hi ,this is my 2nd power booster and master cyl ,and the brakes are still messing up , they work great sometimes , and the all of a sudden , the pedal is hard as a rock, when it is acting up ,if I take it out of gear and just glid to a stop in neutral ,, they work fine ,checked my vacuum and it was 20. so if any one can help me , thanks in advance, also car is a 65 starfire , thanks again ,will.

 

My 65 Starfire is acting the same