Have you ever found yourself approaching a stop light in your vehicle from a high rate of speed and when you apply the brakes, the steering wheel shakes significantly? This phenomenon is caused by the front brake rotors on your vehicle becoming heat warped.
Since both brake pads and brake rotors are made of metal, when you apply the brakes and the brake pads come in contact with the face of the rotor, a considerable amount of heat is generated. Over time, the great amount of heat generated by braking along with the pressure exerted on the rotors by the brake pads can cause the rotors to warp ever so slightly. You can't tell that a rotor is warped simply by removing the wheel and looking at it, but you can sure feel it in the steering wheel when you stop your vehicle.
There are two methods to remedy this problem. The first is to have your rotors machined or resurfaced. Basically, the front rotors are removed from your vehicle and placed on a machine called a brake lathe. This machine has two very fine blades which run across the face of the rotor and remove any high spots. This provides a smooth surface to lessen any vibration and also helps your vehicle stop better. Unfortunately, machining rotors can be a slippery slope because it makes the rotors thinner and therefore more susceptible to heat warping.
The second option to deal with warped rotors is to replace the rotors themselves. Many high performance vehicles come with vented or slotted rotors that cannot be machined on a brake lathe. There are also some rotors that are made of special alloys that do not respond well to machining. In both of these cases, you'll have to purchase new rotors from the dealership or a local parts supplier. Replacing rotors is by far the more expensive route to take, but in many ways it's the best one. A new rotor will provide superior braking performance, and it enables you to get the smoothest braking possible.
The important thing to keep in mind when dealing with warped rotors is that it's not a safety issue. Although warped rotors can be a major annoyance and be uncomfortable during long trips, they don't affect the actual braking performance of your vehicle. Just because your car shakes when you stop does not mean that your brakes are going bad, but the problem will not get better. You need to either have your rotors machined or replaced.