ECU JEEP CHEROKEE 1995 Service User Guide

fied. This causes pull to switch direction in favor of
the brake unit that is functioning normally.
When diagnosing a change in pull condition, re-
member that pull will return to the original direction
if the dragging brake unit is allowed to cool down
(and is not seriously damaged).
REAR BRAKE GRAB
Rear grab (or pull) is usually caused by contami-
nated lining, bent or binding shoes and support
plates, or improperly assembled components. This is
particularly true when only one rear wheel is in-
volved. However, when both rear wheels are affected,
the master cylinder could be at fault.
BRAKES DO NOT HOLD AFTER DRIVING THROUGH
DEEP WATER PUDDLES
This condition is caused by water soaked lining. If
the lining is only wet, it can be dried by driving with
the brakes lightly applied for a mile or two. However,
if the lining is both wet and dirty, disassembly and
cleaning will be necessary.
CONTAMINATED BRAKELINING
Brakelining contaminated by water is salvageable.
The lining can either be air dried or dried using heat.
In cases where brakelining is contaminated by oil,
grease, or brake fluid, the lining should be replaced.
Replacement is especially necessary when fluids/lu-
bricants have actually soaked into the lining mate-
rial. However, grease or dirt that gets onto the lining
surface (from handling) during brake repairs, can be
cleaned off. Spray the lining surface clean with Mo-
par brake cleaner.
BRAKE FLUID CONTAMINATION
There are two basic causes of brake fluid contami-
nation. The first involves allowing dirt, debris, or
other materials to enter the cylinder reservoirs when
the cover is off. The second involves adding non-rec-
ommended fluids to the cylinder reservoirs.
Brake fluid contaminated with only dirt, or debris
usually retains a normal appearance. In some cases,
the foreign material will remain suspended in the
fluid and be visible. The fluid and foreign material
can be removed from the reservoir with a suction gun
but only if the brakes have not been applied. If the
brakes are applied after contamination, system flush-
ing will be required. The master cylinder may also
have to be disassembled, cleaned and the piston seals
replaced. Foreign material lodged in the reservoir
compensator/return ports can cause brake drag by re-
stricting fluid return after brake application.
Brake fluid contaminated by a non-recommended
fluid may appear discolored, milky, oily looking, or
foamy. However, remember that brake fluid will
darken in time and occasionally be cloudy in appear-ance. These are normal conditions and should not be
mistaken for contamination.
If some type of oil has been added to the system,
the fluid will separate into distinct layers. To verify
this, drain off a sample with a clean suction gun.
Then pour the sample into a glass container and ob-
serve fluid action. If the fluid separates into distinct
layers, it is definitely contaminated.
The only real correction for contamination by non-
recommended fluid is to flush the entire hydraulic
system and replace all the seals.
BRAKE NOISE
Squeak/Squeal
Factory installed brakelining is made from as-
bestos free materials. These materials have dif-
ferent operating characteristics than previous
lining material. Under certain conditions, as-
bestos free lining may generate some squeak,
groan or chirp noise. This noise is considered
normal and does not indicate a problem. The
only time inspection is necessary, is when noise
becomes constant or when grinding, scraping
noises occur.
Constant brake squeak or squeal may be due to lin-
ings that are wet or contaminated with brake fluid,
grease, or oil. Glazed linings, rotors/drums with hard
spots, and dirt/foreign material embedded in the
brake lining also cause squeak. Loud squeak, squeal,
scraping, or grinding sounds are a sign of severely
worn brake lining. If the lining has worn completely
through in spots, metal-to-metal contact occurs.
Thump/Clunk
Thumping or clunk noises during braking are fre-
quentlynotcaused by brake components. In many
cases, such noises are caused by loose or damaged
steering, suspension, or engine components. However,
calipers that bind on the slide surfaces can generate
a thump or clunk noise. In addition, worn out, im-
properly adjusted, or improperly assembled rear
brakeshoes can also produce a thump noise.
Chatter/Shudder
Brake chatter, or shudder is usually caused by
loose or worn components, or glazed/burnt lining. Ro-
tors with hard spots can also contribute to chatter.
Additional causes of chatter are out of tolerance ro-
tors, brake lining not securely attached to the shoes,
loose wheel bearings and contaminated brake lining.
WHEEL AND TIRE PROBLEMS
Some conditions attributed to brake components
may actually be caused by a wheel or tire problem.
A damaged wheel can cause shudder, vibration and
pull. A worn or damaged tire can also cause pull.
Severely worn tires with very little tread left can
JSERVICE BRAKE DIAGNOSIS 5 - 7

