DRIVELINE VIBRATE/GEAR RATTLE WITH TCC APPLIED (NEW ASSY.)

SUBJECT: DRIVELINE VIBRATION AND/OR GEAR RATTLE WITH TCC APPLIED (INSTALL NEW TORQUE CONVERTER ASSEMBLY)

MODELS: 1992-93 S/T TRUCKS

CONDITION:

--------- Some 1992-93 S and T trucks equipped with 4.3 liter (L35) engine and the HYDRA-MATIC 4L60 or 4L60-E transmission built before Julian Date 223 (August 10, 1992) may exhibit a rattle or driveline vibration with the torque converter clutch (TCC) applied at low engine speeds (1000-2000 RPM).

CAUSE:

----- The rattle or driveline vibration may be due to the stiffness of the spring rate of the damper springs in the torque converter.

CORRECTION:

---------- Install a new torque converter assembly which improves the rattle in the 1000-2000 RPM operating range.

DIAGNOSIS INFORMATION:

The rattle or driveline vibration condition only occurs in fourth gear with TCC applied. Use the following procedure to determine if the vehicle has this condition:

1. Accelerate the vehicle to achieve fourth gear and confirm that TCC is applied.

2. Maintain low engine speed (1000-2000 RPM) then crowd the throttle to above 25 percent TPS to induce the rattle or driveline vibration.

NOTE: Excessive throttle input will disengage the TCC. Applying the brake will also disengage the TCC.

SERVICE PARTS INFORMATION:

PART NUMBER DESCRIPTION ------ ----------- 8688904 Torque Converter Assembly (DBAF)

Parts are expected to be available on October 26, 1992. In case of limited inventory, parts will be placed on 400 control to waive VIP surcharges. Only verifiable emergency VIP orders will be accepted. GMSPO will make every effort to obtain parts. However, the part will be shipped premium transportation at dealer's expense and all other order types will be placed on back order until the 400 control is removed.

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.