1994 JEEP CHEROKEE service

(2) If red warning light is illuminated, or if neither
warning light is illuminated, make several stops and
note pedal action and brake response.
(3) Check brake pedal response with transmission
in Neutral and engine running. Pedal should remain
firm under steady foot pressure. If pedal falls away,
problem is either in vacuum booster or master cylin-
der.
(4) During road test, make normal and firm brake
stops in 25-40 mph range. Note faulty brake opera-
tion such as pull, grab, drag, noise, fade, pedal pul-
sation, etc.
(5) Inspect suspect brake components and refer to
problem diagnosis information for causes of various
brake conditions.
COMPONENT INSPECTION
Fluid leak points and dragging brake units can
usually be located without removing any compo-
nents. The area around a leak point will be wet with
fluid. The components at a dragging brake unit
(wheel, tire, rotor) will be quite warm or hot to the
touch.
Other brake problem conditions will require compo-
nent removal for proper inspection. Raise the vehicle
and remove the necessary wheels for better visual ac-
cess.
During component inspection, pay particular atten-
tion to heavily rusted/corroded brake components
(e.g. rotors, caliper pistons, brake return/holddown
springs, support plates, etc.).
Heavy accumulations of rust may be covering se-
vere damage to a brake component. It is wise to re-
move surface rust in order to accurately determine
the depth of rust penetration and damage. Light sur-
face rust is fairly normal and not a major concern (as
long as it is removed). However, heavy rust buildup,
especially on high mileage vehicles may cover struc-
tural damage to such important components as
brakelines, rotors, support plates, and brake boosters.
Refer to the wheel brake service procedures in this
group for more information.
DIAGNOSING SERVICE BRAKE PROBLEMS
BRAKE WARNING LIGHT OPERATION
The red brake warning light will illuminate under
the following conditions:
²for 2-3 seconds at startup as part of normal bulb
check
²parking brakes applied
²low pedal caused by malfunction in front/rear
brake hydraulic circuit (differential switch valve ac-
tuated)
If the red light remains on after startup, first ver-
ify that the parking brakes are fully released. Then
check pedal action and fluid level. A red light indi-
cates that the valve in the differential pressureswitch has been actuated. If a problem is confirmed,
inspect the hydraulic system and wheel brake compo-
nents.
On models with ABS brakes, the amber warning
light only illuminates when an ABS component has
malfunctioned. The ABS light operates indepen-
dently of the red warning light. Refer to the antilock
brake section for more detailed diagnosis informa-
tion.
PEDAL FALLS AWAY
A brake pedal that falls away under steady foot
pressure is generally the result of a system leak. The
leak point could be at a brakeline, fitting, hose,
wheel cylinder, or caliper. Internal leakage in the
master cylinder caused by worn or damaged piston
cups, may also be the problem cause.
If leakage is severe, fluid will be evident at or
around the leaking component. However internal
leakage in the master cylinder will not be physically
evident. Refer to the cylinder test procedure in this
section.
LOW PEDAL
If a low pedal is experienced, pump the pedal sev-
eral times. If the pedal comes back up, worn lining
and worn rotors or drums are the most likely causes.
However, if the pedal remains low and/or the warn-
ing light illuminates, the problem is in the master
cylinder, wheel cylinders, or calipers.
A decrease in master cylinder fluid level may only
be the result of normal lining wear. Fluid level will
decrease as lining wear occurs. It is a result of the
outward movement of caliper and wheel cylinder pis-
tons to compensate for normal wear.
SPONGY PEDAL
A spongy pedal is most often caused by air in the
system. However, thin drums or substandard brake
lines and hoses will also cause a condition similar to
a spongy pedal. The proper course of action is to
bleed the system, or replace thin drums and suspect
quality brake lines and hoses.
HARD PEDAL OR HIGH PEDAL EFFORT
A hard pedal or high pedal effort may be due to
lining that is water soaked, contaminated, glazed, or
badly worn. The power booster or check valve could
also be faulty. Test the booster and valve as de-
scribed in this section.
BRAKE DRAG
Brake drag occurs when the lining is in constant
contact with the rotor or drum. Drag can occur at
one wheel, all wheels, fronts only, or rears only. It is
a product of incomplete brakeshoe release. Drag can
be minor or severe enough to overheat the linings,
rotors and drums.
5 - 8 BRAKESJ

Brake drag also has a direct effect on fuel economy.
If undetected, minor brake drag can be misdiagnosed
as an engine or transmission/torque converter prob-
lem.
