For 1990-2009 cars

# REAR BRAKE NOISE OR VIBRATION (MAYBE ROTOR DISTORTION)

REAR BRAKE VIBRATION AND NOISE

#### VEHICLES AFFECTED: 1986-1988 ELDORADO AND SEVILLE -----------------

Some 1986-1988 Eldorados and Sevilles equipped with steel wheels and wire wheel disc (option code N91) may experience a minor vibration and/or noise from the rear of the vehicle when braking. The noise (boom) and vibration will appear in the 70-55 kph range on deceleration and may be more noticeable in higher ambient temperatures or on smooth road surfaces.

This condition may be caused by distortion in the rotor braking surfaces. To repair this condition, use the following procedure:

#### Installation:

1. Remove the rear rotors as described in the appropriate Service Information Manual.

2. Clean the hub flange and rotor mating surfaces of any corrosion or foreign material.

3. Install the shim, P/N 1648437 (two required per car), on the hub flange and place the locating tabs in the hub and bearing bolt access hole (large), refer to Figure.

4. Reassemble the rear brakes and install new encapsulated caliper mounting bolts, P/N 25524723, and torque to 113 N-m (80 lbs.ft.) four required per car).

5. Install wheels and torque to 140 N-m. (100 lbs. ft).

6. If some noise is still present, re-index wheel assembly on hub and road test. If noise is still noticed, replace rear wheel assemblies.

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.