SPEEDOMETER MALFUNCTION POSTAL VEHICLES(NEW GEAR)

Subject: MALFUNCTION OF THE SPEEDOMETER DRIVE GEAR, DRIVEN GEAR AND/OR SPEEDOMETER

Model and Year: 1987-91 S1 (LLV POST OFFICE VEHICLES)

TO: ALL CHEVROLET DEALERS

Some of the above postal vehicle chassis may experience a malfunction of the speedometer drive gear, driven gear, and/or speedometer adapter.

Effective January 24, 1990 with chassis' VIN 1GBCSl0E2M2901183, a new driven gear was installed in production. The new driven gear can be recognized visually as the following table illustrates.

GM PART COLOR # OF TEETH ------- ----- --------- NEW 3987920 BLUE 20

OLD 3860347 YELLOW 24

IMPORTANT: The new driven gear has eliminated the need for the speedometer adapter.

Recommended service procedures are outlined below:

Service Procedure #1

1 . Remove and discard speedometer adapter (GM Part # 368025).

2. Remove original speedometer driven gear and inspect for damaged teeth. If damaged, follow service procedure #2. If it is not damaged, replace the (yellow) 24 tooth driven gear with the (blue) 20 tooth driven gear (GM Part # 3987920).

For vehicles repaired under warranty use:

Labor Operation: #T1611

Labor Time: .3 hr.

FAILURE CODE: 92

NOTE: The above procedures do not apply to 1991 Postal Vehicles (LLV) with L38 engines. Effective August 13, 1990 with chassis VIN 1GBCS10A0M2912017, a new engine (L38) and rear axle ratio (GU6) were installed in production. As a result of the axle ratio change, a new driven gear is required. Use (gray) 22 tooth driven gear (GM Part Number 3987922) if vehicle is. equipped with L38 and GU6.

Service Procedure #2

1 . Remove and discard speedometer adapter.

2. Remove driveshaft and rear transmission extension housing.

3. Replace both speedometer drive and driven gear with:

Drive Gear (blue) GM Part 96040176 Driven Gear (blue) GM Part 3987920

NOTE:The above procedures do not apply to 1991 Postal Vehicles (LLV) with L38 engines. Effective August 13, 1990 with chassis VIN 1GBCS10A0M2912017, a new engine (L38) and rear axle ratio (GU6) were installed in production. As a result of the axle ratio change, a new driven gear is required. Use (gray) 22 tooth driven gear (GM Part Number 3987922) if vehicle is equipped with L38 and GU6.

Parts are currently available from GMSPO.

WARRANTY INFORMATION

For vehicles repaired under warranty use:

Labor Operation: #T1612

Labor Time: 1.0 hr.

FAILURE CODE: 92

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.