Parallelism

PURPOSE
Parallelism is the variation in the thickness of the disc brake rotor. If the two rubbing surfaces of the disc brake rotor are not parallel, the disc brake rotor may cause excessive brake pedal travel, a pulsating brake pedal, or noise.

SETUP

NOTE: If rotor is to be removed, use touch-up paint to mark a stud and the rotor to ensure proper realignment.

- Raise vehicle and support.
- Remove wheel and tire assembly. Do not damage brake caliper bleeder screw fitting during removal.
- Remove brake caliper and anchor plate.

MEASUREMENT USING A MICROMETER
Two methods can be used to check if the two faces of a disc brake rotor are parallel. A micrometer can be used to measure the disc brake rotor thickness at 12 points approximately 30 degrees apart and 25.4 mm (1 inch) from the outer edge of the disc brake rotor.

MEASUREMENT USING A LATHE
The other method is to measure the disc brake rotor on a precision lathe designed for machining disc brake rotors.
^ Attach two dial indicators, one on each side of the disc brake rotor, so that the stylus of each indicator contacts the rubbing surface, directly opposite each other, approximately 9.5 mm (.38 inch) from the outer edge of the disc brake rotor.
^ Zero both indicators and rotate the disc brake rotor while watching both dials.
^ If the total readings of both indicators exceed the specified limit for parallelism (0.010 mm/0.0004"), the disc brake rotor must be refinished or replaced.