Brake Rotor/Disc: Service and Repair

NOTE:
^ DO NOT refinish brake rotors when performing routine brake maintenance such as replacing worn disc brake pads.

^ Refinish a rotor only under the following circumstances:
- There is a complaint of brake pulsation.
- There are heat spots or excessive scoring.

REFINISHING BRAKE ROTORS
All brake rotors have a minimum thickness dimension cast into them. This dimension is the minimum wear dimension and not a refinish dimension. Do not use a brake rotor that will not meet specifications.

Refinished Too Thin
A rotor which has been refinished too thin will not have proper heat transfer capabilities. Replace it with a new brake rotor. Accurate control for the rotor tolerances is necessary for proper performance of the disc brakes.

Use Only Precision Equipment
Machining of rotors should be done only with precision equipment. The equipment should be serviced on a regular basis following the manufacturer's recommended maintenance procedure. When refinishing rotors, the attaching adapters, tool holders, vibration dampeners, and tool bits must be in good condition. Always use sharp cutting tools or bits and use only replacement cutting bits recommended by the equipment manufacturer. Dull or worn tools leave a poor surface finish which will affect initial braking performance.

NOTE: Vibration dampening attachments should always be used when refinishing braking surfaces. These attachments eliminate tool chatter and will result in a better surface finish. Make sure adapters are clean and free of nicks.

ON-VEHICLE REFINISHING
In the cases where rotors are being refinished to correct a problem with brake pulsation, it is recommended that an On-Vehicle brake lathe be used to achieve best results. Follow the lathe manufacturer's recommended specifications and procedure.

Off-Vehicle Refinishing:

OFF-VEHICLE REFINISHING
Refer to chart showing two recommended procedures that achieve adequate results using two different vendor's off-vehicle drum/disc brake lathes (If any other vendor's lathe is used, follow that vendor's recommended procedure). It is very important that the rotor surface be made non-directional by dressing the rotor surfaces with a sanding disc power tool such as Ammco 8350 Safe Swirl Disc Rotor Grinder, or equivalent, using 120 grit aluminum oxide sandpaper. Sand each rotor surface with moderate pressure for a minimum of 60 seconds. An alternate method is to use a sanding block with 150 grit aluminum oxide sandpaper. With the rotor turning approximately 150 RPM, sand each rotor finish for a minimum of 60 seconds using moderate pressure. After the rotor has been sanded, clean each surface with denatured alcohol or suitable brake cleaner. The finish rotor surface should be as close to that of a new rotor as possible. Failure to obtain the best possible rotor finish may affect initial braking performance.

NOTE: After brake pads have been replaced and/or rotors have been refinished, it is recommended that the new braking surface be broken in, or burnished. This can be accomplished by making 20 stops from 30 mph, using medium to firm pedal pressure with a minimum of 15 seconds between stops. Take care to avoid overheating the brakes.