I have some problems with my 86 GT . Goes just fine, just doesn't stop so good. I have replaced the master cylinder and blew the stew out of the brakes and I do not have fluid to the rear. Anyone ever have problems with the proportional valve or what should I look for ?
Have you tried disconnecting the rear lines from the prop.valve and the wheel cylinders and blowing air through them?
If air flows through the lines , I'd replace(upgrade ) the prop.valve.