2002 JEEP LIBERTY Workshop Manual

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. 33).
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.
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. 34).
(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.
Fig. 32 BOOSTER PUSH ROD
1 - MASTER CYLINDER ASSEMBLY
2 - BRAKE BOOSTER
3 - CLIP
4 - BRAKE PEDAL
5 - BOOSTER ROD
KJBRAKES - BASE 5 - 21
PEDAL (Continued)

(4) Apply 15-20 inches vacuum at large end of
check valve (Fig. 35).
(5) Vacuum should hold steady. If gauge on pump
indicates vacuum loss, check valve is faulty and
should be replaced.
REMOVAL
(1) Disconnect the wire to the fluid level switch at
the bottom of the reservoir.(2) Remove the master cylinder (Refer to 5 -
BRAKES/HYDRAULIC/MECHANICAL/MASTER
CYLINDER - REMOVAL).
(3) Disconnect vacuum hose from booster check
valve.
(4) Remove the brake lines from the master cylin-
der and the HCU (abs vehicles only) or the junction
block for clearence.
(5) Disconnect the HCU from the mounts and
move to the side for clearence of the booster.
Fig. 33 Power Brake Booster±Typical
1 - VACUUM CHECK VALVE
2 - FRONT DIAPHRAGM
3 - REAR DIAPHRAGM
4 - HOUSING
5 - SEAL
6 - AIR FILTER7 - 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
5 - 22 BRAKES - BASEKJ
POWER BRAKE BOOSTER (Continued)

(6) Remove knee blocker under the steering colum-
n,(Refer to 23 - BODY/INSTRUMENT PANEL/KNEE
BLOCKER - REMOVAL).
(7) Remove retaining clip that secures booster
push rod to brake pedal (Fig. 36).(8) Remove nuts attaching booster to the dash
panel (Fig. 37).
(9) In engine compartment, slide booster studs out
of dash panel, tilt booster upward, and remove
booster from engine compartment.
INSTALLATION
(1) Align and position booster on the dash panel.
(2) Install booster mounting nuts. Tighten nuts
just enough to hold booster in place.
(3) Slide booster push rod onto the brake pedal.
Then secure push rod to pedal pin with retaining
clip.
NOTE: Lubricate the pedal pin and bushing with
Mopar multi-mileage grease before installation.
Fig. 34 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. 35 TYPICAL - VACUUM CHECK VALVE AND
SEAL
1 - BOOSTER CHECK VALVE
2 - APPLY TEST VACUUM HERE
3 - VALVE SEAL
Fig. 36 BOOSTER PUSH ROD
1 - BRAKE PEDAL
2 - BOOSTER ROD
Fig. 37 BOOSTER MOUNTING
1 - BRAKE BOOSTER
KJBRAKES - BASE 5 - 23
POWER BRAKE BOOSTER (Continued)

(4) Tighten booster mounting nuts to 22.6 N´m
(200 ft. lbs.).
(5) Install the knee blocker,(Refer to 23 - BODY/
INSTRUMENT PANEL/KNEE BLOCKER - INSTAL-
LATION).
(6) If original master cylinder is being installed,
check condition of seal at rear of master cylinder.
Replace seal if cut, or torn.
(7) Clean cylinder mounting surface of brake
booster. Use shop towel wetted with brake cleaner for
this purpose. Dirt, grease, or similar materials will
prevent proper cylinder seating and could result in
vacuum leak.
(8) Align and install master cylinder on the
booster studs. Install mounting nuts and tighten to
22.6 N´m (200 in. lbs.).
(9) Connect vacuum hose to booster check valve.
(10) Remount the HCU. Tighten bracket mounting
nuts to 22.6 N´m (200 in. lbs.).
(11) Connect and secure the brake lines to HCU or
junction block and master cylinder. Start all brake
line fittings by hand to avoid cross threading.
(12) Connect the wire to fluid level switch at the
bottom of the reservoir.
(13) Fill and bleed base brake system,(Refer to 5 -
BRAKES - STANDARD PROCEDURE).
(14) Verify proper brake operation before moving
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. 38).
(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. 39).
(5) Vacuum should hold steady. If gauge on pump
indicates vacuum loss, check valve is faulty and
should be replaced.
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.
5 - 24 BRAKES - BASEKJ
POWER BRAKE BOOSTER (Continued)

