Suzuki front breaks heat up and lock up

Sticking pistons in the brake calipers is the most common cause of this, but you also have to look for signs of brake fluid contaminated with a petroleum product. If the fluid is contaminated, the new master cylinder should have solved the problem for a few days, but then it would return again.

The place to start is by getting the brakes to lock up again, then stop on a slight incline, shift to neutral, place a block about a foot downhill of one tire so you don't have to run chasing after your vehicle, then open the hydraulic system at various places to see where the fluid is being trapped. If you loosen the line nuts at the master cylinder and the brakes release, you either have contaminated fluid, the booster push rod is adjusted too far out, or the brake light switch is misadjusted and holding the brake pedal down a little.

If you can open the bleeder screws on the calipers and the brakes still don't release, the pistons are sticking. We used to rebuild calipers at every brake job to prevent this from happening, but today commercially-rebuilt calipers are so inexpensive, it doesn't really pay to rebuild them yourself.

Tee hee hee. Even a blind mouse bumps into a piece of cheese now and then.

The question is how did that switch get out of adjustment? What I forgot to mention, and what would have helped you find that, is to loosen the nuts holding the master cylinder to the booster when the brakes are locked up, then pull the master cylinder forward 1/8". If the brakes release, you know everything else is okay and it's either the push rod is too long or the brake pedal is being held down.

Very happy I was able to help and that you found it.

Few things I forgot to mention. This shouldn't apply to your vehicle, but when you have just one front brake locking up and overheating, on vehicles that have a metal strap crimped around the middle of the rubber flex hose, rust can build up inside that crimp and constrict the hose. You'll get brake fluid through from pedal pressure but it won't release. The clue is it doesn't release when you loosen the line at the master cylinder but it does if you open the bleeder screw on the caliper.

Next, I alluded to contaminated brake fluid. It only takes a few drops of engine oil, or greasy fingers when you pop the rubber bladder seal back into the reservoir cap. Even a funnel that has been wiped clean after filling oil or transmission fluid will have enough residue to contaminate the system. After a few days all the rubber parts that contact the brake fluid will swell and get mushy. The lip seals in the master cylinder grow past the fluid return ports and that's what traps the fluid. The ONLY proper fix for that is to replace every part that has rubber, including wheel cylinders and calipers, hoses, master cylinder, and combination valve, and to flush and dry all the steel lines, THEN install the new parts. That already can cost more than older vehicles like I drive are worth, but if you add an anti-lock brake hydraulic controller to the list, the cost really goes up. If any rubber part is not replaced, the contamination will leach out of it and recontaminate all the new parts. This is just to let you know to be careful and how serious it is. I'd rather take the time to do that than to type for an hour on how to fix the problem.

And Merry Christmas to you too.