PIP4885F

File in Section:
Service Bulletin
Bulletin No.:
Date:
PIP4885F
October, 2012
PRELIMINARY INFORMATION
Subject:
NQG 4WD Models With Noise, Vibration On Dry Pavement
Models:
2007-2013 Chevrolet Silverado
2007-2013 GMC Sierra
Equipped with manual shift transfer case NQG
The following diagnosis might be helpful if the vehicle exhibits the symptom(s) described in this PI.
Condition/Concern
Groan, growl, or moan coming from the vehicle when operating the vehicle in four wheel drive.
Recommendation/Instructions
Notice: Driving on clean, dry pavement in Four-Wheel Drive High or Four-Wheel Drive Low for an extended period
of time may cause premature wear on your vehicle’s power train. Do not drive on clean, dry pavement in Four-Wheel
Drive High or Four-Wheel Drive Low for extended periods of time. While driving on clean dry pavement and during
tight turns, you may experience vibration in the steering system. Section 9 of the vehicle owner’s manual entitled
Drive Systems has the exact statement printed above. For more information regarding driveline noises while in four
wheel drive refer to the latest version of technical service bulletin 01-04-18-001G.
The typical noise and vibration that is heard or felt is due to a combination of the transfer case chain link frequency,
engine firing frequency, tire circumference variation, and various other tolerances’ in the 4 wheel drive system. The
noise may seem to be increased, compared to vehicles with NQF/NQH/NP0 transfer cases due to the noise transfer
path of the shift lever sticking up through the floor. The noise may also be more noticeable in vehicles equipped with
vinyl flooring due to the vinyl flooring not having as much mass and noise dampening effect as carpet.
The first thing that should be done is to compare with a like vehicle. Ensure that interior content is the same i.e.: both
vehicles have carpet or vinyl flooring, same model and both do or do not have plow provisions RPO VYU. Further
diagnostics would include shifting the transfer case to 4WD high and then disconnecting the shift linkage from the
shift lever, at one of the points shown below, and reevaluating the vehicle operation. If the noise is greatly reduced or
eliminated then the shift lever is the transfer path for the noise and is an operating characteristic. No repairs are
recommended for this condition.
Note: Warranty analysis on nearly every bearing that has been replaced due to customer noise complaints on NQG
T-cases have been identified as no trouble found. If the noise heard while in 4wd inside the cab is eliminated by
linkage removal then do not disassemble the T-case. Engineering is in the process of validating a revised shift rod to
eliminate this noise and should be released 2013 time frame. Replacement of part number light duty: 15007687,
heavy duty: 25910465 will not change this noise. This pi will be updated when parts become available.
2789284
Warranty Information
For vehicles repaired under warranty use:
Labor Operation
Description
Labor Time
K4134
K4134 Transfer Case Control Rod
Replacement
Use Published Labor
Operation Time
On certain models, such as 3/4 and 1 ton vehicle, tire pressures can vary from front to rear based on the
manufacturer’s specifications which will further aggravate this condition. As an example the manufacturer’s
specification for tire pressures on a 2011 K2500 Silverado could be front: 65 PSI, rear: 80 PSI. The difference in tire
pressures affects the rolling tire circumference from front to rear which can increase driveline noise while in 4WD
which is an operating characteristic. For test purposes, drop the tire pressure in the rear to match the front. If the
noise is reduced or eliminated this confirms the difference in tire pressures from front to rear can affect the noise
when operated in 4WD. Set the rear tire pressure back to the manufacturer’s specification. For vehicles with the
same tire pressures front to rear, swap tires from an identically built vehicle that does not seem to exhibit the concern
and reevaluate both vehicles.
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.