1994 JAGUAR XJ6 brake

Brakes
The pressure at the inlet valves corresponds to the opening pressure of the relief valve (item 15) incorporated in the
isolation valve. Excess brake fluid is drained to the suction side of the pump via the relief valve and returns either to
the TMC secondary circuit and on to the
fluid reservoir, or is directly drawn on by the pump.
As soon as the spinning wheel has been braked down into the normal range of wheel spin, the NO valves (items
16 or 17) close to prevent any further increase in brake pressure. Depending upon the acceleration of the wheel, the NC
valve (item
20 or 21) may open to decrease thesecondary circuit brake pressure. NCvalves (item 17 or 18) may remain
closed in orderto achieve a brake pressure holding phase. If the pressure in the secondarycircuit needs to be increased
again, the NC valve closes again (if open) and the NO valve opens, diverting the necessary volume flow. This control
action, keeps the wheel in the range of optimum slip until the spinning tendency ceases.
The NO isolation valve
(14) remains closed throughout the traction control cycle.
An actuation of the brake, sensed by the control module, causes the traction control mode to be terminated and the
isolation valve (item
14) to be opened. The TMC pressure simultaneously closes the hydraulic inlet valve (item 13) so that the pump can no longer draw fluid from it. The ABS / TC CM now operates in normal ABS mode.
m: When traction control is initiated, speed control is deactivated (if in operation) and requires re-setting after
the traction control mode has terminated. Gear shift is inhibited on automatic transmission vehicles; no down- shifts are allowed and upshifts occur at 4800 RPM.
X300 VSM 15 Issue 1 August 1994

12.2 FAULT DIAGNOSIS AND TESTING
rrouble
-ong brake pedal
dibration during braking
'oor braking performance
3rakes pull to one side
3rakes do not release
ixcessive pedal travel
Cause
Brake caliper piston or caliper guide
pins sticking
Worn
I damaged brake pads
Worn
1 damaged brake pads
Loose caliper mounting bolts
Insufficient grease on sliding parts
Foreign material
or scratches on
brake rotor contact surface
Damaged brake rotor contact surface
Leak
in hydraulic system
Air
in system
Worn
I damaged brake pads
Foreign material on brake pads
Brake caliper piston malfunction
Tandem master cylinder malfunction
Vacuum booster fault
Disconnected
or damaged vacuum
hose
Low brake
fluid level
Worn
I damaged brake pads
Foreign material on brake pad
Failing valves
in ABS valve block
Abnormal wear or distortion on front
brake rotor
Incorrect wheel alignment
Incorrect tire pressure
No brake pedal free play
Vacuum booster
binding
Tandem master cylinder return port faulty
Faulty valve
in ABS valve block
Leak
in hydraulic system
Air
in system
Remedy
Service or renew caliper or caliper
guide pins
Renew brake pads
Renew brake pads
Tighten caliper mounting bolts
Apply grease where necessary
Clean brake rotor contact surface
Renew brake
rotor
Repair leak. Check all pipework con-
nections. Refill and bleed the system
Check the system
for leaks and bleed
brakes
Renew brake pads
Examine brake pads and clean
or
renew as necessary
Renew faulty brake caliper piston
Service
or renew tandem master cyl- inder
Renew vacuum booster
Renew vacuum hose
Check for leaks, refill and bleed the
system
Renew brake pads
Examine brake pads and clean
or renew as necessary
Renew valve block
Examine front brake
rotor and service
or renew as necessary
Carry out wheel alignment. Refer to
Section
11, iv Service Data
Inflate tire
to correct pressure
Adjust brake pedal free play
Renew vacuum booster
Clean return
port on tandem master cy I i nder
Renew valve block
Repair leak. Check all pipework con
- nections. Refill and bleed the system
Check the system
for leaks and bleed
brakes
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Issue 1 August 1994 16 X300 VSM

