Many vehicles today use disc brakes up front and drum brakes in the rear. Drum brakes use brake drums that rotate with the wheels they are mounted on. Stepping on the brake pedal pushes brake shoes out toward the inside of the drums, generating the stopping force that slows down and eventually stops the car. Brake drums and their related components tend to wear out over time, but how long do they actually last?
Drum Brake Service Life: How Long Do They Last?
Automotive components, including the drum brake system, should be durable enough to withstand the demands of driving. Nonetheless, the parts also wear out over time. The service life of the components is the period of time for which they are meant to be operable before they begin to present issues that might require the repair or replacement of parts.
The housing of drum brakes is designed to be operable typically for around 150,000 to 200,000 miles, while the shoes are meant to last for 40,000 miles. These values, however, are rated for regular driving conditions, and various factors could affect the longevity of the brake drums.
The friction from braking wears out the drum brake pads or friction lining as well as the drum itself. Other components of the drum brake could also become worn or damaged over time, such as the wheel cylinders developing leaks.
It could be dangerous when the drum brakes become worn to the point where they can no longer produce the needed force to stop the vehicle. When this occurs, it is best to have the degraded parts or the entire assembly replaced.
When the brake drum has become too thin, the shoes and lining would not be able to make contact with the drum walls and produce the required friction. As the distance between the brake shoes and drums increases, the pedal may also need to travel further and be harder to use. This space may also cause the pistons in the wheel cylinder to overextend and result in leaks and breakage.
The brake drums also need to absorb and dissipate heat. When they have thinned, they would be unable to provide the needed cooling function and the brake system could overheat. Additionally, worn-out brake drums could disintegrate.
When replacing the worn or damaged brake parts, the hardware should ideally be replaced as well. This ensures that the newly installed braking system will work as it should.
What are Drum Brakes?
One of the braking devices that was invented and developed alongside the automobile was the drum brake. It is named for its structure, which is a hollow cylinder that houses most of the unit’s parts. Although all modern vehicles have front disc brakes, some still use drum brakes in the rear.
Basic Parts of a Drum Brake:
Usually a thick steel disk, the backing plate serves as a mount for the actuating components of the drum brake, support for the brake drum, and shield for the assembly. It is typically mounted on the axle or wheel spindle and remains stationary as the vehicle runs.
Drum brakes are equipped with a pair of shoes. These are also made of metal, such as steel, like the backing plate. They feature a crescent-shaped plate called the web and a curved panel called the lining table, which holds and supports the friction materials. These two metal pieces are welded together perpendicularly. When the brake shoes are mounted, the web is positioned parallel to the backing plate while the lining table faces towards the sides of the brake drum.
The small tube in the drum brake that is connected to the hydraulic hose is called the wheel cylinder. It has pistons on each end meant to actuate the two brake shoes. Since the wheel cylinder serves as a conduit for the brake fluid, it has to be liquid-tight. The pistons also feature rubber seals to prevent leaks.
Although they look like simple ring pans, brake drums need to be made to certain specifications to ensure the braking system works properly. These should ideally be made of metal that can diffuse heat and is resistant to wear to sustain the forces they are required to generate for braking. The inside of the drum is also machined to a certain diameter that the shoes could easily grip.
The other components of the brake drums that are essential to its operation include the friction linings, return springs, and anchor.
How Do Drum Brakes Work?
The braking power generated by the drum brakes is created through the contact of surfaces that produces friction. In drum brakes, these surfaces are the friction lining held by shoes and the inner walls of the drum. The drum itself is coupled to the wheel and spins as the vehicle is moving. Meanwhile, the brake plate that holds the shoes is typically mounted on the axle or wheel spindle and remains stationary.
When the brake pedal is applied, hydraulic fluid from the master cylinder is forced into the tubes and hoses leading to the wheel cylinders in each drum brake unit. As the fluid cannot be compressed, it creates pressure that causes the pistons to move outwards. They then push on the brake shoes that press the friction lining against the inner wall of the brake drum. The linings then grip the spinning drum that is coupled with the wheel, causing the vehicle to slow down and stop.
Once the brake pedal is disengaged, the fluid in the wheel cylinder returns though the lines, allowing the pistons to retract into the cylinder. The return springs are then able to pull the brake shoes away from the sides of the brake drum so that the wheels could move freely.
Should You Get a Brake Disc and Drum Kit?
Most vehicles feature a combination of disc and drum brakes. Since braking throws most of a vehicle’s weight forward, disc brakes are usually used for the front wheels to address their need for greater braking power. Meanwhile, drum brakes are commonly used on the rear wheels.
Brake disc and drum kits include most parts needed to replace the braking units on all wheels of a vehicle. The kits include both front disc and rear drum brake parts. In addition to the components, some kits also include all the related hardware for use in installation.
It is important to take note of your vehicle’s year, make, and model when purchasing a brake disc and drum kit. These details help ensure that the replacement parts are compatible with your car.
Luxury and high-performance cars use all-disc braking systems most of the time. On the other hand, some older cars use all-drum braking systems. Vehicles equipped with disc and drum brakes might also feature different system configurations.