Vital info is: 1967 mustang with 289 (mildly built) and automatic trans. Replaced the front drums with 77 Granada and the master cylinder with a 77 mustang power unit. I added a proportioning valve into the rear brake line. I have adjusted the rear brakes and bled the whole system several times. (by the way, all brake lines have been replaced, the rear brakes complete rebuilt as was the fronts, new rotors reman calipers, etc. sparing no change) The problem is I can tell that the vacuum assist is working and the pedal will move a little over 1 1/2 " (at the pedal not the plunger rod) then I get the actual hard pedal and can pressure up enough push for about another 1" of pedal travel. The car will start to come to a stop but does not nose dive and the wheels lock. No matter how hard I push the pedal it will only slowly come to a stop. Got any ideas? Also I've adjusted the proportioning valve either way with the same results and I have bench bled the cylinder twice. help please.