The Brake System (An Overview)

The braking system is the most important system in your car. If the brakes fail, the result can be disastrous. The brakes are in essence energy conversion devices, which convert the kinetic energy (momentum) of your vehicle into thermal energy (heat). When you step on the brakes, you command a stopping force ten times as powerful as the force that puts the car in motion. The braking system can exert as much as 1,000 pounds of hydraulic pressure on each of the four brakes. In modern systems, the master cylinder is separately power-assisted to activate the front and rear brakes. If one set fails, the other can provide adequate braking power. Many such safety systems within the braking system make modern brakes very complex, but much safer than earlier braking systems. High-performance disc brakes originally were developed for racing, but are now used on many newer cars. On most cars, the front brakes are of the disc type, and the ones in the rear are the drum type. The parking brake is a cable operated system, which usually is attached to the rear wheels. In almost all braking systems, the brake pedal is connected to a "master cylinder" by a push rod. The master cylinder is connected to the brake cylinders ("slave cylinders") at each wheel by steel brake lines and flexible rubber hoses. The entire hydraulic system is filled with a special brake fluid, which is forced through the system by the movement of the master cylinder pistons. The front disc brakes use friction "pads" which are mounted in "calipers". The pads are forced against machined surfaces of a rotating disc called the "rotor". The rear brakes are usually of the "drum" type. In these, the internal expanding brake "shoes" are forced against the inside machined surface of a rotating drum. In recent years, brakes have changed greatly in design. Disc brakes, due to their lighter weight and better performance, are replacing drum types on the rear wheels. Instead of linings which press outwards against the inside of a drum, a disc attached to the axle is gripped from either side by friction pads attached to the calipers. The greatest advantage of disc brakes is that they are essentially "fade" free. That is, repeated application does not result in excessively high temperatures developing in the linings and drums, lowering the stopping power of the brake. Commonplace on newer cars are "anti-lock" brake systems, (ABS) which prevent the wheels from completely stopping when the brakes are applied in a panic stop. As impressive as these advances are, the basic process of converting a vehicle's momentum into (wasted) heat has not changed since the days of horse and buggy. To stop carriages, the driver would pull on a lever which would rub on the wheel. But with the advent of brake-charging electric vehicles, a new braking equation is opening up the possibility of recapturing this lost energy, instead of warming the air with it. In modern electric cars, when you step on the brake the motor switches into "generator mode", and stores the car's momentum as chemical energy in the battery, to be used when the light turns green! In 1923, a Packard was the first car in America with four-wheel brakes. In 1927, four-wheel brakes were introduced in the Lincoln production cars.