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    1. How Do Brakes Work?
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Home > Brake Mechanics > How Do Brakes Work?

How Do Brakes Work?

The Basics:

Even though the engineering science behind how brakes work can be complicated, the actual mechanics of how brakes work is simple. Brakes work on a principle known as friction. To stop a spinning wheel on a motor vehicle, whether it is an automobile, motor cycle, farm tractor, trailer or semi truck, a brake lining comes into contact with a metal surface affixed to wheels and stops them from spinning. Those who have ever heard that terrible grinding sound of metal on metal when they have waited too long to replace their brakes know that hard metal upon metal will cause damage.

Consequently, the linings on brakes are softer than the metal which it is pressed against. The trade off for preventing damage is that a little bit of the brake lining is rubbed away each time you step upon the brake pedal. Brake linings deteriorate similar to the action of rubbing a pencil eraser on piece of paper. Just as little pieces of the eraser rub away and become dust on the paper, little bits of brake lining rub away and collect on metal structures of the brake assembly. Because asbestos was cheap and prevented brakes from squeaking, some manufactures ignored the known health hazards and continued to manufacture asbestos brake linings well into the 1990's, despite widely available substitutes.

Drum vs. Disc Brakes

The two most widely used brake systems are drum brakes and disc brakes. Before the 1970's, drum brakes were used almost exclusively on motor vehicles. Disc brakes gradually came into wider use on passenger vehicles. At first they were used only on the front wheels, but by the 1980's, disc brakes were often used on all four wheels. Drum brakes are still used on the rear axles of some passenger vehicles and trucks. Drum brakes are predominant on buses and large commercial trucks used in construction and for hauling of freight.

Likewise, disc brakes offer better stopping performance than drum brakes, and the braking force is proportional to the pressure placed on the braking pedal. When sports cars were first introduced, disc brakes were commonly used because these vehicles demanded better braking performance.

More detail on the following braking systems can be found below:

Drum Brakes
Drum Brakes on Tractor Trailers
Disc Brakes