why do my rear brakes adjust themselves on 1998 Chevrolet 2500 Pickup

on a 1996 chevrolet pickup truck

1 answer 2 comments
THAT' WHAT SELF ADJUSTING DRUM BRAKES ARE SUPPOSED TO DO.
NOW, ARE THEY BINDING UP? OR WHY DO YOU ASK?
yes binding up thanks mark
CHECK PARK BRAKE CABLES SOUNDS LIKE ONE OR BOTH ARE STICKING.