produce a condition similar to grab as the tire loses
and recovers traction.
Flat-spotted tires can cause vibration and wheel
tramp and generate shudder during brake operation.
A tire with internal damage such as a severe bruise
or ply separation can cause vibration and pull. The
pull will be magnified when braking.
DIAGNOSING PARKING BRAKE MALFUNCTIONS
Adjustment Mechanism
Parking brake adjustment is controlled by a ca-
ble tensioner mechanism. The cable tensioner,
once adjusted at the factory, will not need further
attention under normal circumstances. There are
only two instances when adjustment is required.
The first is when a new tensioner, or cables have
been installed. And the second, is when the ten-
sioner and cables are disconnected for access to
other brake components.
Parking Brake Switch And Warning Light Illumination
The parking brake switch on the lever, or foot
pedal, is in circuit with the red warning light. The
switch will illuminate the red light only when the
parking brakes are applied. If the light remains on
after parking brake release, the switch or wires are
faulty, or cable tensioner adjustment is incorrect.
If the red light comes on while the vehicle is in mo-
tion and brake pedal height decreases, a fault has oc-
curred in the front or rear brake hydraulic system.
Parking Brake problem Causes
In most cases, the actual cause of an improperly
functioning parking brake (too loose/too tight/wont
hold), can be traced to a drum brake component.
The leading cause of improper parking brake
operation, is excessive clearance between the
brakeshoes and the drum surface. Excessive
clearance is a result of: lining and/or drum
wear; oversize drums; or inoperative shoe ad-
juster components.
Excessive parking brake lever travel (sometimes de-
scribed as a loose lever or too loose condition), is the re-
sult of worn brakeshoes/drums, improper brakeshoe
adjustment, or incorrectly assembled brake parts.
A ``too loose'' condition can also be caused by inop-
erative brakeshoe adjusters. If the adjusters are mis-
assembled, they will not function. In addition, since
the adjuster mechanism only works during reverse
stops, it is important that complete stops be made.
The adjuster mechanism does not operate when roll-
ing stops are made in reverse. The vehicle must be
brought to a complete halt before the adjuster lever
will turn the adjuster screw.
A condition where the parking brakes do not hold, will
most probably be due to a wheel brake component.
Items to look for when diagnosing a parking brake
problem, are:
²rear brakeshoe wear or adjuster problem
²rear brake drum wear
²brake drums machined beyond allowable diameter
(oversize)
²parking brake front cable not secured to lever
²parking brake rear cable seized
²parking brake strut reversed
²parking brake strut not seated in both shoes
²parking brake lever not seated in secondary shoe
²parking brake lever or brakeshoe bind on support
plate
²brakeshoes reversed
²adjuster screws seized
²adjuster screws reversed
²holddown or return springs misassembled or lack
tension
²wheel cylinder pistons seized
Brake drums that are machined oversize are diffi-
cult to identify without inspection. If oversize drums
are suspected, diameter of the braking surface will
have to be checked with an accurate drum gauge.
Oversize drums will cause low brake pedal and lack
of parking brake holding ability.
Improper parking brake strut and lever installation
will result in unsatisfactory parking brake operation.
Intermixing the adjuster screws will cause drag, bind
and pull along with poor parking brake operation.
Parking brake adjustment and parts replacement pro-
cedures are described in the Parking Brake section.
MASTER CYLINDER/POWER BOOSTER TEST
(1) Start engine and check booster vacuum hose
connections. 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.
(a) If pedal holds firm, proceed to step (5).
(b) If pedal does not hold firm and falls away,
master cylinder is faulty due to internal leakage.
Overhaul or replace cylinder.
(5) Start engine and note pedal action.
(a) If pedal falls away slightly under light foot
pressure then holds firm, proceed to step (6).
(b) If no pedal action is discernible, or hard pedal
is noted, power booster or vacuum check valve is
faulty. Install known good check valve and repeat
steps (2) through (5).
(6) Rebuild booster vacuum reserve as follows: Re-
lease brake pedal. Increase engine speed to 1500
rpm, close throttle and immediately turn off ignition.
5 - 8 SERVICE BRAKE DIAGNOSISJ

