Operation Check (Without Gauges)

CAUTION: When checking operation, be sure to apply the parking brake securely.

Check without gauges
This method can not determine exactly what part is defective. But it is possible to identify the outline of the defect by performing the check according to the following procedures.
Air tightness check
Start the engine, and idle it for 1 to 2 minutes, then turn it OFF. Depress the brake pedal several times applying the normal pedal force. The pedal stroke should be the longest at the 1st depression, and it should become shorter at each successive depression. If no change occurs in the pedal height when pressed, the brake booster is faulty.

Fig 1: Checking Air Tightness Of Parking Brake
Courtesy of SUBARU OF AMERICA, INC.

NOTE:

In case of defective operation, inspect the condition of the check valve and vacuum hose as well.
Replace them if faulty, and perform the test again.
If no improvement is observed, check precisely with gauges.

While the engine is OFF, depress the brake pedal several times applying the same pedal force, to check for a change in pedal height.

Fig 2: Depressing Brake Pedal
Courtesy of SUBARU OF AMERICA, INC.
With the brake pedal depressed, start the engine.
As the engine starts, the brake pedal should move slowly toward the floor. If the pedal height does not change, the brake booster is faulty.
NOTE: If faulty, check precisely with gauges.
- Loaded air tightness check
Depress the brake pedal while the engine is running, and turn the engine to OFF while the pedal is depressed. Keep the pedal depressed for 30 seconds. If the pedal height does not change, the function of brake booster is normal. If the pedal height increases, it is faulty.

NOTE: If faulty, check precisely with gauges.