DRIVE CLICK-RUMBLE NOISE AT LOW MILEAGE

MODELS AFFECTED: 1987 CENTURYS WITH 2.5L (LR8) ENGINE (VIN CODE R) AND AIR CONDITIONING

Some new vehicles, at low mileage, may temporarily exhibit one or both of the following conditions:

1. A clicking noise coming from the tensioner when the tensioner moves while engine is idling. The tensioner can be confirmed as the cause by observing the tensioner motion while changing the accessory loading. If the noise is from the tensioner, it will be present when the tensioner moves at high load, and will disappear when the tensioner stops moving at light load.

2. A short duration (approximately one second) light rumble that occurs immediately upon application of power to accelerate from a stop. The noise is most likely to occur under conditions of high accessory load. The rumble is caused by resonance of the belt span between the A/C compressor and crank pulley. Positive diagnosis of the rumble can be made by installing a non A/C belt, Part No. 10041195, that bypasses the compressor and eliminates the noise.

Both conditions are caused by variations in tensioner damping during initial operation:

o The clicking is due to a sticking condition that occurs once most of the grease has been displaced, but before the outer case has been "polished" by the damping band.

o The rumble is due to lower than normal damping while a corrosion preventive grease is being displaced from between the damping band and the outer case.

These conditions will dissipate with continued operation of the vehicle. Most occurrences should disappear within 200 miles. Experience has shown that the clicking noise disappears within this mileage range. The light rumble, in some instances, may take considerably more than 200 miles to dissipate. Neither condition has any adverse effect on system function or durability, and replacing parts with those presently available will not alleviate these conditions.

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.