the bore surface is normal and acceptable but only if
the surface is in good condition.
Replace the cylinder if the bore is scored, corroded,
or pitted.Do not hone the cylinder bore in an at-
tempt to restore the surface. Replace the cylin-
der if the bore is corroded or if doubt exists
about cylinder bore condition.
Check the outer and inner surfaces of the cylinder
for cracks or porosity, especially if wet spots were
noted on the cylinder outer surface during removal
and disassembly.
Inspect the cylinder cover, seal and retainer spring.
Replace the seal if torn or distorted and replace the
cover and spring if either part is bent or damaged in
any way.
MASTER CYLINDER ASSEMBLY
(1) Coat cylinder bore and new piston assemblies
with brake fluid.
(2) Install secondary piston in bore with push and
turn motion (Fig. 7).Do not use any tools to start
seals into bore. Tools can cut seal and scratch
bore.
(3) Insert primary piston in bore (Fig. 5).(4) Push primary piston inward and install snap
ring (Fig. 4).
MASTER CYLINDER AND COMBINATION VALVE
REMOVAL (WITH ABS)
(1) Disconnect 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. 8).
(4) Remove two bolts and one nut that secure air
cleaner housing to body (Fig. 8).
Fig. 8 Air Cleaner Components
Fig. 5 Removing/Installing Primary Piston
Fig. 6 Removing Secondary Piston Assembly
Fig. 7 Installing Secondary Piston
JMASTER CYLINDERÐCOMBINATION VALVE 5 - 17

(5) Remove air cleaner housing from engine com-
partment.
(6) Disconnect wire from combination valve pres-
sure differential switch (Fig. 9). Do not pull wire to
disconnect. Unsnap lock tabs on wire connecter.
(7) Disconnect canister vacuum line at manifold
fitting (Fig. 10).
(8) Disconnect brake booster vacuum hose at in-
take manifold fitting (Fig. 11). Move hose aside for
working clearance.(9) Unseat small S-clip that secures brakelines
(Fig. 12).
(10) Remove brakeline that connects master cylin-
der front port to combination valve front port (Fig.
12).
(11) Disconnect master cylinder rear brakeline at
cylinder. Then loosen line at combination valve and
swing line around to opposite side of cylinder (Fig.
13).
(12) Disconnect rear brakeline at HCU (Fig. 14).
(13) Disconnect both flex brakelines at HCU (Fig.
14).
(14) Disconnect HCU line to rear brakes at HCU
port (Fig. 14).
(15) Remove nut attaching combination valve
bracket to brake booster stud.
(16) Remove combination valve and brakelines as
assembly (Fig. 15). Work valve bracket off booster
stud. Then work brakelines around cylinder and
HCU and remove assembly.
Fig. 9 Pressure Differential Switch Wire Connection
Fig. 10 Canister Vacuum Line Location (At Manifold
Fitting)
Fig. 11 Booster Vacuum Hose Removal/Installation
(From Manifold Fitting)
Fig. 12 Master Cylinder Front Brakeline Removal/
Installation
Fig. 13 Disconnecting Master Cylinder Rear
Brakeline
5 - 18 MASTER CYLINDERÐCOMBINATION VALVEJ

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

(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

(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