Ok.. on my 84 all of the brakes are new..everything!! now after 5-10 minutes of driving the pedal gets hard.. I have to go unhook the vacuum line from the booster and hook it back up to get the brakes to work. then it does the same thing again..when I pull the vacuum line it makes a big pressure noise...could the booster already be bad?

 

Is the check valve on the right way? In-line of the vacuum line supplying the booster...

 

yup..I thought it was bad so I put a new one on it..and double checked that it was on the right way..

 

Fixed!!! ANOTHER bad booster!!!