The car industry is always exploring new tech. We see super efficient GDI engines, electric vehicles, and even advanced autopilots becoming more common. But, this industry also keeps using older technology. This mix of old and new is really evident in braking systems. Take the brake drum, for example. It’s been around since 1900 and we’re still using it today. It’s interesting that we’re driving with technology from the early days of cars.
What is a Brake Drum?
If you ask someone about car brakes, they’ll likely talk about brake discs or rotors. These are simple, effective, and popular in modern cars. But rotors aren’t the first type of brakes. That honor goes to drum brakes.
Drum brakes work with a brake drum and brake shoes to slow down a car. The brake drum is the part you see from the outside, but it’s just one piece of a more complex system.
How do Brake Drums work?
Friction has always been key in braking, but the way it’s used has evolved. Today’s brakes, like big brake rotors with strong 4-piston calipers, work on the same basic idea as drum brakes.
To get how drum brakes work, let’s look at their main parts:
- Brake drum
- Brake shoes
- Adjuster mechanism
- Brake cylinder
- Handbrake mechanism
Here’s how these parts work together. Drum brakes, like modern rotor brakes, use hydraulic fluid.
The process is straightforward — when you press the brake pedal, it sends hydraulic pressure to the brake drums. Each drum has a brake cylinder at the top.
Hydraulic fluid enters this cylinder, expanding two pistons, one on each side. These pistons push the brake shoes against the brake drum. When you let go of the brake pedal, the pressure goes down, pulling the pistons back and the brake shoes return to their starting position.
There’s also an adjuster mechanism for manual brake tension adjustment. But, most modern drum brakes adjust themselves, so you usually don’t need to use this.
What’s the Handbrake?
Drum brakes don’t just slow down vehicles; they also act as the handbrake. When you look inside a typical drum brake, you’ll see that the hydraulic cylinder mainly works on the upper to middle part of the brake shoes.
Usually, a used set of brake shoes shows more wear on the top. This is because this area presses against the brake drum when you hit the brake pedal. The lower part of the brake shoe tends to stay in better shape since it’s used for the handbrake.
Besides the hydraulic cylinder at the top, there’s a mechanical device at the bottom of the drum. This connects to your handbrake with cables. Pulling the handbrake makes this mechanism push the bottom part of the shoe against the brake drum.
Why do we still use Drum Brakes?
While brake drum designs are quite effective, they’re now considered outdated compared to modern disc brakes. If you’re looking only at performance, disc brakes outshine them in every aspect. However, drum brakes are still in use and aren’t likely to disappear soon because they’re affordable, long-lasting, and dependable.
Drum brakes are affordable
The primary reason drum brakes are still being produced is their cost-effectiveness. Financial considerations are crucial in the car industry. Many pickup truck manufacturers, for example, are sticking with drum brakes to avoid increasing their vehicles’ prices by switching to rotors.
However, you’ll hardly ever see drum brakes on the front wheels of vehicles now. Rotors have taken over there. Drum brakes are typically found on the rear axles, particularly in budget-friendly front-wheel-drive cars. Whether this cost-saving measure is justifiable is a matter of debate.
Many critics believe that brake rotors are not only reasonably priced for widespread use, but also the safer option. In a world where safety is a top priority, rotors should be more common, they argue. However, the issue seems to be not the cost of the brake discs themselves, but the expense of updating manufacturing lines to accommodate them.
Drum brakes are durable
One commonly mentioned advantage of drum brakes is their durability, and there’s some truth in this. The enclosed design of a brake drum offers better resistance to weather. Also, brake shoes usually wear down evenly.
In contrast to brake rotors, which can warp or wear out quickly, drum brakes don’t face these issues. The enclosure seen after removing the wheel is what makes contact with the brake shoes during braking.
This durability argument holds up to some extent. However, it’s worth noting that many mechanics find servicing drum brakes particularly challenging. If the sarcasm in that statement is clear, you understand the sentiment.
Replacing brake shoes in drum brakes is tougher than changing pads in disc brakes, even on modern vehicles. Handling springs, self-adjusting mechanisms, leaky hydraulic cylinders, and other complexities is a regular part of servicing rear drum brakes.
