The Difference Between Drum and Disc Brakes

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When you step on the brakes, your life is in your foot’s hands. -George Carlin 
The brakes on an automobile are one of those things that we always expect to work, and rarely give a second thought otherwise. The only time we pay any attention to our brakes is when they are acting up, or making odd noises. But every time we drive, we are quit literally trusting our lives with the belief that our brakes will work, and yet very few people understand brakes at all.

It’s an odd thought to consider that countless people entrust their brakes with keeping them safe and alive, yet have no idea how they work. It is the first line of defense to fend off an accident from occurring, or at least reducing the severity of it. Most every other safety feature was created to step in once the point of brake use had passed. Seat belts, airbags, shatter proof windshields, the durability of the frame, etc. All of these are mostly only necessary once an accident has occurred. Beyond steering, brakes are the only other function that can help to avoid an accident or reduce the severity of it. Everything else only helps after the accident has occurred.

Disc Brakes

So to help demystify automobile brakes, lets talk about the most two common types that can be found on the road today. Disc brakes and Drum brakes. They both perform the same function, but in two different ways. Well discuss what comprises each, and how they work. So perhaps at least for those who don’t know, they’ll understand what exactly it is that they trust their lives with every time they drive their automobile.

Drum Brakes
Drum brakes use shoes to press on the inner surface of a rotating drum-shaped part called a brake drum. When the shoes press upon the outside of the drum, this is called a clasp brake. When the drum is pinched between two shoes, one outside and one inside, this is called a pinch drum brake but these are rarely seen.
Drum

Drum Brake Components
Back Plate:  This piece is what the rest of the components attach to and provides the base for Drum Brakes. Since all the other parts attach to this one, it is generally the strongest piece and extremely wear-resistant.

Brake Shoe: The brake shoe, or brake pad, is what is applied to the brake drum to slow it down. The shoes are generally made from sheets of steel welded together, with the friction material either being riveted into place, or applied adhesive.

Brake Drum: This piece is generally made from cast-iron that is heat and wear-resistant. It is placed near the brake shoe but does not actually touch it as it spins with the axle and wheel. When the brakes are applied, the brake shoe pushes against the surface of the drum slowing the spin of the axle and wheel.

Wheel Cylinder: The wheel cylinder is what applies the brake shoe to the brake drum on each wheel. The wheel cylinder is operated with hydraulic pressure that pushes the shoes outward against the drum.

Disc Brakes
Disc brakes use brake pads and brake discs to slow the rotation of a wheel. The brake pads squeeze the disc that is located within the wheel. The idea is similar to that of brake drums, its just the set up is different. Rather than a drum, you have a disc, which is what slows the wheel. Disc brakes have what are called brake calipers, which is essentially the housing compartment for the braking system.

Disc Brake Components
Calipers: As mentioned before, calipers are for disc brakes what the back plate is to brake drums. It is essentially the housing compartment where everything is stored within the wheel well. Calipers are mostly made from aluminum or chrome-plated steel. There are two types of calipers, floating and fixed. A fixed caliper, as the name implies, does not move in relation to the disc. A floating caliper moves with the disc, but are more prone to malfunctions.

Brake Shoe: The brake pads or shoes for disc brakes are for the most part the same as those in brake drums. The only difference is really in their shape so that they fit within a brake caliper.

Brake Disc: The brake disc is the disc that the brake pads are applied to in order to slow down the wheel. The designs vary widely for the discs dependent on what their intended use will be for such as normal driving, racing, industrial and construction, etc. Due to the heat generated from disc brakes, warping and other problems are common, but in recent years, heat-dissipating disc brakes have been created which reduced the number of brake failures.
  •  License: Royalty Free or iStock source:
  •  License: Royalty Free or iStock source:
Damien S
About the Author:

The author of this article is Damien S. Wilhelmi. If you enjoyed this piece, you can follow me on Twitter @MetalPedal. If you are looking for automotive assistance such as a transmission repair, and live in Colorado, please visit AAMCOColorado.com.

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