENTS

page

BASE BRAKE SYSTEM . . . . . . . . . . . . . . . . . . . . . . 1

ANTILOCK BRAKES . . . . . . . . . . . . . . . . . . . . . . . 33

BASE BRAKE SYSTEM

TABLE OF CONTENTS

page

DESCRIPTION AND OPERATION

DIAGNOSIS AND TESTING

SERVICE PROCEDURES

BRAKE FLUID LEVEL . . . . . . . . . . . . . . . . . . . . . 12
MASTER CYLINDER BLEEDING . . . . . . . . . . . . . 12
BASE BRAKE BLEEDING. . . . . . . . . . . . . . . . . . . 13
DISC ROTOR MACHINING. . . . . . . . . . . . . . . . . . 13
BRAKE DRUM MACHINING . . . . . . . . . . . . . . . . . 14
BRAKE TUBE FLARING . . . . . . . . . . . . . . . . . . . . 14

REMOVAL AND INSTALLATION

BRAKE LAMP SWITCH . . . . . . . . . . . . . . . . . . . . 15

DISASSEMBLY AND ASSEMBLY

MASTER CYLINDER RESERVOIR . . . . . . . . . . . . 24
DISC BRAKE CALIPER . . . . . . . . . . . . . . . . . . . . 25
WHEEL CYLINDER . . . . . . . . . . . . . . . . . . . . . . . 28

CLEANING AND INSPECTION

CALIPER . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
REAR DRUM BRAKE . . . . . . . . . . . . . . . . . . . . . . 29
WHEEL CYLINDER . . . . . . . . . . . . . . . . . . . . . . . 29

ADJUSTMENTS

BRAKE LAMP SWITCH . . . . . . . . . . . . . . . . . . . . 30
REAR DRUM BRAKE . . . . . . . . . . . . . . . . . . . . . . 30
PARKING BRAKE CABLE TENSIONER . . . . . . . . 31

SPECIFICATIONS

BRAKE FLUID . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
BRAKE COMPONENTS . . . . . . . . . . . . . . . . . . . . 32
TORQUE CHART . . . . . . . . . . . . . . . . . . . . . . . . . 32

SPECIAL TOOLS

BASE BRAKES . . . . . . . . . . . . . . . . . . . . . . . . . . 32

BRAKES

5 - 1

DESCRIPTION AND OPERATION

BRAKE SYSTEM

DESCRIPTION

Power assist front disc and rear drum brakes are

standard equipment. Disc brake components consist
of single piston calipers and ventilated rotors. Rear
drum brakes are dual shoe units with cast brake
drums.

The parking brake mechanism is lever and cable

operated. The cables are attached to levers on the
rear drum brake secondary shoes. The parking
brakes are operated by a hand lever.

A dual diaphragm vacuum power brake booster is

used for all applications. All models have an alumi-
num master cylinder with plastic reservoir.

All models are equipped with a combination valve.

The valve contains a pressure differential valve and
switch and a fixed rate rear proportioning valve.

Factory brake lining on all models consists of an

organic base material combined with metallic parti-
cles. The original equipment linings do not contain
asbestos.

SERVICE WARNINGS & CAUTIONS

DESCRIPTION

WARNING: DUST AND DIRT ACCUMULATING ON
BRAKE PARTS DURING NORMAL USE MAY CON-
TAIN ASBESTOS FIBERS FROM AFTERMARKET
LININGS. BREATHING EXCESSIVE CONCENTRA-
TIONS OF ASBESTOS FIBERS CAN CAUSE SERI-
OUS

BODILY

HARM.

EXERCISE

CARE

WHEN

SERVICING

BRAKE

PARTS.

NOT

CLEAN

BRAKE PARTS WITH COMPRESSED AIR OR BY
DRY BRUSHING. USE A VACUUM CLEANER SPE-
CIFICALLY DESIGNED FOR THE REMOVAL OF
ASBESTOS FIBERS FROM BRAKE COMPONENTS.
IF A SUITABLE VACUUM CLEANER IS NOT AVAIL-
ABLE, CLEANING SHOULD BE DONE WITH A
WATER DAMPENED CLOTH. DO NOT SAND, OR
GRIND BRAKE LINING UNLESS EQUIPMENT USED
IS DESIGNED TO CONTAIN THE DUST RESIDUE.
DISPOSE OF ALL RESIDUE CONTAINING ASBES-
TOS FIBERS IN SEALED BAGS OR CONTAINERS
TO MINIMIZE EXPOSURE TO YOURSELF AND OTH-
ERS. FOLLOW PRACTICES PRESCRIBED BY THE
OCCUPATIONAL SAFETY AND HEALTH ADMINIS-
TRATION AND THE ENVIRONMENTAL PROTECTION
AGENCY FOR THE HANDLING, PROCESSING, AND
DISPOSITION OF DUST OR DEBRIS THAT MAY
CONTAIN ASBESTOS FIBERS.

