Car repair

I have a 1985 thunderbird with a brake problem,After a few moments of operation the front brakes start to lock up. I have replaced both calipers,brake hoses,master cylinder,booster,and ran a vacuum line directly from the intake.I also replaced pads and rotors. I am at a loss to what may be causing the problem.

I seem to remember that many cars of that age had a valve used to balance pressure. Do you know if you have such an animal?