DISC BRAKE ROTOR SURFACE REFINISHING PROCEDURES

VEHICLES AFFECTED: All Light Duty Vehicles Equipped With Semi-Metallic Brake Linings

Semi-metallic brake linings are designated for use on many vehicles based upon brake system performance requirements. In order to maintain this performance, semi-metallic linings are also specified for service replacement.

Good contact is important between the friction surfaces of any brake system, but this is more important with semi-metallic linings, as they are less tolerant to a poorly refinished rotor surface. Poor finish on rotor surfaces can cause reduced braking effectiveness. A brake pull condition may result from an improperly refinished rotor installed opposite a finished rotor.

The original equipment new disc brake rotors have an initial surface finish of 20 to 60 micro inches and all have a non-directional swirl pattern.

SERVICE RECOMMENDATION

- Routine replacement of disc brake linings does not require rotor refinish.

- Should rotor refinish be required because of parallelism, runout, or because of deep scoring, the rotor requires a micro-inch surface refinish equivalent to the new vehicle rotor specification.

- The recommended procedure for obtaining this finish is as follows:

ROUGH CUT FINISH CUT --------- ---------- Spindle Speed 200 RPM 200 RPM Depth of Cut Per Side .005 IN. .002 IN. Tool Cross Feed Per Rev. .006 IN.-.010 IN. .002 IN. MAX Vibration Dampener Yes Yes Swirl Pattern - 120 GRIT No Optional*

* Duplication of new rotor and smoother finish for best initial brake effectiveness.

When installing new rotors from service stock 'do not' refinish the surface as these parts are to recommended finish. It also is not required to refinish a rotor on a vehicle which has a smooth finish with runout within specifications.

When refinishing brake rotors for semi-metallic linings, the following is important:

- The brake lathe must be in good working order and have capability to produce the intended surface finish.

- Use correct tool feed and arbor speeds. Too fast a speed or too deep a cut can result in a rough finish.

- Cutting tools must be sharp.

- Adapters must be clean and free of nicks.

- Lathe finish cuts should be further improved and made non-directional by dressing rotor surface with a sanding disc power tool (AMMCO Model 8350 Safe Swirl Disc Rotor Grinder or equivalent).

- Rotor surfaces are to be refinished to 20 to 60 micro-inch.

To become familiar with the required surface finish, drag a fingernail over the surface of a new rotor from parts stock or one on a new vehicle. If your brake equipment cannot produce this smooth a finish when correctly used, contact the equipment manufacturer for corrective instructions.

General Motors bulletins are intended for use by professional technicians, not a "do-it-yourselfer". They are written to inform those technicians of conditions that may occur on some vehicles, or to provide information that could assist in the proper service of a vehicle. Properly trained technicians have the equipment, tools, safety instructions and know-how to do a job properly and safely. If a condition is described, do not assume that the bulletin applies to your vehicle, or that your vehicle will have that condition. See a General Motors dealer servicing your brand of General Motors vehicle for information on whether your vehicle may benefit from the information.