Hy Donsz, I realise that a drum/drum system does not neccesarily require a "proportioning valve", but if your master cylinder was designed for a disc/disc system, there will be no "resisdual pressure" valves built into it. Resisdual pressure valves are required for drum/drum systems to function properly, without them the first pedal pump or portion will only bring the shoes into contact with the drums, the second pump, or portion of the first pump will start applying the brakes, hope that helps.
