Manual Disc Master Cylinder

[Tabasco]

I backed the '57 out a few weeks ago, stepped on the brakes and it just kept rolling. I decided that it is time to do away with roller bearings, front drum brakes and single master cylinder.

I ordered a disc brake kit and proportioning valve from Speedway Motors. I figured I would buy a master cylinder locally. I am going to go with manual brakes. I was going to buy a 1" bore disc/drum master cylinder from a late 60s, early 70s GM mid size car.

Oreilly's, NAPA and Autozone all list 1" bore drum/drum or a 1 1/8 bore Disc/Drum. Is there such a thing as a 1" bore Disc/drum master cylinder that will fit my car?

I used the search feature here and saw a reply by Rick L to a post with a similar question to mine. He said a early 70s Corvette disc/disc master cylinder would work. If I go with a disc/disc master cylinder, will there be any problem using it on a disc/ drum system?

[chevynut]

If I understand it correctly all you have to do is remove the residual pressure valve from the front brake outlet of a drum-drum MC. I don't think you want the disc-disc one unless you have discs in the rear.

[Rick_L]

The only deal with using an early 70s Corvette disc/disc style master cylinder is the lack of residual valves. The Camaro/Chevelle/Nova drum/drum master cylinders from 67-68 model years came originally with residual valves but few rebuilt or aftermarket ones have them anymore.

Other than the size of the fluid reservoirs, the residual valves are the only functional difference between the drum/drum Camaro style, and the disc/disc Corvette style. All the big reservoir does is let you wear the full thickness of the pad without adding fluid. The little reservoir will require you to top off before the pads are worn out.

I recently read on another site that the reason for that is that the replacement wheel cylinders for those cars have a heavier spring in them these days, eliminating the need. What I didn't find out was how to know whether you got the stronger springs or if stronger springs are now in use on other wheel cylinders such as 55-64 Chevys.

If you use a GM style combination valve for disc/drum, it has a residual valve in the outlet port for the rear brakes.

I think that explanation goes a ways to explain why some say the residual valves aren't needed with a disc/drum conversion setup, but some insist that having them has positive results.

[Tabasco]

Thank you both. Now I understand a little more about brakes and know what to get.