Minor drag will usually cause slight surface char-
ring of the lining. It can also generate hard spots in
rotors and drums from the overheat/cool down pro-
cess. In most cases, the rotors, drums, wheels and
tires are quite warm to the touch after the vehicle is
stopped.
Severe drag can char the brake lining all the way
through. It can also distort and score rotors and
drums to the point of replacement. The wheels, tires
and brake components will be extremely hot. In se-
vere cases, the lining may generate smoke as it chars
from overheating.
An additional cause of drag involves the use of in-
correct length caliper mounting bolts. Bolts that are
too long can cause a partial apply condition. The cor-
rect caliper bolts have a shank length of 67 mm
(2.637 in.), plus or minus 0.6 mm (0.0236 in.). Refer
to the Disc Brake service section for more detail on
caliper bolt dimensions and identification.
Some common causes of brake drag are:
²loose or damaged wheel bearing
²seized or sticking caliper or wheel cylinder piston
²caliper binding on bushings or slide surfaces
²wrong length caliper mounting bolts (too long)
²loose caliper mounting bracket
²distorted brake drum or shoes
²rear brakeshoes binding on worn/damaged support
plates
²severely rusted/corroded components
²misassembled components.
If brake drag occurs at all wheels, the problem may
be related to a blocked master cylinder compensator
port or faulty power booster (binds-does not release).
The brakelight switch can also be a cause of drag.
An improperly mounted or adjusted brakelight
switch can prevent full brake pedal return. The re-
sult will be the same as if the master cylinder com-
pensator ports are blocked. The brakes would be
partially applied causing drag.
BRAKE FADE
Brake fade is a product of overheating caused by
brake drag. However, overheating and subsequent
fade can also be caused by riding the brake pedal,
making repeated high deceleration stops in a short
time span, or constant braking on steep roads. Refer
to the Brake Drag information in this section for
causes.
PEDAL PULSATION
Pedal pulsation is caused by components that are
loose, or beyond tolerance limits.
Disc brake rotors with excessive lateral runout or
thickness variation, or out of round brake drums arethe primary causes of pulsation. Other causes are
loose wheel bearings or calipers and worn, damaged
tires.
PULL
A front pull condition could be the result of:
²contaminated lining in one caliper
²seized caliper piston
²binding caliper
²wrong caliper mounting bolts (too long)
²loose caliper
²loose or corroded mounting bolts
²improper brakeshoes
²damaged rotor
²incorrect wheel bearing adjustment (at one wheel)
A worn, damaged wheel bearing or suspension
component are further causes of pull. A damaged
front tire (bruised, ply separation) can also cause
pull. Wrong caliper bolts (too long) will cause a par-
tial apply condition and pull if only one caliper is in-
volved.
A common and frequently misdiagnosed pull condi-
tion is where direction of pull changes after a few
stops. The cause is a combination of brake drag fol-
lowed by fade at the dragging brake unit.
As the dragging brake overheats, efficiency is so
reduced that fade occurs. If the opposite brake unit is
still functioning normally, its braking effect is mag-
nified. 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 or proportioning valve could be
at fault.
BRAKES DO NOT HOLD AFTER DRIVING
THROUGH DEEP WATER PUDDLES
This condition is generally 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, dis-
assembly and cleaning will be necessary.
BRAKE FLUID CONTAMINATION
There are two basic causes of brake fluid contami-
nation. The first involves allowing dirt, debris, or
other liquid materials to enter the cylinder reservoirs
JBRAKES 5 - 9

CAUTION: Do not allow the master cylinder reser-
voir to run dry while bleeding the brakes. Running
dry will allow air to re-enter the system making a
second bleeding operation necessary.
(6) Perform ``Bleed Brake'' procedure with DRB II
scan tool. Procedure is described in DRB II software
information and diagnostic manual.
(a) Connect DRB II scan tool to diagnostic con-
nector.
(b) Run Bleed Brake procedure as described in
tester manual.
(7) Repeat conventional bleeding procedure out-
lined in steps (1) through (8).
(8) Top off master cylinder fluid level if necessary.
(9) Verify proper brake operation.
BRAKELINES AND HOSES
Metal brakelines and rubber brake hoses should be
inspected periodically and replaced if damaged.
Rubber brake hoses should be replaced if cut,
cracked, swollen, or leaking. Rubber hoses must be
replaced. They are not repairable parts.
When installing new, or original brakelines andhoses, lubricate the fitting threads with brake fluid
before connection.
