JEEP CHEROKEE 1995 Service Repair Manual

POWER BRAKE BOOSTER REMOVAL
(XJ WITH ABS)
(1) Disconnect vacuum and vent hoses at air
cleaner cover.
(2) Loosen clamp securing air cleaner hose to in-
take manifold. Use screwdriver to tap clamp loose.
(3) Remove air cleaner cover and hose. Then re-
move air filter from air cleaner housing (Fig. 4).
(4) Remove two bolts and one nut that secure air
cleaner housing to body (Fig. 4).
(5) Remove air cleaner housing from engine com-
partment (Fig. 4).
(6) Disconnect wire at combination valve pressure
differential switch (Fig. 5). Do not pull on wires to
disconnect. Unsnap lock tabs on connecter to remove
wires.
(7) Disconnect canister vacuum line at manifold
fitting (Fig. 6).(8) Disconnect brake booster vacuum hose at in-
take manifold fitting (Fig. 7). Move hose aside for
working clearance.
(9) Unseat small S-clip that secures brakelines
(Fig. 8).
(10) Remove front brakeline that connects master
cylinder front port to combination valve front port
(Fig. 8).
Fig. 3 Power Brake Booster Internal Components
5 - 24 POWER BRAKE BOOSTERÐBRAKE PEDALÐBRAKELIGHT SWITCHJ

Fig. 4 Air Cleaner Components
Fig. 5 Pressure Differential Switch Wire Connection
Fig. 6 Canister Vacuum Line Location
(At Manifold Fitting)
Fig. 7 Booster Vacuum Hose Removal/Installation
(From Manifold Fitting)
Fig. 8 Master Cylinder Front Brakeline Removal/
Installation
JPOWER BRAKE BOOSTERÐBRAKE PEDALÐBRAKELIGHT SWITCH 5 - 25

(11) Disconnect master cylinder rear brakeline at
cylinder. Then loosen line at combination valve and
swing line around to opposite side of cylinder (Fig. 9).
(12) Disconnect rear brakeline at HCU (Fig. 10).
(13) Disconnect both flex brakelines at HCU (Fig.
10).
(14) Disconnect HCU line to rear brakes at HCU
port (Fig. 10).
(15) Remove nut attaching combination valve
bracket to brake booster stud.
(16) Remove combination valve and brakelines as
assembly (Fig. 11). Work valve bracket off booster
stud. Then work brakelines around cylinder and
HCU and remove assembly.
(17) Remove nuts attaching master cylinder to
booster studs and remove cylinder (Fig. 12).
(18) Remove master cylinder reservoir cap and
drain fluid.
(19) Disconnect HCU solenoid harness from main
harness (Fig. 13).
(20) Disconnect HCU pump motor harness (Fig.
14).(21) Disconnect lines at lower left side of HCU
(Fig. 15).
(22) Remove nuts attaching HCU mounting
bracket to stud plate and body. Then remove HCU
and bracket as assembly.
(23) In passenger compartment, remove instru-
ment panel lower trim cover.
(24) Remove retaining clip that secures booster
push rod to brake pedal (Fig. 16).
(25) Remove nuts attaching booster to passenger
compartment side of dash panel.
(26) In engine compartment, slide booster studs
out of dash panel, tilt booster upward, and remove
booster from engine compartment.
(27) Remove booster spacer, if equipped.
(28) Remove dash seal from booster, or dash panel.
Fig. 9 Disconnecting Master Cylinder Rear Brakeline
Fig. 10 Location Of HCU Flexlines And HCU Line To
Rear Brakes
Fig. 11 Combination Valve And Brakeline Removal
Fig. 12 Master Cylinder Attaching Nut Removal
5 - 26 POWER BRAKE BOOSTERÐBRAKE PEDALÐBRAKELIGHT SWITCHJ

