Why Are Drum Brakes Still in Modern Cars?

The first word your mind associates with brakes is probably disc, right? Disc brakes have been around for decades and have replaced drum brakes on the front wheels of most cars. Their superior stopping power, especially in wet weather, makes them a big step forward in safety.

It might surprise you to learn, then, that many modern cars still have drum brakes — especially on the rear wheels. Why? It turns out there are several reasons.

Manufacturing

Drums are more economical for automobile manufacturers. Disc brakes actually complicate things quite a bit. Using disc brakes on the rear wheels requires automakers to install a separate brake just for parking duty. In such a competitive industry, rear drums are a sound choice for a carmaker’s bottom line.

Safety

Because of their superior heat capacity, discs are arguably safer than drums. But most of the braking power comes from your front brakes. Even in panic stops, your rear brakes get less stress and less heat than your front brakes.

In high-performance cars and vehicles intended for towing, automakers sometimes use disc brakes in both the front and rear. In everyday driving for a typical passenger vehicle, however, there’s no disadvantage to disc brakes in the front and drums in the rear. That’s part of why drum brakes are still a norm in new cars, despite their vintage technology.

Longevity

Because of the lower stress, reduced heat and closed environment that keeps potentially damaging material out of your drum brakes, it’s very likely that your drum brake shoes in the back will last longer than your disc brake pads in the front.

If your car has drum brakes, it is good to get them checked out once in a while. Since a drum is enclosed, there’s nothing you can really eyeball. Unless you have experience doing your own brake jobs, pulling a drum brake apart is something best left to the pros. When you have your tires rotated, it’s a perfect time for a brake inspection and/or brake service.

Advantages of Drums:

• Efficiency:  Greater torque production at a given line pressure for same diameter drum vs. disc.  This is why the disc is almost always larger diameter than the drum it replaces on cars that could have either brake system.  The larger disc diameter is needed for adequate torque production.
• Weight: Drum systems weigh less than comparable disc systems.
• Parking Brake: Drum brakes make a superior park brake due to the wedging action of the shoe against the drum.  Once the park brake is set, any attempt to rotate the wheel causes the drum brake to grip harder (like a wedge type door stop).
• Drag:  Much time is spent designing systems that will pull the pads away from the disc to minimize energy loss due to pad drag on the rotor.   In a drum brake system, springs pull the shoes away from the drum so that, at normal operating temperatures, there is little or no brake drag.  I think I would argue that drums have a higher loss than disc due to how they’re typically adjusted.  But if adjusted correctly, there should be slight drag when cold, but as the drum heats and expands, drag is reduced, or is it negligible?

Check out all the brake system products available on NAPA Online or trust one of our 17,000 NAPA AutoCare locations for brake maintenance and repairs. For more information on drum brakes, chat with a knowledgeable expert at your local NAPA AUTO PARTS store

Photo courtesy of Wikimedia Commons.