I have a 71 that Ive put 72 ss spindles and new rotors and everything else on a drum/drum car. I have read all the posts for brake conversions and understand that everyone has done it a little differently and had good success w/ almost all of them. I have a problem w/ my front calipers dragging. What causes this? Here's my setup: Original brake lines from front to back. New hoses, new rotors(old ones cracked) I went from power to manual booster w/ a 1970's to 1980's truck master cylinder(1 1/8 bore), I have a willwood adjustable proportioning valve installed right out of the rear line at the master cyl., and I would like to install my new line lock somewhere on the front lines but I still have the original distribution block.
What In The Hell have I done wrong Please!!!!!

Is the stock distribution block on a 71 drum/drum car also a proportioning valve? Is this my problem? I had someone tell me that my pedal rod that goes into the master could be too long but it has a little bit of tolerance to it so thats not it. I DON'T KNOW. Any help is greatly appreciated. Oh by the way I drag race it if ya haven't figured it out yet so brakes are kinda important!! Thanks for any help. Kevin

Clean the caliper screws, sleeves and caliper bores. White lithium once they are clean. Calipers are new? If not, rebuild them polish the pistons and bores bores -- surprising how much gunk and stuff can get into the bores.

How much are they dragging? They do drag a little normally. That is how they operate. The piston and pads do not retract completely away from the disc. In the late 80's I think there was such a thing as a quick take-up MC, but it had its problems. Normally they do drag a little. I think new cars have improved on the quick take-up idea that was put in place to help improve mph slightly.

well, w/ the front wheels off the ground it takes both hands to turn either front tire.

Okay then...that is too much drag! :clonk:

I think the problem might be in your brake pressure switch...that is the one on the frame. In a drum/drum setup it is both a metering block and a proportioning valve. Your old drum brake setup had residual pressure valves to keep the seals against the bores in the slave cylinders. Not sure where they are in a '71. They are probably located there. Sometimes they have been in the master cylinder itself. In the Disc/Drum setup the valve in the frame is called a combination valve. The combination valve also has a switch in it that indicates brake power loss. This switch is just a metering valve that if it gets un-balanced it grounds out a circuit that lights a bulb in the dash. Sometimes when you change components in the system that valve gets unbalanced and you cannot properly bleed the system. There is a button at the front of the valve that is covered with a rubber piece. You need to depress that rubber piece when bleeding (the back brakes I believe) the system and you can't get any pressure to the back brakes. If you don't have the dragging problem in the rear...maybe it is because of that valve. My Parts and Illustration catalog lists different part numbers for the valve in the frame between disc and drum, and the disc setup also had a seperate delay valve assembly for the rear brakes up near the MC itself. My bet is the valve in the frame.

The P/N for that disc/drum valve in the frame for your car should be: 18004049

Thanks Erik. Is that a GM part no. or a particular suppliers part no.?

so this delay valve you're talking about up by the MC that I don't have needs to be added instead of the Wilwood proportioning valve on the rear brake line yes? Is that the technical name for it? Ive never heard anyone call it that.