(2) Attach bleed tubes to cylinder outlet ports.
Then position each tube end into reservoir (Fig. 40).
(3) Fill reservoir with fresh brake fluid.
(4) Press cylinder pistons inward with wood dowel.
Then release pistons and allow them to return underspring pressure. Continue bleeding operations until
air bubbles are no longer visible in fluid.
REMOVAL
(1) Siphon and drain the fluid from the reservoir.
(2) Remove the brake lines at the master cylinder.
(3) Disconnect the fluid level electrical connector
from the reservoir.
(4) Remove mounting nuts from the master cylin-
der.
(5) Remove master cylinder.
(6) Remove cylinder cover and drain the rest of the
fluid.
(7) If master cylinder reservoir requires service-
,(Refer to 5 - BRAKES/HYDRAULIC/MECHANICAL/
FLUID RESERVOIR - REMOVAL). (Fig. 41)
INSTALLATION
NOTE: If master cylinder is replaced, bleed cylinder
before installation.
(1) Clean cylinder mounting surface of brake
booster.
(2) Install master cylinder onto brake booster
studs.
(3) Install mounting nuts and tighten to 25 N´m
(220 in. lbs.).
(4) Connect the brake lines to the master cylinder
and tighten to 20 N´m (180 in. lbs.).
(5) Connect fluid level electrical connector to the
reservoir.
(6) Fill and bleed base brake system,(Refer to 5 -
BRAKES - STANDARD PROCEDURE).
Fig. 38 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. 39 TYPICAL - VACUUM CHECK VALVE AND
SEAL
1 - BOOSTER CHECK VALVE
2 - APPLY TEST VACUUM HERE
3 - VALVE SEAL
Fig. 40 MASTER - TYPICAL
1 - BLEEDING TUBES
2 - RESERVOIR
KJBRAKES - BASE 5 - 25
MASTER CYLINDER (Continued)

FLUID RESERVOIR
REMOVAL
(1) Install prop rod on brake pedal to keep pres-
sure on the brake system.
(2) Remove reservoir cap and siphon fluid into
drain container.
(3) Remove the electrical connector from the fluid
level switch in the reservoir.
(4) Remove the reservoir mounting bolt.
(5) Remove the reservoir from the master cylinder
by pulling upwards.
(6) Remove old grommets from cylinder body.
INSTALLATION
(1) Fill and bleed master cylinder on bench before
installation in vehicle.
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.
(2) Lubricate new grommets with clean brake fluid
and Install new grommets in cylinder body. Use fin-
ger pressure to install and seat grommets.
(3) Start reservoir in grommets. Then rock reser-
voir back and forth while pressing downward to seat
it in grommets.
(4) Install the mounting bolt for the reservoir to
the master cylinder.
(5) Reconnect the electrical connector to the fluid
reservoir level switch.(6) Remove the prop rod from the vehicle.
(7) Fill and bleed base brake system,(Refer to 5 -
BRAKES - STANDARD PROCEDURE).
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 PROCEDURES - MASTER
CYLINDER FLUID LEVEL
Always clean the master cylinder reservoir and cap
before adding fluid. This will prevent dirt from fall-
ing in the reservoir and contaminating the brake
fluid.
The reservoir has a ADD and a FULL mark on the
side (Fig. 42) fill to the FULL mark.
Fig. 41 MASTER CYLINDER
1 - FLUID RESERVOIR
2 - BOOSTER
3 - FLUID LEVEL SWITCH
4 - MASTER CYLINDER
5 - FLUID LEVEL MARKS
Fig. 42 TYPICAL - MASTER CYLINDER FLUID
LEVEL
1 - FLUID LEVEL MARKS
2 - RESERVOIR
5 - 26 BRAKES - BASEKJ
MASTER CYLINDER (Continued)

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
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 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.
DRUM
DIAGNOSIS AND TESTING - BRAKE DRUM
The maximum allowable diameter of the drum
braking surface is indicated on the drum outer edge.
Generally, a drum can be machined to a maximum of
1.52 mm (0.060 in.) oversize. Always replace the
drum if machining would cause drum diameter to
exceed the size limit indicated on the drum.
BRAKE DRUM RUNOUT
Measure drum diameter and runout with an accu-
rate gauge. The most accurate method of measure-
ment involves mounting the drum in a brake lathe
and checking variation and runout with a dial indi-
cator.
Variations in drum diameter should not exceed
0.076 mm (0.003 in.). Drum runout should not exceed
0.20 mm (0.008 in.) out of round. Machine the drum
if runout or variation exceed these values. Replace
the drum if machining causes the drum to exceed the
maximum allowable diameter.
STANDARD PROCEDURES - BRAKE DRUM
MACHINING
The brake drums can be machined on a drum lathe
when necessary. Initial machining cuts should be lim-
ited to 0.12 - 0.20 mm (0.005 - 0.008 in.) at a time as
heavier feed rates can produce taper and surface
variation. Final finish cuts of 0.025 to 0.038 mm(0.001 to 0.0015 in.) are recommended and will gen-
erally provide the best surface finish.
Be sure the drum is securely mounted in the lathe
before machining operations. A damper strap should
always be used around the drum to reduce vibration
and avoid chatter marks.
The maximum allowable diameter of the drum
braking surface is stamped or cast into the drum
outer edge.
CAUTION: Replace the drum if machining will cause
the drum to exceed the maximum allowable diame-
ter.
SUPPORT PLATE
REMOVAL
REMOVAL - 198 RBI AXLE
(1) Remove wheel and tire assembly.
(2) Remove the brake drum.
(3) Remove the brake shoes.
(4) Remove parking brake cable from parking
brake lever.
(5) Compress parking brake cable retainer tabs.
Then push retainer and cable through and out of
support plate.
(6) Disconnect brake line at wheel cylinder.
(7) Remove wheel cylinder from support plate,(Re-
fer to 5 - BRAKES/HYDRAULIC/MECHANICAL/
WHEEL CYLINDERS - REMOVAL).
(8) Remove the four bolts attaching the support
plate to axle and remove the support plate with the
axle, bearing and seal.
(9) Remove axle shaft,(Refer to 3 - DIFFEREN-
TIAL & DRIVELINE/REAR AXLE/AXLE SHAFTS -
REMOVAL).
REMOVAL - 8 1/4 AXLE
(1) Remove the wheel and tire assembly.
(2) Remove the brake drum.
(3) Install the brake pedal prop rod.
(4) Remove the brake shoes (Refer to 5 - BRAKES/
HYDRAULIC/MECHANICAL/BRAKE PADS/SHOES
- REMOVAL).
(5) Remove parking brake cable from parking
brake lever.
(6) Compress parking brake cable retainer tabs.
Then push retainer and cable through and out of
support plate.
(7) Disconnect the brake line at wheel cylinder.
(8) Remove the wheel cylinder from the support
plate,(Refer to 5 - BRAKES/HYDRAULIC/MECHAN-
ICAL/WHEEL CYLINDERS - REMOVAL).
KJBRAKES - BASE 5 - 27
FLUID (Continued)

