Brake Drums
What are drum brakes?A drum brake uses friction caused by a set of pads that press outward against a rotating cylinder called a brake drum.
How do drum brakes work?Wheels have a metallic band (or drum) attached near the wheel’s outer edge. A brake shoe is a curved piece of metal that matches the curvature of the drum. It’s located inside this drum. In most cases, two brake shoes are positioned on each opposite wheel. There is a primary and secondary shoe.
Brake shoes have a lining with material designed to offer maximum grip or friction against the brake drum. The three main options are organic, semi-metallic, and ceramic. When the brake pedal is pressed, brake fluid is pushed through the brake lines to the calipers located on each side of the wheel. They contain pistons that are pushed out by the hydraulic fluid. The pistons push the shoes against the inside of the drum. This creates friction to slow down the vehicle and stop it.
Why do some vehicles only have rear drum brakes?Drum brakes contain fewer parts so they are less expensive and easier to maintain than disc brakes. But they are less effective in stopping the vehicle. Most vehicles rely on the front brakes for most of the stopping ability.
Do cars still use drum brakes?While many vehicles today use four-wheel disc brakes, many trucks and some compact cars still rely on drum brakes on the rear wheels. In addition, some hybrid and electric cars use regenerative braking systems, which reclaim energy to charge batteries. These regenerative braking systems sometimes use rear drum brakes for stopping.
How do you adjust drum brakes?Most modern drum brakes use an automatic adjusting screw to slowly move the brake shoes closer to the brake drum to offset the increased distance caused by wear. The distance can be manually adjusted by removing the tire to access the brake shoes. After removing the tire, you can pull off the brake drum and access the adjuster.
Can drum brakes fade?When a drum brake is used continuously, such as on a long, steep hill, heat and friction wear out the shoes. As a result, a driver must apply more effort by stepping harder and longer on the brake pedal. Going downhill in lower gears (and allowing the brakes to cool off) minimizes brake fade. Drum brakes are more prone to fade than disc brakes because they are enclosed and don’t allow heat to dissipate as easily.
Why do brake drums get hot?Friction is created when the brake shoe is forced against a moving brake drum, and friction generates heat. The drums can glow red and crack from the heat in extreme situations. Excessive heat from continuous and rapid braking events at high speeds can result in excessive wear to the braking system.
Can brake drums be repaired?Yes, but the cost to repair may be similar to the cost to replace. Over time, heat from friction will cause the brake drum to become uneven or warped. The brake drum can be resurfaced, drilled, or patched.
Are brake drums and rotors the same thing?No. Brake rotors are a component of a disc brake system. Drum brakes contain a rotating drum with two brake shoes used to create friction. Rotors are flat discs squeezed by brake pads for friction.
What types of brake shoe linings are available today?These are the three primary brake lining materials sold today:
- Organic (non-asbestos), the most common and usually the least expensive option
- Semi-metallic use fillers to create the pad instead of all metal
- Ceramics are the most effective and the most expensive
Typically, when a brake shoe needs replacement, the shoe on the opposite side of the same wheel should also be replaced. Likewise, the brake shoes on the opposite side of the axle need replacement. Most vendors sell a set of four brake shoes.
Are brake shoes expensive?Brake shoes are usually an inexpensive repair item, depending on the friction material used.
Are disc brakes or drum brakes better for a trailer?Brake systems for trailers require different considerations. While drum brakes are less expensive, they are less effective for stopping heavy trailers. Disc brakes are more resistant to fade, meaning they will be effective even when hot. Also, consider the vehicle towing the trailer when deciding on the best braking system and how it should be integrated with the vehicle’s brakes.
Electric drum brakes are the standard trailer option. An electric-over-hydraulic drum brake uses a small pump to increase the trailer braking pressure. The premium approach is electric-over-hydraulic disc brakes, designed for heavy loads and shorter stopping distances.