Are you talking about a ridge on the inside of the drum (where the shoes ride) near the outside. If so, you may need to find some new drums. This ridge is there because the shoes have worn the metal away just inside this ridge and you may have an unsafe situation. Just think about how they turn drums. They start removing metal from the very edge of the drum first and the cutter moves toward the middle. This ridge, that I think you are referring to, is what makes these drums so hard to remove especially when the wheel cylinders are rusted tight.
