Before you can understand brake failure, you must understand how brakes work.
The brake system is rather like this children's song verse, "The head bone's connected to the neck bone, the neck bone's connected to the shoulder bone ..." In vehicles, the brake pedal is connected to the pistons, and the pistons are connected to the brakes. Most modern cars have disc front brakes and drum rear brakes.
Functioning brakes stop a vehicle by using friction. In this way, they are unlike the engine, which must always be kept lubricated to run smoothly. In front brakes, friction stops the brake calipers and pads. In rear brakes, friction hits the brake drums and shoes.
Several factors can interfere with this friction and lead to brake failure:
- Grease or oil on brakes causes brake failure, because it interferes with friction. If oil leaks, it may indicate that an oil seal has failed.
- When the brakes overheat to a great degree, the metal in the brake rotors or drums develops hard spots. These are known as hot spots. The hot spots resist the friction from the brake shoes and pads. Because the shoes or pads have nothing they can grasp, there's no friction. Consequently, braking power is lost.
- Brakes that squeal indicate that the brake pads are wearing thin. By the time the brakes begin making a grinding sound, they've worn down past the pads to the rotors, which will cost more than pads to replace [source: Gray].
Do you know anyone who nervously "rides the brake" when driving? How about the scaredy-cat driver who often stops in a panicked way? This type of driver is headed for crystallized brake pads or shoes. Because of the heat generated over repeated overuse of the brake, the pads and the shoes grow hard and are ineffective. Brake material has to be flexible and able to grasp the disc or drum in order to stop the vehicle.
Now let's look at the dangers a driver faces when brakes fail.