1995 JEEP XJ brake

(6) Disconnect both flex brakelines at HCU (Fig. 18).
(7) Disconnect HCU solenoid harness from main
harness (Fig. 19).
(8) Disconnect HCU pump motor harness (Fig. 20).(9) If HCU mounting bracket will be left in place,
it will be necessary to remove HCU solenoid harness
connecter from mounting bracket. Remove connecter
fasteners, by squeezing them closed with needle nose
pliers; then pulling them out of bracket.
(10) Disconnect lines to front/rear brakes at lower
left side of HCU (Fig. 21).
(11) Remove HCU as follows:
(a) If only the HCU will be removed, remove
three shoulder bolts attaching HCU to mounting
bracket and remove HCU (Fig. 22).
(b) If HCU and bracket will be removed as as-
sembly, remove three nuts attaching HCU to stud
plate and remove HCU and bracket as assembly.
Fig. 18 Disconnecting Flex Lines From HCU
Fig. 19 Disconnecting HCU Solenoid Harness
Fig. 20 Disconnecting HCU Pump Harness
Fig. 21 HCU Front/Rear Brakeline Connections
Fig. 22 HCU Assembly
5 - 42 ABS OPERATION AND SERVICEJ

HCU INSTALLATION (XJ)
(1) 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. 23 and 24). 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. 25).
(2) If HCU mounting bracket was not removed,
press solenoid harness connecter fasteners into
mounting bracket.
(3) Connect HCU pump motor and solenoid har-
nesses (Figs. 19 and 20).
(4) Connect brakelines from front/rear brakes to
HCU. Start brakeline fittings in HCU ports by handto avoid cross threading (Fig. 26). Then tighten line
fittings snug but not to required torque at this time.
(5) Connect flex lines to HCU (Fig. 18). Start
brakeline fittings in flex line ports by hand to avoid
cross threading. Then tighten line fittings snug but
not to required torque at this time.
(6) Bleed brakes. Refer to procedure in Brake Flu-
id-Brake Bleeding-Brakelines And Hoses section.
(7) Tighten brakeline fittings to following torques
after brake bleeding: 15- 18 Nzm (130-160 in. lbs.) at
HCU and master cylinder and 18-24 Nzm (160-210 in.
lbs.) at combination valve.
(8) Install engine air cleaner assembly and hoses.
(9) Connect vacuum lines to manifold fittings.
(10) Check brake pedal action before moving vehi-
cle. Bleed brakes again if pedal is not firm (feels soft/
spongy).
Fig. 23 Installing HCU Front Shoulder Bolt
Fig. 24 Installing HCU Rear Shoulder Bolts
Fig. 25 HCU And Bracket Mounting (RHD Models)
Fig. 26 Starting Brakelines In HCU (By Hand)
JABS OPERATION AND SERVICE 5 - 43

HCU REMOVAL (YJ)
(1) Place shop towels under master cylinder and
HCU brakelines.
(2) Disconnect flex lines at upper part of HCU.
(3) Disconnect solenoid and pump harness wires at
HCU harness connecters.
(4) Disconnect lines to front/rear brakes at lower
part of HCU.
(5) Remove shoulder bolts attaching HCU to
mounting bracket and remove HCU.
HCU INSTALLATION (YJ)
(1) Position HCU in mounting bracket (Fig. 27).
(2) Install shoulder bolts that attach HCU to
bracket.
(3) Connect brakelines to HCU. Start brakeline fit-
tings by hand to avoid cross threading. Tighten fit-
tings snug but not to torque at this time.
(4) Connect HCU pump and solenoid harness wires
to engine compartment harness.
(5) Fill and bleed brake system.
(6) Tighten brakeline fittings to 15-18 Nzm
(130-160 in. lbs.) at HCU and master cylinder, and to
18-24 Nzm (160-210 in. lbs.) at combination valve.
Fig. 27 HCU Mounting (YJ)
5 - 44 ABS OPERATION AND SERVICEJ

