I have a 1970 Challenger w/ power drum brakes originally.

I wanted to change over to front disk to improve my stopping ability, there was nothing wrong with the drums, just wanted to upgrade.

I bought the master cylinder from Ehrenberg ( 1 1/4" bore?) and the spindles are out of a 73 B body. The bearings, hoses, and discs are new, the calipers are rebuilt-pin type. I retained the original hard lines, power booster, and distribution block. I bought a Wilwood adjustable prop valve from Mancini to be able to adjust the rear drum lock up.

Everything went together well and the front brakes do work, just not well. No matter how I adjust the prop valve, the rears lock up first while testing. I can turn the dial on the proportionaing valve all the way to the stop at "less brake" and the rear drums still lock up before the fronts, if the fronts lock up at all.

I deduced the line pressure was not enough to operate the calipers so I bought another master cylinder, a 7/8" bore to increase the line pressure but after another test, I get the same result; the rears lock up before the fronts. The brakes pedal feels only marginally better.

I have another problem that I found out after I assembled everything, the calipers and caliper brackets are off a B body and put the caliper in a position to interfere with the lower control arm if I turn too hard either way. I guess I need M body calipers ( not sure on that either ... ) and brackets to fix this but before I buy anything else, I need to address the lack of front disc brake performance.

Anyone else experience this problem before? I did a search and found a ton of brake conversion info but nothing similar to what I'm experiencing.

Any suggestions what to look at first?