Ford Repair: Rear brake lock up., local wrecking yards, rear brakes

Question
I have a 74 Ford F100( 4 speed, 6 cyl) that I just purchased. The rear brakes lock up the moment you touch the brake pedal. The truck appears to have new brakes and a rebuilt master cylinder. I suspect a proportioning valve. I have not taken a look at the whole system as it is parked at a friends house. Should I start at the master cylinder? It does not have power brakes. I am having a dificult time finding the correct proportioning valve at the local wrecking yards.

Answer
Mr. Rankin,

I would start with your proportioning valve first as the purpose of that valve is to keep the rear brakes from locking up before the front brakes kick in. If you can not find the correct proportioning valve at your local salvage yard try a reputable auto parts store such as Auto Zone or Napa. Hope that this helps and good luck.

Ken