Please post the year of your machine. Do you have the cover off? There is a cover bolted on over the brake drum. If so, does the drum wiggle at all, or is it completely stuck? Make sure the brakes are completely released, you may try loosening the adjustment screws all the way. Also, there may be a dampener ring in the drum that is hanging up on the shoes. You may find a service manual to be of great help as well.
Yours truly, sincerelly, love always, Josh aka The DirtDemon.