What Master Cylinder for dual piston disc brake conversion?

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aeromech
Posts: 43
Joined: August 6, 2009, 10:40 pm
Location: San Diego CA

What Master Cylinder for dual piston disc brake conversion?

Post by aeromech »

We have transplanted the entire front suspension from a heavy axle 1979 F-250 into a 1966 F-250. The heavy axles use the double piston brake calipers and I need a part number for a manual (not vacuum power boost) master cylinder.
I have done a couple of conversions on 1965 F-100s and used the Raybestos MC39469 manual master cylinder with good results on the single piston calipers on the F-100. This master cylinder has a 1 inch bore and works fine with the single piston calipers. The power brake master cylinder for the dual piston appliction, Raybestos MC36352 lists a 1 1/4 inch bore. Do I need a manual master cylinder with a larger bore than 1 inch to adequately power the dual piston calipers or is the larger size due to the vacuum booster application. Comparing the single and double piston calipers the surface area of the caliper pistons seem to be pretty close since the diameter of the single piston is much larger than the diameter of each of the double pistons on the double piston caliper. The Raybestos tech line will not give any information on non stock installations due to liability concerns. All thoughts and experiences will be greatly appreciated and a part number would be outstanding.
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foodstick
Posts: 3364
Joined: March 15, 2006, 6:45 pm

Re: What Master Cylinder for dual piston disc brake conversi

Post by foodstick »

For some reason it seems like people were mostly using the 67 F250 master cylinder, or the 68 Mustang cylinder...for a low dollar upgrade. If I recall one has brake lines exiting to the driver side. The other to the passenger side. I think I updated a few trucks to the dual piston wheel cylinders without much problem. It seems like we had to run a small dremel stone around the mounting hole for the wheel cylinder to slide into the back plate. But that was it.

Also I believe the Master cylinder pushrod needs to be shortened a hair. Grind and polish the pushrod until it doesn't rest against the cylinder while the pedal is at rest. There should be a tiny bit of movement before it touches in the cylinder. Hopefully someone that has done this in the last ten years will chip in ! ;)

Sheesh, I just reread your post and totally missed you were doing disc brakes....Well I will leave this up anyhow.. maybe it will be of use to someone ? hahahahah
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