Have you ever been driving in your vehicle and when trying to stop, discovered it vibrated so hard your coffee wouldn’t stay on the dash? Did it feel like the vehicle was going to bounce off the road? If you have experienced this sensation, you’ll know what I am talking about. In varying degrees, this can happen when the brake rotors become warped and are no longer straight or flat.
What does this mean? In the picture to the left, you will see the brake rotor from a Nissan that has been set up for racing. It looks basically the same as a generic rotor, other than the holes that have been drilled for heat dissipation. In the picture, you will also see the brake caliper. This is the device that is applied around the brake rotor when the brake pedal is depressed. When the brake rotor is new, it is flat. In other words, the surface that the brake pads are applied to is a smooth, flat surface. This is what allows your vehicle to stop smoothly and quickly. When one or more of the brake rotors become warped, this causes its surface to have high and low spots, thus causing a vibration when the brakes are applied. In some instances, this is not a safety issue, depending on how bad the warpage is. If it is bad enough, it can cause a feeling of panic and possibly cause you to lose control of the vehicle.
Now that we have determined the cause of the vibration, you may ask another question. What can cause a brake rotor to become warped? This question has more than one answer. If the brakes have been applied enough to generate a significant amount of heat, and the vehicle is ran through a puddle of water, this can cause the rotor to cool quickly. This fast cooling can cause the rotor to warp. The heat buildup of the brake action can also cause warpage.
What to do about the vibration? In most cases, it can be as simple as machining the brake rotors. This is a method of attaching the rotors to a brake lathe and machining the surface to be true and flat, once again. The brake pads may need to be replaced at the same time, depending on their thickness. There is also a minimum thickness stamped on the casting of the rotor. If the rotor thickness measures at or near this specification, the rotor can not be machined and must be replaced. This is a safety issue, as a brake rotor that is below the minimum thickness may not be able to dissipate the heat and may crack.
If you feel a vibration when applying the brake let your mechanic know. It could mean a world of difference in how your vehicle stops.