The steel brakelines should be checked every time
the vehicle is in for normal maintainence. This is im-
portant on high mileage vehicles. It is even more im-
portant when a vehicle is operated in areas where
salt is used regularly on the road surface during win-
ter.
Heavily rusted/corroded brake rotors, drums, sup-
port plates, and brakelines should be cleaned and
carefully inspected. Heavy rust buildup can hide se-
vere damge to a component. Severely rusted parts
should be replaced if you are unsure about their con-
dition.
COMBINATION VALVE
The combination valve is not a serviceable part.
The valve must be replaced if a malfunction occurs.
BRAKELINE CHARTS
Brakeline charts are provided in illustration Fig-
ures 1 through 8. The illustrations show typical
brakeline routing, hose connections and component
position.
Fig. 1 Front Brakeline Routing (XJ With ABS Brakes)
JBRAKES 5 - 15

STANDARD MASTER CYLINDER
INDEX
page page
General Service Information................ 20
Master Cylinder Installation................. 20Master Cylinder Overhaul.................. 20
Master Cylinder Removal.................. 20
GENERAL SERVICE INFORMATION
The service information in this section covers the
standard (non-ABS) master cylinder only. The center
feed master cylinder used with the ABS system is
covered in the antilock brake component service sec-
tion.
MASTER CYLINDER REMOVAL
(1) Disconnect brake lines at master cylinder.
(2) Remove cylinder mounting nuts and remove
master cylinder.
(3) Remove cylinder cover and drain fluid.
MASTER CYLINDER INSTALLATION
(1) Bleed master cylinder on bench before installa-
tion. Refer to overhaul assembly procedure in this
section for bleeding method.
(2) Install cylinder on brake booster studs and in-
stall cylinder attaching nuts. Tighten nuts to 21 NIm
(15 ft. lbs.).
(3) Connect brakelines to cylinder.
(4) Fill and bleed brake system.
MASTER CYLINDER OVERHAUL
CYLINDER DISASSEMBLY
(1) Remove cylinder cover and drain fluid.
(2) Examine cylinder cover seal. Discard seal if
torn or distorted.
(3) Clamp cylinder in vise (Fig. 1).
(4) Press primary piston inward with wood dowel
or phillips screwdriver and remove snap ring (Fig. 2).
(5) Remove and discard primary piston (Fig. 3).
Piston is serviced only as an assembly.
(6) Remove secondary piston (Fig. 4). Apply air
pressure through rear outlet port to ease piston out
of bore. Cover small ports at bottom of rear reservoir
with towel to prevent air leakage.
(7) Discard secondary piston. Do not disassemble
piston as components are only serviced as assembly.
CLEANING AND INSPECTION
Clean the cylinder with Mopar brake cleaning sol-
vent or clean brake fluid. Remove cleaning residue
with compressed air.
Inspect the cylinder bore. A light discoloration of
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.
Fig. 1 Cylinder Mounted In Vise
Fig. 2 Removing/Installing Piston Snap Ring
5 - 20 BRAKESJ

POWER BRAKE BOOSTER
INDEX
page page
Power Brake Booster Installation............. 23
Power Brake Booster Operation............. 22Power Brake Booster Removal.............. 22
Service Information....................... 22
SERVICE INFORMATION
The power brake booster is not a serviceable com-
ponent. If a booster malfunction occurs, the booster
must be replaced as an assembly. The booster (Figs.
1 and 2), is attached to the dash panel and pedal sup-
port.
POWER BRAKE BOOSTER OPERATION
Booster Components
The booster assembly consists of a housing divided
into separate chambers by an internal diaphragm.The outer edge of the diaphragm is attached to the
booster housing. The diaphragm is in turn, connected
to the booster push rod.
Two push rods are used to operate the booster. One
push rod connects the booster to the brake pedal. The
second push rod (at the forward end of the housing),
strokes the master cylinder pistons. The rear push
rod is connected to the two diaphragms in the booster
housing.
The atmospheric inlet valve is opened and closed
by the push rod connected to the brake pedal. The
booster vacuum supply is through a hose attached to
a fitting on the intake manifold. The hose is con-
nected to a vacuum check valve in the booster hous-
ing. The check valve is a one-way device that
prevents vacuum leak back.
How Brake Boost Is Generated
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 an inlet valve at the rear of the housing.
The forward portion of the booster housing (area in
front of the two diaphragms), is exposed to manifold
vacuum. The rear portion (area behind the dia-
phragms), is exposed to normal atmospheric pressure
of 101.3 kilopascals (14.7 pounds/square in.).