DISC BRAKES
INDEX
page page
Caliper Assembly......................... 50
Caliper Cleaning and Inspection.............. 50
Caliper Disassembly....................... 48
Caliper Installation........................ 51
Caliper Operation and Wear Compensation...... 45
Caliper Removal.......................... 48
Disc Brake Rotor Refinishing................. 53
Disc Brake Rotor Runout.................... 52Disc Brake Rotor Thickness................. 52
Disc Brake Rotor Thickness Variation.......... 52
Disc Brakeshoe Installation.................. 47
Disc Brakeshoe Removal................... 46
General Information....................... 45
Rotor Installation.......................... 51
Rotor Removal........................... 51
Wheel Nut Tightening...................... 54
GENERAL INFORMATION
Jeep XJ/YJ models are equipped with single piston,
floating-type disc brake calipers. Ventilated, cast ro-
tors are used for all applications.
The disc brake calipers are supported in mounting
arms that are an integral part of the steering
knuckle. The calipers slide on mounting bolts that
also attach the calipers to the steering knuckle.
CALIPER OPERATION AND WEAR COMPENSATION
Caliper Operation
The significant feature of single piston caliper op-
eration is that the calipers are free to slide laterally
on the mounting bolts. It is the freedom of lateral
movement that allows continuous compensation for
lining wear.
A simplified cross section of a single piston caliper
is shown in Figure 1. The illustration graphically
portrays the forces at work when the brakes are ap-
plied.
Upon brake application, fluid pressure exerted
against the caliper piston increases greatly. Of equal
importance, is the fact that fluid pressure is exerted
equally and in all directions. What this means, is
that pressure in the caliper bore, will be exactly the
same as pressure on the piston. In other words, pres-
sure against piston and caliper bore is equal.
Fluid pressure applied to the piston is transmitted
directly to the inboard brakeshoe. This forces the
shoe lining against the inner surface of the disc
brake rotor (Fig. 1).
At the same time, fluid pressure within the piston
bore, forces the caliper to slide inward on the mount-
ing bolts. This action brings the outboard brakeshoe
lining into contact with the outer surface of the disc
brake rotor (Fig. 1).
In summary, fluid pressure acting simultaneously
on both piston and caliper, produces a strong clamp-
ing action. When sufficient force is applied, friction
will stop the rotors from turning and bring the vehi-
cle to a stop.Brakeshoe Wear Compensation
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 brakeshoes 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 be-
tween 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. 2).
When the brakes (and fluid pressure) are released,
the seal relaxes and retracts the piston.
Fig. 1 Disc Brake Caliper Operation
JDISC BRAKES 5 - 45

The amount of piston retraction is determined by
brakelining wear. Generally, the amount is just
enough to maintain contact between the piston and
inboard brakeshoe. Brakelining running clearance at
the rotor, will be held between zero and a maximum
of 0.12 mm (0.005 in.).
DISC BRAKESHOE REMOVAL
(1) Raise vehicle and remove front wheels.
(2) Drain small amount of fluid from master cylin-
der front brake reservoir with suction gun.
(3) Bottom caliper piston in bore with C-clamp. Po-
sition clamp screw on outboard brakeshoe and clamp
frame on rear of caliper. Typical C-clamp attachment
is shown in Figure 3.Do not allow clamp screw to
bear directly on outboard shoe retainer spring.
Use wood or metal spacer between shoe and
clamp screw if necessary.
(4) Remove caliper mounting bolts (Fig. 4).If
brakeshoes are being removed to correct a pull
or drag condition, verify length of caliper bolts
as they may be incorrect length. Refer to bolt
information in brakeshoe installation proce-
dure.
(5) Tilt top of caliper outward. Use pry tool if nec-
essary (Fig. 5).
(6) Lift caliper off steering knuckle (Fig. 6).(7)If original brakeshoes will be used, keep
them in sets (left and right); they are not inter-
changeable.
Fig. 2 Lining Wear Compensation By Piston Seal
Fig. 3 Bottoming Caliper Piston With C-Clamp
Fig. 4 Removing/Installing Caliper Mounting Bolts
Fig. 5 Tilting Caliper Outward
Fig. 6 Caliper Removal
5 - 46 DISC BRAKESJ

