Rotor Refinishing

Tools Required:

• Rotunda Disc Brake Lathe 054-00020
• Rotunda Rotor Mounting Adapter 054-00032

The rear disc rotor is a hat section-type composite rotor of steel and cast iron. A new simplified method of measuring maximum allowable stock removal using a standard hand micrometer eliminates the need for special tools as on previous rear disc rotors. However a Rotunda mounting adapter will be required for use on the brake lathe for refinishing.

All rotor refinishing must adhere to the rule that equal amounts of rotor stock are removed from each braking surface each time a rotor is refinished.

The minimum allowable overall rotor thickness continues to be stamped on the rotor and must not be exceeded.

1. With a suitable micrometer, measure the overall thickness of the rotor braking surface at four equally spaced points around the rotor.

   NOTE: Using a micrometer to measure rotor thickness simplifies previous rotor measurement procedure, but it is mandatory that an equal amount of material be removed from each side of the rotor each time the rotor is turned.

2. Using the lowest reading from Step 1, subtract the minimum allowable thickness stamped into the rotor (22.75mm). The difference, if any, represents the total amount of material available for machining. A thickness reading less than the minimum rotor thickness requires rotor replacement.

3. After measuring the rotor, the rotor should be installed in the lathe arbor using the special adapter that is required for proper rotor alignment. Never use a lathe that cuts only one face of the rotor at a time, it must be a simultaneous straddle cut. Install a dial indicator to read rotor lateral runout near the center of the rotor face. If runout is 0.050mm (0.002-inch) or below, proceed to machine rotor. If runout is over 0.050mm (0.002-inch), loosen rotor on the arbor, and rotate the rotor 90 degrees. Reread the runout, and if it is below 0.050mm (0.002-inch), proceed to machine the rotor. If runout is still over 0.050mm (0.002-inch), again loosen the rotor, and rotate it an additional 90 degrees. Recheck the runout. If runout is 0.050mm (0.002-inch) or less, proceed to machine the rotor. If the runout still exceeds 0.050mm (0.002-inch), return the rotor to the best runout position obtained. If the rotor runout can be brought below 0.127mm (0.005-inch), proceed to machine the rotor. If the rotor cannot be brought below 0.127mm (0.005-inch) runout, it must be replaced.

4. Set the cutting tool to just contact the high spots on the rotor, then adjust the cutting tool to the minimum depth required to clean up the rotor face. Equal material must be removed from each side. Do not exceed the allowable stock removal. Clean all cuttings and chips from the rotor before installing it to the axle.