If the driver feels vibration in the brake pedal while braking, it may indicate that the brake drums need to be re-machined or replaced.
To re-machine, or resurface, brake drums, the technician removes the brake drums from the vehicle and machines them on a lathe. Brake drums need to be re-machined if the vehicle has been driven with worn-out brake linings or if the drums have become damaged by heat (which may result in a vibration when the brakes are applied). When brake drums are re-machined, damaged material is removed.
There is a maximum amount of damaged material that can be removed before the brake drums are deemed not serviceable and must be replaced.