DRIVELINE RATTLE/VIBRATION W/ENG. UNDER LOAD: TCC APPLIED

Subject: DRIVELINE RATTLENIBRATION WITH ENGINE UNDER LOAD, TCC APPLIED

Model and Year: 1989-90 K TRUCK WITH 4L60 (THM 700-R4) AUTOMATIC TRANSMISSION AND 4.3L (VIN CODE Z) ENGINE

TO: ALL CHEVROLET DEALERS

BULLETIN COVERS;

Service and parts information for HYDRA-MATIC 4L60 (THM 700-R4) transmissions which may produce a driveline vibration or rattle with the engine under load at approximately 40 mph and with the torque converter clutch (TCC) applied. This condition may occur in the following HYDRA-MATIC 4L60 (THM 700-R4) models that are used with 4.3L LB4 engines: 9MRM, OKAM

To reduce this condition, a torque converter containing damper springs with a higher spring rate and torque capacity has been released for production and service.

DATE OF PRODUCTION CHANGE:

The following information shows the transmissions which are in vehicles that may exhibit, this condition:

Model Date of Production

9MRM All OKAM All

DIAGNOSIS INFORMATION:

The following diagnosis information will help you determine if a vehicle has the driveline noise or rattle condition:

- Gear Range: Drive 4 (overdrive) with TCC engaged

- Vehicle Speed: Beginning at approximately 40 mph (or higher) with TCC engaged - then step into the throttle slightly.

- Conditions: 1. Noise, vibration or rattle 2. Low frequency noise that builds up until the truck bed rattles 3. Low growl or driveline grumble

Road grades or trailer loads may cause the conditions to be more prominent or extended. The conditions should disappear when the TCC is disengaged. Brake can be lightly applied to disengage the TCC for testing.

SERVICE INFORMATION:

Converters replaced under this bulletin should be charged to Labor Code T8145. Do not use Labor Code K7020 as would normally be used tor converter replacements. SERVICE PARTS INFORMATION:

Part Number Description 8681952 Converter Asm. Pkg. 298mm (DEAF)

Parts are expected to be available on August 27, 1990. Until then normal part orders will not be accepted by GMSPO. Only verifiable emergency VIP orders will be accepted. SPO will make every effort to obtain parts. All parts will be placed on 400 control to waive VIP surcharges. However, the part will be shipped premium transportation at dealer's expense. All other order types will be cancelled as incorrectly ordered while the 400 control is in place.

SERVICE MANUAL REFERENCE:

Information on converter assembly removal and installation is covered in the Automatic Transmission Unit Repair section of the appropriate Service Manual.

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.