Truck Brake Faceoff: Drum vs. Air Disc
By: Megan B 

When it comes to equipment that you want working properly on your vehicle, we’ll bet your brakes are at the top of the list. Because when you’re hauling a trailer that can weigh tens of thousands of pounds, you want to make sure you can stop reliably.

But when discussing brakes, there’s a lot to cover – you’ve got air vs hydraulic brakes, drum vs disc brakes, and so on. While the former is a topic that deserves its own article, today, we’re going to break down the key differences between drum and disc brakes.

Brakes 101

Before we launch into the difference between the disc and drum brakes, we’re going to take a quick detour and break down how brakes work.

Physics tells us that the greater the weight of a moving object, the greater the force required to stop it. So how does a driver’s foot pressing a brake pedal translate to the slowing of a tractor-trailer weighing tens of thousands of pounds?

The parts that make up your brakes vary depending on what sort of braking system you have, but at the end of the day, all brakes generally do the same thing. When you press down your brake pedal, the force is put through a brake booster, which is essentially the power brakes (or power-assisted brakes) that amplifies the force put out by your foot to be enough to slow your rig. The booster can be vacuum-assisted or hydraulic-assisted, depending on the vehicle, but the former is more common for tractor-trailers.

Drum Brakes

Drum brakes have hollow drums attached to the wheel, turning with it. The drum has an open back that is covered by a backplate sporting two curved shoes with friction linings.

When the brakes are applied, these shoes push outward and press the lining to slow the drum to stop it. Because of the rotation of the drum, the leading shoe gets pulled against it when contact is made and thus improves the braking.

Drums are often touted to be less efficient than disc brakes, as they have more parts and thus, can be harder to service. However, they are less expensive, and have a design that enables a parking brake to be incorporated easily.

Disc Brakes

Disc brakes are comprised of a few key parts: the calipers, pads, and rotors (or discs). The calipers have pads on each side that squeeze against the rotor when the brakes are applied, effectively creating friction, and slowing the vehicle.

The discs often have holes cut out to help with dissipating heat caused by braking.

Simply put, the drum brakes push out, and the disc brakes squeeze to cause the wheels to slow.

We hope you’ve enjoyed this quick explanation between disc and drum brakes. In case you’re in need of some new drum brakes, we have some on special for this month starting midway through August. Keep your eye trained on Express and our in-store flyers so you can get yours.

As always, stay tuned for more articles on all things truck-related, with new content added monthly.