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XJ
BRAKES
5 - 1
BRAKES
TABLE OF CONTENTS
page
page
BASE BRAKE SYSTEM
TABLE OF CONTENTS
page
page
DESCRIPTION AND OPERATION
DIAGNOSIS AND TESTING
SERVICE PROCEDURES
REMOVAL AND INSTALLATION
DISASSEMBLY AND ASSEMBLY
CLEANING AND INSPECTION
ADJUSTMENTS
SPECIFICATIONS
SPECIAL TOOLS
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BRAKES
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DESCRIPTION AND OPERATION
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.
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.
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.
SERVICE WARNINGS & CAUTIONS
DESCRIPTION
BRAKE PEDAL
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. DO 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
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.
OF
DUST
OR
DEBRIS
THAT
MAY
CONTAIN ASBESTOS FIBERS.
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BRAKES
5 - 3
DESCRIPTION AND OPERATION (Continued)
RED BRAKE WARNING LAMP
MASTER CYLINDER
DESCRIPTION
A red warning lamp is used for the service brake
portion of the hydraulic system. The lamp is located
in the instrument cluster.
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 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.
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.
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.
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
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.
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.
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BRAKES
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DESCRIPTION AND OPERATION (Continued)
Fig. 1 Power Brake Booster–Typical
1 – VACUUM CHECK VALVE
2 – FRONT DIAPHRAGM
3 – REAR DIAPHRAGM
4 – HOUSING
5 – SEAL
6 – AIR FILTER
7 – PRIMARY PUSH ROD (TO BRAKE PEDAL)
8 – ATMOSPHERIC INLET VALVE ASSEMBLY
9 – BOOSTER MOUNTING STUDS (4)
10 – SECONDARY PUSH ROD (TO MASTER CYLINDER)
11 – MASTER CYLINDER MOUNTING STUD (2)
12 – SPRING
FRONT DISC BRAKES
pressure
exerted
against
the
caliper
piston
and
within the caliper bore will be equal (Fig. 2).
Fluid pressure applied to the piston is transmitted
directly to the inboard brake shoe. This forces the
shoe lining against the inner surface of the disc
brake rotor. At the same time, fluid pressure within
the piston bore forces the caliper to slide inward on
the mounting bolts. This action brings the outboard
brake shoe lining into contact with the outer surface
of the disc brake rotor.
DESCRIPTION
The calipers are a single piston type. The calipers
are free to slide laterally, this allows continuous com-
pensation for lining wear.
OPERATION
When the brakes are applied fluid pressure is
exerted against the caliper piston. The fluid pressure
is exerted equally and in all directions. This means
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BRAKES
5 - 5
DESCRIPTION AND OPERATION (Continued)
Fig. 3 Lining Wear Compensation By Piston Seal
1 – PISTON
2 – CYLINDER BORE
3 – PISTON SEAL BRAKE PRESSURE OFF
4 – CALIPER HOUSING
5 – DUST BOOT
6 – PISTON SEAL BRAKE PRESSURE ON
REAR DRUM BRAKE
Fig. 2 Brake Caliper Operation
1 – CALIPER
2 – PISTON
3 – PISTON BORE
4 – SEAL
5 – INBOARD SHOE
6 – OUTBOARD SHOE
DESCRIPTION
The rear brakes use a leading shoe (primary) and
trailing shoe (secondary) design (Fig. 4).
OPERATION
When the brake pedal is depressed hydraulic pres-
sure pushes the rear brake wheel cylinder pistons
outward. The wheel cylinder push rods then push the
brake shoes outward against the brake drum. When
the brake pedal is released return springs attached
to the brake shoes pull the shoes back to there orig-
inal position.
In summary, fluid pressure acting simultaneously
on both piston and caliper, produces a strong clamp-
ing action. When sufficient force is applied, friction
will attempt to stop the rotors from turning and
bring the vehicle to a stop.
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 brake shoes 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
between 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. 3).
When the brakes (and fluid pressure) are released,
the seal relaxes and retracts the piston.
The amount of piston retraction is determined by
the amount of seal deflection. Generally the amount
is just enough to maintain contact between the pis-
ton and inboard brake shoe.
PARKING BRAKE
DESCRIPTION
The parking bake is a hand lever and cable oper-
ated system used to apply the rear brakes.
OPERATION
A hand operated lever in the passenger compart-
ment is the main application device. The front cable
is connected between the hand lever and the ten-
sioner. The tensioner rod is attached to the equalizer
which is the connecting point for the rear cables (Fig.
5).
The rear cables are connected to the actuating
lever on each secondary brake shoe. The levers are
attached to the brake shoes by a pin either pressed
into, or welded to the lever. A clip is used to secure
the pin in the brake shoe. The pin allows each lever
to pivot independently of the brake shoe.
To apply the parking brakes, the hand lever is
pulled upward. This pulls the rear brake shoe actu-
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