Leak Test

Press brake pedal with engine running, then stop engine. If pedal height does not vary while pressed for 30 seconds, the vacuum booster is okay. If the pedal rises, booster is faulty. Turn engine off and wait 30 seconds. Press brake pedal several times using normal pressure. When pedal is first pressed, it should be low. On consecutive applications, the pedal height should gradually rise. If pedal position does not vary, check booster check valve. See BOOSTER CHECK VALVE TEST  .