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Old 01-08-2012, 09:30 PM
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Disc/Drum Sizes and Valving

I am about to run my e-brake cables and I kinda hit a snag. I am not sure if my rear drums are the size I want. Looking for input from folks with similar experience.

Car is a 41 Chevy 2 door sedan. 350/350.

The booster is an 8 inch dual diaphragm. The pedal ratio is about 4.5:1. Corvette style MC.

The front brakes are 11 inch rotors with metric calipers (2-1/4" (?) piston).

I thought the rear was out of a G body. It is definitely GM and it has the mounts still there for the upper trailing arms. I never looked at the brakes that close and assumed they were the 9-1/2" brakes. When I started fitting up the e-brake cables, I realized the rear had 11" drums. The rear wheel cylinders are 15/16" units.

I intend to run a GM style combi valve (metering, rear wheel residual pressure, proportioning, and differential pressure switch).

My question - Will the 11 inch rears cause brake balance issues? If so, should I:

1. Switch to 9-1/2" rear drums?
2. Put an adjustable proportioning valve in the rear line?
3. Set it up and test it, putting in an adjustable proportioning valve only if needed?
4. See if I can find some smaller wheel cylinders which will fit the backing plate (7/8" or 13/16" maybe)?
5. Combination of the above?

If I go the adjustable proportioning valve route, do I remove the proportioning valve from the combi valve or just run them in series?

What do you think?

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Old 01-08-2012, 10:09 PM
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I am no expert
but I would just go with what you have
bigger drums are always better
then tweak the system later, if you have to balance it out better
maybe someone with more of a working knowledge, of how that combo will work, will chime in
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