Some modern cars still use drum brakes and most vehicles use drum brakes on the rear wheels. The brake drum is attached to the wheel and rotates along with it. When the brakes are applied, the brake shoes come into contact with the brake drum, slowing the vehicle. Brake shoe material wears over time. If the brakes shoe material wears completely off, then the metal backing will be exposed and can come into contact with the brake drum and wear grooves into the drum causing it to become damaged. Then a brake drum replacement/resurface will be necessary.
When performing a brake drum replacement, the technician must remove the wheel. After the brake drum is removed, brake components are inspected for wear or damage. After the new brake drum is installed, the wheel is put back on and the brakes adjusted.
If the brake drum is not too damaged, then it can be resurfaced. To resurface brake drums, the technician must remove the brake drums from the vehicle and machines them on a lathe. When brake drums are re-machined, the damaged material is removed. There is only so much damaged material that can be removed. Once the maximum amount has been removed, then the brake drum will need to be replaced.
While most manufacturer factory warranties and extended auto warranties do not cover brake drum replacement/resurface, there are maintenance plans that will cover the cost of inspecting the brake shoes. By having the brake shoes inspected, the technician can see a worn brake shoe and replace it before any damage is done to the brake drum.