How Brakes Work

Your vehicle's brake system is one of those things you only think about when it fouls up (or you do). Like when the service guy says, "You need your rotors ground and it's gonna cost $200," or you're surprised by a yellow light at an intersection. Suddenly your brakes are of acute interest. Why wait for unpleasant surprises? A general understanding of your vehicle's brake system can save you money, and may allow you to drive more safely and save a lot more than just cash. After all, the more you know, the better you can care for your car.

Braking Theory A general understanding of your vehicle's brake system can save you money.
Ask any of your physicist pals, and they'll tell you that brakes convert the kinetic energy of vehicle motion into heat. Translation: Brakes stop the car—or more accurately, brakes stop the wheels. There's a big difference, because the most powerful brakes in the world will not stop your vehicle effectively if the road surface has little or no traction. Mash the brake pedal and the wheels will stop turning sure enough, but the vehicle will skid along happily. You, on the other hand, will be a lot less happy. Many drivers tend to think of a skid as "brake failure" when in fact the situation is really a failure of the driver to understand the traction conditions and to drive accordingly.

Brake Basics
The typical passenger-vehicle brake system is relatively simple. When you step on the brake pedal, the force your leg exerts is applied to a device called a master cylinder. The master cylinder contains a piston that pressurizes a network of hydraulic brake lines that lead to each of the vehicle's wheels. At each wheel, that brake fluid pressure operates the brakes by driving pistons that force replaceable linings against a rotating drum or disc. Friction is what slows the wheel, and in turn, the entire vehicle.


When the friction material (a.k.a. pads, linings, shoes) is almost worn out, metallic tabs are designed to create a squealing noise when the brakes are applied to (hopefully) alert the driver that the brake linings are due for replacement. Heed the warning. Worn linings have less fade-resistance than new linings. Plus, if you ignore the warnings long enough, you can do costly damage to the rotors, drums and other components. Even with regular replacement of the linings, some additional service is typically required over the long haul. The surfaces of drums and discs wear unevenly in normal use and eventually need to be re-machined to work properly.


All modern braking systems are many times more powerful than the vehicle's engine, so at full throttle, even a very powerful vehicle can be easily stopped with the brakes. All vehicles also have a parking brake (sometimes called the emergency brake) that works independently of the regular brake system. The parking brake typically acts on only the rear wheels and is mechanically operated to work in case of a hydraulic problem with the regular service brakes.