What are brake drums and shoes and where are they located?

Brake drums and shoes are a major component of some vehicle's braking systems—which consists of brake drums, shoes, backing plates, and wheel cylinders. Brake drums are usually made from cast iron and connect to the wheels and spin at the same rate as them. The remaining braking parts can be found inside of the drum.

When you pump the brakes, hydraulic pressure is transmitted to the wheel cylinder, causing the pistons to extend. The brake shoes then press out to squeeze the drum, which in turn stops your vehicle. Brake shoes are curved and made of steel with a brake block lining the exterior to create the friction needed to stop. At one point in time, drum brakes were the standard for all vehicles. Rear drum brakes are still found on many vehicles today. Some cars or trucks may only use brake drums, but most have them in the rear with two front brake rotors in the front.

What are brake pads and rotors and where are they located?

Brake pads and rotors are part of the disc braking system. When you press the brake pedal, hydraulic pressure moves the brake caliper pistons and presses the brake pads into the rotors, which slows down your vehicle. On most models, the rotors are placed inside the wheel and tire and are connected to the wheel hubs.

Most cars and trucks produced after 1972 have come standard with front disc brakes. Many vehicles today have rear disc brakes too, but some models still use brake drums and brake shoes in the rear, making the rear brakes different on some models.

Do I have brake rotors or drums?

To tell if you have brake rotors or drums in the rear, you can look at the brake assembly through the wheel. Rotors will have a clunky metal piece called the caliper attached to it. Brake drums will look cylindrical with no caliper, since the brake shoes are located inside.

What are brake shoes on a car?

Brake shoes have a lot in common with brake pads. Both have thermal material attached to the shoe or pad that’s used to create friction. In automobiles, brake shoes slow the vehicle down by sitting inside the brake drum and expanding against it when the brake pedal is pushed.

What do disc brakes and drum brakes have in common?

Disc brakes and drum brakes have a bit in common. They both rub against the brake pad or brake shoe material to create the friction and heat needed to slow down the wheel. Disc brakes can dissipate heat at a faster rate, but drum brakes can make for a stronger emergency brake.

Are front brake pads different from rear brake pads?

Front brake pads are different from rear brake pads. When you stop your vehicle, the weight will shift to the front of the car, making front brakes responsible for much of the stopping power. Since front brakes do more work than the rear, front brake rotors and pads need to be thicker.

Why are my brakes squeaking?

If your brakes squeak when you stop, it could be that your brake pads have worn down. Friction helps your vehicle come to a stop, and over time it breaks down the brake pad material. Heat, rust, moisture, or other outside elements can also cause your brakes to squeak, which doesn’t always signify a problem.

Why does my brake pedal vibrate?

Your brake pedal will usually vibrate, pulsate, or the front end will wobble from warped brake rotors. Brake rotors usually warp from excessive heat and from the use of worn out brake pads. Any sign of cracking, corrosion, or uneven disc surface is a good reason to replace your brake rotors. 

How do I know if my brake pads and rotors need to be replaced?

You should replace your brake pads and/or rotors when you hear a squeaking or squealing sound coming from the wheels. Most brake pads come with a wear tab. Some cars use electronic wear sensors that will illuminate a “service brake” light. A vibrating brake pedal or wobbling front end could also indicate rotor warpage or corrosion.

When should I replace my brake pads?

You’ll know your brake pads need to be replaced if they have a wear tab. As the surface of the pads wears away, the wear tab will grind into the rotors, creating the “metal on metal” noise. This is usually heard when the brakes are applied, but it can be heard during normal driving with worn out pads.

At that point the squeaker will rub and wear grooves into the rotor, leaving you to find a replacement. In this case you could have the rotors machined or turned to a smooth surface, but this can only be done so many times before the rotor wears too thin to be reused. To reduce curb weight, modern rotors are designed with less thickness than ones from the past, so replacing rotors with the brake pads may be your best bet.

How do I know if my brake drums and shoes need to be replaced? 
 

Brake shoes will usually last longer than brake pads, but they are not as efficient at dissipating heat. There are a couple ways to tell if brake drums are not working properly. You might hear screeching each time you press the brakes, or, even worse, grinding—both of which may indicate a needed replacement of brake shoes. The emergency brake might also not hold as strongly as it used to, and this might be an indication that shoes need replacing.

One of the best ways to inspect the brake drum components is to look at them. If the shoes are exceptionally thin or almost worn down to the metal, they should definitely be replaced. Brake drums can be resurfaced or machined as long as there is enough material to do so. All brake drums have a discard diameter determined by the manufacturer, which is the maximum inside diameter the drum can be machined to before they are deemed unsafe. You should measure the inside diameter with a micrometer at multiple points to ensure the drum is not uneven or out of round, and is within specification.