Jeep XJ. Manual — part 49
the drum if machining causes the drum to exceed the
maximum allowable diameter.
BRAKE LINE AND HOSES
Flexible rubber hose is used at both front brakes
and at the rear axle junction block. Inspect the hoses
whenever the brake system is serviced, at every
engine oil change, or whenever the vehicle is in for
service.
Inspect the hoses for surface cracking, scuffing, or
worn spots. Replace any brake hose immediately if
the fabric casing of the hose is exposed due to cracks
or abrasions.
Also check brake hose installation. Faulty installa-
tion can result in kinked, twisted hoses, or contact
with the wheels and tires or other chassis compo-
nents. All of these conditions can lead to scuffing,
cracking and eventual failure.
The steel brake lines should be inspected periodi-
cally for evidence of corrosion, twists, kinks, leaks, or
other damage. Heavily corroded lines will eventually
rust through causing leaks. In any case, corroded or
damaged brake lines should be replaced.
Factory replacement brake lines and hoses are rec-
ommended to ensure quality, correct length and supe-
rior fatigue life. Care should be taken to make sure
that brake line and hose mating surfaces are clean
and free from nicks and burrs. Also remember that
right and left brake hoses are not interchangeable.
Use new copper seal washers at all caliper connec-
tions. Be sure brake line connections are properly
made (not cross threaded) and tightened to recom-
mended torque.
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.
SERVICE PROCEDURES
BRAKE 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. 11) fill to the FULL mark.
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.
BLEEDING PROCEDURE
(1) Mount master cylinder in vise.
(2) Attach bleed tubes to cylinder outlet ports.
Then position each tube end into reservoir (Fig. 12).
Fig. 10 Measuring Rotor Thickness
1 – MICROMETER
2 – ROTOR
Fig. 11 Master Cylinder Fluid Level
1 – FLUID LEVEL MARKS
2 – RESERVOIR
5 - 12
BRAKES
XJ
DIAGNOSIS AND TESTING (Continued)
(3) Fill reservoir with fresh brake fluid.
(4) Press cylinder pistons inward with wood dowel.
Then release pistons and allow them to return under
spring pressure. Continue bleeding operations until
air bubbles are no longer visible in fluid.
BASE BRAKE BLEEDING
Use Mopar brake fluid, or an equivalent quality
fluid meeting SAE J1703-F and DOT 3 standards
only. Use fresh, clean fluid from a sealed container at
all times.
Do not pump the brake pedal at any time while
bleeding. Air in the system will be compressed into
small bubbles that are distributed throughout the
hydraulic system. This will make additional bleeding
operations necessary.
Do not allow the master cylinder to run out of fluid
during bleed operations. An empty cylinder will allow
additional air to be drawn into the system. Check the
cylinder fluid level frequently and add fluid as
needed.
Bleed only one brake component at a time in the
following sequence:
• Master Cylinder
• Combination Valve
• Right Rear Wheel
• Left Rear Wheel
• Right Front Wheel
• Left Front Wheel
MANUAL BLEEDING
(1) Remove reservoir filler caps and fill reservoir.
(2) If calipers, or wheel cylinders were overhauled,
open all caliper and wheel cylinder bleed screws.
Then close each bleed screw as fluid starts to drip
from it. Top off master cylinder reservoir once more
before proceeding.
(3) Attach one end of bleed hose to bleed screw
and insert opposite end in glass container partially
filled with brake fluid (Fig. 13). Be sure end of bleed
hose is immersed in fluid.
(4) Open up bleeder, then have a helper press
down the brake pedal. Once the pedal is down close
the bleeder. Repeat bleeding until fluid stream is
clear and free of bubbles. Then move to the next
wheel.
PRESSURE BLEEDING
Follow the manufacturers instructions carefully
when using pressure equipment. Do not exceed the
tank manufacturers pressure recommendations. Gen-
erally, a tank pressure of 15-20 psi is sufficient for
bleeding.
Fill the bleeder tank with recommended fluid and
purge air from the tank lines before bleeding.
Do not pressure bleed without a proper master cyl-
inder adapter. The wrong adapter can lead to leak-
age, or drawing air back into the system. Use
adapter provided with the equipment or Adapter
6921.