POWER BRAKE BOOSTER INSTALLATION (XJ WITH
ABS)
(1) If new booster is being installed, install new
check valve and vacuum hose (Fig. 17). Also install
dash seal and spacer on new booster, if equipped.
(2) Position booster on dash panel (Fig. 17) seat
booster studs in dash panel holes.
(3) Working inside vehicle, install nuts on booster
mounting studs. Tighten nuts just enough to hold
booster in place.
(4) Attach booster push rod to brake pedal. Secure
push rod with retainer clip.
(5) Tighten booster attaching nuts to 41 Nzm (30 ft.
lbs.) on XJ and 34 Nzm (25 ft. lbs.) on YJ.
(6) If necessary, bleed master cylinder on bench be-
fore installation. Refer to procedure in master cylin-
der section.
(7) If new master cylinder is being installed,re-
move plastic protective sleeve from primary
piston shank.
Fig. 13 Disconnecting HCU Solenoid Harness
Fig. 14 Disconnecting HCU Pump Harness
Fig. 15 HCU Front/Rear Brakeline Connections
Fig. 16 Push Rod Attachment At Brake Pedal
Fig. 17 Brake Booster Positioned On Dash Panel
JPOWER BRAKE BOOSTERÐBRAKE PEDALÐBRAKELIGHT SWITCH 5 - 27

(8) Check condition of seal at rear of master cylin-
der (Fig. 22). Clean and reposition seal if dislodged.
Replace seal if cut, or torn.
(9) Clean cylinder mounting surface of brake
booster (Fig. 19). Use shop towel wetted with brake
cleaner for this purpose. Dirt, grease, or similar ma-
terials will prevent proper cylinder seating and could
result in vacuum leak.
(10) Position master cylinder on booster studs (Fig.
20).Be sure booster push rod is centered and
seated in master cylinder piston shank.
(11) Install and tighten master cylinder attaching
nuts to 25 Nzm (220 in. lbs.) torque.(12) Install HCU as follows:
(a) If only the HCU was removed, position HCU
in mounting bracket. Then install and tighten
three shoulder bolts that attach HCU to bracket
(Figs. 21 and 22). One bolt is used at forward end
of bracket and two at rear as shown.
(b) If HCU and bracket were removed as assem-
bly, position bracket on studs and install attaching
nuts. Tighten nuts to 10-13 Nzm (92-112 in. lbs.)
torque.
(c) On right hand drive models, If brackets were
removed, assemble brackets. Then position lower
bracket on body studs and install attaching nuts
and the one attaching bolt (Fig. 23).
(13) If HCU mounting bracket was not removed,
press solenoid harness connecter fasteners into
mounting bracket holes.
(14) Connect HCU pump motor and solenoid har-
nesses (Figs. 13 and 14).
(15) Connect brakelines to HCU. Start brakeline
fittings in HCU ports by hand to avoid cross thread-
ing (Fig. 24). Then tighten line fittings snug but not
to required torque at this time.
Fig. 18 Checking Master Cylinder Seal
Fig. 19 Cylinder Mounting Surface Of Brake Booster
Fig. 20 Master Cylinder Installation
Fig. 21 Installing HCU Front Shoulder Bolt
Fig. 22 Installing HCU Rear Shoulder Bolts
5 - 28 POWER BRAKE BOOSTERÐBRAKE PEDALÐBRAKELIGHT SWITCHJ

