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Disc Brakes and Drum Brakes Explained!

Regarding brake parts located at each wheel, can you distinguish between "pads" & "shoes"? Between "discs" and "drums"? We clarify the appearance and function of each.
Brake Pads
Disc and Drum Brake Rotors

After owning a car or truck for more than a few months, you undoubtedly become aware that your vehicle's brakes occasionally need replacing. Let's face it, we can be hard on our brakes. Highway speeds, stop-and-go traffic, and heavy cargo loads are some of the more significant factors which increase brake wear. Brakes are considered a normal wear-and-tear item, so sooner or later (sooner for the heavy-footed among us) brake parts always need replacing. Our related article Is It Time For New Brakes? discusses the telltale signs of worn brake components.

But what is your mechanic referring to when he tells you that you need "pads AND rotors"? Or tells you that, "you need front pads, rear shoes, and one caliper is sticking"? Do you know what kind of brake system is on your ride? More importantly, if you're purchasing the parts yourself, do you know the difference between "pads" and "shoes"? Between "rotors", "discs" and "drums"? Read on and find out!

Keep in mind that we are covering only brake components located at the wheels in this article, so we won't confuse you with brake master cylinders, parking brakes, or other items positioned elsewhere on the vehicle.

Two Types Of Traditional Braking Systems

There are two different types of traditional braking systems used on modern cars and light trucks: "drum brake systems" and "disc brake systems". (Your car may have both systems, one in the front, and the other in the rear.) While both set-ups use a friction material pressed against a rotating object to provide stopping power, they share almost no parts or part names. We've left off hybrid-electric braking systems as they use friction resistance from electrical generators to assist in the braking effort.

Disc Brake Type
Drum Brake Type

Disc Brake Systems

First, disc brake systems. These systems use a disc, also known as a rotor (same part, alternate name), which rotates along with your wheel/tire combo. All light duty vehicles sold in the U.S. in the past few decades have used disc brakes in the front; many, but not all, modern cars and trucks also have disc brakes in the rear.

Wheel Brakes
A typical disc brake rotor.
Working Scheme of a Disk Brake

To stop the rotation, brake pads, located within a caliper, press against the two sides of the disc or rotor. The caliper is the bridge between the hydraulic system and the wheel brakes, and it's the caliper which provides the force when the pads are clamped against the rotor. The resulting friction slows down the disc, and the vehicle also slows down.

Disc brakes are very efficient. Their design allows for lots of air to circulate around the rotor, which carries away the tremendous heat generated from the friction. The pad location within the caliper makes pad replacement a rather straightforward service job on most vehicles.

If you’re interested in performance brake pads designed to provide higher levels of stopping power compared to OEM brakes, take a quick look at our article Which Performance Brake Pads Work Best On My Car? Interested in brake rotors that weigh less and offer more grip? Read our article How To Select & Install Performance Brake Rotors.

Drum Brake Systems

Drum brake systems, which pre-date disc brakes, use different wheel brake components. There is no name sharing between the two systems! The rotating member here is the brake drum; the drum mounts over a pair of brake shoes, and the shoes, which contain the friction surface and are secured to a backing plate, sit inside the drum.

A Drum Brake Shoes Set
A set of drum brake shoes.
EBC Brakes
A set of disc brake pads by EBC Brakes.
Wilwood Disc Brake Caliper
A disc brake caliper by Wilwood.
A Typical Automotive Drum Brake System
A brake drum used in a typical automotive drum brake system.
Chrome Brakes
Disc brake rotors by Chrome Brakes.
Inside View of a Brake Drum
A closer look at the basic drum brake components.

When the brakes are applied, the shoes move outward and press against the inside surface of the drum. It's the wheel cylinder which converts hydraulic pressure to mechanical movement, and which causes the shoes to move against the drum. The result is the same: application of friction against the rotating drum slows it down, and in turn slows the vehicle down.

Dorman Drum Brake System Wheel Cylinder
The Dorman Drum Brake Wheel Cylinder.

While a very simple set-up, drum brakes do not shed heat with the same efficiency as disc brakes. They also tend to require more labor at service time. Because of their low cost of manufacturing, many automakers continue to use drum brakes at the rear of economy-priced vehicles.

Disc Brakes / Drum Brakes Variety Gallery

To summarize:

  • DISC brake systems have discs or rotors, pads, and calipers.
  • DRUM brake systems have drums, shoes, and wheel cylinders.

Knowing these simple terms will help you comprehend exactly what's needed the next time your ride is in for brake work. We hope this also gives you the confidence to shop for the needed brake parts yourself! But if you have any questions, we welcome your inquiries seven days a week.

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