Lee Zook

I have a 1986 944 turbo. I have been trying to figure this out for a while (2 years). The rear brakes are sticking. I have replaced the rubber flex hoses, calipers, pads, etc. I have also replaced the master cylinder with a good used one, and the problem did not go away. The parking brake is working fine, too. When the brakes grab, I can pull the brake pedal towards me and it helps to slightly "release" the calipers.

The only 2 items I can think that are left are the brake pressure proportioning valve/regulator that reduces the pressure to the rear lines or the brake booster. Has anyone experienced either of these 2 items failing and resulting in the rear calipers sticking/grabbing?

Thanks,
Lee