Classic/Antique Car Repair: brakes, brake hoses, rear brakes

Question
My 1952 Cadillac brake system will build pressure as I drive. I sometimes have to relieve pressure  on the system. The master cylinder and all brake cylinders have been rebuilt.

Answer
The first thing that I would check is the free play in the bake pedal. If the brake pedal is not returning all the way it will cause the brakes to build up pressure. Second is it only the front or rear brakes building pressure? If so check the flex brake hoses. They have been know to deteriorate internally and restrict the return flow of the fluid to the master cylinder. Then there is the master cylinder itself, it could be defective internaly.
Brad