I have a problem with my brakes, I have a 34 Plymouth with Mechanical brakes from a 65-66 Ford Ranchero. The front end is from a Mustang 2 Disc brakes and the back are drum. The problem I am having is that the front brakes stay locked up? I have replaced everything but the Proportioning valve even the Master Cylinder?? could the Proportioning valve be screwed up so that its not allowing the pressure to release the front brakes???? I also cannot find a replacement Proportioning valve and the ones I have found are for Dual bowl and power brakes I cant seem to find any for my mechanical brakes??? Any help would be appreciated because I am tearing my hair out and I did not have much to begin with!