All drums and rotors should either be resurfaced or replaced prior to installing new pads or shoes to ensure a smooth and parallel mating surface.
- All drum and rotors have a minimum machining thickness (rotors) or maximum diameter (drums) after which you must replace instead of resurface
- If the drum or rotor has a groove cut in it that is below the minimum thickness or maximum diameter, it needs to be replaced
- Any drum/rotor that has lateral runout beyond specification needs to be replaced
The fluid from the master cylinder is forced into a caliper where it presses against a piston. The piston, in-turn, squeezes two brake pads against the disc (rotor), which is attached to the wheel, forcing it to slow down or stop.
With drum brakes, fluid is forced into the wheel cylinder, which pushes the brake shoes out so that the friction linings are pressed against the drum, which is attached to the wheel, causing the wheel to stop.