Jaguar XJ (X350). Manual — part 159

Brake caliper piston(s)

Parking brake module

Parking brake caliper piston(s) Parking brake switch

Brake discs

Damaged or corroded wiring harness

Wheel bearings

Brake master cylinder fluid level switch

Brake pads

Adjustable pedal motor

Power brake booster

Adjustable pedal switch

Brake pedal linkage

Brake booster vacuum hose

Tires

Debris

Adjustable pedal drive cables

Carry out a road test to compare actual vehicle braking performance with the performance standards

expected by the driver. The ability of the test driver to make valid comparisons and detect

performance deficiencies will depend on experience.

The driver should have a thorough knowledge of brake system operation and accepted general

performance guidelines to make good comparisons and detect performance concerns.

An experienced brake technician will always establish a route that will be used for all brake diagnosis

road tests. The roads selected will be reasonably smooth and level. Gravel or bumpy roads are not

suitable because the surface does not allow the tires to grip the road equally. Crowned roads should

be avoided because of the large amount of weight shifted to the low set of wheels on this type of

road. Once the route is established and consistently used, the road surface variable can be

eliminated from the test results.

Before a road test, obtain a complete description of the customer concerns or suspected condition.

From the description, the technician's experience will allow the technician to match possible causes

with symptoms. Certain components will be tagged as possible suspects while others will be

eliminated by the evidence. More importantly, the customer description can reveal unsafe conditions

which should be checked or corrected before the road test. The description will also help form the

basic approach to the road test by narrowing the concern to specific components, vehicle speed or

conditions.

Begin the road test with a general brake performance check. Keeping the description of the concern

in mind, test the brakes at different vehicle speeds using both light and heavy pedal pressure. To

determine if the concern is in the front or rear braking system, use the brake pedal and then use the

parking brake control. If the condition (pull, vibration, pulsation) occurs only with the parking brake,

the concern is in the rear brake system.

If the concern becomes evident during this check, verify it fits the description given before the road

test. If the concern is not evident, attempt to duplicate the condition using the information from the

description.

If a concern exists, use the Symptom Chart in order to isolate it to a specific sub-system and

condition description. From this description, a list of possible sources can be used to further narrow

the cause to a specific component or condition.

Brakes noisy

Possible Source(s):

•

Brake pads.

•

Brake discs.

Action(s) to take:

•

GO to Pinpoint Test A.

Vibration when brakes are applied

Possible Source(s):

•

Wheels require balancing.

•

Wheel hub nuts.

•

Brake caliper mounting bolts.

•

Brake pads.

•

Foreign material/scratches/corrosion on brake disc contact surfaces.

•

Excessive brake disc thickness variation.

•

Excessive brake disc runout.

•

Wheel bearing wear or failure.

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•

Suspension bush wear or failure.

•

Steering bush wear or failure.

Action(s) to take:

•

Go to Pinpoint Test B.

The brakes pull or drift

Possible Source(s):

•

Tire pressures/wear.

•

Brake calipers.

•

Brake pads.

•

Brake discs.

•

Wheel alignment adjustment.

•

Wheel bearing.

•

Suspension bushes and ball joints.

Action(s) to take:

•

GO to Pinpoint Test C.

The pedal feels spongy

Possible Source(s):

•

Air in brake system.

•

Leak in hydraulic system.

•

Brake booster/master cylinder.

•

Brake pads.

Action(s) to take:

•

GO to Pinpoint Test D.

The pedal goes down fast

Possible Source(s):

•

Air in brake system.

•

Leak in hydraulic system.

•

Brake booster/master cylinder.

•

Brake pads.

Action(s) to take:

•

GO to Pinpoint Test E.

The pedal goes down slowly

Possible Source(s):

•

Air in brake system.

•

Brake booster/master cylinder.

Action(s) to take:

•

Go to Pinpoint Test F.

Excessive brake pedal effort

Possible Source(s):

•

Brake pads.

•

Brake booster.

Action(s) to take:

•

GO to Pinpoint Test G.

Brake lockup during light brake pedal

force

Possible Source(s):

•

Brake pads.

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