When repairing drum brakes, first remove the drum, and then inspect for wear. If repair is necessary, either resurface the drums or replace them altogether.
To remove the brake drums, remove the wheels, back off the brake shoes using a brake adjuster tool, and pull the drum off the axle. Next, use a special drum gauge to measure the drum wear. The drum gauge tool is available at most auto parts stores, and is critical to take an accurate measurement. If the inside diameter of the drum exceeds the specifications, it is worn out and in need of replacing. The maximum inside diameter specification is stamped or cast on the outside of most drums.
After the initial inspection for wear, examine the drum for damage such as pitting or cracks. Damage of any kind can weaken the drum or cause uneven braking. Check for an egg-shaped drum that results from applying the parking brake when the drum is hot. After assessing the condition of the drum, decide whether full replacement or just resurfacing is required to properly repair the brakes. When installing the repaired drums, clean the inside of the drums, and adjust the brake shoes appropriately so they clear the drum.