Working on a 96 Cherokee. New master cylinder, booster, wheel cylinders, calipers, equalizer block, New pads.and shoes. Everything but the lines and the dogged pedal. Everything starts off fine and then the fronts progressively tighten until they're smoking. Occurs whether driving and will tighten down if lest sitting at an idle. Pump the pedal a couple times and it releases. Any ideas. I'm to the point wherey next move could be the crusher. Thanks in advance.

 

Could be your rubber brake lines. They collapse inside over time, not allowing the fluid to flow in and out of the caliper/wheel cylinder correctly. They usually look fine from the outside but are pinched shut (or close to it) inside. I would replace all four if it was me. Hope that helps.

 

Do you have a FSM? Mine's not handy at the moment, but I'd check and see what the procedure is for installing the master cylinder, particularly if there is certain procedure for the booster rod to the brake linkage. And, if the brakes are tight while idling before driving try jacking up one wheel, try turning the wheel by hand then disconnect the vacuum line to the booster and see if the brakes release. It could also be the vacuum check valve at the manifold.

And, as suggested, the rubber brake lines will get weak over time and will create pressure in the system by expanding and not returning to their normal size.