Regardless of chamber size or slack adjuster arm length, adjust the slack mechanism so there is 3/4 in. (19 mm) or less push rod travel when manually (by hand) extended to place the shoes in contact with the drum.
After adjustment, check for brake contact by gently striking the brake drum with a metal hammer. When the brake shoes are away from the drum, a ringing sound will be heard. A dull sound indicates brake drag and that re-adjustment is required until drag is eliminated
Check push rod travel after adjustment
Note: If the brakes can’t be adjusted by either of these two methods, inspect the foundation assembly for worn or broken components.