the breakdown on brakes

By Pep Sanchez

Many consider car ownership as a hobby of sorts and part of that hobby is putting a good deal of attention to removing friction. Whether it’s adding special additives to the engine oil, greasing all exposed hinges and moving joints, or installing aftermarket body parts for improved aerodynamics, making our machines as slippery as possible can sometimes approach obsession.

But there are a couple of areas in the workings of the automobile where friction is welcomed, or more accurately, implemented by design. One very important area is in braking. In fact, it doesn’t matter if your vehicles can go only 20 mph or 120 mph: unless it can be slowed down or stopped at exact measures, a car is nothing more than a metal death trap. Without braking technology, wheeled transport is surely a lot less appealing.

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For this week, we’re going to talk a lot about the braking system of the automobile, including some braking basics, the kinds we have in our cars, and a few common problems with the system that could come up and would require your attention. Since having good brakes is an important safety consideration, knowing a lot about how they work is always best.

It Takes Two

​There are two common types of brake designs used by passenger cars: drum brakes and disc brakes. There’s also a new third method, called regenerative braking used in most electric and hybrid cars but as the name suggests, it is designed more to recoup some energy lost in braking. This third type works in conjunction with more traditional braking designs when it comes to actually stopping a vehicle, and so for our purposes, we’re just going to talk about the first two.

Drum-roll Please...

The older of the two designs is the drum brake. Like the disc brake, the drum brake is part of the wheel assembly of a car and they stop the wheels from spinning by manner of friction or converting the rotational motion of the wheel to heat.

Inside the brake drum is a pair of curved arms shaped to fit the inside walls of the drums. Special wear and heat resistant material line the braking surface of these arms. Through hydraulics, an actuator pushes these arms outward and against the inner rim of the drum, slowing and stopping the spin of the drum, and therefore the wheel.

Up until a few decades ago, all automobiles used drum brake designs on all the wheels of their cars. Since all of the moving parts are housed within the drum, the parts are protected from dust, dirt and water, making these brakes work well in less than ideal road conditions. This brake type arguably has a longer service life and needs less maintenance. Additionally, in spite of their complexity (relative to disc brakes), drum brakes are also cheaper to make which is probably why they are still used in lower end car models.

Drums do have a few disadvantage. For one, confining the braking assembly within the drum limits the area of the braking surface to the dimensions of the drum’s circumferential wall. In turn, this limits braking power. Another limitation inherent to the drum’s design is in heat dissipation.

Heat generated by friction needs to be dissipated quickly to maintain the effectivity of the brakes especially in successive hard braking scenarios. With drum brakes, only the outer housing of the drum is exposed to the outside air while the inner walls and braking assembly are sealed off. This means cooling surface is a bit limited.

Disc-o Inferno

Disc brakes provide better braking performance than drum brakes and as such, they are the most popular and common braking device for cars today. Much of their performance is owed to the design.

Discs are so called for the metal rotor that’s part of the wheel assembly. Through hydraulic action, brake calipers lined with special braking material hold-on and squeeze the rotor to slow down or stop the wheel’s spin. The disc brake design offers a larger braking surface area (greater stopping power) and the exposed rotor ensures better heat dissipation (more consistent braking).

They have a few disadvantage. One is cost since the metal alloys used for rotors and brake assembly have to be special enough to withstand the stresses of modern driving. Two, disc brakes are also exposed to the elements making discs less effective in muddy and very wet road conditions.

Next Time

​We’ll talk about symptoms of brake trouble and things you can do to better take care of your brake system.