Doesn’t sound like a master cylinder. You did calipers and hoses?

Just had similar problems with a chrysler town and country. Owner changed all calipers and hoses because different side of vehicle would get hot randomly. Ended up chasing it back to the hcu.

Hydraulic control unit or basically your abs pump. Was a pain to get at on that vehicle, but completely fixed random lock-ups. Go to a junkyard unless willing to pay $1200.00 for OEM. Got ours used for $65.00.

You will have to bleed the heck out of them and I couldn’t get abs bleed on scanner to do much good so had to bleed several times and drive to a local gravel road to apply brakes to engage abs several times.

Another thought, I had a 99 Chevy truck once that was a split year between models. I was given the wrong rotors, and they didn’t fit correctly. Did you make sure everything spins freely with the wheels torqued down?

You pushed the calipers back when you installed new pads and rotors. Presumably, you didn’t open the bleeders on the calipers when you did it. Almost nobody does. 99% of the time it’s not an issue, but you are potentially pushing debris back into the lines, proportioning valve, and ABS unit.

I’d try an ABS bleed procedure with a scan tool to try to dislodge anything that might have gotten into the system. The only way to precisely narrow down the cause would be to use a pressure gauge at each fitting, starting from the master cylinder and working to the calipers.

You’d need a variety of fittings to adapt each connection. Since it’s moving from side to side, I suspect the ABS unit since the master cylinder and proportioning valve only have one circuit (the proportioning valve is a simple y or t in the line in front of the regulator for the rear brakes). Good luck finding the cause of your issue.

I know how frustrating it can be.

You didn’t clamp off the brake hose with vice grips when replacing the calipers did you? If so you have crushed the inside of the hose and created a one way valve in which high pressure fluid can flow to the caliper, but pressure is not released when brakes are released causing overheated brakes.

When you squeezed the piston back on the first brake job, you may have sent some rusty fluid into the ABS module and now one of the valves in the module is stuck.

You can diagnose this. Pump the brakes a few times. Check the suspect wheel to see if it’s dragging. Now crack loose the metal brake line BEFORE it turns into the rubber section of brake hose. If the drag frees up, the problem is in the ABS unit. If the drag is still there, it’s the rubber hose or the brake caliper.