Four wheel disc. what master cylinder to use?

[chevyrestoguy]

I am planning on putting rear discs on my '73, and I have read through the threads from the guys using the Cadillac and Impala setups. I have seen lots of posts about what master cylinders guys are using, and they are quite varied. Some have used the stock disc/drum units, some use the ones from the donor vehicle (caddy or impala), others use aftermarket. I want this to look like the original setup from '73, so would a '68-81 Corvette disc/disc master cylinder work? I am amazed at how cheap they are at NAPA. I understand that the key to making it all work right lies in the porportioning valve, and I'll definately use the correct one there, but I don't care much for the look of the later master cylinders with the plastic reservoirs.

Would the 'Vette one work? If not, any other suggestions that are not budget-breakers?

[cparman]

I am not sure, but think that you could use the master that you have, and get a disc/disc prop valve. I have used Master power brakes for some time. There used to be a guy there named PAT. He has since went to a company : Brake Tech Solutions. He really knows his stuff, and if you google him he will be very helpful in getting you the stuff you need. I am thinking that you need a prop valve

[Shane]

i'm pretty sure the 'Vette master cylinder is the same casting as our truck's m/c but has a larger 1 1/2" bore ...

[dznucks]

i did read on a link in another post that if you up that bore size you have to change the rod length or something to get the proper output to the brakes. It confused the crap out of me.

I am curious about this too.

[chevyrestoguy]

I just got off the phone with Brake Tech Solutions and asked them the question about master cylinders. They said that the Corvette unit will work fine, but he suggested to look at the piston in the end to ensure if it's a shallow or long version. He said that the pushrods can be interchanged, and in certain cases, the piston internal to the master cylinder can be swapped for the correct one for the application. He said that using a long pushrod in an application that requires a short one can lead to major brake dragging issues because it doesn't allow free play in the brakes and the master cylinder is applying brake pressure all the time. The guy I spoke with at Brake Tech Solutions was very helpful, and didn't mind answering all my questions.

I recall a post not too long ago on the 73-87 forum about this exact same issue.