What is the drum brake and what is it used for

The drum brake is a fundamental part of the braking system of our vehicle and as such is responsible for ensuring our driving safety.

Nowadays, vehicles are fitted with what are known as “disc brakes”. However, many cars still have drum brakes on the rear axle, while disc brakes are located at the front.

Invented in 1902 by Louis Renauly, this system of drum brakes reduces the speed of the car more quickly and effectively. Buying a vehicle with drum brakes on the rear axle is not a bad product choice, as these parts are perfectly efficient and capable of slowing down your car.

In this post by Frenkit, a company specialising in the manufacture and distribution of brake components for passenger cars and light vehicles, we explain what are drum brakes, what types of brakes are available on the market and how these drum brakes work.

What are drum brakes

The drum brake is a type of brake which, when the vehicle pedal is depressed, produces friction through the brake pads which, in turn, press against the inner surface of a rotating drum connected to the axle or wheel of the car.

When disassembling the drum brakes of our vehicle, the first thing we are going to find is the drum, a rotating part made of cast iron that takes away all the heat generated when we press the pedal of the car. The next external part is the brake plate which, together with the drum, makes up the drum brake assembly. Finally, the brake pads or brake shoes are the third element that make up the drum brake system, which are made up of two welded steel plates and have the function of braking by friction with the drum.

If you want to learn more about each of these parts, in another of our posts we will talk in more detail about the components of the drum brake.

Before explaining the types of drums, it is necessary to explain how the brake pads work inside the drum. We speak of a primary brake pad when force is applied on the side against the rotation, this causes more friction. And we talk about a secondary brake pad when more force is applied on the side in favour of the rotation, this generates less friction.

There are four types of drum brakes on the market, depending on how the braking system works on the drum and the force it exerts:

• Simplex brake drum. This type of system is the simplest of the existing systems, as it only has a double piston cylinder that presses both brake shoes against the drum. The cylinder of the simplex drum brake is located at the top of the brake pads, while at the bottom are the brake pad support. The disadvantage of this system is that more force is applied to the primary brake pad (against the direction of rotation) than to the secondary brake pad (for the direction of rotation). When the direction of rotation changes, the primary brake pad becomes secondary. This results in braking that is not very effective. However, not as much heat is generated.
• Duplex brake drum. This braking system has two single piston cylinders, one at the top and one at the bottom. In contrast to the simplex brake drum, in the duplex, each cylinder only moves one brake pad. This causes both brake pads to become primary, as they both exert force in the opposite direction to the direction of rotation of the drum and braking is more effective. However, when the direction of rotation changes, both brake pads become secondary.
• Twinplex brake drum. This type of brake is very similar to the previous one. The difference lies in the fact that each cylinder has a double piston and moves both brake pads. In addition, the type of support, instead of being a fixed point, is floating. This means that the brake pads are secondary (they apply force in favour of the rotation) but they do so over the entire surface simultaneously. Moreover, even if the direction of rotation changes, the pads remain secondary.
• Duo-servo brake drum. In this system the brake pads are both primary because they are actuated and moved by a double piston cylinder located at the top and at the bottom is an actuating rod. As in the simplex system, the cylinder moves both pads, but the primary pad pushes the secondary pad through the rod causing the secondary pad to become primary. This system manages to generate a high frictional force and is therefore very effective in braking. Moreover, if the direction of rotation changes, the brake pads continue to exert the same force.

How do drum brakes work

As mentioned above, drum brakes are a very important part of our car 's braking system, as they ensure our safety on the road.

If used properly, drum brakes should work instantaneously when the brake pedal of our vehicle is applied. When the brake is applied, the drum pads press internally on the drum to stop the car’s movement through friction.

The hydraulic system of the drum brake transports the brake fluid through the brake pedal to the brake cylinders. The next step is to press the brake pads against the drum by means of pistons. In turn, if the brake pedal is released, springs separate the brake pads from the drum.

From Frenkit we also offer you the possibility to learn how to check the drum brake of your car or how to remove the drum brakes of your vehicle.

If you need to fix your car's drum brake, at Frenkit we have a wide range of products for vehicles.

You can now access all our brake repair kits through our website and, if you are interested, you can purchase spare parts for your vehicle through our online shop.