Pressing the brake pedal causes the rear push rod
to open the inlet valve. This exposes the area behind
the diaphragm to atmospheric pressure. The result-
ing force applied to the diaphragm is what provides
the extra apply pressure for power assist.
POWER BRAKE BOOSTER REMOVAL
(1) Loosen but do not remove nuts attaching mas-
ter cylinder to booster (Fig. 3).
(2) Remove instrument panel lower trim cover.
(3) Remove retaining clip attaching booster push
rod to brake pedal (Fig. 4).
(4) Remove bolts/nuts attaching booster to dash
panel.
(5) In engine compartment, loosen vacuum hose
clamp and disconnect vacuum hose from booster
check valve (Fig. 5).
(6) Remove master cylinder attaching nuts and re-
move cylinder from mounting studs on booster.
Fig. 1 Power Brake Booster (XJ)
Fig. 2 Power Brake Booster (YJ)
5 - 22 BRAKESJ

ence) of piston and caliper boot groove (Fig. 24).
Grease serves as corrosion protection for these areas.
(8) Press caliper piston to bottom of bore.
(9) Seat dust boot in caliper with Installer Tool
C-4842 and Tool Handle C-4171 (Fig. 25).
(10) Install caliper bleed screw if removed.
CALIPER INSTALLATION
(1) Install brakeshoes in caliper (Figs. 11, 12).
(2) Connect brake hose fitting to caliper but do not
tighten fitting bolt completely at this time.Be sure
to use new washers on fitting bolt to avoid leaks
(Fig. 26).
(3) Install caliper. Position mounting notches at
lower end of brakeshoes on bottom mounting ledge(Fig. 13). Then rotate caliper over rotor and seat
notches at upper end of shoes on mounting ledge
(Fig. 13).
(4) Coat caliper mounting bolts with GE 661 or
Dow 111 silicone grease. Then install and tighten
bolts to 10-20 Nzm (7-15 ft. lbs.) torque.
CAUTION: If new caliper bolts are being installed,
or if the original reason for repair was a drag/pull
condition, check caliper bolt length before proceed-
ing. If the bolts have a shank length greater than
67.6 mm (2.66 in.), they may contact the inboard
brakeshoe causing a partial apply condition. Refer
to Figure 14 for the required caliper bolt length.
(5) Position front brake hose clear of all chassis
components and tighten caliper fitting bolt to 31 Nzm
(23 ft. lbs.) torque.
CAUTION: Be sure the brake hose is not twisted or
kinked at any point. Also be sure the hose is clear
of all steering and suspension components. Loosen
and reposition the hose if necessary.
(6) Install wheels. Tighten wheel lug nuts to 109-
150 Nzm (80-110 ft. lbs.) torque.
(7) Fill and bleed brake system. Refer to proce-
dures in Service Adjustments section.
ROTOR REMOVAL
(1) Raise vehicle and remove wheel.
(2) Remove caliper.
(3) Remove retainers securing rotor to hub studs
(Fig. 27).
(4) Remove rotor from hub (Fig. 27).
(5) If rotor shield requires service, remove front
hub and bearing assembly.
ROTOR INSTALLATION
(1) Install rotor on hub.
(2) Install caliper.
Fig. 24 Typical Caliper/Piston Areas To Be Lightly
Coated With Silicone Grease
Fig. 25 Seating Caliper Piston Piston Dust Boot
Fig. 26 Front Brake Hose And Fitting Components
5 - 30 BRAKESJ

DISC BRAKE ROTOR REFINISHING
When To Refinish
Rotor braking surfaces can be refinished by sand-
ing and/or machining in a disc brake lathe. However,
the rotor should be cleaned and inspected before-
hand. Careful inspection will avoid refinishing rotors
with very little service life left in them.
Pay particular attention to rotors that are heavily
rusted, or corroded. Accumulated rust/corrosion on
braking surfaces and ventilating ribs may extend to
a depth beyond acceptable limits. This can be espe-cially true on: (a) high mileage vehicles; (b) vehicles
regularly exposed to road salt during winter months;
(c) vehicles operated in coastal regions where salt
air/road splash is a factor; (d) and vehicles used for
extensive off-road operation.
Recommended Refinishing Equipment
The brake lathe must be capable of machining both
rotor surfaces simultaneously with dual cutter heads
(Fig. 31).Equipment capable of machining only
one side at a time will produce a tapered rotor.
The lathe should also be equipped with a grinder at-
tachment, or dual sanding discs for final cleanup or
light refinishing.
