Astro Van AWD V6-4.3L VIN X (2003)
Fluid - Transfer Case: Customer Interest
Drivetrain - Transfer Case Shudder On Tight Turns
Bulletin No.: 99-04-21-005E
Date: November 28, 2005
TECHNICAL
Subject:
Transfer Case Shudder (Flush and Replace Transfer Case Fluid)
Models:
1999-2005 Chevrolet Astro (AWD)
1999-2005 GMC Safari (AWD)
1999-2001 Oldsmobile Bravada
with All-Wheel Drive (NV 136) Transfer Case (RPO NP4)
Supercede:
This bulletin is being revised to update the correction information. Please discard Corporate Bulletin Number 99-04-21-005D (Section 04 -
Driveline/Axle).
Condition
Some customers may comment on a vibration (shudder) during tight turning maneuvers on dry pavement at vehicle speeds less than 8 km/h (5 mph).
Cause
This condition may be caused by a slip-stick of the clutch plates in the transfer case clutch pack. On 1999 to 2002 models, the preload that is designed
into the clutch pack may contribute to the condition. In addition, contamination of the fluid may interfere with the friction modifiers.
Correction
Flush and replace the transfer case fluid on affected vehicles using the following procedure and the part number listed below.
Perform the following diagnosis prior to flushing and replacing the transfer case fluid in order to properly identify the shudder.
Diagnosis
1.
Verify the shudder in the vehicle. The vehicle needs to be at operating temperature (driven at least 8 km (5 mi) for proper diagnosis. After the
vehicle is at operating temperature, drive in a tight circle just short of steering wheel lock, at a speed less than 8 km/h (5 mph) in order to identify
the shudder.
2.
Identify what rear axle type the vehicle has.
^
If the vehicle has a standard rear axle, then proceed to step 3.
^
If the vehicle has a locking rear axle, remove the front propeller shaft. Refer to the Propeller Shaft subsection in the Service Manual. Drive the
vehicle as outlined in step 1.
^
If the shudder goes away, install the front propeller shaft and proceed to step 3. Refer to the Propeller Shaft subsection in the Service Manual.
^
If the shudder does not go away, the locking rear axle may be the cause. Evaluate the condition using diagnostic information in the appropriate
Service Manual.
^
Install the front propeller shaft. Refer to the Propeller Shaft subsection in the Service Manual.
3.
Flush the transfer case with the blue colored fluid (AUTO-TRAK II) using the procedure and part number listed below. Perform the flush
procedure even if the transfer case contains the blue colored AUTO-TRAK II fluid in order to remove any possible contaminants. The
AUTO-TRAK II fluid contains an improved friction modifier that should correct the slip-stick condition. Refer to the Transfer Case subsection in
the Service Manual for information on draining and filling the transfer case.
Flush Procedure
