4 wheeler brake drum won't come off
 

I have a 1988 Yamaha Moto 4 that I am trying to replace the brakes on. However, I can't seem to get the brake drum to slide off. It should just come off but after hitting it with a hammer and a lot of cussing it just won't budge.

Any ideas?

Thanks.
p.s. Yes I did get the axle nuts off. Nothing else other than the fact that it's been on there 20 years should be keeping it on.