(9) Remove the axle shaft, (Refer to 3 - DIFFER-
ENTIAL & DRIVELINE/REAR AXLE - 8 1/4/AXLE
SHAFTS - REMOVAL).
(10) Remove the bolts attaching the support plate
to the axle and remove the support plate (Fig. 43).
INSTALLATION
INSTALLATION - 198 RBI AXLE
(1) Install the support plate on the axle flange.
Tighten 75 N´m (55 ft. lbs.)
(2) Install the axle, bearing and seal into the hous-
ing and tighten the four attaching bolts to 61 N´m
(45 ft. lbs.).
(3) Install the wheel cylinder,(Refer to 5 -
BRAKES/HYDRAULIC/MECHANICAL/WHEEL
CYLINDERS - INSTALLATION).
(4) Install the brake line in the wheel cylinder.
(5) Install the parking brake cable in the support
plate.
(6) Connect parking brake cable to lever on sec-
ondary shoe and install brake shoes on support plate.
(7) Adjust the brake shoes to the drum with the
brake gauge.
(8) Install the brake drum and wheel and tire
assembly (Refer to 22 - TIRES/WHEELS/WHEELS -
STANDARD PROCEDURE).
(9) Bleed brake system,(Refer to 5 - BRAKES -
STANDARD PROCEDURE) OR (Refer to 5 -
BRAKES - STANDARD PROCEDURE).
INSTALLATION - 8 1/4 AXLE
(1) Install the support plate on the axle flange.
Tighten attaching bolts to 61 N´m (45 ft. lbs.) (Fig.
43).(2) Install the wheel cylinder,(Refer to 5 -
BRAKES/HYDRAULIC/MECHANICAL/WHEEL
CYLINDERS - INSTALLATION).
(3) Install the brake line in the wheel cylinder and
tighten the line to 14 N´m (124 in.lbs.)..
(4) Remove the brake pedal prop rod.
(5) Install the parking brake cable in the support
plate.
(6) Install the axle shaft, (Refer to 3 - DIFFEREN-
TIAL & DRIVELINE/REAR AXLE - 8 1/4/AXLE
SHAFTS - INSTALLATION).
(7) Connect the parking brake cable to the lever on
the primary shoe and install the brake shoes on the
support plate (Refer to 5 - BRAKES/HYDRAULIC/
MECHANICAL/BRAKE PADS/SHOES - INSTALLA-
TION).
(8) Adjust the brake shoes to the drum with the
brake gauge (Refer to 5 - BRAKES/HYDRAULIC/
MECHANICAL/BRAKE PADS/SHOES - ADJUST-
MENTS).
(9) Install the brake drum.
(10) Install the wheel and tire assembly (Refer to
22 - TIRES/WHEELS/WHEELS - STANDARD PRO-
CEDURE).
(11) Bleed the brake system,(Refer to 5 - BRAKES
- STANDARD PROCEDURE).
WHEEL CYLINDERS
REMOVAL
(1) Remove wheel and tire assembly.
(2) Remove brake drum.
(3) Install brake pedal prop rod.
(4) Disconnect wheel cylinder brake line.
(5) Remove brake shoe return springs and move
shoes out of engagement with cylinder push rods.
(6) Remove cylinder attaching bolts and remove
cylinder from support plate (Fig. 44).
DISASSEMBLY
(1) Remove push rods and boots (Fig. 45).
(2) Press pistons, cups and spring and expander
out of cylinder bore.
(3) Remove bleed screw.
CLEANING
Clean the cylinder and pistons with clean brake
fluid or brake cleaner only. Do not use any other
cleaning agents.
Dry the cylinder and pistons with compressed air.
Do not use rags or shop towels to dry the cylinder
components. Lint from cloth material will adhere to
the cylinder bores and pistons.
Fig. 43 SUPPORT PLATE 8 1/4
1 - SUPPORT PLATE
2 - MOUNTING NUTS
5 - 28 BRAKES - BASEKJ
SUPPORT PLATE (Continued)