Shudder on Turns - keywords 136 236 246 4WD automatic AWD bind case contaminated NP4 NP8 vibration

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

The NVG 136 All Wheel Drive (AWD) Transfer Case and the 236 and 246 NVG Selectable Transfer Cases operating in the Auto Mode may exhibit a condition of a vibration/shudder during low speed turns such as a parking lot maneuver, up to approximately 5 MPH (8 km/h).

Note: Review TSB 99-04-21-005B (or any superseded version of this TSB) and change the Transfer Case fluid regardless of which category the vehicle falls into and even if the fluid was previously changed.

Drive the vehicle a minimum of 5 miles (8 km) to obtain operating temperature. Once at operating temperature drive the vehicle into a tight turn just short of the steering wheel lock/stop at a speed of less than 5 MPH (8 km/h). If the shudder is present perform the following diagnostics.

1. Remove the TCCM fuse and see if the condition is gone. If the condition is gone, then proceed to step 2. If the condition is unchanged, then skip to step 4.
2. If the condition is gone, begin swapping the wheels and tires from an identically built vehicle that does not exhibit the concern and re-evaluate the condition.
3. If removing the TCCM fuse corrects the condition and swapping tires from another identically built vehicle does not improve the concern, then proceed with the following.

NVG136

•	Inspect the TCCM for module part numbers and replace as required.

•	98-01 Oldsmobile Bravada - 15748801 (or any superseded number).

•	99-01 Chevrolet Astro, GMC Safari - 15748744 (or any superseded number).

NVG 236

•	Inspect the TCCM for module part number 15748800 (or any superseded number) and replace as required.

•	99 - 01 Chevrolet Blazer and S10, GMC Envoy Jimmy and Sonoma.

NVG 246

•	Inspection of the TCCM is not required.

•	99-02 Cadillac Escalade, Chevrolet Suburban Silverado Tahoe, GMC Sierra Yukon XL Yukon.

4. If the shudder was not eliminated by removing the ATC/TCCM fuse, remove the encoder motor from the transfer case and test drive the vehicle again at operating temperature.

•	If the shudder is eliminated, replace the encoder motor.

•	If the shudder was not eliminated, reinstall the encoder motor and fuse. Verify the shudder is still present and remove the front prop shaft.

•

Drive the vehicle at operating temperature with the front prop shaft removed, if the condition is still present and the vehicle is equipped with a G80 locking differential . The axle fluid should changed and driven in several left and right hand circles then driven at least 50 miles (80 kms) under normal driving to remove any glazing from differential clutches.

5. If the above steps have not eliminated the shudder condition, the transfer case clutch pack needs re-shimmed. To perform the shimming procedure use Service Information (eSI).

Note: When performing the shim selection process eSI indicates to select a shim(s) + or - .004 in. (0.10 mm). On a 136 Transfer Case, the shim(s) should be - 0.004 in. (0.10 mm) for best performance

Please follow this diagnosis 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.