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. Use only
fresh brake fluid or Mopar brake cleaner to clean or
flush brake system components. These are the only
cleaning materials recommended. If system contam-
ination is suspected, check the fluid for dirt, discol-
oration, or separation into distinct layers. Also
check the reservoir cap seal for distortion. Drain
and flush the system with new brake fluid if con-
tamination is suspected.

CAUTION: Use Mopar brake fluid, or an equivalent
quality fluid meeting SAE/DOT standards J1703 and
DOT 3. Brake fluid must be clean and free of con-
taminants. Use fresh fluid from sealed containers
only to ensure proper antilock component opera-
tion.

CAUTION: Use Mopar multi-mileage or high temper-
ature grease to lubricate caliper slide surfaces,
drum brake pivot pins, and shoe contact points on
the backing plates. Use multi-mileage grease or GE
661 or Dow 111 silicone grease on caliper slide pins
to ensure proper operation.

BRAKE PEDAL

DESCRIPTION

A suspended-type brake pedal is used, the pedal

pivots on a shaft mounted in the pedal support
bracket. The bracket is attached to the dash panel
and steering support bracket. The unit is serviced as
an assembly, except for the pedal pad.

OPERATION

The brake pedal is attached to the booster push

rod. When the pedal is depressed, the primary
booster push rod is depressed which move the booster
secondary rod. The booster secondary rod depress the
master cylinder piston.

BRAKE LAMP SWITCH

DESCRIPTION

The plunger type brake lamp switch is mounted on

a bracket attached to the brake pedal support. The
switch can be adjusted when necessary.

OPERATION

The brake lamp switch is used to for the brake

lamp, speed control and brake sensor circuits.

5 - 2

BRAKES

RED BRAKE WARNING LAMP

DESCRIPTION

A red warning lamp is used for the service brake

portion of the hydraulic system. The lamp is located
in the instrument cluster.

OPERATION

The red warning light alerts the driver if a pres-

sure differential exists between the front and rear
hydraulic systems or the parking brakes are applied.
The lamp is turned on momentarily when the igni-
tion switch is turn to the on position. This is a self
test to verify the lamp is operational.

POWER BRAKE BOOSTER

DESCRIPTION

The booster assembly consists of a housing divided

into separate chambers by two internal diaphragms.
The outer edge of each diaphragm is attached to the
booster housing. The diaphragms are connected to
the booster primary push rod.

Two push rods are used in the booster. The pri-

mary push rod connects the booster to the brake
pedal. The secondary push rod connects the booster
to the master cylinder to stroke the cylinder pistons.

OPERATION

The atmospheric inlet valve is opened and closed

by the primary push rod. Booster vacuum supply is
through a hose attached to an intake manifold fitting
at one end and to the booster check valve at the
other. The vacuum check valve in the booster housing
is a one-way device that prevents vacuum leak back.

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 a filter and inlet valve at the rear of the
housing (Fig. 1).

The chamber areas forward of the booster dia-

phragms are exposed to vacuum from the intake
manifold. The chamber areas to the rear of the dia-
phragms, are exposed to normal atmospheric pres-
sure of 101.3 kilopascals (14.7 pounds/square in.).

Brake pedal application causes the primary push

rod to open the atmospheric inlet valve. This exposes
the area behind the diaphragms to atmospheric pres-
sure. The resulting pressure differential provides the
extra apply force for power assist.

The booster check valve, check valve grommet and

booster seals are serviceable.

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.

COMBINATION VALVE

DESCRIPTION

The combination valve contains a pressure differ-

ential valve and switch and a rear brake proportion-
ing valve. The valve is not repairable and must be
replaced as an assembly if diagnosis indicates this is
necessary.

OPERATION

PRESSURE DIFFERENTIAL VALVE

The pressure differential switch is connected to the

brake warning light. The switch is actuated by move-
ment of the switch valve. The switch monitors fluid
pressure in the separate front/rear brake hydraulic
circuits.

A decrease or loss of fluid pressure in either

hydraulic circuit will cause the switch valve to shut-
tle to the low pressure side. Movement of the valve
pushes the switch plunger upward. This action closes
the switch internal contacts completing the electrical
circuit to the red warning light. The switch valve will
remain in an actuated position until repairs to the
brake system are made.

PROPORTIONING VALVE

The proportioning valve is used to balance front-

rear brake action at high decelerations. The valve
allows normal fluid flow during moderate braking.
The valve only controls fluid flow during high decel-
erations brake stops.

BRAKES

5 - 3

DESCRIPTION AND OPERATION (Continued)

Content .. 44 45 46 47 ..