Test thickness variation by measuring the rotor thickness at 4 or more points around the circumference of the rotor. Use a micrometer calibrated in ten-thousands of an inch. Make all measurements at the same distance in from the edge of the rotor.

A rotor that varies in thickness by more than 0.025 mm (0.001 in) may cause pedal pulsation and/or front end vibration during brake application. Replace or refinish to specifications, a rotor that does not meet these specifications.