I was reading in one of my car mags and it got me thinking. They were talking about rear drum cars having a special type of master cylinder that always put about 10psi of pressure on the rear lines so that the shoes would be right up against the drums when you go to step on the brakes. My question is..do third gens have this type of master? If so..i need to get another master cylinder for a 4 wheel disk car cause i just found the cause of my slight dragging that ive had from my PBR rear calipers.

 

The only difference between disc and drum master cylinders is the diameter of the bore. They're interchangeable. The combo valves are different, though.

 

The residual pressure check valves have been incorporated into the combo valve for a number of years. Older vehicles such as 1st gen f-bodys the residual pressure check valve was in the outlet port of the M/C.

So when switching from drum to disc brakes it needed to be removed.

Also, the purpose of the residual pressure check valve was not to keep the shoes against the drums. A 10 psi valve is not enough to do that.

The purpose was to keep a small amount of pressure on the brake wheel cylinder seals. Which prevented them from: leaking and pulling air into the brake cylinder.

There are other reasons for using residual pressure check valves. Such as having the M/C located lower then the brake calipers or brake wheel cylinders.

In your case you need a combo valve for a 4-wheel disc car. Or eliminate the combo valve and run just a proportioning valve to the rear.

RBob.

 

Ok then im all set. When i did the rear disk swap i put a SSBC adjustable prop valve in.