Diesel Bombers - 94 cummins NO BRAKES

hey guys,

Ive got a 94 cummins with auto, 4x4 abs.

Last night I was driving along and hit the brakes pretty hard, truck stopped perfectly. After that I kept driving and went to take the next turn, hit the brakes, went right to the floor!!! uh ohhh, got out of the truck to see if there was any leaks/blown brake lines. Nothing. Its quite strange, when I depress the pedal it goes down then almost catches then goes the rest the way down. Alllllll the way at the bottom I can get them to work a little bit, but only once. will barley keep the truck stopped when I put it in drive.

I have been having some brake issues, ABS hasn't worked in awhile, rear brakes like to lock up when applied pretty hard. It does have fluid.

Another strange symptom is that when I press the pedal with the heater on, it changes the sound of the heater and makes it stop blowing.... :argh:

I had to drive 30 miles to work today! scary scary. I do work at a tractor shop with all the tools I need, so hopefully I can get some input on what I should try doing. I am very mechanically inclined, but don't have much experience with brakes.

Thanks for all future help guys!:c: