Hy Village_Idiot, yes you understand me correctly, if the master cylinder is designed for drum brakes all around then it already has residual pressure valves built into it. It seems to me that the brake system suppliers have contributed to the confusion over this issue, they market a master cylinder originally for a Corvette, which had disc brakes all around. That master cylinder would require residual pressure valves if used in a drum brake application. Also if a disc brake master cylinder is mounted below the level of the calipers or wheel cylinders then a 2 p.s.i. residual pressure valve is required for the disc brake circuit, in addition to the 10 p.s.i. residual pressure valve required for the drum brake circuit, regardless of the master cylinder mounting position, I hope this clarifies the need for residual pressure valves.
