EVALUATING FRONT DRIVELINE VIBRATION-FAULT TREE

Model and Year: 1990 L ASTRO VAN

THIS BULLETIN CANCELS AND SUPERSEDES DEALER SERVICE BULLETIN NO. 90-270-4A, DATED JUNE 1990. THE BULLETIN NO. ON THE FLOW CHART HAS BEEN CHANGED. ALL COPIES OF 90-270-4A SHOULD BE DISCARDED.

The purpose of the bulletin is to provide a logical approach to evaluating and diagnosing vibration and imbalance generated by the front propshaft, front axle or transfer case. The following diagnosis tree is designed to be used as a guide, and when properly utilized, can help isolate and identify causes of front driveline vibration.

Service Procedure:

Road test vehicle on a smooth, level road to verify customer concern. It is usually beneficial to have the customer present. Note speed and condition at which the disturbance is most noticeable. Follow arrows and perform the required service action. Never bypass or skip a step.

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.