1994 JAGUAR XJ6 brake fluid

12.1.9
The TMC primary circuit (item 1) applies brake pressure to the front brakes. Individual control of the front wheels is
provided by solenoid valves, Valves (items
15 and 18) control the front left brake circuit (item 21). Valves (items 16and 19) control the front right brake circuit (item 22). The TMC secondary circuit (item 2) applies brake pressure to the rear
brake circuit (item 20) via valves (items 14 and 17), on a 'select low' principle.
Hydraulic Operation - A BS CM
8
I I + I
I t 1
'0281
1. TMC 1 (primary circuit) 9. Low pressure accumulator 17. Outlet valve NC 2. TMC 2 (secondary circuit 10. Electric pump motor 18. Outlet valve NC
3. Tandem master cylinder 11. Two circuit hydraulic pump 19. Outlet valve NC 4. Vacuum booster 12. Damping chamber 20. Rear brake circuit 5. Central valve 13. Valve block 21. Front brake circuit (left)
6. Fluid reservoir 14. Inlet valve NO 22. Front brake circuit (right) 7. Fluid level indicator 15. Inlet valve NO 8. Pump motor unit 16. Inlet valve NO
Fig.
1
Should the ABS be initiated by a locking tendency of any wheel during braking, the pump unit (item 8) is started and
the appropriate NO inlet valve (item 14, 15 or 16) closes in response to signals from the control module. This action
prevents further increase of brake pressure by blocking the supply of brake fluid from the TMC (item 3). If excessive
deceleration continues, the appropriate NC outlet valves (item 17,18 or 19) opens, releasing brake pressure to the low
pressure accumulators (item 9) until the wheel accelerates again.
Issue 1 August 1994 12 X300 VSM

From the low pressure accumulators,volume is pumped back into theTMC, forcing the brake pedal back. To optimize the friction coefficient between tire and road, brake pressure is increased in small steps by closing the outlet valve and
opening the inlet valve and re-charging brake pressure.
During the pressure build
up phase, the volume required for replenishment is supplied by the TMC and additionally
by the pump from the low pressure accumulators. Since the delivered flow is generally greater than volume flow
drained from the brake circuits, the low pressure accumulators serve as intermediate accumulators to compensate for
temporary volume flow peaks.
The TMC piston positions, and therefore the brake pedal, vary with the fluid displacement in the brake caliper. As con
-
trolled pressure in the brake caliper decreases and increases during ABS, the brake pedal 'cycles', informing the driver
that controlled braking is in progress.
Actuation of the brake pedal, causes the central valve (item
5) in the TMC to close. This action prevents damage to the
TMC piston seals.
At the end of a brake application, volume is restored to the TMC, at
low pressure from the fluid reservoir (item 6).
Issue 1 August 1994 X300 VSM 13

12.1.1 0 Hydrauric Operation - ABS 1 TC CM
ABS/TC CM hydraulic modules incorporate inlet valves (items 16 and 17) and outlet valves (items 20 and 21) for each
driven wheel. This enables individual pressure modulation to the rear brakes under wheel spin conditions, i.e. traction
control.
Increased wheel spin of
a driven wheel under acceleration causes the NO isolation valve (item 14) to be closed and the
pump (item 10) to be switched on. This in response to signals from the control module.
Closing of the isolation valve blocks delivery of the pump to the secondary circuit (item
2) of the TMC. The pump now
draws fluid from the reservoir via the open hydraulically operated inlet valve (item 13). Increased pressure is now avail-
able at the inlet valves (items 16 and 17) for actuating the rear brakes, thus decreasing the tendency of wheel spin.
The hydraulic inlet valve (item
13) switches when traction control is initiated to change the suction connection
of the pump from the accumulators (item 9) to the fluid reservoir (item 6) via the TMC.
1. TMC 1 (primary circuit)
8
I 1-
I
10. Electric DumD motor 19. Inlet valve NO
170 280
2. TMC 2 (secondary circuit) 11. Two-cirh hydraulic pump 20. Outlet valve NC
3. Tandem master cylinder 12. Damping chamber 21. Outlet valve NC
4. Vacuum booster 13. Hydraulic inlet valve 22. Outlet valve NC
5. Central valve 14. Isolation valve NO 23. Outlet valve NC
6. Fluid reservoir 15. Relief valve 7. Fluid level indicator 16. Inlet valve NO 8. Motor pump unit 17. Inlet valve NO 9. Low pressure accumulator 18. Inlet valve NO
Fig.
1 24.
Rear
brake circuit (left) 25. Rear brake circuit (right) 26. Front brake circuit (left) 27. Front brake circuit (right) ~
Issue 1 August 1994 14 X300 VSM

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
0
0
0
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