I cannot figure out the source of my brake issues but it seems like there is always pressure applied (front only) and when driving for awhile (5-10 miles) they begin to overheat and get to a smoking point. Bleeding off pressure at either caliper allows continued driving but use of the brakes begins the cycle again.
The previous owner treated the vehicle terribly and I noticed right away the brakes were an issue. Opening the reservoir (no ABS) revealed heavy contamination of the fluid. The driver rotor and pads had heavy grooves imprinted. I've replaced the front rotors, calipers, pads and brake hoses. I replaced the master reservoir and made sure to bleed it prior to install. I've bled the whole system at all 4 corners and although not 100% perfect, it's mostly clear and no particles or bubbles. I've done all of this over a period of time and each time I think I've got it fixed up, the issue returns. I thought maybe the pressure from the booster was an issue as the pedal stays firm but even taking the master off the posts didn't solve the sticking issue so I'm convinced its not that. The caliper slide pins are lubricated well and the rubber bushings are new and staying put. I replaced the wheel bearings with the rotors (they are joint on mine) and ensured sufficient lubrication with those.
With the caliper fully compressed the wheel spins and rotates just fine but after a few pedal presses it's like the caliper wont release fully. I think I installed the pad clips properly (only thing I'm not 100% on as the previous brake job didnt have them) but I admit I even took them off completely to drive it and the issue still occurred. Only thing I can think of at this point is either a line has gone bad or the combination valve is faulty. I tried cracking the line directly at the master cylinder and it didn't relieve pressure. The combination valve lines are extremely hard to get to and I suspect I will damage them trying as they are old so trying to avoid it if possible. Any thoughts or suggestions, I'm growing tired of just throwing parts at it hoping? For clarity, it is only the front brakes that are sticking (driver side seems worse)... no issues from the rears.

 

Im not saying this is true...don't know if a visual is good enough but rotors and hubs are different from early years to later years and a mismatch will cause binding. Somewhere in the past you might have been mismatched and your just continuing the issue by matching what was in there.? Or the axle was changed and thus mismatch. Do a search for rotor and hub differences... i posted a great link a year or so ago but can't find it easy

 

How old are the rubber brake lines? These can delaminate internally causing the hose to act like a one-way valve and keep pressure on the caliper. (I had this happen on a 1975 AMC Hornet that I used to own.)

 

That combo valve sounds like where I'd start. Its not THAT hard to get to.

 

I had the same issue with my non-ABS XJ. Front wheels would turn fine when brakes were cold, but the brakes would apply substantial brake-force after driving a few miles. At the time it happened, it had new stainless steel brake lines, and fluid was in great shape - only a few years since bleeding. Turns out it was the calipers. The piston was somehow seizing to the caliper body when the brakes warmed up. I had the same thing happen with the rear calipers on my 2009 Honda Civic. Replacing the calipers resolved the issue for both vehicles.

If there is nothing wrong with the ABS system and the brake lines are in good shape, you might want to consider replacing the calipers.

A couple of side notes regarding your vehicle - I've not seen those wire clips that are attached to the caliper mounts. What do those do?? Also, there are some decent size grooves in the caliper mounts where the pads rest. Those should be weld-filled and resurfaced.

 

Appreciate all the feedback. It's a 2wd, so not sure that axle swaps would matter much unless a conversion was attempted which it doesn't appear so. Not the best answer, but the components look similar between the stock shown model in the Haynes manual and what I have.

I did discover that I had gotten a bad driver caliper and replaced it again. The defective one was not retracting and was concluded based on it sticking despite the banjo bolt being loosened and even removed. However after replacement and about 10 highway miles put on, the passenger started sticking. I brought it back home and decided to swap that caliper as well with a new just to rule it out. I ensured bolts were lubricated, pads move smoothly and had lube on the ears. Both fronts bled. Again on the drive, vehicle started pulling a little to the right and got bad enough I had to pull over and relieve pressure at the bleed screw and limp home. Of note, I noticed the brake pedal kept getting firmer and firmer and would only press slightly by the time I had to pull over. I did replace the master cylinder while troubleshooting previously and I didn't see anything about adjusting the pushrod screw that sits behind it. Is it possible it is extended too far and not allowing the master to release pressure properly? These issues only seem to get worse once I get on the highway and things heat up both with the brakes (obviously) and the engine. I've not found anything suggesting to adjust that screw at any point. The passenger tire only rotated about half a rotation when I got home and jacked it, whereas the driver was just over a full rotation. It had several minutes to cool before I thought to, but backing off the master cylinder screw allowed additional rotation, hence my thought on the pushrod screw. I guess the only thing going against this thought is that it's not both fronts overheating and mainly just the passenger side now. However both do seem hot.

Edit: I just discovered there is a brake push rod depth gauge specific to adjusting it, pardon my newbie self. I ordered it and should be here by Tuesday. Tempted to shorten the screw in the meantime and see if it gets me any closer to "right" in the meantime.

 

Max - The pistons not retracting properly does seem to be the issue. But it keeps changing. All new rotors, hubs, calipers, pads and anti-rattle clips have been installed on both sides. I've also replaced the master cylinder and bled all 4 brakes. The lines are old, but I don't imagine them causing the issues I am having, especially as it keeps changing. The wire clips are the anti-rattle clips that should hold the pads in place. When I got the vehicle they had a set but were installed incorrectly and deformed so I had to get new ones.