What causes rear brakes to be locked up the self adjuster keeps adjusting until the wheels won't turn?

What causes rear brakes to be locked up the self adjuster keeps adjusting until the wheels won't turn?
The problem with the rear brakes locking up may be the selfadjusting screws themselves. They should only tighten whenreversing the car and hitting the brakes, putting the pressure onthe drums in back instead of the rotors in front.