Which 7/8 master cylinder?

pushrod is too long. The Spring DOES move the pedal as far as it can, but if the pushrod is too long the C-port does not open and so pressure remains in the system, dragging the brakes. Unbolting or just loosening the M/C allows the too-long pushrod to move all the back which opens the port and relaxes the pressure, releasing the brakes. This is the proof-test for a too-long pushrod, or a brake pedal not parking properly.