(16) Install combination valve as follows:
(a) Work combination valve and brakelines into
position.
(b) Slide combination valve bracket onto booster
stud closest to driver side fender (Fig. 25). Then in-
stall bracket attaching nut but do not fully tighten
nut at this time.
(c) Connect flex lines to HCU. Start lines by
hand to avoid cross threading.
(17) Swing rear brakeline around and connect it to
master cylinder. Then install and connect front
brakeline to combination valve and master cylinder.
Start brakelines by hand to avoid cross threading.
(18) Tighten combination valve bracket attaching
nut to 25 Nzm (220 in. lbs.) torque.
(19) Install clip on lines from master cylinder to
combination valve.
(20) Connect wire to pressure differential switch
on combination valve.
(21) Connect flex lines to HCU (Fig. 10). Start line
fittings by hand to avoid cross threading. Then
tighten fittings snug but not to required torque at
this time.(22) Bleed brakes. Refer to procedure in Brake
Fluid-Brake Bleeding-Brakelines And Hoses section.
(23) Tighten brakeline fittings to 15-18 Nzm (130-
160 in. lbs.) at HCU and master cylinder, and 18-24
Nzm (160-210 in. lbs.) at combination valve.
(24) Install air cleaner assembly.
(25) Connect vacuum lines to manifold fittings.
(26) Check brake pedal action before moving vehi-
cle. Bleed brakes again if pedal is not firm (feels soft/
spongy).POWER BRAKE BOOSTER REMOVAL (XJ WITHOUT
ABS)
(1) Disconnect vent and vacuum hose from engine
air cleaner cover.
(2) Remove engine air cleaner cover, filter, housing
and hoses (Fig. 4).
(3) Disconnect brakelines at master cylinder.
(4) Disconnect wire at combination valve differen-
tial pressure switch.
(5) If combination valve does not have an integral
bracket, disconnect brakelines at combination valve
and remove valve.
(6) If combination valve has integral bracket, re-
move nut attaching valve bracket to booster studs
and remove valve.
(7) Remove nuts attaching master cylinder to
booster studs and remove cylinder.
(8) Disconnect vacuum hose from booster check
valve.
(9) In passenger compartment, remove instrument
panel lower trim cover.
(10) Remove retaining clip that secures booster
push rod to brake pedal (Fig. 5).
Fig. 23 HCU And Bracket Mounting (RHD Models)
Fig. 24 Starting Brakelines In HCU
Fig. 25 Combination Valve Installation
JPOWER BRAKE BOOSTERÐBRAKE PEDALÐBRAKELIGHT SWITCH 5 - 29

(11) Remove nuts attaching booster to passenger
compartment side of dash panel.
(12) In engine compartment, slide booster studs
out of dash panel, tilt booster upward, and remove
booster from engine compartment.
(13) Remove dash seal from booster.
(14) If booster is only being removed for access to
other components, cover booster front opening with
clean shop towel.
POWER BRAKE BOOSTER INSTALLATION (XJ
WITHOUT ABS)
(1) If original booster is being installed, test check
valve with vacuum tool before booster installation.
Replace check valve if it will not hold vacuum.
(2) Install dash seal on booster.
(3) Align and position booster on dash panel (Fig.
17).
(4) In passenger compartment, install nuts that at-
tach booster to dash panel. Tighten nuts just enough
to hold booster in place.
(5) Slide booster push rod onto brake pedal. Then
secure push rod to pedal pin with retaining clip.
(6) Tighten booster attaching nuts to 41 Nzm (30 ft.
lbs.) on XJ and 34 Nzm (25 ft. lbs.) on YJ.
(7) Install instrument panel lower trim cover.
(8) If original master cylinder is being installed,
check condition of seal at rear of master cylinder
(Fig. 18). Clean and reposition seal if dislodged. Re-
place seal if cut, or torn.
(9) 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.
(10) Align and install master cylinder on booster
studs. Tighten cylinder attaching nuts to 13-25 Nzm
(115-220 in. lbs.) torque.
(11) Connect vacuum hose to booster check valve.
(12) Connect and secure brakelines to combination
valve and master cylinder. Start all brakeline fittings
by hand to avoid cross threading.
(13) If combination valve has integral bracket, po-
sition bracket on booster studs. Then install and
tighten bracket attaching nuts to 13-25 Nzm (115-220
in. lbs.) torque.
(14) Connect wire to combination valve switch.
(15) Top off master cylinder fluid level.
(16) Bleed brakes. Refer to procedures in section
on brake bleeding.
(17) Install engine air cleaner and hoses.
(18) Verify proper brake operation before moving
vehicle.
POWER BRAKE BOOSTER REMOVAL (YJ)
(1) Disconnect brakelines at master cylinder. Then
loosen lines at combination valve and move lines
away from cylinder.
(2) Remove nuts master cylinder to booster studs.
(3) If combination valve has integral bracket, slide
bracket off studs and move valve aside.
(4) Remove master cylinder. Slide cylinder off
studs and remove it from engine compartment.
(5) Working under instrument panel, remove re-
tainer clip that secures booster push rod to brake
pedal.
(6) Disconnect vacuum hose at booster check valve.
(7) On non-ABS models, remove nuts attaching
brake booster spacer to dash panel and remove
booster (Fig. 26).
(8) On ABS models, remove nuts attaching booster
to spacer and remove booster (Fig. 27).
POWER BRAKE BOOSTER INSTALLATION (YJ)
(1) Install seal on booster spacer, if equipped.
(2) Position booster on dash panel, or on spacer.
(3) Secure booster push rod to brake pedal with re-
taining clip.
(4) Install and tighten booster attaching nuts to
27-47 Nzm (20-35 ft. lbs.) torque. Nut torque applies
to both styles of booster.
Fig. 26 Booster Mounting (4-Cyl. Models)
Fig. 27 Booster Mounting (With ABS)
5 - 30 POWER BRAKE BOOSTERÐBRAKE PEDALÐBRAKELIGHT SWITCHJ

