Help,I believe my proportioning valve is out of wack. Brake warning light stays on. I have to pump up brake petal to stop and it feels as though only front disks are working when I do this. I disconnected the electrical wire to the proportioning valve and warning light goes out. I was told that this means there is something wrong with the valve itself (possibly the proportioning valve piston is not centered). What steps do you take to get the piston re-centered correctly. Brakes were fine when car was put away last fall.

1971 Demon front disks rear drums