NP249J Viscous Coupler and seal kit 1992-On with full time 4X4. This package comes with the a viscous coupling and all the seals you will need to seal your transfer case back up. You can identify this transfer case by the tag on the back of the rear case half that says NP249J . The main symptom of Viscous Coupling (VC) failure include chirping or spinning of the front tires during sharp, slow turns on pavement where you would not expect any chirping. The VC is a sealed unit and does NOT operate using the fluids within the transfer case so changing the fluids within the case will NOT fix any problems with the VC. Changing the fluids will, however, aid in keeping the rest of the transfer case in good shape. Heat buildup inside the VC is both what can destroy it and what operates it. Whenever the speed of the front and rear drive shafts does not match perfectly, the plates inside the VC are slipping in the internal fluids, creating heat. Minimizing that heat is the key to long life. One common tool to diagnose failure is to drive the vehicle in tight figure 8's. If it hops or chirps, there is a high probability that the Viscous is in need of replacement.