ok this problem wen t away for a while but its back. when i start my Jeep and take off ill be going real slow barely touch the brakes and they lock up but after a couple minutes they work fine and sometimes after they lock up they be groaning sometimes its the backs sometimes its the fronts...i just left school was doing like 7mph touched the brakes and slid a couple feet on sand.

i have recent brand new rotors and pads with new slides.
i need to do my back brakes cause its all rotted.

what would cause this...do i need calipers and wheel cylinders, or a master cylinder, or what

 

any help

 

mine does this too but only on the rear and only after it rains i think it just has to do with small amounts of rust on the drum causing to lock