What are Brake Drums?
Brake Drums are cylindrical brake system components that are shallow and drum-like in shape. They transfer friction into torque used to slow the vehicle. Drum brake components include the backing plate, brake drum, wheel cylinder, brake shoe, and various springs and pins.
How do Brake Drums Work?
The brake drum fastens via a flange arranged perpendicular to the braking surface to the axle flange. The inner surface of the drum rotates with the road wheel and at the exact rotational speed of the wheel. When hydraulic or mechanical actuation of the brake shoes (friction) occurs, the shoes are pressed into contact with the braking surface that comprises the inner surface of the drum. Friction material (shoes) contact with the drum creating interference that impedes the motion of the road wheel, thereby creating the braking action. The harder the brake pressure, the more braking power (and heat) from the brake drum. Braking force is transferred from the brake shoes through the drum and into the road wheel.
How are Brake Drums Made?
Brake drums are almost invariably cast from a ferrous metal, either steel or iron. A secondary machining processes cuts a uniform mounting flange and cuts the braking surface. The braking surface is cut to be exactly perpendicular with the mounting flange. Brake drums frequently have cast-in features such as fins along their outer surface to assist in cooling. The finished brake drum is usually coated with an anti-rust chemical to prevent it from rusting or corroding during shipping and storage.
Why do Brake Drums Fail?
- Wear and tear
- Excessive heat
- Severe rust
What are Symptoms of Brake Drum Failure?
- Cracks
- Unusual sounds, such as scraping
What are the Consequences of Brake Drum Failure?
- Drums that are cut beyond the safety maximum diameter are thin, do not have adequate structural strength, and are unable to dissipate heat properly. Such a brake drum can fail without warning and are not safe.
- Out-of-round brake drums that cannot be adequately machined reduce braking effectiveness and are not safe to drive on.