(8) Remove outboard shoe. Press one end of shoe
inward to disengage shoe lug. Then rotate shoe up-
ward until retainer spring clears caliper. Press oppo-
site end of shoe inward to disengage shoe lug and
rotate shoe up and out of caliper (Fig. 7).
(9) Remove inboard shoe. Grasp ends of shoe and
tilt shoe outward to release springs from caliper pis-
ton (Fig. 8). Then remove shoe from caliper.
(10) Secure caliper to nearby suspension part with
wire.Do not allow brake hose to support caliper
weight.
(11) Wipe caliper off with shop rags or towels.Do
not use compressed air. Compressed air can un-
seat dust boot and force dirt into piston bore.
(12) Inspect condition of caliper piston dust boot
(Fig. 9). Overhaul caliper if there is evidence of leak-
age past piston and dust boot. Then inspect caliper
bushings and boots (Fig. 9). Replace boots if torn or
cut. If bushings or boots are damaged, replace them.
DISC BRAKESHOE INSTALLATION
(1) Clean brakeshoe mounting ledge slide surfaces
of steering knuckle with wire brush. Then apply light
coat of Mopar multi-mileage grease to slide surfaces
(Fig. 10).
(2) Lubricate caliper mounting bolts and bushings
(Fig. 10). Use GE 661 or Dow 111 silicone grease.
(3) Keep new or original brakeshoes in sets. Do not
interchange them.
(4) Install inboard shoe in caliper (Fig. 11). Be sure
shoe retaining springs are fully seated in caliper pis-
ton.
(5) Install outboard shoe in caliper (Fig. 12). Start
one end of shoe in caliper. Rotate shoe downward and
into place until shoe locating lugs and shoe spring
are seated.
(6) Verify that locating lugs on outboard shoe are
seated in caliper (Fig. 6).
(7) Install caliper. Position notches at lower end of
brakeshoes on bottom mounting ledge (Fig. 13). Then
Fig. 7 Removing Outboard Brakeshoe
Fig. 8 Removing Inboard Brakeshoe
Fig. 9 Caliper Dust Boots And Bushing Locations
Fig. 10 Caliper Lubrication Points
JDISC BRAKES 5 - 47

install caliper over rotor and seat upper ends of
brakeshoes on top mounting ledge (Fig. 11).
CAUTION: Before securing the caliper, be sure the
caliper brake hose is not twisted, kinked or touch-
ing any chassis components. Also be sure the hose
is clear of all suspension and steering components.
Loosen and reposition the hose if necessary.
(8) Install and tighten caliper mounting 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 will contact the inboard
brakeshoe causing a partial apply condition. Refer
to Figure 14 for required caliper bolt length.
(9) Install wheels. Tighten lug nuts to 102 Nzm (75
ft. lbs.) torque.
(10) Pump brake pedal until caliper pistons and
brakeshoes are seated.(11) Top off brake fluid level if necessary. Use Mo-
par brake fluid or equivalent meeting SAE J1703 and
DOT 3 standards only.
CALIPER REMOVAL
(1) Raise vehicle and remove front wheels.
(2) Remove fitting bolt and disconnect front brake
hose at caliper. Discard fitting bolt gaskets. They
should not be reused.
(3) Remove caliper mounting bolts (Fig. 4).
(4) Rotate caliper rearward by hand or with pry
tool (Fig. 5). Then rotate caliper and brakeshoes off
mounting ledges.
(5) Remove caliper from vehicle.
CALIPER DISASSEMBLY
(1) Remove brakeshoes from caliper.
Fig. 11 Installing Inboard Brakeshoe
Fig. 12 Installing Outboard Brakeshoe
Fig. 13 Caliper Installation
Fig. 14 Caliper Mounting Bolt Dimensions
5 - 48 DISC BRAKESJ

(2) Pad interior of caliper with minimum, 2.54 cm
(1 in.) thickness of shop towels or rags (Fig. 15). Tow-
els are needed to protect caliper piston during re-
moval.
(3) Remove caliper piston withshort burstsof low
pressure compressed air. Direct air through fluid in-
let port and ease piston out of bore (Fig. 16).
CAUTION: Do not blow the piston out of the bore
with sustained air pressure. This could result in a
cracked piston. Use only enough air pressure to
ease the piston out. In addition, NEVER attempt to
catch the piston as it leaves the bore. This will re-
sult in personal injury.(4) Remove caliper piston dust boot (Fig. 17). Col-
lapse boot with suitable tool and remove and discard
boot.
(5) Remove and discard caliper piston seal with
wood or plastic tool (Fig. 18). Do not use metal tools
as they will scratch piston bore.
(6) Remove caliper mounting bolt bushings and
boots (Fig. 19).
Fig. 15 Padding Caliper Interior To Protect Piston
During Removal
Fig. 16 Removing Caliper Piston
Fig. 17 Removing Caliper Piston Dust Boot
Fig. 18 Removing Caliper Piston Seal
Fig. 19 Caliper Bushing And Boot
JDISC BRAKES 5 - 49