Rotor Lateral Runout
Lateral runout is the side to side movement of the brake rotor as it rotates. When this gets excessive, pad and rotor wear will result. This excessive movement will result in a vibration and pulsation in the steering wheel or seat of a vehicle. A vibration in the steering wheel indicates a problem with the front rotors. A vibration in the seat indicates a problem with the rears.
Lateral runout is diagnosed with a dial indicator. Torque lug nuts to specification. Lateral runout can be caused by uneven torque, damaged studs, or a burr or rust between the hub and rotor. Excessive lateral runout is caused by thickness variation of the rotor. This variation can be tested with a dial indicator. If there is excessive variation found, use an outside micrometer to test and compare to the minimum thickness stamped on the rotor. A rotor can often be resurfaced to correct this variance. Always check several different spots around the rotor to find the thinnest spot.