Jaguar XJ (X350). Manual — part 163

•

Do the disc brake caliper pistons and pins bind, leak or stick?

-> Yes

INSPECT the brake calipers and parking brake cables. INSTALL new components as necessary. Road

test vehicle.

-> No

GO to Pinpoint Test

G189234t33

.

G189234t33 : CHECK BRAKE BOOSTER

1. Check the brake booster connecting rod alignment and travel. For additional information, refer to

<<206-07>>

.

•

Is the connecting rod OK?

-> Yes

Vehicle is OK.

-> No

INSTALL a new brake booster. For additional information, refer to

<<206-07>>

. TEST the system for

normal operation.

PINPOINT TEST G189234p10 :
EXCESSIVE/ERRATIC BRAKE PEDAL
TRAVEL

G189234t34 : TEST ON ROUGH ROAD

1. Road test the vehicle on rough road conditions. 2. Apply the brakes slowly.

•

Is the brake pedal effort and brake pedal travel normal?

-> Yes

Vehicle is OK.

-> No

GO to Pinpoint Test

G189234t35

.

G189234t35 : CHECK BRAKE FLUID LEVEL

1. Check the brake master cylinder reservoir fluid level.

•

Is the fluid level OK?

-> Yes

GO to Pinpoint Test

G189234t36

.

-> No

CHECK brake master cylinder reservoir sealing points. For additional information, refer to Brake

master cylinder in this section. ADD brake fluid and BLEED the brake system. For additional

information, refer to General Procedures. TEST the system for normal operation. REPEAT road test if

necessary.

G189234t36 : CHECK BRAKE PEDAL RESERVE

1. Engine is idle. 2. Apply the brake pedal lightly three or four times. 3. Wait 15 seconds for the

vacuum to replenish. 4. Push down on the brake pedal until it stops moving downward or an

increased resistance to the brake pedal travel occurs. 5. Hold the brake pedal in the applied position

while increasing the engine speed to 2000 revs/min. 6. Release the accelerator pedal.

•

Does the brake pedal move downward as the engine speed returns to idle?

-> Yes

GO to Pinpoint Test

G189234t37

.

-> No

CHECK the vacuum to the brake booster. For additional information, refer to

<<206-07>>

.

G189234t37 : CHECK THE FRONT HUB AND BEARING ASSEMBLY

1. Check the front hub and bearing assembly. For additional information, refer to

<<204-00>>

•

Are the front wheel bearings loose?

-> Yes

INSTALL a new front wheel bearing if damaged. For additional information, refer to

<<204-00>>

TEST

the system for normal operation.

-> No

CHECK the front brake discs for thickness variances. For additional information, refer to General

Procedures.

PINPOINT TEST G189234p11 : SLOW
OR INCOMPLETE BRAKE PEDAL
RETURN

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G189234t38 : CHECK FOR BRAKE PEDAL RETURN

1. Run the engine at fast idle while making several brake applications. 2. Pull the brake pedal

rearward with approximately 44.5 N (10lb) force. 3. Release the brake pedal and measure the

distance to the toe board. 4. Make a hard brake application. 5. Release the brake pedal and measure

the brake pedal to toe board distance. The brake pedal should return to its original position.

•

Does the brake pedal return to its original position?

-> Yes

Vehicle is OK.

-> No

GO to Pinpoint Test

G189234t39

.

G189234t39 : CHECK FOR BRAKE PEDAL BINDING

1. Check the brake pedal to make sure it is operating freely.

•

Is the brake pedal operating freely?

-> Yes

INSTALL a new brake booster. For additional information, refer to

<<206-07>>

. TEST the system for

normal operation.

-> No

REPAIR or INSTALL new brake pedal. TEST the system for normal operation.

Component Tests

Brake Booster

1 . Check all hoses and connections. All unused vacuum connectors should be capped. Hoses and

their connections should be correctly secured and in good condition with no holes and no collapsed

areas. Inspect the valve on the brake booster for damage.

2 . Check the hydraulic brake system for leaks or low fluid.

3 . With the transmission in PARK (automatic transmissions) or in NEUTRAL (manual transmissions),

stop the engine and apply the parking brake. Pump the brake pedal several times to exhaust all

vacuum in the system.

4 . With the engine switched off and all vacuum in the system exhausted, apply the brake pedal and

hold it down. Start the engine. If the vacuum system is operating, the brake pedal will tend to move

downward under constant foot pressure. If no motion is felt, the vacuum booster system is not

functioning.

5 . Remove the vacuum hose from the brake booster. Manifold vacuum should be available at the

brake booster end of the hose with the engine at idle speed and the transmission in PARK or

NEUTRAL. Make sure that all unused vacuum outlets are correctly capped, hose connectors are

correctly secured and vacuum hoses are in good condition. When it is established that manifold

vacuum is available to the brake booster, connect the vacuum hose to the brake booster and repeat

Step 3. If no downward movement of the brake pedal is felt, install a new brake booster.

6 . Operate the engine for a minimum of 10 seconds at a fast idle. Stop the engine and allow the

vehicle to stand for 10 minutes. Then, apply the brake pedal with approximately 89 N (20lb) of force.

The pedal feel (brake application) should be the same as that noted with the engine running. If the

brake pedal feels hard (no power assist), install a new valve and then repeat the test. If the brake

pedal still feels hard, install a new brake booster. If the brake pedal movement feels spongy, bleed

the brake system.

Brake Master Cylinder

Usually, the first and strongest indicator of anything wrong in the brake system is a feeling through

the brake pedal. In diagnosing the condition of the brake master cylinder, check pedal feel as

evidence of a brake concern. Check for brake warning lamp illumination and the brake fluid level in

the brake master cylinder reservoir.

Normal Conditions

The following conditions are considered normal and are not indications that the brake master

cylinder is in need of repair.

•

New brake systems are designed to produce a pedal effort that is not as hard as in the past.
Complaints of light pedal efforts should be compared to the pedal efforts of another vehicle
of the same model and year.

•

The fluid level will fall with brake pad wear.

Abnormal Conditions

NOTE:

Prior to carrying out any diagnosis, make sure the brake system warning indicator is functional.

Changes in the brake pedal feel or brake pedal travel are indicators that something could be wrong in

the brake system. The diagnostic procedure and techniques use brake pedal feel, warning indicator

illumination and low brake fluid level as indicators to diagnosing brake system concerns. The

following conditions are considered abnormal and indicate that the brake master cylinder is in need

of repair:

•

Brake pedal goes down fast. This could be caused by an external or internal leak.

•

Brake pedal goes down slowly. This could be caused by an internal or external leak.

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