The Stovebolt Site Forums The Shop Area Driveline need a master cylinder

hello , i have a 1939 chevy 1.5ton truck . i have oregonal front drum brakes , on the rear i have a 1999 dana 70HD dually with disc brakes , this system worked ok for stopping with the oregonal single master cylinder , manual .

i have tried a dual master cylinder , with a proportioning valve and a 12 LB front residual valve on the front for drum brakes and a 2 LB residual valve on the rear for the disc brakes . this system did not work as good as the single master cylinder with out residual valves .

this is sure a learning challenge . from what i found on the internet about what to put on this truck , i am missing something . because of a budget and parts that became available is why i have disc on the rear and drums on the front .

is there a reasonable solution to put on a dual master cylinder ? thank you 1pete1

Hy 1pete1, what was the original application for the dual master cylinder you installed, was it for disc brakes or drum brakes or disc/drum? Residual pressure valves are built into master cylinders for drum brakes or the drum brake section of a disc/drum master cylinder. When we have a mixture of brake types (Disc and Drum) we usually require a proportioning valve to stop the drum side of the braking system from locking up under the increased pressure that the disc brake side of the system needs to perform properly. Master cylinder bore size is also important, I would not use a master cylinder with a bore smaller than the one that controlled the brakes on the truck that you got the rear axle from.