DISC ROTOR MACHINING
The disc brake rotor can be machined if scored or
worn. The lathe must machine both sides of the rotor
simultaneously with dual cutter heads. The rotor
mounting surface must be clean before placing on the
lathe. Equipment capable of machining only one side
at a time may produce a tapered rotor. A hub
Fig. 12 Master Cylinder Bleeding–Typical
1 – BLEEDING TUBES
2 – RESERVOIR
Fig. 13 Bleed Hose Setup
1 – BLEED HOSE
2 – FLUID CONTAINER PARTIALLY FILLED WITH FLUID
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BRAKES
5 - 13
SERVICE PROCEDURES (Continued)
mounted on-vehicle lathe is recommended. This type
of lathe trues the rotor to the vehicles hub/bearing.
CAUTION: Brake rotors that do not meet minimum
thickness specifications before or after machining
must be replaced.
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
diameter.
BRAKE TUBE FLARING
A preformed metal brake tube is recommended and
preferred for all repairs. However, double-wall steel
tube can be used for emergency repair when factory
replacement parts are not readily available.
Special bending tools are needed to avoid kinking
or twisting of metal brake tubes. Special flaring tools
are needed to make a double inverted flare or ISO
flare (Fig. 14).
DOUBLE INVERTED FLARING
(1) Cut off damaged tube with Tubing Cutter.
(2) Ream cut edges of tubing to ensure proper
flare.
(3) Install replacement tube nut on the tube.
(4) Insert tube in flaring tool.
(5) Place gauge form over the end of the tube.
(6) Push tubing through flaring tool jaws until
tube contacts recessed notch in gauge that matches
tube diameter.
(7) Tighten the tool bar on the tube
(8) Insert plug on gauge in the tube. Then swing
compression disc over gauge and center tapered flar-
ing screw in recess of compression disc (Fig. 15).
(9) Tighten
tool
handle
until
plug
gauge
is
squarely seated on jaws of flaring tool. This will start
the inverted flare.
(10) Remove the plug gauge and complete the
inverted flare.
ISO FLARING
To make a ISO flare use Snap-On
t Flaring Tool
TFM-428 or equivalent.
(1) Cut off damaged tube with Tubing Cutter.
(2) Remove any burrs from the inside of the tube.
(3) Install tube nut on the tube.
Fig. 14 Inverted Flare And ISO Flare
1 – ISO-STYLE FLARE
2 – DOUBLE INVERTED-STYLE FLARE
Fig. 15 Inverted Flare Tools
5 - 14
BRAKES
XJ
SERVICE PROCEDURES (Continued)
(4) Position the tube in the flaring tool flush with
the top of the tool bar (Fig. 16). Then tighten the tool
bar on the tube.
(5) Install the correct size adaptor on the flaring
tool yoke screw.
(6) Lubricate the adaptor.
(7) Align the adaptor and yoke screw over the tube
(Fig. 16).
(8) Turn the yoke screw in until the adaptor is
squarely seated on the tool bar.
REMOVAL AND INSTALLATION
BRAKE LAMP SWITCH
REMOVAL
(1) Remove steering column cover and lower trim
panel for switch access (if necessary).
(2) Press brake pedal downward to fully applied
position.
(3) Rotate switch approximately 30° in counter-
clockwise direction to unlock switch retainer. Then
pull switch rearward and out of bracket.
(4) Disconnect switch harness and remove switch
from vehicle (Fig. 17).
INSTALLATION
(1) Pull switch plunger all the way out to fully
extended position.
(2) Connect harness wires to switch.
(3) Press and hold brake pedal in applied position.
(4) Install switch as follows: Align tab on switch
with notch in switch bracket. Then insert switch in
bracket and turn it clockwise about 30° to lock it in
place.
(5) Release brake pedal. Then pull pedal lightly
rearward. Pedal will set plunger to correct position
as pedal pushes plunger into switch body. Switch will
make ratcheting sound as it self adjusts.
CAUTION: Booster damage may occur if the pedal
pull exceeds 20 lbs..
BRAKE PEDAL
REMOVAL
(1) Remove knee blocker under the steering col-
umn.
(2) Remove retainer clip securing booster push rod
to pedal (Fig. 18).
(3) Remove brake lamp switch.
(4) Remove nuts securing the booster to the pedal
support bracket and nuts to the column bracket.
(5) Remove pedal and support bracket as an
assembly from the vehicle.
Fig. 16 ISO Flaring
1 – ADAPTER
2 – LUBRICATE HERE
3 – PILOT
4 – FLUSH WITH BAR
5 – TUBING
6 – BAR ASSEMBLY
Fig. 17 Brake Lamp Switch
1 – SWITCH
2 – HARNESS CONNECTOR
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BRAKES
5 - 15
SERVICE PROCEDURES (Continued)
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