Rear Disc Brake Conversion

[Manta22]

Like all drum brakes, the Corvair rear drum left a lot to be desired so it is recommended to convert the rear brakes to a disc setup.

Fortunately, the conversion is relatively easy (as most conversions go) if you stick to Chevy parts. After removing the brake drum, disconnecting the emergency brake cable and axle universal joints, the hubs were removed from the trailing arms. The drum backing plate and associated hardware was removed and the old wheel bearings were removed and replaced with new ones.

Since Chevrolet made no provision for re-lubricating these beings, I drilled a small hole through the hub into the bearing housing and tapped the opening for a 10-32 screw for sealing out dirt & water. To lubricate the bearings, I use a syringe and inject grease into the drilled hole. While the hubs are off it is a good time to remove the trailing arms and replace the rubber bushings. After 50 years, chance are that they are shot. New bushings will allow the rear suspension to be aligned properly and the improvement in handling will be immediately apparent. U-joints may need to be replaced as well; use "Heavy- Duty" joints.

I used brake rotors and calipers from a 1988 Corvette. The rotors simply slip on the Corvair hubs and brackets to mount the nice Australian- made Girlock aluminum calipers are easy to make. I cut out two pieces of aluminum plate and bolted them together with high grade bolts; this provides the proper offset for the calipers to fit over the rotors. A drawing is shown below. The '88 Corvette and some models of Pontiac Firebird use this caliper. It has a "pull" lever for a parking brake cable. This can be adapted to the original Manta parking brake cable without much trouble.

Check the original Ford Thunderbird brake proportioning valve. It may be full of rust and not functioning at all. Replace it and set it to about 50% as a starting point for adjusting the F & R bake percentage.

[Sulley]

This is good information Neil. I have the rear drum units still and wanted to upgrade to disc. I thought I would have to go the route of C3 Corvette trailing arms. How thick was the aluminum material you used for your bracket? Do you have a picture of where you drilled out for the small hole in the hub? So if I was putting together a parts list for this conversion would it look like this:

(2) C4 Rear Rotors
(2) Girlock aluminum calipers
(4) C4 Rear Wheel Bearings
Corvair trailing arm bushings
(1) Pair C4 Rear pads
(2) C4 Rear universal joints
(1) Brake proportioning valve (Can this be any universal part or should I stay with Thunderbird)

[Manta22]

I just realized that I had not answered your question. The aluminum was 1/4" or 5/16" plate but I can't remember which.

[Manta22]

Look carefully at the first photo, Ken. There is a socket head cap screw sticking out directly at you in that picture. Any proportioning valve will work; a Thunderbird valve was what Manta Cars used.

[Sulley]

Yes I see that now, these old eyes missed it! Nice work.

[Jerry]

In my case '88 Corvette discs are bigger diameter than my Mustang 2 fronts. The proportioning valve is not going to be the total answer.

I have been looking at 12" front rotor and calipers.


http://www.rjays.com/Brakes/MII-Brakes-01.htm


I am looking for smaller rear and larger front till the sizes look right.
Front rotors than can accept GM Chevy wheels is a plus also I guess.
I need the emergency brake mechanical too to pass inspection.

[Jerry]

This is a cheap way to get 11" in the front:

http://www.speedwaymotors.com/Mustan...tern,2007.html


The Vette rear would be 11.5" though ...

any better ideas?

The Factory five GTM mid engine has rotors 1" bigger in the front than the rear. This or equal size is probably good?

[Blueovalz]

I studied this for my car, and with the weight distribution and CG values I used earlier in the project, the results were to use identical sets front and rear. So I'm using the C4 front rotors (12" x .81") with some Outlaw four-piston calipers (1.75"/1.87" pistons in each caliper), which gives a decent feel using 3/4" master cylinders and a 6:1 pedal. I haven't done any emergency braking yet to verify the balance, but so far it feels normal and stops well.