# 1966 GTO Dual Master Cylinder Swap



## Lennox (Oct 17, 2012)

Hello everyone. I installed 1970 Chevelle front disc brakes/spindles(prop Valve) on my car. The rear brakes are original rebuilt. The car has the original brake booster for the 4 wheel drum power brake set up. My question is, what other master cylinder can I use that dimensionally is smaller that the stock 1970 Chevelle one I have now. I'm in the process of building the car now. The stock MC is long enough that I think it will come in contact with the hood. I have read that the 1970 Chevelle MC can be a 1" bore or a 1 1/8 bore. Does anyone know of a MC that will work for my application. Thanks.


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## ALKYGTO (Mar 29, 2010)

Why do you need a smaller (physically) MC? 

Do you want it to look original-ish? Or is function your primary goal. Could try a late model like an S-10 MC. Or spend a little more and get an aftermarket like a Wilwood.


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## Instg8ter (Sep 28, 2010)

the vette master cylinders are a bit more streamlined dont think they are smaller though.


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## ALKYGTO (Mar 29, 2010)

^I used a Vette MC on my first 4 wheel disk brake swap, 1968 Vette offered 4 wheel manual disc so perfect for that...but I'm not sure if it will work for a disc/drum setup. My car had manual disc/drum when I first put it on the street and I used a MC for a 70 Olds 442 which offered manual disc/drum.


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## Instg8ter (Sep 28, 2010)

if your using the stock booster (9" i believe) it will fit, it just looks like it won't.


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## gjones (Oct 8, 2012)

Why did they put such a steep angle on it? seems like they could have straightened it out A BIT.


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## Rukee (Feb 8, 2007)

Is it possible that the bracket on the back of that booster is upside down Instg8ter?


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## Instg8ter (Sep 28, 2010)

not according to tuff stuff...steep angel is to clear inner wheel house and valve cover on drivers side. The smaller aftermarket boosters should have less rake and more clearance. Camera angle of first pic makes it seem more severe, and yes it does look like it will hit the hood, but clearance is fine and brakes work flawlessly with 14 PSI vacuum. You will also want to modify the clevis rod wit a barrel nut and threaded rod to easily adjust the throw from the pedal if you use a later model booster.


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## xconcepts (Jan 4, 2009)

Grrr, I can't find A body front disc brakes/spindles for the life of me around here.


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## Instg8ter (Sep 28, 2010)

try Tuff Stuff, SSBC, NAPA, i believe most conversions use the 70'+ stock splindles.


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## gjones (Oct 8, 2012)

*kickdown*

Hey Instg8ter, is that an electrical kickdown on your gas pedal? If it is, would there be any way to take a picture of it, so we could see the connecting parts?


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## Instg8ter (Sep 28, 2010)

No G thats the adjustable link for the power brake conversion with later model booster, electrical is the brake light switch, i have TH350 that uses a manual kickdown, have not been able to find a bracket to work for it with the stock throttle cable bracket.


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## Lennox (Oct 17, 2012)

Having a hard time getting rear brakes. 1968 MC (new) original vacuum booster(rebuilt) 1970 chevelle proportioning valve, spindles, calipers and hoses. Original 1966 GTO rear drum brakes, new cylinders and rear flex line. I'm thinking I have a stuck prop valve. I notice your brass prop valve has dual outlets for the front brakes. I believe mine only has the front bottom "out" line going to a "tee" for the front brakes. The one port on the top front of the prop valve has a plug in it. I can stop the car with the front brakes but it has lots of pedal travel. Anyone have any ideas. Sorry if I have missed any key info.......getting tired


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