(5) Connect vacuum hose to brake booster check
valve.
(6) Install master cylinder and combination valve.
(7) Bleed brakes. Then tighten brakeline fittings to
15-18 Nzm (130-160 in. lbs.) at master cylinder and
18-24 Nzm (160-210 in. lbs.) at combination valve.
BRAKE PEDAL REMOVAL
(1) Remove lower trim panel and A/C duct if nec-
essary.
(2) Remove steering column lower trim panel and
bezel.(3) Remove necessary dash panel-to-instrument
panel brace rods.
(4) Disconnect and remove brakelight switch.
(5) Remove retainer clip securing booster push rod
to pedal (Fig. 16).
(6) Remove nut securing pedal shaft in support
bracket.
(7) Slide pedal shaft outward for clearance and re-
move brake pedal (Figs. 28 and 29).
(8) Remove pedal bushings if they are to be re-
placed.
BRAKE PEDAL INSTALLATION
(1) Install new bushings in pedal. Lubricate bush-
ings and pivot pin with Mopar multi mileage grease.
(2) Position pedal, sleeve and spacer(s) in bracket
and install pivot pin.
(3) Install new nut on pivot pin.Pivot pin nut is
specially formed and should not be reused. Be
sure to install new nut to secure pin.
(4) ) Tighten new pivot pin nut to 27 Nzm (20 ft.
lbs.) on models with manual transmission. Tighten
nut to 35 Nzm (26 ft. lbs.) on models with automatic
transmission.
(5) Install booster push rod on pedal pin (Fig. 16).
Secure push rod with original, or new retainer clip if
necessary.
(6) Install and connect brakelight switch.
(7) Install dash brace rod, if equipped.
(8) Install instrument panel and steering column
trim covers.
Fig. 28 Brake Pedal And Support Bracket (YJ)
Fig. 29 Brake Pedal And Support Bracket (XJ)
JPOWER BRAKE BOOSTERÐBRAKE PEDALÐBRAKELIGHT SWITCH 5 - 31

BRAKELIGHT SWITCH REMOVAL
The brakelight switch is mounted in the pedal sup-
port bracket and is operated by the pedal. The switch
is secured in the bracket with a retainer (Fig. 30).
(1) Remove steering column cover and lower trim
panel for switch access, if necessary.
(2) Disconnect switch wire harness.
(3) Thread switch out of retainer, or rock switch
up/down and pull it rearward out of retainer.
(4) Inspect switch retainer, if equipped. Replace re-
tainer if worn, distorted, loose, or damaged.
BRAKELIGHT SWITCH INSTALLATION
(1) Insert replacement switch in retainer. Thread
switch into place or rock it up/down until switch
plunger touches brake pedal. Insert switch in bracket
and thread clip onto plunger to secure switch.
(2) Connect switch wires.
(3) Check switch operation. Adjust switch position
if necessary. Refer to procedures in this section.
(4) Install trim panels (if removed).
BRAKELIGHT SWITCH ADJUSTMENT
A plunger-type brakelight switch is used on XJ and
YJ models (Fig. 30). The switch plunger is actuated
directly by the brake pedal.
The switch internal contacts are open when the
brake pedal is in the released position. Brake appli-
cation moves the pedal away from the switch allow-
ing the plunger to extend. As the plunger extends,
the switch internal contacts close completing the cir-
cuit to the brakelights.
The switch is retained in the bracket by a clip. The
clip has tangs that seat in the threads of the switch
plunger barrel.
SWITCH ADJUSTMENT PROCEDURE
(1) Check switch adjustment. Move the brake
pedal forward by hand and note operation of the
switch plunger. Plunger should extend when pedalfree play is taken up and brake application begins. A
clearance of approximately 3 mm (1/8 in.) should ex-
ist between plunger and pedal at this point.
(a) If switch-to-pedal clearance is OK and brake-
lights operate correctly, adjustment is not required.
(b) If switch plunger does not extend and clear-
ance between pedal and plunger is insufficient, ad-
just switch position as described in step (2).
(2) Grasp brake pedal and pull it rearward as far
as possible. Switch plunger barrel will ``ratchet'' rear-
ward in retaining clip to correct position.
(3) Verify brakelight switch operation and proper
clearance between switch plunger and brake pedal.
CAUTION: Be very sure the brake pedal returns to a
fully released position after adjustment. The switch
can interfere with full pedal return if too far forward.
The result will be brake drag caused by partial
brake application.
Fig. 30 Brakelight Switch Mounting And Location
(XJ/YJ)
5 - 32 POWER BRAKE BOOSTERÐBRAKE PEDALÐBRAKELIGHT SWITCHJ

