In addition to removing rust, you also want to sand down the lip on the inside of the drum. Use more brake cleaner to clear that all off. Once your drum is prepped, slide it back over the shoes ...

Working of drum & disc brakes Quite literally a drum brake is a small round drum that has a set of shoes inside of it. ... A disc brake has a disc shaped metal rotor spinning within a wheel.

Drum brakes work by forcing 2 arched “shoes ... forces brake fluid to fill the caliper. A metal piston inside the caliper is then forced against the back of each brake pad.