Posted by clueless [201.237.45.94] on Tuesday, July 08, 2014 at 19:33:03 :
In Reply to: Re: from jalopy posted by clueless [201.237.45.94] on Tuesday, July 08, 2014 at 19:25:15 :
Any MC designed for drum brakes, be it front and rear or rear only, will have a residual pressure valve built in. This valve prevents the springs on the brake shoes from pushing the brake fluid back into the MC and thus increasing the distance between the shoe and drum. These valves can also be purchased and placed in systems that have a MC lower than the wheel cylinders and/or calipers.
Not entirely correct. Residual valves disappeared in the early 70's from most/all drum/drum and disc/drum masters because of wheel cylinder cup expanders, which keep air from entering past the cups during quick brake release, the main purpose of residuals. (they were never used on modern disc brakes) NO WAY can a 8-20 lb residual valve prevent 70-100 lb shoe return springs from fully returning the shoes to their anchors, along with returning fluid back to the master. With the shoes fully returned and properly adjusted, there should be about .025"-.030" total shoe-to-drum clearance.
Residual(s) in 60's/70's dual master cylinders are located behind the tube seats. They are small rubber spring-loaded check valves, and can be felt when GENTLY inserting a paper clip or small drill bit into the port.
Keep in mind Corvettes never had disc/drum systems-they went from drum/drum to disc/disc in '65, dual system in '66, so there will be no residuals in any Corvette dual master, and the chamber sizes more than likely will be, or appear the same in all Corvette dual masters. (FYI, residual valves were never used on the disc circuits of US vehicles using modern spot disc brakes)
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