What’s the Difference Between Drum and Disc Brakes?

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What’s the Difference Between Drum and Disc Brakes?

Difference Between Drum and Disc BrakesIt’s always good to know what’s the difference between drum and disc brakes and how it affects stopping distance and safety, but it’s also good to know that our technicians at Dakota Ridge Automotive in Littleton can repair and maintain either brake system.

According to an Edmunds article, manufacturers began switching from drum to disc brakes in the early 1970s. Most of a vehicle’s stopping power is in the front wheels, so during this time, only the front brakes were upgraded to disc. Now, many car manufacturers have four-wheel disc brakes on their high-end and performance models as well as their economy cars.

There have been times like in 1999 when the Mazda Protege’s manufacturer changed from the four-wheel disc to drum brakes for the rear wheels to cut both production costs and the purchase price. Brake technology has advanced with components like carbon fiber, sintered metal, and lightweight steel, along with the adoption of ABS, and have contributed to reduced stopping distances and generally safer vehicles.

Let’s examine the difference between drum brakes and disc brakes.

How Do Friction and Heat Stop the Car?

It’s important to understand how drum and disc brakes use friction and heat to stop your car. By applying resistance, which is friction, to a turning wheel, your car’s brakes cause the wheel to slow down and stop, creating heat as a result.

How much the car weighs, the total braking surface area, and the braking force all determine the rate at which a wheel can be slowed. It also relies on how well your braking system converts wheel movement into heat from friction and then how quickly this heat is removed from the brake components. This is where you can see the biggest difference between drum brakes and disc brakes.

Let’s compare the two types of brakes.

What are Drum Brakes?

The Edmonds article explains, after the early times of using hand levers to brake, cars moved to a drum design at all four wheels for a braking system. The components are housed in a round drum that rotates along with the wheel. Inside is a set of shoes. As you push on the brake pedal, it forces the shoes against the drum and slows the wheel down.

Fluid is used to transfer the movement of the brake pedal into the brake shoes movement. The shoes are made of a heat-resistant friction material similar to that used on clutch plates.

The drum brake design worked most of the time but during high braking conditions, like going down a steep hill with a heavy load or repeated high-speed slow downs, the drum brakes would regularly fade and lose effectiveness. Most of the time, this fading was the consequence of too much heat build-up within the drum.

Braking involves turning kinetic energy, the wheel movement, into thermal energy which is heat. Drum brakes can only work as long as they can absorb the heat generated by slowing a vehicle’s wheels. However, once the brake components become saturated with heat, they lose the ability to halt a vehicle. This can create a very dangerous situation.

What are Disc Brakes?

Disc brakes also use friction and heat to slow your car, but the disc brake design is much better than the drum brake design. With disc brakes, instead of housing the major components within a metal drum, they use a slim rotor and small caliper to stop the wheel movement.

Inside the caliper are two brake pads, one on each side of the rotor, which clamps together when you push the brake pedal. Fluid is also used to transfer the movement of the brake pedal into the movement of the brake pads.

Disc brakes are different from drum brakes, which allow heat to build up inside the drum during heavy braking. Instead, the rotor used in disc brakes is fully exposed to outside air. This constantly cools the rotor, which decreases overheating and fading.

These differences are shown during car racing. Racers with disc brake systems are able to carry their speed deeper into a corner and apply greater braking force at the last possible second without overheating the car’s components. This improvement in technology demonstrated by racing performance soon was used by other cars outside of racing.

Which One is Better?

Today it’s common to see four-wheel disc brakes as standard equipment on medium-priced, non-performance models. But a lot of new vehicles still use the front disc and rear drum combination brake setup.

Some people criticize the choice of car manufacturers for not using four-wheel disc brakes in all cars, saying that it compromises car safety just to save a few dollars by only installing disc brakes on only the front wheels. But according to the Edmonds article, the combination of disc and drum brake design is good enough for most new cars. Both designs have been vastly improved over the last 20 years, so much so, that today’s rear drum brakes provide better stopping power than the 1970s disc brakes.

It’s generally accepted that most of a car’s stopping power comes from the front wheels which are the disc brakes and provide exceptional stopping response and the advanced drum brakes are sufficient for the rear wheel brakes.

The Edmonds article points out there are some high-performance cars often used for racing, like the Viper, 911, and Corvette that do need a four-wheel disc brake system, but for most cars, the dual brake system is good enough. If all cars came with the four-wheel disc brake system, it would significantly increase the car’s purchase price.

It’s good to know what’s the difference between drum and disc brakes and how it affects stopping distance and safety, but it’s also good to know that our technicians at Dakota Ridge Automotive in Littleton can repair and maintain either brake system. If you notice any of these symptoms or have other problems coming to a stop, Dakota Ridge Auto in Littleton is your trusted source for new brake pads and rotors, as well as repairs for any other issues your braking system might be having. We perform complete anti-lock brake diagnosis and repair, as well as provide on-site machining of rotors and drums to help get you back on the road quickly. If you have brake problems, we can help you.

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