Problem: brake builds pressure and locks up front disc brakes on 1937 Buick Special. Tried so far: New rubber lines (twice) New master cylinder with factory residual pressure brake line seats COMPLETELY REMOVED ZERO inline residual pressure valves. Did have 2# to discs and 10# to drums. Rod from pedal to booster has 1/4" free travel Rod from booster to MC has 1/4" free travel When cold pedal is only 1/3 of its travel off floor Kit is from Scarebird and uses Riviera rotors and Astro calipers. Brakes are perfect for first half dozen stops and then build till pedal is solid with no free travel and drag old straight eight engine down to a stand still. Only part not replaced is 7" dual diaphram booster. System worked fine for thirty years with drum/drum configuration. HELP!