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1997 - 2000 Corvette: Service Bulletin: Intermittent Accessory Drive Rumble During Garage Shift

Subject: Intermittent Accessory Drive Rumble Noise During Garage Shift and/or During Parking Lot Maneuvers (Install New Generator with Decoupler Pulley and Accessory Drive Tensioner)
Source: Chevrolet Dealer Technical Service Bulletin
Number: 99-06-04-029A

Models: 1997-2000 Chevrolet Corvette with 5.7 L Engine (VIN G -- RPO LS1) and 4L60-E Automatic Transmission (RPO M30)

This bulletin is being revised to update the correction procedure. Please discard Corporate Bulletin Number 99-06-04-029 (Section 06 -- Engine).

Condition: Some customers may comment on an intermittent accessory drive rumble noise when performing a garage shift and/or during parking lot maneuvers, such as turning the steering wheel to the lock position. This noise may also occur when turning on the air conditioning at idle conditions.

Cause:  Engine idle speed may drop below 600 RPM while performing a garage shift, turning the steering wheel to the lock position, or turning on the air conditioning. This noise may be amplified by a large rate of change in engine RPM. This condition can also be aggravated by different low engine RPM driving conditions.

Correction: A new Generator with Decoupler Pulley and reduced damping Accessory Drive Tensioner was implemented for all Corvettes with automatic transmissions at 2001 SOP (Start Of Production). The generator with decoupler pulley is used only on Corvettes equipped with an automatic transmission. The reduced damping accessory drive tensioner is used on all 2001 Corvettes.

The new decoupler pulley generator and tensioner assembly should be used to service 1997-2000 Corvettes with automatic transmissions that exhibit the idle rumble noise. Refer to the Engine Electrical and Mechanical sub-sections of Engine in the Service Manual for generator and tensioner replacement

Parts Information:

Part Number




Generator Assembly w/Decoupler Pulley



Accessory Drive Tensioner


Warranty Information:

For vehicles repaired under warranty, use:

Labor Operation


Labor Time


Generator Assembly - Replace

Use Published Labor Time



Tensioner, Accessory Drive - Replace

Use Published Labor Time


GM bulletins are intended for use by professional technicians, NOT a "do-it-yourselfer". They are written to inform these 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 your GM dealer for information on whether your vehicle may benefit from the information.


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