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Brake master cylinder upgrade help


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I have a 1964 Sportwagon that uses the single master cylinder to all four wheels. To say this is a concern is a bit of an understatement. While I would eventually like to make a drum for disc brake swap, lack of finances and other areas that need attention take priority. Is it possible to convert this setup to a dual unit? I have heard past discussions that GM may have even offered a dual unit retrofit at one time. Any help is greatly appreciated. GH

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Having lost my brakes twice I know where you are coming from. The "suicide cyl" is not the greatest. I own a 65 and have researched this the previous post is correct you will need to go to 67 and change out your front wheel cyl. I have not done mine yet. I did meet a very mechanical guy who found that a 1970 Chevy Monticarlo changed out with his buick (1965) he did the master and had disc and drum brakes!! I believe the only modification he had to make was the rod going to his power brakes. Just my 2 cents.

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I believe that '67 was the first year that all vehicles without the dual master cylinders got them from the factory as part of a safety-related agenda. Dual master cylinders for drum brakes typically had two equal fluid areas whereas those with front disc brakes had different sized reservoirs, typically, not to mention the "residual pressure valve" that was specific to the type of brakes (disc or drum, I don't recall which needs it as I write this, but feel sure that one type does) being supplied from the respective reservoir. The residual pressure valve would be the main difference in the disc brake and drum brake master cylinders, I suspect. I believe the '70 Monte Carlo would have had disc/drum brakes from the factory.

In doing these upgrades, how the master cylinder piston diameters compare to the existing master cylinder piston diameters might be of some concern (using one of equal or slightly larger piston diameter and not one of smaller diameter) as that has a relationship to the wheel cylinder piston diameters (and related fluid force issues).

On drum brake dual master cylinder systems, what appears to be similar to the proportioning valve in the disc/drum brake system is just a divider block that houses the switch to warn of pressure loss in one of the fluid circuits. On the disc brake vehicles, the "combination valve" combines the proportioning valve function with the divider block switch mounting functions. They might look similar, but have different functions and internals.

As stated, with the correct parts the changeover should be rather easy and simple to do. You can bench bleed the master cylinder prior to installation and then can draw a vacuum on the master cylinder reservoirs after you get everything hooked up. This will keep any air in the system pretty much localized in the areas highest in the fluid circuit. An extra master cylinder top and rubber diaphram seal (with a fitting plus a hole in the rubber for each side of the cylinder), some small screw-in fittings, and a hand vacuum pump could accomplish that activity.

Just some thoughts . . .

NTX5467

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Correct. Its important to make sure you don't just install a dual system without checking how it will react. I am doing this by memory but if Motors has it correct in 1967 the front wheel cylinders were a larger diameter than 64 65 66. The reason was in 67 with the dual cyl because of the resivor being the same size it was necessary to make the wheel cylinders inside diameter larger. This way all four wheels are stopping at the same time. Just another 2 cents.

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I did this master cylinder upgrade to my '66 last Spring.

That was part of a general brake renewal that included new lines, hoses, drums, wheel cylinders, and PraiseDyno Kevlar brake shoes.

I can tell you that it was a long and frustrating project. The hardest things to find are (1) the correct distribution block for 4-drum setup, which must come from a junk car, (2) the correct adapter fittings between the MC and the distribution block tubing, and (3) correct short-short or long-long booster and MC combinations. I can't emphasise these items enough.

GM made two vacuum boosters and two MC's during the late 1960's. One with a long push rod and one with a short rod. The booster and MC must be a matched set. Even the Chevelle experts can't define without exception why there are two types.

Also, the tubing diameter is wider for the duals than the single, so be prepared to bend some pipe.

I am happy with my car's braking now. And, I did not want to change to 15" wheels, which is required by the disk conversion kits. But, just aware that this swap requires some time and research.

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