I have disc fronts and drum rear. Upon reading a hydrabrake article it talks about two different combo valves used. One that is for a disc/disc combo that has a black rubber plug on the end of it, and another that has a flat surface with no black rubber plug on it for a disc/drum setup. I am having a major problem with the brakes working properly(I dont have the hydrabrake system just a normal camaro setup) and an wondering if you can use either combo valve in place of the other. The valve I have looks exactly like the one they show for a disc/disc setup. LIke I said I have a disc/drum setup. Does it matter?

It sure does matter. The disc/drum systems have the valves in them that adjust for the differences between disc and drum brakes. Master Power Brakes has a great tutorial on combination valves.

http://www.mpbrakes.com/mpfaqvalving.htm

I'm under the impression that the disc/drum combo valve has the black button and the one without the button is for disc/disc. The button is part of the metering or hold off valve. The idea is it holds off pressure to the front until the pressure in the rear overcomes the springs on the rear shoes as described in the link above...

All these companys sell the same product and describe them differently. If you go to the mpp site or call them they will tell you the combo valves come with built in residuals (2lb for for rear disc and 10lb for rear drum) and the site linked above shows adding the residual to the combo...

Mark could you tell us more specifically what your problems are with the brake setup... are the problems new and in response to a brake set up change... ?

I hope Dennis is right or I got the wrong combo valve on my car. If it's the wrong one it works real good on my disc drum setup. I got it off of a 78 Nova sedan so I'm pretty sure it didn't have rear discs. smile.gif

Same here.... I grabbed a comb. valve from a '72 El Camino that had disc\drum and this comb. valve HAS the button with black rubber cover over it on the end.