It may be the shoes and drums are grooved, locking the drum in place.
You can remove the rubber inspection piece on the backing plate, use a screwdriver to turn adjuster in to move the shoes in as far as possible.
If all else fails use a cutting wheel and cut it off.
December, 3, 2009 AT 7:56 PM
Purchase two M8 1.25 x 40 bolts and screw them into the drum (there are 2 holes, 180 degrees opposite each other at the inner part of the drum). Using a socket, turn each bolt, alternating between the two and slowly turn the bolts clockwise. This will cause the drum to loosen up and come off of the wheel hub