I have the knob (not lever) styled proportioning valve (260-2220)installed to limit pressure to my rear brakes in my B car. Throughout the last race, I have been slowly dialing out rear pressure to avoid rear lockup and axle hop. During the last session of the weekend, I had a rear caliper begin to drag severely and finally ended my day with a glowing red rear rotor. Figuring I had a line problem or caliper issue, I re-built the system using all new lines from the master cylinder,new calipers, new rotors and new pads. I finally got the system bled today and noticed that again the rear calipers would not release after pumping the brake pedal. I manually released the line pressure through the bleed screw and the calipers released. I repeated the test with the same results. The third time, I adjusted the proportioning valve in (increase direction) to approx 1 turn from stop. (I turned it 8 complete turns to the increase direction, so I was pretty far out to begin with, but the manual seems to indicate that the usable range is from stop to stop)). I then repeated the test and found the rear calipers to not have stuck and the brakes seem to be operating normally.

So, My question is.. is there a limit to how far you can turn the prop valve in the "decrease" direction?? Do I have a defective valve that needs to be replaced?? Anyone ever had a similar issue??
Thoughts??