Transfer Case Driveline Growl at 1100-1200 RPM - keywords gear noise rattle

This PI is being superseded to add model years. Please discard PIP3156A.

The following diagnosis might be helpful if the vehicle exhibits the symptom(s) described in this PI.

1999 - 2007 4WD Silverado or Sierra Pickups with an automatic or manual transmission with the 261 (NP2) transfer case may experience a condition described as driveline growl or driveline rattle when the engine RPM is between 1100 and 1200 (approximately). Engine firing pulses transferring through the drivetrain, suspension and body are causing this condition.

Automatic Transmission 4L60E, 4L65E, 4L80E, 4L85E or LCT1000:

The condition of driveline growl/rattle can be present when engine RPM is between 1100 and 1200 (approximately) and the transmission is in 4th gear with TCC applied. The growl/rattle will go away by disabling the TCC with the Tech II scan tool or by applying the brake pedal. Also operating the vehicle in manual 3rd range will reduce and in some vehicles eliminate the growl rattle by raising engine RPM and reducing the overall load on the engine.

Manual Transmission NVG 3500 (MG5), NVG 4500 (MW3) or ZF6 (ML6):

The condition of driveline growl rattle can be present when engine RPM is between 1100 and 1200 (approximately) and the transmission is in 5th gear or 5th and 6th gear (ML6 equipped). The growl rattle can be greatly reduce to eliminated by driving the vehicle in 4th gear which increases the engine RPM and reduces the overall load on the engine

Using an Electronic Vibration Analyzer will help to determine if this noise is caused by either engine firing pulses or an out of balance condition. Any first order propshaft or engine vibrations should be corrected first as that would be an abnormal vibration. Third order (6 cylinder engines) and fourth order (8 cylinder engines) vibrations should be addressed as follows:

1999 - 2002 K1500 4.3 L35:

There is not a correction available for this application and there are no plans to release a correction.

1999 K1500 4.8 LR4, and 5.3 LM7:

TSB 99-07-30-010 should be followed. This TSB provides calibration updates which raise the MPH at which TCC applies.

2000 - 2002 K1500 4.8 LR4:

A revised TCC calibration has been released. This calibration will raise the minimum TCC apply speed approximately 10 mph and may reduce fuel economy up to 4 MPG. Customers should be advised of the potential fuel economy reduction before installation of this calibration. This calibration is available on TIS 2000. This calibration information is above and beyond the information provided in TSB 99-07-30-024.

2000 - 2002 K1500 5.3 LM7:

TSB 99-07-30-024 provides the latest calibration information for the 5.3 engine application. All 2001 and 2002 model years equipped with the 5.3 LM7 were produced with the latest calibration.

Manual Transmission NVG 3500 (MG5), NVG4500 (MW3), ZF6 (ML6) and Automatic Transmission 4L60E, 4L65E, 4L80E, 4L85E, LCT1000:

There is not a correction available for 2003 - 2007 trucks equipped with the transmissions as shown above. The condition is considered to be a design characteristic due to normal engine firing pulse transmitting through the drivetrain along with stackup tolerances in the transmission, transfer case and rear axle.

Note: An improvement for this concern is to place 12mm thick foam washers on the shift linkage between the ball studs and link arm. Part number for the washers are 12475651. For linkage illustration see Document ID # 825257. NO repairs other than these washers and calibrations listed above should be attempted as they will not successfully repair the concern.

Manual Transmission:

Operating the vehicle in 4th gear instead of 5th or 5th instead 6th (ML6 equipped) should improve this condition by raising the engine RPM and reducing the overall engine load.

Automatic Transmission:

Operating the vehicle in manual 3rd range will reduce and in some vehicles eliminate the growl rattle by raising engine RPM and reducing the overall engine load.

Please follow this diagnostic or repair process thoroughly and complete each step. If the condition exhibited is resolved without completing every step, the remaining steps do not need to be performed.