02/09/2011
Understanding the components of your car's braking system is fundamental to ensuring its optimal performance and your safety on the road. While disc brakes have become the prevalent choice for many modern vehicles, drum brakes remain a common feature, particularly on the rear wheels of older cars or certain types of vehicles. Knowing whether your car utilises this braking mechanism can help you better understand its maintenance needs and potential issues. This guide will delve into how to identify drum brakes and the tell-tale signs that indicate they might require attention.
What are Drum Brakes?
Drum brakes are a type of braking mechanism that operates differently from the more widely recognised disc brake system. Instead of calipers pressing brake pads against a rotor (disc), drum brakes employ a system where brake shoes are expanded outwards to press against the inner surface of a rotating drum. This drum is attached to the wheel hub, and as the brake shoes make contact, friction is generated, slowing the wheel's rotation and thus the vehicle. This ingenious, albeit older, design relies on the same principle of friction to bring your car to a halt.
How Drum Brakes Work
When you depress the brake pedal, hydraulic pressure is sent to the wheel cylinders. These cylinders contain pistons that, when pushed outwards by the fluid pressure, force the brake shoes against the interior of the brake drum. The resulting friction slows the rotation of the drum and, consequently, the wheel. It's a robust system that has served motorists for decades. However, like all mechanical components subjected to constant use and heat, brake drums and shoes are subject to wear and tear.
Identifying Drum Brakes on Your Car
The most straightforward way to determine if your car has drum brakes is to visually inspect the wheels, particularly the rear ones. Drum brakes are typically housed within a round, bowl-shaped metal casing, which is the brake drum itself. This casing encloses the brake shoes and other internal components. In contrast, disc brakes feature a more exposed rotor (disc) that is clearly visible through the spokes of the wheel, with the caliper assembly mounted on the outside.
Visual Inspection:
- Look at the rear wheels: If your car has drum brakes, you'll likely see a solid, often metallic, cover where a disc brake rotor would be. This cover is the brake drum.
- Check the front wheels: While less common in modern cars, some older vehicles might have drum brakes on the front as well. The visual cues remain the same.
- Consult your owner's manual: Your car's manual will detail the specific braking system components used in your vehicle.
- Check your car's MOT history: If your car has had MOT failures related to the braking system, the report will specify whether the issue was with drums, shoes, discs, or pads, indirectly confirming the type of brakes fitted.
Common Signs of Worn Drum Brakes
Worn drum brakes can manifest in several noticeable ways, often serving as an early warning that attention is required. Ignoring these signs can lead to reduced braking efficiency, potential safety hazards, and even MOT failure. Here are the most common indicators:
1. Weak Braking Performance
One of the most significant indicators of worn drum brakes is a noticeable reduction in braking power. If you find that your car is taking longer to slow down or come to a complete stop when you apply the brakes, it's a clear sign that something isn't right. While other braking system issues can cause this, worn brake shoes or drums are a frequent culprit. The friction material on the brake shoes wears down over time, reducing their ability to effectively engage with the drum. This reduced effectiveness means more pedal travel and a longer stopping distance, which is particularly concerning in emergency situations. If your car's MOT history shows a failure in the braking system, it's worth investigating whether drum brake wear was the cause.
2. Unusual Brake Noises
Brake noises are never a good sign, and worn drum brakes often produce characteristic sounds. As the brake shoes wear down, they may begin to scrape against the brake drum. This can result in a grating, grinding, or squealing noise when you apply the brakes. Drum brakes are also less efficient at dissipating heat compared to disc brakes. Repeated braking can cause the drums to overheat, putting stress on the system and potentially leading to the shoes making contact in an uneven manner, exacerbating noise issues. These noises are not just annoying; they are a critical warning sign that your braking system needs professional assessment. A car failing its MOT due to braking system faults will detail the specific component at fault.
3. Brake Pedal Vibrations
When brake drums wear unevenly or develop a "lip" around the edge, they can cause vibrations to be felt through the brake pedal when you apply the brakes. This is because the worn surface of the drum is no longer perfectly smooth, and the brake shoes may not make consistent contact. These vibrations can range from a slight pulsing to a more pronounced shaking, depending on the severity of the wear. While you might initially dismiss these vibrations as minor, they are a strong indication that the brake drums are no longer providing a smooth and consistent braking surface. It's crucial to treat these pedal sensations as an early warning and have your braking system inspected promptly.
4. Loose Parking Brake
The parking brake, often referred to as the handbrake, is directly linked to the rear braking system, and in vehicles with drum brakes, it typically operates by expanding the brake shoes. If the brake shoes are significantly worn, they may not be able to engage effectively with the brake drum, even when the parking brake is fully applied. This can result in a "loose" feeling parking brake or the vehicle not holding firmly on an incline. A faulty parking brake is a common reason for MOT failure. If you notice that your parking brake doesn't feel as secure as it used to, or if the car rolls slightly after application, it could be a sign of worn drum brake shoes or even a damaged brake cable. A thorough inspection by a qualified technician is recommended in such cases.
Comparison: Drum Brakes vs. Disc Brakes
To better understand the context of drum brakes, it's helpful to compare them with their more modern counterpart, disc brakes.
| Feature | Drum Brakes | Disc Brakes |
|---|---|---|
| Mechanism | Brake shoes expand outwards against the inner surface of a drum. | Brake pads are squeezed against the outer surface of a disc (rotor). |
| Heat Dissipation | Generally less efficient; prone to 'brake fade' under heavy use. | More efficient; better at dissipating heat, reducing fade. |
| Performance in Wet Conditions | Can be less effective when wet as water can be trapped. | Generally perform better in wet conditions as water is more easily cleared from the disc surface. |
| Maintenance | Can be more complex to service; drums may need machining or replacement. | Generally simpler to service; pads and rotors are common wear items. |
| Common Application | Rear wheels of older cars, some trucks, and utility vehicles. | Front wheels of most cars, increasingly rear wheels of modern vehicles. |
| Typical Wear Signs | Weak brakes, noises, pedal vibrations, loose parking brake. | Squealing or grinding noises, pulsating pedal, reduced stopping power. |
Frequently Asked Questions (FAQs)
Q1: How often should drum brakes be inspected?
A: Drum brakes should be inspected as part of your regular vehicle maintenance schedule, typically every 12,000 miles or 12 months. However, if you notice any of the signs mentioned above, it's crucial to get them checked sooner.
Q2: Can drum brakes be converted to disc brakes?
A: Yes, it is possible to convert drum brakes to disc brakes, but it's a complex and often expensive modification that requires specialised parts and expertise. It's usually undertaken for performance or aesthetic reasons rather than necessity.
Q3: What is "brake fade" in drum brakes?
A: Brake fade occurs when the braking system's effectiveness is reduced due to overheating. With drum brakes, the heat generated during heavy or prolonged braking can cause the brake shoes and drums to expand, reducing the friction between them and leading to weaker braking. This is why efficient heat dissipation is a key advantage of disc brakes.
Q4: Is it safe to drive with worn drum brakes?
A: No, it is not safe to drive with significantly worn drum brakes. Reduced braking performance compromises your ability to stop the vehicle effectively, increasing the risk of accidents. Furthermore, worn brakes are a common cause of MOT failure.
Conclusion
The brake drums and shoes are fundamental elements of your vehicle's braking system. Recognizing the signs of wear is paramount for maintaining your car's safety and ensuring it passes its MOT test. If you suspect your drum brakes are worn, or if you're unsure about the type of braking system your car has, it's always best to consult a qualified mechanic. Regular checks and timely maintenance of your braking system will not only keep you safe but also prevent more costly repairs down the line.
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