What Is Drum Brake? How Does It Work?

Brakes in a vehicle play a key role in safety maintenance. There are four types of brakes in a vehicle. Two of them are service brakes which include drum brakes and disc brakes. Drum brakes last longer and are capable of offering more braking force compared to a disc brake of equal diameter. Moreover, these brakes are cheaper to manufacture.

Wondering how the drum brake system work? Read on to find out.

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What Is a Drum Brake?

Drum brakes are a type of brake mainly consisting of a brake lining that generates a stopping force when pressed against the drum.

Drum brakes are mainly located on the rear axle of a vehicle. There are usually no brake pads in drum brakes to produce friction. A drum brake consists of wheel cylinders attached to pistons. These pistons exert pressure on the inner wall of a spinning drum.

How Does a Drum Brake Work?

A drum brake system works as follows:

A driver applies brake pedals.
A brake booster or servo system amplifies the power generated.
There is a master cylinder that converts this power into hydraulic pressure, also known as oil pressure.
There is a brake oil or brake fluid that conducts this pressure to the pistons on individual wheels.
These pistons exert pressure on the brake linings.
Brake linings produce friction against the inner surface of a brake drum.
Since a brake drum rotates with vehicle’s wheels, it gradually slows them down and ultimately stops the vehicle.

The working of drum brake is quite simple and easy to understand. Additionally, its structure is also not much complex.

What Are the Construction and Mechanism of a Drum Brake?

Drum brakes consist of the following parts:

1. Backing Plate

The backing plate, also known as the torque plate, serves as a base for the other parts such as brake drums, wheel cylinders, and brake shoes. It plays a key role in absorbing the torque from the braking action. When a driver presses the brakes, maximum pressure is exerted on the backing plate.

Backing plates must be wear-resistant to lower the friction and operate as smoothly as possible. Additionally, it must be strong enough to support the other components. It protects the drum brake from dust and road debris as well as increases the rigidity of drum brakes. Recently, automatic brake adjusters and levers were added for emergency brakes to enhance their performance.

2. Brake Shoes

Brake shoes comprise two steel pieces welded together. It has a crescent-shaped piece containing holes and slots of different shapes. This supports the return springs, parking brake linkage, hold-down hardware and self-adjusting components. The friction-causing material is attached using adhesive or riveted to the inner lining.

The wheel cylinder passes on the force to the brake shoes through inner lining. They comprise two types of shoes, primary and secondary. There are three “V” – shaped notches called ribs on the edge of the lining table.

3. Wheel Cylinder

There is a separate wheel cylinder operating on each wheel. The leading shoe that is present closer to the front of the vehicle is known as the secondary shoe. On the contrary, the trailing shoe is the primary shoe.

At the end of each wheel, there are two different pistons operating the shoes. There is a master cylinder that generates hydraulic pressure on the piston cup, pushing them downwards. This forces them against the drum. The brake shoe restores them to their original positions as soon as a driver releases the brakes.

4. Brake Drum

It generally rotates along with the wheel and axle. Wear-resistant and heat-conductive cast iron is used for the construction of a brake drum. As soon as a driver presses the brakes, the lining exerts a radial force on the drum's inner surface. This ensures that the wheel axle slows down and ultimately stops. The friction generated during this process is strong enough to stop the vehicle.

What Are the Advantage and Disadvantages of a Drum Brake?

The advantages of drum brakes are as follows:

Comparatively longer life.
Provides an increased automated braking force.
Cheaper to produce.
It can be easily remanufactured.
Requires less money and frequency of maintenance.
Low heat generation due to less friction.
Easy reconditioning of wheel cylinders.
Comparatively lower maintenance frequency.
Provides a scope of remanufacturing brake shoes.
Installation of these brakes is not much complex.
Provides protection to the brakes against ice, water, and mud.
Requires less input force.

The disadvantages of drum brakes are as follows:

Heat dissipation mechanism is not very efficient.
Require extensive break-in period.
Captures water if there is excess rain.
Fading of brakes is faster.
Heats up faster.
It can be complex at times.
A sudden increase in diameter during hard braking.
Vaporise brake fluid at times.

Now that you know about the drum brake system, you can find out other specifications if you wish to. However, remember to check your vehicle's brakes before going out to stay safe from accidents.

Frequently Asked Questions

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Why do drum brakes have a longer life?

Drum brakes have an increased contact area which decreases friction. Hence, they do not wear out easily and can last for a longer time.

What are the different types of drum brakes?

There are three types of drum brakes, duo–servo type, leading or trailing shoe type, and twin leading shoe type. Twin leading shoe comprises two leading shoes and a two–wheeled cylinder. Leading shoe is the primary shoe that moves in the direction of rotation. Duo servo consists of both a primary and a secondary brake shoe. These are linked together with an adjuster.

How are primary brake shoes different from secondary brake shoes?

A key difference between primary and secondary brake shoes is their lining position. The primary brake shoe is generally located in front. However, these two shoes might look extremely similar at times. You must closely observe to differentiate between them.

How to know that drum brakes need servicing?

You can easily perform a visual inspection through a rivet. Additionally, squeaking or squealing gives an indication that you need to replace your vehicle’s brakes to ensure maximum safety on road.