Understanding the Function of Parking Brakes in Drum Brake Systems

How Does a Parking Brake Work on Drum Brakes?

The parking brake, also known as the emergency brake or hand brake, is an essential component of a vehicle's braking system that ensures the vehicle remains stationary when parked. While most vehicles are equipped with a standard braking system that utilizes either disc or drum brakes, the parking brake often employs a mechanism that is separate yet related. In this article, we will explore how a parking brake works specifically on drum brakes.

Understanding Drum Brakes

Before delving into the functionality of the parking brake, it is important to understand the basics of drum brakes. Drum brakes consist of a cylindrical drum that rotates with the wheel and brake shoes that are situated inside the drum. When the brake pedal is pressed, hydraulic pressure pushes the brake shoes against the inner surface of the drum, creating friction that slows down or stops the vehicle.

The Role of the Parking Brake

The primary function of the parking brake is to keep the vehicle stationary, especially when parked on an incline. Unlike the primary braking system that relies on hydraulic pressure, the parking brake typically operates mechanically, which means it relies on cables and levers rather than fluid pressure. This independence is what makes the parking brake a reliable backup system in case of hydraulic failure.

Mechanism of the Parking Brake in Drum Brakes

In vehicles equipped with drum brakes, the parking brake system is connected to the rear brakes. It usually consists of a lever (often referred to as the handbrake or foot-operated lever) and a set of cables that run from the lever to the rear brake assembly.

1. Activation When the driver pulls the parking brake lever, it pulls the cable which mechanically engages the brake shoes. Some systems may have a ratchet mechanism to keep the brakes locked in place once activated.

2. Engaging the Brake Shoes As the cable is pulled, it exerts tension on the rear brake shoes. This tension causes the shoes to move outward against the drum's inner surface, creating friction and effectively clamping the brake shoes against the drum.

3. Holding Position Once engaged, the friction created by the clamped brake shoes ensures that the vehicle remains stationary. The tension in the cable holds the brake shoes in place, preventing them from retracting.

4. Release Mechanism To release the parking brake, the driver must pull the lever again, which loosens the cable and allows the brake shoes to retract. This release mechanism is essential for simple operation while getting back on the road.

Advantages of Drum Brake Parking Brakes

One of the advantages of using drum brakes in parking brake systems is their ability to provide consistent holding power. Drum brakes can generate significant friction, which helps keep the vehicle stationary, especially under various loads.

Moreover, drum brake parking systems are less susceptible to corrosion compared to disc systems. In wet conditions, where water can affect the performance of disc brakes, drum brakes tend to be more reliable for parking applications.

Potential Limitations

Despite their advantages, drum brake parking systems do have limitations. Over time, the brake shoes can wear out, which may lead to reduced effectiveness. Additionally, if the parking brake is not engaged properly, it can lead to slippage, especially on steep grades.

Conclusion

In conclusion, the parking brake on drum brakes serves a vital role in vehicle safety and stability. By understanding how it functions—from the mechanical engagement of brake shoes to the consolidation of friction against the drum—drivers can better appreciate its importance. Regular maintenance and inspection of the parking brake system are essential to ensure it remains effective, providing peace of mind that your vehicle will stay put when parked.