12.2 (continued)
rrouble
Excessive pedal travel (Cont'd)
Brakes grab
Brakes drag
Hard brake pedal when pressed
Excessive brake noise
Cause
Worn tandem master cylinder piston
seals or scored cylinder bore
'knock back'. Excessive brake rotor
run
-out or loose wheel bearings
Brake pads contaminated by grease
or brake fluid
Brake pads distorted, cracked or
loose
Loose caliper mounting bolts or
guide pins
Seized or incorrectly adjusted parking
brake or cable
Broken or weak parking brake return
springs
Caliper pistons seized
Brake pedal binding
at pivot points
Vacuum booster binding
Tandem master cylinder faulty
Lack of vacuum
at the vacuum
booster
Tandem master cylinder
pushrod
binding
Frozen tandem master cylinder pis
-
ton
Brake caliper piston or caliper guide
pins seized
Worn brake pads
Bent or cracked parking brake shoes
Foreign objects in brake pads or
park- ing brake shoes
Broken
/ loose parking brake hold
down springs or return springs
Loose caliper mounting bolts
Remedy
Renew tandem master cylinder
Check brake rotor run
-out and renew
as necessary. Adjust wheel bearing
Renew brake pads. Check
pipework for leaks
Renew brake pads
Check caliper and repair
/ renew as
necessary
Examine parking brake and repair
/
renew as necessary
Renew parking brake return springs
Examine calipers and repair
/ renew
as necessary
Examine brake pedal bushings and
repair
/ renew as necessary
Renew vacuum booster
Examine tandem master cylinder and
repair
/ renew as necessary
Check vacuum hose. Repair or renew
as necessary
Renew tandem master cylinder
Renew tandem master cylinder
Examine caliper and renew/ repair as
necessary
Renew brake pads
Renew parking brake shoes
Examine brake pads and and parking
brake shoes. Clean or renew as
necessary
Examine parking brake assembly.
Re- pair or renew as necessary
Re
-torque caliper mounting bolts

12.3 BRAKE FLUID LEVEL CHECK
WARNING: AVOID SKIN / EYE CONTACT OR INGESTION OF BRAKE FLUID. IF SKIN OR EYES ARE ACCIDENTALLY
SPLASHED WITH BRAKE FLUID, RINSE THE AFFECTED AREA IMMEDIATELY WITH PLENTY OF WATER
AND SEEK MEDICAL AlTENTlON IMMEDIATELY.
Checking the fluid level
CAUTION: Fluid must not be allowed to contact the vehicle paintwork. Remove any spilt fluid from the paintwork
by rinsing away with running water. Methylated spirit (denatured alcohol) must not be used to clean the contaminated area.
Correct brake fluid level is essential for the efficient oper- ation of the brake system. Check that the fluid level is be- tween the MAXand MIN marks on the fluid reservoir (Fig. 1). Top up if necessary with recommended brake fluid.
BMQ: The efficiency of the brakes may be impaired if fluid
is used which does not meet specifications. Use
ONLY brake and clutch fluid that conforms to
a mini- mum DOT 4 specification. Also do not use brake
fluid that has been exposed to atmosphere for any
length of time. Moisture absorbed from the atmos
- phere impairs the efficiency of the brake fluid.
JLX- 081
Fig. 1
Issue 1 August 1994 18 X300 VSM

Brakes
12.4 BRAKE SYSTEM BLEEDING
WAR-: GREAT CARE MUST BE EXERCISED WHEN SERVICING OR REPAIRING THE SYSTEM. AVOID SKIN/ EYE
CONTACT OR INGESTION OF BRAKE FLUID. IF SKIN OR EYES ARE ACCIDENTALLY SPLASHED WITH
BRAKE FLUID,
RINSETHE AFFECTED AREA IMMEDIATELY WITH PLENTY OF WATER AND SEEK MEDICAL
ATTENTION. IF BRAKE FLUID IS INGESTED, SEEK MEDICAL ATTENTION IMMEDIATELY.
CAUm: Fluid must not be allowed to contact the vehicle paintwork. Remove any spilt fluid from the paintwork
by rinsing away with running water. Methylated spirit (denatured alcohol) must not be used to clean the
contaminated area.
CAUTION: Never use methylated spirit (denatured alcohol) for component cleaning purposes. Use only a proprietary
brake cleaning fluid.
WARNING : THROUGHOUT THE FOLLOWING MAINTENANCE / SERVICE OPERATIONS, ABSOLUTE CLEANLINESS
MUST BE OBSERVED TO PREVENT FOREIGN MATTER CONTAMINATING THE BRAKE SYSTEM.
12.4.1 System Bleeding - General Instructions
Use a brake bleeder bottle with a clear bleeder tube. Also recommended is a filler unit with a fill pressure of 1.0 bar. If a filler unit is not used, ensure that their is sufficient brake fluid in the reservoir throughout the bleeding procedure.
m: Always bleed the caliper furthest away from the actuation unit first. On right hand drive vehicles, bleed in the
following order: front
left (FL),front right (FR), rear left (RL) and rear right (RR). On left hand drive vehicles bleed in the following order: FR, FL, RR and RL.
12.4.2
. Ensure that the vehicle is standing level. Switch the igni-
tion off.
Check that the fluid level in the reservoir is between the min and max marks.
. Connect the bleeder bottle tube to the relevant front cali- per (see'note' above) bleeder screw (1 Fig. 1) and open the
screw.
rn Bleed until new, clear, bubble free fluid is observed in the
tube and then close the bleeder screw.
. Repeat this procedure at each remaining caliper.
With the motorrunning check brake pedal travel.
If excess- ive, check for leaks and repeat the bleed procedure.
Fill the reservoir to the max level.
System Bleeding After Brake Fluid Renewal
12.4.3 System Bleeding After Tandem Master Cylinder
Renewal
Ensure that the vehicle is standing level. Switch the igni- tion off.
rn Check that the fluid level in the reservoir is between the min and max marks.
Connect the bleeder bottle tube to the relevant front cali- per (see'note'above) bleederscrew(1 Fig. 1) and open the
screw.
Ficr. 1
X300 VSM 19 Issue 1 August 1994

