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dundirtcheap 06-06-2006 07:56 PM

GM drum to disc swap
Swapped from drum to disc on the rear of my race car. Limited to stock parts, and used the calipers from the front of a Caprice wagon '85 model. Used manual master cylinder, with no proportionary valve. Problem: no pedal without pumping several times. Minimal pedal with numerous pumps. Not enough to stop car. Need stock combination to allow me to utilize the rotors I have. They are after-market .81 thick, purchased from Speedway Motors and are the only part I can use that is after-market. ANY and ALL assistance appreciated.........thanks.

TooMany2count 06-06-2006 11:44 PM

get a proportionary valve for 4 wheel disc brakes it should matter if they were power or not because the valve cant tell if u have power brakes or not. but then i would most likely run a power booster also if it was me.......joe

Triaged 06-07-2006 01:16 AM

What master are you using?

Starting in about 83 GM started to change the angles cut in the calipers for the square cut o-ring. This allowed the pistons to retract more from the rotor yielding more MPG because of less drag. However to do this they needed to use a step bore master cylinder. They had a large (40mm mostly) piston that would move lots of fluid and would transition to the smaller bore (1.125" in the case of the caprice) to keep peddle effort down. As you found out mixing the 2 up doesn't work too well. I also bet that you have way too much braking in the rear. Best bet would be new MC with a larger bore and smaller calipers in the rear (like metric calipers)

dundirtcheap 06-07-2006 03:44 PM

If I obtained some calipers from the front of a 79 Camaro or 'bird, and used a single cell master cylinder (50's style), would I solve my problem? Trying to solve the problem before sat. nite.........gotta big race comin up........

Triaged 06-07-2006 05:21 PM

I don't know if it is in the rules but a residual pressure valve should help part of your problem. The 50's MC would just make things worse. If the peddle effort isn't too high you might try a larger (power brake) MC...but your rear calipers will still be too big.

bfhduh 07-30-2012 08:40 AM

I am building a v8 s10 and been having issues stopping my tires at a stand still and i switched from stock drums to a 2004 stock blazer 3.73 dis1c and it solved about 70% of my problem. if that helps. didnt have to change anything bolted right up

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