Refinishing Brake Rotors (Disc Brakes)
It is not necessary to refinish brake rotors when doing routine brake maintenance such as replacing brake shoe and lining assemblies. Refinish rotors only under the following circumstances:
- There is complaint of brake pulsation.
- There are heat spots or excessive scoring.
Brake rotors have a minimum thickness 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 the dimensions shown in the specifications chart after refinishing. A rotor that is too thin will not have the proper heart transfer capabilities. Replace it with a new rotor. Accurate control of rotor tolerances is necessary for the proper performance of disc brakes. Precision equipment should be used for machining. Service machining equipment on a regular basis. Always use sharp cutting tools or bits and use only replacement cutting bits recommended by the equipment manufacturer. Always use vibration dampening attachments when refinishing brake surfaces. They allow for a better surface finish.
Locate the deepest score and turn the rotor micrometer knobs until the tool bit bottoms out at the deepest point of the score. Zero the scale and back out the tool bits. Advance the cutter hand-wheel until the bits have cleared the inner edge of the rotor face. Adjust the micrometer knobs for approximately .005" (.0127 mm) more than the first reading. This will ensure clearing the rotor in one cut. It is very important that you make the rotor surface non-directional by dressing the rotor surfaces with a sanding disc power tool such as Ammco 8350 Safe Swirl Disc Rotor Grinder using 120 grit aluminum oxide sandpaper. Sand each rotor surface using 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 surface using moderate pressure for a minimum of 60 seconds. After sanding the rotor clean with brake cleaner.
The finished rotor surface should be as close to that of a new rotor as possible. Failure to obtain the best possible rotor finish can affect initial braking performance.