I have a 1982 F250 with single piston calipers. The right frt. brake will not release. I first though it was the caliper as it was binding. Replaced the caliper, bled out and I had the same thing. I can open the bleeder with it locked up and there is no excessive pressure. With the bleeder open I can push the piston back in with no problem(now after changing caliper). Go to the cab pump the brake pedal a couple of times and the wheel is locked down again. Left side is fine. I thought about the Press. Diff. Valve, but with the left not locking I'm not sure. I'm beginning to wonder if I have some restriction in the line. Maybe in the rubber line from the frame to the caliper that is only blocking fluid from returning. Any ideas from people will be appreciated! Thank you.