A problem with the brake disk rotors is the most common cause of vibration when braking at high speeds. Rotors are circular metal parts found behind the wheel of the vehicle that the brake pads press against to create friction and stop the vehicle. Small irregularities in the rotors transfer to the steering wheel when applying the brakes. Another cause of vibration is improperly tightened lug nuts.
To test the rotors, a mechanic removes the wheels and spins each rotor independently. He holds his hand against the rotor to feel for imperfections. He uses a micrometer, a tool that makes precise measurements, to detect any differences in the thickness of the rotor and determine the extent of the problem. Re-machining problem rotors on a lathe removes a small layer of metal and recreates a smooth surface. If the wear is too great, the rotors require replacement.
If the vibration begins after changing the tires, the problem could be loose lug nuts. These nuts hold the wheel in place on the vehicle. When tires are changed, the technician should tighten them in a star pattern and ensure he tightens them to the correct torque. Loose lug nuts continue to unscrew, and unless the driver fixes the problem, the tire could fall off the vehicle.