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

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

MODEL and YEAR: 1992-93 S/T TRUCKS WITH 4.3L (L35) ENGINE AND 4L60 OR 4L60-E AUTOMATIC TRANSMISSION

TRANSMISSION APPLICATIONS:

1992 HYDRA-MATIC 4L60 (MD8) 1993 HYDRA-MATIC 4L60-E (M30)

TRANSMISSION MODELS:

2TAM, 2TBM, 3TAD, 3TBD

SUBJECT: ------- Driveline Vibration and/or Gear Rattle with TCC Applied

VEHICLE APPLICATIONS:

S/T Trucks with L35

Condition:

--------- Some 1992-1993 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 corrects 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 Name Part Number --------- ----------- Torque Converter Assembly (DBAF) 8688904

Parts are currently available from GMSPO.

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.