ok so I have a wildwood adjustable prob valve but for some reason no matter how much pressure u want to it to make the rear brakes lock up nothing happens im using a 89 master cylinder from a gta that has pbr brakes so it should work do u think the master cylinder is bad the front brakes lock up no problem when pedal is applied

 

How and where in the brake circuit did you install it? Is it front and rear or just rear? Did you bypass the existing prop valve or install in series with it? The symptoms make it sound like the last set up. Picture?

 

i had to take the spring out of the original prop valve to get any pressure to the rear when i swapped in the disc brake rear out of an '02... they literally did nothing unless i pumped the hell out of the brakes to build pressure.. removing the spring put too much pressure to the rears and i got immediate lockup. the adjustable valve in the rear line allowed me to dial it in- if i remember right, i wound up with the valve adjusted to about the halfway point by the time i got it dialed in just right.