Posted by clueless [108.162.210.234] on Friday, September 09, 2016 at 11:15:20 :
The disc reservoir on a disc/drum master will be the larger of the two. A disc/disc master will usually have larger reservoirs than drum/drum masters, but are essentially the same, except for residual valves in the drum ports up until the early 70's.
Disc/disc masters can be used on drum/drum or disc/drum systems, and disc/drum masters can be used on drum/drum systems. Check for residuals in the drum ports, and add 10 lb valves if necessary for drums, and 2 lb valves to discs ONLY if the master is located below the floor.
V8 BOB, AUG 31, 2011 SHARE POST#5
V8 Bob
V8 Bob
ALLIANCE MEMBER
from Granger (Northern) Indiana
57 HEAP said: ↑
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.
so my disc disc mc would not need residual check valves--cuz it has wheel cylinder cup expanders in it??????
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