Ford Repair: 1992 ford explorer XLT, ford explorer xlt, caliper pistons

Question
front brakes siezing, replaced rotors, pads and calibers, new master (i think) old owner said something about a shim in master cylinder? Haven't been able to drive since i brought the darn thing,

Answer
Open the bleeder on each front caliper, see if there is any residual pressure there when brake pedal is at rest. Do both front rotors turn by hand, or are one or more dragging too much? Did you lube the caliper slides with an appropriate disc brake lubricant?

If you are not sure of the master cylinder, or it might be a rebuilt unit, replace it with a new one. Rebuilt masters aren't worth the cheap price or the hassle. Does this explorer have 4wheel ABS? If so there could be blockage or a stuck valve.

All this is assuming there are no kinked brake lines or collapsed hoses. If both sides are locking up this may not be the case. Are you able to drive it at all and then the fronts lock up, or not move at all?

You have to eliminate the obvious and then look at each part of the system. I haven't seen too many of these lock up the brakes, and many times it is stuck calipers or caliper pistons.