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Which Master Cylinder for 4 Wheel Disc?

themechanic

Oklahoma is OK
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I installed a 4 wheel disc kit from Doctor Diff. I recently learned the rear brakes will drag with a disc/drum MC due to the residual valve for the rear brakes.

So, which MC should I get that is made for a disc/disc system?

Thanks FBBO

P.S. I searched and found that most folks only upgraded their front brakes to disc.
 
You should definitely hit up Cass with Dr. Diff for this. Strictly speaking, I don't know of any stock B-Body setups that would have shipped from the factory with all wheel disc. That said, you might end up needing some sort of proportioning valve (should you decide to keep with one of the stocker MC's). Cass will definitely steer you in the right direction.
 
I don't know of any stock B-Body setups that would have shipped from the factory with all wheel disc
Some mid 70's Imperials did tho. Maybe RockAuto one of those if you can find one and see if that helps???
 
Cass told me I do not need an adjustable prop valve for his 4 wheel disc kit since the rear calipers are so much smaller than the front. He said just to use the drum brake distribution block. Cass sells a 4-to-2 bolt adapter and a modern disc/disc MC kit. So, I bought a similar combo from Summit.

Dorman M-99294 Master Cylinder (The photo shows a white plastic reservoir but it is really black.)

Mopar Performance Master Cylinder Adapter P5249315
 
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Take a paper clip, spread one end out and heat it red hot and with the front MC line off push it in the nipple hole and melt a hole through the rubber residual check valve. Heat and do it several times to make sure you have a good hole in it. You can also remove the brass nipple and remove the check valve and little spring then press the nipple back in. I've used the melt method several times with no problems.
 
I purchased my rear disc setup from Dr. Diff. Already had disc on front. Cass recommended I get a new MC so I got the one from his site. Had to get an adapter plate also. Do not need an adjustable prop valve.
Frank
 
I always recommend the late model aluminum MC with the plastic reservoir for disc brake conversions. No reason to have the brake fluid sitting in a rusty cast iron master cylinder.
 
In my experience a big factor is the bore size of the MC, I initially ran a 1 1/32" on my Cuda but went to a 15/16 which worked well, I do have an adjustable P valve as well.
 
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