Master cylinder help !!

[dkauffman05]

I'm working on a buddy's 52 with a disc drum conversion. It's got an aftermarket kit on inside frame rail . I need a new master cylinder the one that's on it is stamped 29969 . From what I can find its for a 74 vette with front and rear disc. The truck never really stopped that great to me . Can anyone help with what master cylinder I can replace it with that I can pick up locally quick ?

[mr48chev]

You can buy a replacement at the local parts house as that isn't really a rare one.
If you have it off you can most likely take it to a parts house with a knowledgeable counter person and find a disk/drum master cylinder that has the same bolt pattern and the same depth of indent in the piston for the push rod.

If it is a Disk/disk master cylinder the truck should have a 2 lb residual valve in the front (disk side) and a 10 lb residual valve on the drum side. The old drum drum master cylinders had/have built in residual valves as do most disk/drum having one in the drum brake side.

There is also the theory that says that a smaller bore master cylinder will produce a higher pressure in the system than a a slightly larger bore master cylinder would on the same system and I see they list both 1 inch bore and 1-1/8 bore master cylinders for 74 Corvettes. http://www.oreillyauto.com/site/c/se...make=Chevrolet I'm thinking that the 1-1/8 bore goes with four piston brake setups due to the larger volume required.

That said, manual brake Corvette master cylinders have been popular for dual piston mc swaps on hot rods and custom installations since they came out in the late 60's. There are a lot of rods out there running disk/drum and disk/disk Corvette manual master cylinders.

One more thing you might look at as far as pedal effort and stopping is the pedal ratio meaning the ratio between the distance from the pedal to the pivot point and the distance from the pivot point to where the master cylinder push rod connects. In the name of making things fit good the people who designed and made it may have created a situation where the pedal isn't putting as much pressure on the master cylinder push rod as it could with a different ratio.