CHUGGLE/SHUDDER AT 45-55MPH W/ TCC APPLIED-REPL TORQUE CONV

TRANSMISSION APPLICATIONS: SUBJECT: ------------------------- ------- 1992 HYDRA-MATIC 4L60 Chuggle/Shudder at 70-90 kph (45-55 mph) With TCC Applied (Replace Torque Converter)

TRANSAXLE MODELS: VEHICLE APPLICATIONS: ---------------- -------------------- 2DDM Buick Roadmaster With 5.7L (LO5)

THIS BULLETIN IS BEING REVISED TO CHANGE THE PART NUMBER FOR THE TORQUE CONVERTER ASSEMBLY.

CONDITION:

--------- Some 1992 Buick Roadmasters with 5.7 litre engines (especially those with 2.56 rear axle ratios) may have a chuggle or shudder at 70-90 kph (45-55 mph) with the torque converter clutch (TCC) applied. The condition becomes more noticeable under load.

CAUSE:

----- Damper springs in the torque converter may become completely compressed (bottom out) during certain engine operating conditions. This allows firing pulse vibrations from the engine to be transmitted to the vehicle in the form of a chuggle or shudder.

CORRECTION:

---------- Install a new torque converter assembly which has a 380 N.m (280 ft-lb) damper. The previous torque converter contained a 298 N.m (220 ft-lb) damper.

DIAGNOSIS INFORMATION:

The chuggle/shudder condition only occurs in fourth gear with the TCC applied. Use the following procedure to determine if the vehicle has this condition:

1. Accelerate the vehicle to above 70 kph (44 mph) and confirm that TCC is applied.

2. Allow vehicle to slow to approximately 69 kph (43 mph), and immediately crowd the throttle to induce the chuggle.

Excessive throttle input will disengage the TCC. If the chuggle was present, disengaging the TCC will eliminate the condition. Applying the brake will also disengage the TCC.

The PCM will unlock the TCC as the vehicle slows through 68 kph (42 mph).

TCC should not apply below approximately 68 kph (42 mph).

DATE OF PRODUCTION CHANGE:

HYDRA-MATIC 4L60 transmissions built starting December 16, 1991 (Julian Date 350) contain the new torque converter with the 280 ft-lb damper. The transmissions that contain the new torque converters also have a new model code designation 2BRM.

In mid-February, 1992, the 2DDM model was changed to a 2BRM. Any 2BRM model already contains the new torque converter.

SERVICE INFORMATION:

The new torque converter can be used to service the 2DDM models of the HYDRA-MATIC 4L60 transmission if a chuggle/shudder condition is present. This torque converter will not fix a boom or vibration condition that may be related to other vehicle systems.

Before ordering a new converter, check to see if the current converter has a blue "DGAF" stamped on it. This would indicate that the converter has already been changed.

SERVICE PARTS INFORMATION:

Part Name Part Number --------- ----------- Torque Converter Assembly (DGAF) 8650935

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.