Refinishing Techniques
If the rotor surfaces only need minor cleanup of rust,
scale, or scoring, use abrasive sanding discs to clean up
the rotor surfaces. However, when a rotor is scored or
worn, machining with cutting tools will be required.
Light cuts are recommended when machining the
rotor surfaces. Heavy feed rates are not recom-
mended and may result in chatter marks, or taper.
CAUTION: Never refinish a rotor if machining would
cause the rotor to fall below minimum allowable thick-
ness.
The final finish on the rotor should be a non-direc-
tional, cross hatch pattern (Fig. 32). Use sanding
discs to produce this finish.
WHEEL NUT TIGHTENING
The wheel attaching nuts must be tightened properly
to ensure efficient brake operation. Overtightening the
nuts or tightening them in the wrong sequence can
Fig. 31 Rotor Refinishing Equipment
Fig. 32 Preferred Rotor Surface Finish
5 - 32 BRAKESJ

(9) Coat cylinder bore, pistons, cups and expander
with brake fluid and reassemble cylinder compo-
nents. Be sure piston cup lips face expander.
WHEEL CYLINDER INSTALLATION
(1) Apply small bead of silicone sealer around cyl-
inder mounting surface of support plate.
(2) Start brakeline in wheel cylinder fitting by
hand.
(3) Align and seat wheel cylinder on support plate
(Fig. 10).
(4) Install cylinder mounting bolts (Fig. 10).
Tighten bolts to 10 Nzm (90 in. lbs.) torque.
(5) Tighten brakeline fitting to 15 Nzm (132 in.
lbs.) torque.
(6) Install brakeshoes. Adjust shoes to drum with
brake gauge.
(7) Install brake drums and lower vehicle.
(8) Fill master cylinder and bleed brakes.
SUPPORT PLATE REPLACEMENT
The support plate should cleaned and inspected
whenever the drum brake components are being ser-
viced.
Check the support plate for wear, or rust through
at the contact pads and replace the plate if neces-
sary. Be sure to lubricate the contact pads with Mo-
par multi-mileage grease before shoe installation.
Lubrication will avoid noisy operation and shoe bind.
(1) Raise vehicle and remove wheel/tire assembly.(2) Remove brake drum, brakeshoes, and wheel
cylinder.
(3) Remove axle shaft as described in Group 3.
(4) Remove support plate attaching nuts and re-
move support plate.
(5) Clean axle tube flange. If gasket is not used on
flange, apply thin bead of silicone adhesive/sealer to
flange.
(6) Position new support plate on axle tube flange.
(7) Apply Mopar Lock N9Seal, or Loctite 242 to
support plate attaching nuts. Then install and
tighten nuts.
(8) Apply light coat of Mopar multi-mileage grease
to contact pads of new support plate.
(9) Install wheel cylinder and brakeshoes.
(10) Adjust brakeshoes to drums. Refer to proce-
dure in this section.
(11) Bleed brakes.
(12) Install wheel and tire assembly.
(13) Adjust parking brake cable tensioner. Refer to
procedure in Parking Brake section.
(14) Lower vehicle and verify proper service brake
and parking brake operation.
BRAKE DRUM REFINISHING
Brake drums can be machined to restore the brak-
ing surface. Use a brake lathe to clean up light scor-
ing and wear.
CAUTION: Never refinish a brake drum if machining
will cause the drum to exceed maximum allowable
brake surface diameter.
Brake drums that are warped, distorted, or se-
verely tapered should be replaced. Do not refinish
drums exhibiting these conditions. Brake drums that
are heat checked or have hard spots should also be
replaced.
If the brake drums are heavily coated with rust,
clean and inspect them carefully. Rust damage on
high mileage drums can be severe enough to require
replacement.
The maximum allowable diameter for the drum
braking surface is usually indicated on the drum
outer face (Fig. 11).
WHEEL NUT TIGHTENING
The wheel attaching lug nuts must be tightened
properly to ensure efficient brake operation. Over-
tightening the nuts or tightening them in the wrong
sequence can cause distortion of the brake rotors and
drums.
Impact wrenches are not recommended for tighten-
ing wheel nuts. A torque wrench should be used for
this purpose.
A light coat of LPS Anti-Corrosion spray lube
around the hub face and on the studs will cut down
on rust/corrosion formation.
Fig. 9 Wheel Cylinder (10-Inch Brake)
Fig. 10 Wheel Cylinder Mounting
JBRAKES 5 - 37