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Discussion Starter #1 (Edited)
Hi everyone: On most new vehicles the disc brakes back completely away from the disc for frictionless running. How is this done? Dosen't the system have residual pressure internally? Can I incorporate this in my street rod which has [Ford] disc front and [Ford] drum rear with a Mustang power brake master cyl. Thanks, Ed Farrell
 

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They use differently shaped seals in the calipers, and a special step bore master cyl.

I dont know if you can just change seals and the master. It depends on if the seal goove is the same for both types. It probably is.

The different seal retracts the piston further, and the step-bore master delivers the extra volume it needs to apply after retracting so far.

Most do not have residual valves that I am aware of, but some have the combination valve built into the master.

I also dont know if you would still need a delay valve for the front discs in this type of system.

Some rods run the low drag calipers with a residual valve and a regular master. The residual pressure defeats the purpose of the low drag seal so they can run the regular master.

Residual valves are primarily used in drum brakes, to help keep the cup seals from leaking, and in systems where the master resivoir is below the wheels.
 
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