May be a bad check valve on the booster .

 

Try starting your car so the vacuum builds up in the booster. Then shut car off and pull the check valve out of the booster and see if you can hear the vacuum escape. If you can't hear it your booster or check valve have gone bad.Then you just have to figure out what one it is.

 

wrong post

 

Mine did the same thing and the booster was bad. I did a search at the time and found a lot of posts with troubleshooting techniques.

 

I do have the vacuum release when I pull the check valve. It is hard as a rock even without the vacuum assist on it.

 

Of course you are going to have a hard pedal WITHOUT vacuum assist. I assume you have a high hard pedal all the time right? If the check valve won't let vacuum inside the booster then it is bad. if it is letting vacuum inside the booster then the booster is bad. A easy test would be to have the engine idle pull the vacuum hose off of the booster does the idle change? If it doesn't then you probably have a defective booster. When power brake boosters work properly the pedal should be lower but soft, but not spongy.

 

I just found a patch of gravel, and tried my brakes. The rear is not locking up first, so I would assume, from everybodys help, that the proportioning valve is working correctly. When idling, and I pull the check valve out of the booster, the idle does change. So the fronts lock up first, the idle changes when the check valve is pulled, and I have a rock hard pedal as if it were stopping on the floor. Booster bad?

 

Powerbrake booster check.
Eng off, pump brakes 3-4 times to empty vac in booster.
With foot pressing brake petal firmly,
Start eng and run to 1500 rpm.
you should feel the brake petal sink down from the booster assisting.
If it doesn't move your booster needs replaced.