Brake Rotor/Disc: Service and Repair
SURFACE REFINISHINGYou do not need to refinish brake rotors when doing routine brake maintenance such as replacing worn brake shoe and lining assemblies. Refinish rotors only under the following circumstances.
1. There is a complaint of brake pulsation.
2. There are heat spots or excessive scoring.
ROTOR REPLACEMENT
A rotor that is too thin will not have the proper heat transfer capabilities. Replace it with a new rotor. Refinishing composite rotors requires using a rotor adapter tool as a holding fixture for the brake lathe.
USE PROPER EQUIPMENT
Accurate control of rotor tolerances is necessary for the proper performance of disc brakes. Machining should be done only with precision equipment. Service the machining equipment on a regular basis following the manufacturers recommended maintenance procedures.
Attaching Adapters And Dull Or Worn Tools
When refinishing rotors, make sure the attaching adapters, tool holders, vibration dampeners, and tool bits are 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 that will affect initial brake performance. Always use vibration dampening attachments when refinishing braking surfaces. These attachments eliminate tool chatter to allow for a better surface finish. Make sure these adapters are clean and free of nicks.
RECOMMENDED LATHE PROCEDURES
Following are examples of two recommended procedures that achieve adequate results using two different off vehicle drum and disc brake lathes. If any other lathe is used, follow that manufacturers instructions and recommendations.
1. Locate the deepest score and turn the rotor micrometer knobs until the tool bit bottoms out at the deepest point of the score.
2. Zero the scale and back out the tool bits.
3. Advance the cutter hand-wheel until the bits have cleared the inner edge of the rotor face.
4. Adjust the micrometer knobs for approximately 0.0127 mm (0.0005 inch) more than the first reading. This will ensure clearing the rotor in one cut.
A Nondirectional Surface Must Be Achieved
It is very important that, you make the rotor surface nondirectional 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 at approximately 150 rpm, sand each rotor surface using moderate pressure for a minimum of 60 seconds. After sanding the rotor, clean each surface with denatured alcohol or a suitable brake cleaner.
CAUTION: 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.