ABS OPERATION AND SERVICE
INDEX
page page
ABS Component Serviceability............... 37
ABS Diagnostic Connector.................. 35
ABS Operation in Antilock Braking Mode........ 36
ABS Operation in Normal Braking Mode........ 35
ABS System Power-Up and Initialization........ 35
Acceleration Switch........................ 35
Acceleration Switch Installation............... 39
Acceleration Switch Operation................ 37
Acceleration Switch Removal................ 39
Combination Valve........................ 34
ECU Installation (XJ Models)................. 40
ECU Operation........................... 37
ECU Removal (XJ Models).................. 40
ECU Removal/Installation (YJ Models).......... 41
Electronic Control Unit (ECU)................ 34
Front Wheel Sensor Installation............... 38
Front Wheel Sensor Removal................ 38HCU Installation (XJ)....................... 43
HCU Installation (YJ)....................... 44
HCU Operation........................... 36
HCU Removal (XJ)........................ 41
HCU Removal (YJ)........................ 44
Hydraulic Control Unit (HCU)................. 33
Ignition Switch........................... 35
Master Cylinder/Power Brake Booster.......... 34
Rear Wheel Sensor Installation and Adjustment . . . 38
Rear Wheel Sensor Removal................ 38
Speed Sensor Air Gap..................... 37
System Description........................ 33
System Relays........................... 35
System Warning Light...................... 35
Wheel Speed Sensor Operation.............. 37
Wheel Speed Sensors..................... 34
SYSTEM DESCRIPTION
The Jeep antilock brake system (ABS) is an elec-
tronically operated, all wheel brake control system.
The system is designed to prevent wheel lockup
and maintain steering control during periods of high
wheel slip when braking. Preventing lockup is accom-
plished by modulating fluid pressure to the wheel
brake units.
The hydraulic system is a three channel design.
The front wheel brakes are controlled individually
and the rear wheel brakes in tandem (Fig. 1). The
ABS electrical system is separate from other electri-
cal circuits in the vehicle. A specially programmed
electronic control unit (ECU) operates the system
components.
ABS system major components include:
²hydraulic control unit (HCU)
²electronic control unit (ECU)
²wheel speed sensors and axle shaft tone rings
²acceleration switch
²main relay and pump motor relay
²ABS warning light
²pump motor sensor
HYDRAULIC CONTROL UNIT (HCU)
The hydraulic control unit (HCU) consists of a
valve body, pump body, accumulators, pump motor,
and wire harnesses (Fig. 2).
The pump, motor, and accumulators are combined
into an assembly attached to the valve body. The ac-
cumulators store the extra fluid released to the sys-
tem for ABS mode operation. The pump provides the
fluid volume needed and is operated by a DC type
motor. The motor is controlled by the ECU.The valve body contains the solenoid valves. The
valves modulate brake pressure during antilock brak-
ing and are controlled by the ECU.
The HCU provides three channel pressure control
to the front and rear brakes. One channel controls
the rear wheel brakes in tandem. The two remaining
channels control the front wheel brakes individually.
During antilock braking, the solenoid valves are
opened and closed as needed. The valves are not static.
They are cycled rapidly and continuously to modulate
pressure and control wheel slip and deceleration.
Fig. 1 Jeep ABS System
JABS OPERATION AND SERVICE 5 - 33