I have changed out the piping and know its not that. My brake booster feels like its leaking from the firewall. Like where the brake booster meets the firewall. I have pressure but it leaks, so when i brake hardm, i lose pressure at the end of braking. And when i turn off my car u can hear it "hisssssssssssssss". Any suggestions of what is wrong is great. thanks.

 

You might have a leaking diaphragm.

get a vaccum pump and attach it to the booster directly (do not leave the check valve installed) and see if it holds vaccum if not then its leaking and bad.

 

could you be more specific, what is a dighragm

 

There is a rubber seal between the booster and MC that holds pressure in, that is probably going bad. Same thing happened to me before.

 

so you think its that seal and not the one behind the actual brake booster.

 

does it get harder to brake?

 

well when i brake it seems alright when i first start to brake but when i brake hard it gets mushy then hard at the end. and it sounds like my brakes lock up, But then again i dont have abs so they would lock up. But it makes weird sound. Like i can be in park and brake and i heard werid noises. But i just want to make the hissing sound stop when i kill the motor.

 

Its inside the booster