GMC 2003 GMT560 T-Series Owner's Manual page 154

4. Put the release stud, nut and flat washer into the
chamber.
5. Turn the stud clockwise one quarter of a turn.
4-36
3. Remove the rubber
cap from the rear of
the chamber.
7. At the repair facility, apply air pressure of at least
70 psi (480 kPa) to the brake chambers, either
from an external air supply or the vehicle's
air system.
8. Turn the stud nut counterclockwise several turns.
Remove the stud from the chamber.
9. Replace the stud and washer and tighten the nut
into the side of the chamber.
10. Replace the rubber cap.
6. Turn the stud nut
clockwise several turns
to release the brakes.
Follow the same
procedure to release
the other brake.