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

TRANSMISSION APPLICATIONS: SUBJECT:

1989-90 K-TRUCK W/4L60 DRIVELINE RATTLE/VIBRATION W/ENGINE 4.3L UNDER LOAD, TCC APPLIED

TRANSMISSION MODELS: VEHICLE APPLICATIONS: 1989-90 K-TRUCK

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 60 kph (40 mph) and with the torque convert 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 60 kph (40 mph) (or higher) with TCC engaged - then stop 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.

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.