The truck has been sitting while my son was at school. We towed it, bqckweards, out of the area it was in and noticed that all wheels turned except the right rear. The drum is frozen. We cannot get it to turn or get it off. I tried backing off the star wheel on the back side of the wheel to loosen the brakes, but it would only move a couple pushes with the screwdriver in either direction. Any thoughts?