Brake Drum Inspection
Brake drums are usually constructed of cast iron and sometimes aluminum lined with steel or iron. Both of these materials will lose their integrity from heat. The whole purpose of the automotive braking system is to convert energy in motion (kinetic) into heat energy through friction. Brake shoes reach temperatures of 450F and as the temperature goes up the braking system loses efficiency. A brake drum uses fins and mass to transfer this heat energy to the atmosphere.
As the brake drum wears minor pitting and warpage will occur. These imperfections can often be removed by resurfacing the inside surface of the drum. When resurfacing a brake drum always locate the minimum allowance and never cut a drum or rotor below these specifications. These specifications apply to the drum after it has been cut, not before.
If a drum has cracks showing it cannot be machined and must be discarded. Small cracks lead to big ones and the crack may be deeper in the cast than it appears. When resurfacing a drum always use a brake drum silencer band to reduce chatter marks caused by vibrations inherent to the process.
Measuring the inside of a brake drum requires a drum gauge and measurements should be taken in several different spots because they wear in different places. A barrel shaped drum will be rounded in the middle. They often wear at the outside edge leaving a bell shaped drum. Drums are cost efficient due to the inexpensive and simple parking brake design easily incorporated into the drum brake system.
