Hy Guys, if the master cylinder was designed for a disc/disc application then it will not have built in residual pressure valves. Residual pressure is required on drum brake applications regardless of where the master cylinder is installed relative to the wheel cylinders. As Hotrod Lincoln stated above 10 p.s.i. for drum brake residual valves, and for applications where the master cylinder is below the level of the disc brake caliper then a 2 p.s.i. residual valve is required. Residual valves were always installed in master cylinders for drum brake applications for the reasons Hotrod Lincoln stated above and because of that we never saw a separate valve, now most of the suppliers are supplying Corvette disc/disc master cylinders and it is up to the installer to install the correct components to have a safe, reliable, and properly functioning system, hope that helps.