. Actuate the brake pedal to the floor, hold for approximately two seconds and then release the pedal. Wait another two seconds and actuate the brake pedal again for a further two seconds. Repeat this action 20 to 30 times until clear,
bubble free brake fluid streams out.
. With the brake pedal actuated, close the bleeder screw. Build up fluid pressure by pumping the pedal and then open
the bleeder screw. Repeat this action three to five times.
If a filler unit is not used, observe the fluid level in the reservoir and top up if necessary.
. Repeat this procedure for the remaining three calipers. (1 Fig. 1) shows the bleeder screw of the rear left caliper.
. With the motor running check brake pedal travel. If excess- ive, check for leaks and repeat the bleed procedure.
. Fill the reservoir to the max level.
12.4.4
Hydraulic control modules are supplied pre-filled to enable
the brake system to be bled in the conventional way.
. Ensure that the vehicle is standing level. Switch the igni- tion off.
. Check that the fluid level in the reservoir is between the
min and max marks.
Connect the bleeder bottle tube to the relevant front cali- per (see 'note' on previous page) bleeder screw (1 Fig. 1) and open the screw.
. Actuate the brake pedal full stroke, wait a moment and
then release. Wait two to three seconds and then actuate
the brake pedal full stroke again. This allows the TMC to
be completely re
-filled with fluid.
. Repeat 20 to 30 times until the fluid in the bleeder tube is
clear and bubble free.
System Bleeding After Hydraulic Control
Module Renewal
I J70 -209
Fig. 1
With the brake pedal actuated, close the bleeder screw. Build up fluid pressure by pumping the pedal and then open
the bleeder screw. Repeat this action three times.
w: If a filler unit is not used, observe the fluid level in the reservoir and top up if necessary.
. Repeat this procedure for the remaining three calipers.
. With the motor running check brake pedal travel. If pedal travel is excessive, check the system for leaks and repeat
Fill the reservoir to the max level.
the
bleed procedure.
12.4.5
Follow the procedure above but only at the affected caliper.
Bleeding After Renewal of Caliper
Issue 1 August 1994 20 X300 VSM

