Parallelism

DESCRIPTION - 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.

TESTING - Two methods can be used to check if the two faces of a disc brake rotor are parallel.
Method 1 - Using a hand held micrometer.

Measuring Thickness Of Disc Brake Rotor Braking Surface:

^ 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.

Method 2 - The other method is to measure the disc brake rotor on a precision lathe designed for machining disc brake rotors.
^ Attach two Rotunda Disc Rotor and Ball Joint Gauges 134-R0199 or equivalent, one on each side of the disc brake rotor, so the stylus of each indicator contacts the rubbing surface, directly opposite each other, approximately 25 mm (1 inch) from the outer edge of the disc brake rotor.
^ Zero both indicators and rotate the disc brake rotor by hand, while watching both dials. If the total readings of both indicators exceeds 0.015 mm (0.0006 inch), the disc brake rotor must be refinished or replaced.