I’ve got an old dry van trailer and right rear brakes caught fire. Pulled wheels and brakes off and inspected. Put new brakes on and wheels back on. Adjusted brakes like we always do. Set the brakes and they lock down. When I release them though all other duals spin free except the right rear. Pulled the service lines off the chambers one at a time with brakes released, no air flowing. Pulled service line off trailer nose, no air through line unless the pedal is hit. Maybe a slack adjuster?