Drum brakes are reliable
Drum brakes are reliable, a result of many design iterations and an understanding of what works and what doesn’t. A key caution with drum brakes is avoiding excessive fading, as they can fade quickly. They don’t dissipate heat as effectively as brake rotors.
While drum brakes are mechanically reliable, they are not the most advanced in braking technology.
Why drum brakes are still used on the rear axle
Nowadays, auto manufacturers are aware that there’s a limit to how much they can rely on drum brakes in newer cars. Trends in Japan show that even the smallest cars are increasingly equipped with brake rotors on all four wheels.
The common placement of drum brakes at the rear of many vehicles is related to weight distribution in modern cars. The typical sedan isn’t a mid-engined performance vehicle with a meticulously balanced center of mass. Rather, these are often front-heavy cars designed for safety and reliability.
As a result, most cars depend primarily on their front brakes for the bulk of braking power. The rear brakes play a supporting role, helping stabilize the car when braking and providing the ability to lock the rear wheels with the parking brake.
How do I know if my brake drums are bad?
When brake drums start to fail, they typically give a couple of early warning signs and an omen, primarily a change in the brake pedal response, the handbrake not holding the car or a grinding noise when the brakes are used.
Change in Brake Pedal Response
Usually, the firts sign of trouble is a difference in how the brake pedal feels. Worn-out brake shoes, when pressed against the brake drum, can lead to vibrations. You might notice the pedal vibrating or pulsing, along with some noise. If you experience this, it’s important to check your brakes.
Parking Brake not holding the car
Another clear indicator of an issue is if the handbrake doesn’t hold properly. This typically suggests a problem with the handbrake mechanism or a lack of friction material on the trailing shoes inside the drum.
Noises when pressing the brake pedal
Finally, if you hear grinding noises from the rear of your car when applying the brakes, it’s a strong indication that your brake shoes are worn and require replacement.
Changing worn brake pads or shoes on drum brakes
Changing brake pads on drum brakes is a bit different than changing pads on disc brakes. Here’s a simplified guide, but remember, if you’re not comfortable doing this yourself, it’s best to consult a professional mechanic.
- Safety First: Park your car on a level surface and engage the parking brake. Use wheel chocks to secure the vehicle. Remember to wear safety glasses and gloves.
- Remove the Wheel: Loosen the lug nuts with a lug wrench, lift the car with a jack, and then fully remove the lug nuts and the wheel.
- Remove the Drum: The brake drum should now be exposed. It may come off easily, or you might need to gently tap it with a hammer to release it. In some cases, there are screws holding it in place which need to be removed first.
- Inspect the Drum and Brake Assembly: Once the drum is off, inspect it for wear and tear. If it’s heavily scored or worn, it may need to be replaced or resurfaced.
- Remove the Old Brake Shoes: Drum brake systems use brake shoes, not pads. These shoes are held in place by springs and pins. Carefully remove these components, noting their arrangement for reassembly. A brake spring removal tool can be very handy here.
- Clean and Inspect: Clean the brake assembly area with brake cleaner to remove dust and debris. Check the wheel cylinder for leaks and the springs for damage.
- Install New Brake Shoes: Place the new brake shoes in the same position as the old ones. Replace the springs and pins, ensuring they are correctly and securely attached.
- Adjust the Brake Shoes: Some drum brakes have an automatic adjuster, but others may require manual adjustment. Ensure the shoes are close to but not touching the drum.
- Reinstall the Drum and Wheel: Put the drum back on. It should fit over the new shoes with a little resistance. If it’s too tight, you may need to adjust the shoes again. Then, put the wheel back on and tighten the lug nuts.
- Test and Adjust: Lower the car and tighten the lug nuts to the specified torque. Before driving, pump the brake pedal several times to ensure the brake shoes are properly seated. Test the brakes at a low speed to ensure they’re working correctly.
It’s important to change the brake shoes on both sides of the vehicle to maintain even braking. Also, always refer to your vehicle’s service manual for specific instructions and torque specifications, we recommend Haynes. If you’re unsure or uncomfortable with any part of this process, it’s best to seek the assistance of a professional mechanic.