I have an 87 GT i was hitting the brakes and heard a wessshhh noise only when i applied the brake,pedal felt fine..Now the pedal is really soft almost to the floor car still stops but the pedal is really soft so could the check valve be bad? or is the booster shot?
No it wooshes when you hit the brake pedal...it stared doing that pedal felt fine now it still does the woosh sound but the pedal is really soft and a lot lower now...bad booster or check valve or mayeb a bad master cylinder?
Power brake booster test:
1.) Check engine vacuum: you should have 14"-18" of vacuum at 625-750 RPM, 18"-21" vacuum at 1000 RPM.
2.) Vacuum checks good, start the car and run the engine up to 1000 RPM for 30 seconds.
3.) Cut off the engine and then press the brake pedal 3 times. It should get harder to press and travel less each time you press it. If it doesn't, then the brake booster is suspect.