Auto questions: how disc brakes work

We hardly notice them when they are functioning properly, but if the frightening occasion arises when they don’t, we develop a new appreciation for our car’s brake system. In this article, we’ll discuss the mechanics of disc brakes.

Invented in 1898 by Elmer Ambrose Sperry of Cleveland, Ohio and used extensively thereafter in Europe, the disc brake didn’t catch on with manufacturers in the United States until 1973. After that, disc brakes have become the most common system used in newly manufactured automobiles.

There are three basic components making up disc brakes: the rotor, the brake pads, and the calipers. The rotor is a circular metal disc that is mounted behind your tire to the hub. Next are the calipers. Picture a circus performer who can spin a dinner plate on the tip of his finger. To stop the plate from spinning, he uses his fingers to clamp down on the plate. The rotor is similar to the plate, and the fingers act similarly to the calipers. At the tips of the fingers would be the brake pads, which are made of a softer material than the rotor in order to keep it free from surface damage. When you apply pressure to the brake pedal, you are squeezing the fingers onto the plate, or the calipers onto the rotor.

How is the energy from the brake pedal passed onto the calipers? There is hydraulic fluid, which is a type of oil, running within a set of lines. These lines are your brakes lines that connect to the piston within the calipers. When actuated, the pressure from the compressing hydraulic fluid causes a piston with a brake pad on one end of the calipers to move outward, and a brake pad on the other end of the caliper to move similarly, squeezing the rotor. Enough friction is created to slow the rotation of the rotor, and therefore the wheels, to bring the automobile to a safe, controlled stop.

Most modern vehicles are equipped with disc brakes on the front wheels, while others have disc brakes on all four wheels. Among the different types of disc brake systems is the single piston, floating caliper, which is the most commonly used today. As the name implies there is one piston per wheel, located at the inside end of the caliper. The caliper is considered floating as it straddles the rotor and each brake pad is applied equally to each side of the rotor.

Today, disc brakes come with other options such as anti-lock systems, which prevent the tires from ‘locking up’. In the past, rotors would be completely stopped by the calipers, causing the tires to stop all rotation and thereby sending the car into an uncontrollable situation. With anti-lock systems, the clamping of the rotor is controlled, allowing the tires to maintain rolling contact with the road.

Disc brakes operate on a simple, but effective principle developed over a century ago. Improvements on the basic concept have increased safety and efficiency, but Mr. Sperry’s invention is still in use, and much appreciated today.