Drum brake components and parts

Drum brakes are applied when a vehicle 's brake pedal is depressed. The system presses hard on the brake shoes, which is coated with a special friction material.

This braking system is essential for any vehicle. If our car has a drum brake, always at the rear, our safety is guaranteed when we get behind the wheel.

At Frenkit, a company that manufactures repair kits for vehicle spare parts according to OEM or customer specifications, we will introduce you to the elements and parts of the drum brake, which are essential for the correct functioning of the car. Read more!

Drum brake components

As explained in previous posts, the drum brake system consists of “a type of brake that, when the vehicle’s pedal is depressed, produces friction through the brake pads pressing against the inner surface of a rotating drum connected to the car’s hub”.

If we disassemble the parts of the drum brake and and we have to check that the drum brake is working properly, they may seem complicated and difficult to understand, as the system is made up of many parts. For this reason, we will take a detailed look at the main components of the drum brake one by one in case you have to make the drum brake assembly:

Brake drum

It is the visible outer part and the part that forms the rotating part of the brake, and therefore receives most of the heat produced when the brake pedal is depressed. The brake drum is made of a grey cast iron material with graphite, which is characterised by its strength and good absorption of the heat produced by friction.

Its diameter depends on the characteristics of each vehicle, which is why there is such a wide variety of diameters. The element is attached to the vehicle by passing holes through threaded rods and is anchored to the vehicle’s hub.

Brake plate

The brake plate consists of a pressed and punched sheet metal support. The hydraulically operated cylinder, the fastening elements and the primary and secondary brake pads are attached to it.

These last ones are connected to the brake plate by a system of elastic springs that allow the brake pads to move towards the drum. Once the brake pedal is released, the springs, located in the central part of the brake plate, help the brake pads to return to their initial position.

Pads

The brake pads or brake shoes are responsible for pressing on the inner face of the drum and thus generate the friction necessary to stop the vehicle. As mentioned above, there are two brake pads: a primary and secondary pad. The primary pad applies a greater force on the side against rotation, thus causing more friction. The secondary pad shoe, on the other hand, uses more force on the side in favour of the rotation, thus causing less friction.

Both brake pads consist of two welded, crescent-shaped steel plates and are usually covered with brake linings on the outside. These lining are attached to the metal brake pads either by gluing or riveting.

Pumps or hydraulic cylinders

These elements of the drum brake are responsible for the lateral movement of the brake shoes to break the drum. When the brake pedal is depressed, the pressure from the brake pump reaches the cylinder and the pistons inside the cylinder move to press the brake shoes against the drum.

We can distinguish between three types of cylinders, depending on their purpose and type of braking:

• Double piston pump. The pistons are housed inside the cylinder in opposition to each other, and the screws that support the brake shoes are located on them. At the same time, it has rubber cups that act as reinforcement to keep the inside of the cylinder closed and the pistons are kept apart by the action of the spring centred on the two cups.
• Single piston pump. Similar to the previous one, the single plunger cylinder has a single piston which is used in systems where both shoes are primary, in duplexes.
• Staggered cylinder tumbler. Also known as a differential cylinder, it has two pistons of different diameters, the smaller one pushing the primary pad and the larger one driving the secondary pad.

Return springs

Once the brake pedal has been applied, the return spring is the part that retracts the brake pads. There are two types of return springs: one spring for primary brake pads and one for secondary brake pads. Both must have sufficient force to cause the brake pads to actuate and bring the vehicle to a stop.

Adjustment mechanism

The adjustment mechanism is the one that maintains the minimum clearance between the brake pads and the brake drum, so that the two elements of the drum brake do not come into contact when you are riding and not pressing the brake pedal, and as the brake pads wear, the clearance between them has to increase to be effective for each brake application. If it did not, then as the brake shoes wore out, we would have to press harder on the brake pedal to apply the brakes.

If you found this post about the elements and parts of the drum brake useful, you may be interested to know that at Frenkit we have a Development Department that is constantly creating new kits for new models and parts for different vehicles.

Are you a professional or do you fix your own car? Do not hesitate and access our user area and find the reference you need.