brakes going crazy.. Overheating fluid?

[78Suburban]

I went wheeling with some buddies yesterday, and my brakes went crazy.. the pedal got really soft and went all the way to the floor. I had to pump it several times for it to start to catch and slow down. I popped open the resevoir, and the big end was full of fluid, and the small chamber was only filled shallowly with fluid. I felt of the fluid, and it was SCALDING HOT!.. wonder what made it heat up like this? Later on in the day, I got my brake pedal back, and it seemed to stop fine.. So whats up with that? I've got stock 3/4 ton brakes, btw.
thanks,
James

 

[88Silverado]

Several things to check first.

The small chamber is for the rear brakes. Pull the wheels and look for a leaking wheel cylindar and worn linings to see if thats what caused the low fluid level. If the level ws very shallow and you were on an incline, you could have sucked air in the system which means you need to re-bleed the system. If that looks OK, you could have a master cylindar going bad.

Brake fluid will become very hot. If its old fluid (or you did suck air in the lines) I would recommend a complete flush of the system with something like Valvoline Syn-3 fluid. Brake fluid will accumulate water over time and when the fluid gets hot, the water boils creating steam and thus no brake peddle. Its not uncommon for fluids to reach 300-400F "DRY" boiling point. Water in the fluid can drop the "WET" boiling point down in the low 100"s. I recommend the Val Syn-3 because its fully compatable and has high Dry & Wet boiling points.