Drum Brakes: Why Are They Still Being Used Today?
All cars need rear brakes to help them stop, and while the two most commonly used types of braking systems vary differently in how they apply stopping force, they carry the same genetic make-up. Essentially, a friction-building compound gets pressed into a piece of metal, thus slowing down the car’s momentum. On one end, rotors (or discs) get grabbed by a set of pads that are wedged between a vice-like clamp called a caliper, and the harder you press the brake pedal, the tighter that caliper squeezes the pads against the spinning piece of metal. These discs can come vented, and typically run cooler due to being exposed to the elements.
According to a write-up by Edmunds, disc brakes were originally designed by racing engineers to improve braking and safety, which quickly spread to the manufacturing side of the industry, becoming widespread by the early 1970s. But since the majority of a vehicle’s stopping power usually tends to be in the front, most automakers at the time left the rear brakes drum-based. Naturally, there were certain performance models that received disc brakes all around, but pretty much everyone else rocked drums in the rear, and even today you still see drums on a lot of new cars. This last fact got us wondering: Why would automakers still use dated technology on modern machines?
But before we get to the reasons of why, let’s first look at what makes the drum brake. While it certainly has saved millions of lives over the years, and when properly maintained it does work quite well, it does have its inherent design flaws. The term “drum brake” refers to the barrel in which the brake components are housed, which like a rotor setup, is attached to the car’s wheel and hub. Inside the drum rests a set of “shoes,” which get forced against the insides of the housing courtesy of an array of springs and tensioners. Like pads, the shoes are made from a heat-resistant friction-forming material similar to that used on clutch plates, which over time will eventually wear down and need replacing.
In order to get a feel for what replacing drums entails, we spoke with multiple mechanics, and got a pretty resounding: “Replacing drums and shoes blows!” from everyone. Also, since many shops charge hourly rates, replacing these time consuming components can cost quite a bit more than popping on a fresh set of pads and rotors. All of those springs and tensioners are tightly wound, and have the tendency to shoot off in any direction on a whim if you aren’t careful. Play it too safe and you won’t have enough stopping friction. Apply too much tension and you’ll cook the brakes, which leads us to the other main issue with drums: Heat.
Under extreme braking conditions, like when descending a steep hill with a heavy trailer behind you, shoes have the tendency to lose bite as a direct result of heat buildup within the drum. Edmunds explains this phenomena best by illustrating that “the principle of braking involves turning kinetic energy (wheel movement) into thermal energy (heat),” and that for this reason, brakes can “only operate as long as they can absorb the heat generated by slowing a vehicle’s wheels.”
So if the brake components become oversaturated with heat, they lose their ability to stop a vehicle, a phenomenon that’s commonly referred to as brake fade or heat fade. While both pads and shoes are susceptible to fade, shoes are far more prone to fading, as drums are a closed unit and do not benefit from the cool air discs and pads get to play in every day. So if they are a pain in the ass to replace, are often inferior to a performance rotor/pad set-up when it comes to stopping power, and don’t dissipate heat as well, why are automotive manufacturers still using them?
While many cars nowadays feature four-wheel disc brakes as standard equipment, a fair amount of vehicles still rock the old front-disc/rear-drum configuration. When we tested the 2016 Toyota Tacoma last summer, the chief engineer insisted that all Tacomas have drums due to being “based on long-term durability” and had nothing to do with Toyota “cutting costs.” Did the truck stop perfectly with nary an issue to prove otherwise? It most certainly did. But that didn’t stop us from wondering why the hardcore Tundra TRD-PRO received rear discs instead of a set of drums.
Car and Driver jumped in the fray as well, saying that Toyota engineers want us to believe that “in this class of trucks, where whatever towing that goes on is light, braking force from the rear wheels is relatively unimportant.” This was a valid point, but when Toyota claimed that drum brakes have an advantage when off-roading because “they’re sealed against rocks, mud, and other crud,” critics and off-road professionals alike raised an eyebrow.
When we test drove the Scion iA, which had drum brakes in the rear, representatives said that owners would more than likely never need to have their rear brakes replaced. We were also told that putting disc brakes all around would require an across-the-board increase in MSRP price, thus dissuading potential buyers. But after pricing out brakes from multiple auto stores, we learned that on average rotors, pads, calipers, brackets, and hardware cost about the same as a complete drum, shoe, and hardware setup. Naturally, there are certain drum systems that do cost less than their caliper counterpart, but oftentimes “shop fees” will obfuscate these facts.
At this point, it’s common knowledge that cars like the first generation Honda Fit came with discs over in Japan, which could have been bolted-up to our American model without issue. But Honda opted to give us drums instead, leading us to wonder if there is another motive at play here. Tackling disc brake jobs is one thing, but as previously mentioned, a drum and shoe replacement is a tedious, finicky process. This means that dealerships have the upper hand when it comes time for a fresh set of shoes, as even mechanics are prone to a groan when confronted with the task of tackling their own drum brakes.
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