Seems like brake booster maybe the fault here. Use the steps below to test it.
Brake Booster Test
1. With engine off, depress brake pedal several times; then, depress the pedal hard and hold that pressure for 15 seconds. If the pedal sinks, the master cylinder, brake line, or brake caliper is bad.
2. Start engine with pedal depressed. If the pedal sinks slightly, the vacuum booster is working. If the pedal height does not vary, the booster or check valve is faulty.
1. Depress the brake pedal with the engine running, then stop the engine. If the pedal height does not vary, while depressed for 30 seconds, the vacuum booster is fine. If the pedal rises, the booster is faulty.
2. With the engine off, depress the brake pedal several times using normal pressure. When the pedal is first depressed, it should be low. On consecutive applications, pedal height should gradually rise. If the pedal position does not vary, check the booster check valve.
Check Valve Test:
1. Disconnect brake booster vacuum hose at booster.
2. Start engine and let it idle. Vacuum should be available--if not, the check valve is not working correctly. Replace the check valve and retest.
Monday, August 30th, 2010 AT 5:30 PM