Typically there is a ridge in the drum.Its about 1/4 inch.Thats where the drum dosent contact the shoes.They can be a bear to get off.You can grind the pin heads off in the backing plate and they usually come off.Ive had to pry some off.Use a few heavy screwdrivers and work them off.When I replace drums I usually cut the outer edge down a bit on the brake lathe.That way the ridge dosent catch like without the slight cut.Same thing when I turn drums.I cut that outer edge about .100 deeper than the drum is turned.Rocky