Forester F4-2.5L SOHC (2004)
Vacuum Brake Booster: Testing and Inspection
Brake Booster
INSPECTION
OPERATION CHECK (WITHOUT GAUGES)
CAUTION: When checking operation, be sure to securely apply the hand brake.
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Checking without gauges
This method cannot determine the exact portion which has failed, but it can provide a rough understanding of the nature of failure if checking
is conducted in accordance with the following procedures.
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Air tightness check
Start the engine, and run it for 1 to 2 minutes, then turn it off. Depress the brake pedal several times applying same pedal force as that used in
ordinary braking operations. The pedal stroke should be greatest on 1st depression, and it should become smaller with each successive
depression. If no change occurs in the pedal height while in a depressed state, the brake booster is faulty.
NOTE:
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In the event of defective operation, inspect the condition of check valve and vacuum hose.
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Replace them if faulty and conduct the test again.
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If no improvement is observed, check precisely with gauges.
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Operation check
1) With the engine off, depress the brake pedal several times applying same pedal force and make sure that pedal height does not vary with
each depression of pedal.
2) With the brake pedal depressed, start the engine.
3) As the engine starts, the brake pedal should move slightly toward the floor. If no change occurs in the pedal height, the brake booster is
faulty.
NOTE: If faulty, check precisely with gauges.
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Loaded air tightness check
Depress the brake pedal while engine is running, and turn off the engine while pedal is still depressed. Keep the pedal depressed for 30