Brakes
a 12.5 GENERAL FI77lNG lNSTRUCTlONS
12.5.1 Brake Fluid
WARNING: BRAKE FLUID IS CORROSIVE. EXTREME CARE MUST BE TAKEN WHEN HANDLING. AVOID SKIN OR EYE
CONTACT. AVOID INGESTION. IF SKIN OR EYES ARE ACCIDENTALLY SPLASHED WITH BRAKE FLUID,
RINSE THE AFFECTED AREA IMMEDIATELY WITH PLENTY OF WATER AND SEEK MEDICAL ATTENTION.
IF BRAKE FLUID
IS INGESTED, SEEK MEDICAL ATTENTION IMMEDIATELY.
CAUTION:
Fluid must not be allowed to contact the vehicle paintwork. Remove any spilt fluid from the paintwork
by rinsing away with running water. Methylated spirit (denatured alcohol) must not be used to clean the
contaminated area.
Cleaning Solvents
CAUTION: Never use methylated spirit (denatured alcohol) for cleaning purposes. Use only a proprietary brake
cleaning fluid.
m: THROUGHOUT THE FOLLOWING MAINTENANCE / SERVICE OPERATIONS, ABSOLUTE CLEANLINESS
MUST BE OBSERVED TO PREVENT GRIT OR OTHER FOREIGN MATTER CONTAMINATING THE BRAKE
TION. TO CLEAN BRAKE SYSTEM COMPONENTS, WASH
IN A PROPRIETARY BRAKE CLEANING FLUID.
REMOVE ALL TRACES OF CLEANING FLUID BEFORE REASSEMBLY. ALL BRAKE SYSTEM RUBBER COh PONENTS MUST BE DIPPED IN CLEAN BRAKE FLUID AND ASSEMBLED USING THE FINGERS ONLY.
SYSTEM.
IFTHE SYSTEM IS TO
BE FLUSHED, USE CLEAN BRAKE FLUID TO MINIMUM DOT 4 SPECIFICA-
12.5.2 Hoses
Fully release the unions (1 Fig. 1) securing each end of the
hose to the fluid pipes. Withdraw the pipe unions (1 Fig. 1) from the hose ends.
Plug the ends of the pipes (2 Fig. 1) to prevent the loss of
fluid and the ingress of dirt.
Remove the mounting bracket locknut (3 Fig. 1) and re- move the hose (4 Fig. 1).
Thoroughly clean the hose and examine for any signs of
wear or damage. Renew the hose if there is any doubt
about its condition. Thoroughly clean the bore of the hose
using compressed air.
. Remove all blanking plugs and fit the new hose to the cali- per / connector. Secure the hose to the mounting bracket.
. Before fully tightening the locknut, ensure that the hose is
neither kinked nor twisted.
. Bleed the brakes.
12.5.3 Pipes
. Fully release the pipe unions (1 Fig. 1).
. Withdraw the pipe (5 Fig. 1) from the vehicle. Plug the
pipes (2 Fig. 1) to prevent the loss of fluid or the ingress of dirt. Thoroughly clean and examine the pipe for signs of damage or deterioration. Renew the pipe if there is any
doubt about its condition.
Thoroughly clean the bore of the pipe using compressed
air.
. Remove all blanking plugs and fit the new pipe to the ve- hicle. Secure the pipe to the body.
. Bleed the brakes.
17
Fig. 1
X300 VSM 21 Issue 1 August 1994

12.6 REAR WHEEL SPEED SENSOR - RENEW
SRO
70.60.04
. Drive the vehicle onto a ramp or raise the back and support
on two stands.
. Cut and remove the ratchet strap securing the speed sen- sor harness to the brake hose.
. Undo and remove the speed sensor to hub carrier secur- ing bolt (Fig. 1).
Remove the speed sensor from the hub carrier and allow
it to hang free, forward of the 'A' frame.
Open both rear doors and displace the rear seat cushion
from the seat pan brackets. Reposition the rear seat
cushion forwards.
9 Push the seat belts/ buckles through the seat cushion slots
and remove the rear seat cushion from the vehicle.
. Displace the RH side of the seat pan sound proofing (1 Fig. 2) to gain access to the speed sensor harness (2 Fig. 2).
9 Displace the speed sensor harness grommet (3 Fig. 2) from the seat pan aperture.
. Feed the speed sensor harness through the seat pan aper- ture and disconnect the multi-plug (4 Fig. 2).
9 Position the new speed sensor harness and connect the
multi-plug.
. Feed the speed sensor harness through the seat pan aper- ture to hang free below the vehicle.
. Refit and fully seat the speed sensor harness grommet to
the seat pan aperture.
Reposition theseat pan sound proofing to its original posi- tion.
Position the rear seat cushion and feed the seat belt / buckles through the slots.
Locate the rear seat cushion into the seat pan brackets (5 Fig. 2).
. Stow the seat belts / buckles.
. Position the speed sensor harness rearwards over the 'A'
Fit and tighten the speed sensor to hub carrier securing
Secure the speed sensor harness to the brake hose using
frame
and locate into the hub carrier.
bolt.
a ratchet strap. Trim the ratchet strap. Fig.
1
Fig. 2
Issue 1 August 1994 22 X300 VSM
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