BRAKE ROTOR REFINISH PARTS ORDERING INFORMATION

CHANGE IN BRAKE EFFECTIVENESS AFTER DISC BRAKE ROTOR REFINISHING/PAD REPLACEMENT AND ON-CAR ROTOR REFINISHING - ALL OLDSMOBILE VEHICLES WITH DISC BRAKES (Section No. 5)

Some comments have been received about a change in perceived braking effectiveness which occurs after rotors have been refinished and/or disc brake pads have been replaced. Most of these comments have been on Cutlass Supreme models, with some comments also received on Eighty-Eight, Ninety-Eight and Toronado models. Following are some recommended ac- tions/procedures to assure proper performance of the brake systems on all vehicles after rotor and/or pad service has been performed: pad service has been performed:

1. When performing routine brake maintenance, such as replacing worn disc brake pads or shoes, DO NOT refinish disc brake rotors or drums unless:

A. There is a brake pulsation condition present, and this pulsation is found to be caused by the brake rotors or drums, or

B. The rotors and/or drums are excessively scored. Light surface scoring that does not exceed 0.015 in. on rotors or 0.020 in. on drums should not affect brake operation.

2. When refinishing disc brake rotors, it is important that the brake lathe be in good operating condition and that all tools or bits are sharp. Recommended vibration dampeners and/or adaptors should be used and should be clean and free of nicks (remember, 1988-90 Cutlass Supreme models require the use of an adaptor (J 37160) because of the two-piece design). The following table shows the recommended procedure for rotor machining:

ROUGH CUT FINISH CUT ----- ---------- Spindle Speed 150 RPM 150 RPM

Depth of Cut (per side) 0.127mm 0.051mm (0.005") (0.002")

Tool Cross Feed (per rev) 0.152mm - 0.254mm 0.051mm (0.006" - 0.010") (0.002") Max

Vibration Damper Yes Yes

Swirl Pattern No Yes (Using 120 Grit)

It is VERY IMPORTANT that the rotor surface finish be made non-directional by dressing the rotor surfaces with a sanding disc power tool such as Ammco model 8350 Safe Swirl Disc Rotor Grinder, or equivalent, using 120 grit. The finished 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.

3. After brake pads have been replaced and/or rotors have been refinished, it is recommended that the new braking surfaces be broken in, or burnished, to properly seat them. This can be accomplished by making 20 stops from 30 mph, using medium to firm pressure. Take care to avoid overheating the brakes.

4. It is strongly recommended that the correct, specified General Motors replacement part(s) be used when servicing GM vehicles. General Motors does not test non-GM parts for proper performance on GM vehicles. Therefore, the use of non-GM parts may result in unacceptable vehicle performance. It is also important that the correct GM part(s) be used in the correct GM application. For example, some Cutlass Ciera model disc brake pads ('A' Heavy) will fit on Eighty-Eight and Ninety-Eight models, but will not provide the same braking performance as the pads specified for use on Eighty-Eight and Ninety-Eight vehicles. It may seem preferable to stock fewer brake pad part numbers, but customer dissatisfaction may result if vehicle performance is affected.

In addition, some comments have been received regarding poor brake rotor finish and/or hard brake pedal feel after refinishing brake rotors using the On-Vehicle Brake Lathe (VGB 320/366, Kent-Moore 38-070400) sold through the GM Dealer Equipment program.

This condition results from using non-original cutting tips. Only original equipment replacement tips should be used.

When replacing the original cutting tips of an On-Vehicle Brake Lathe, use only replacement tips ordered from Kent-Moore Tool and Equipment Division.

The replacement cutting tips can be ordered from Kent-Moore (1-800-GM-TOOLS) as follows:

Tool Number: J 37704-13-Cutting Tips (Box of Ten)

We believe this source and their equipment to be reliable. There may be additional manufacturers of such equipment. General Motors does not en- dorse, indicate any preference for or assume any responsibility for the products or equipment from this firm or for any such items which may be available from other sources.

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.