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The NP249/NV249(New Process/New Venture):

Offered ZJ Grand Cherokee. Shift pattern: 4 HIGH - N - 4 LO. It is an aluminum case with chain drive and can use a center differential for its front/rear power split or lock the shafts together depending on mode. Under normal driving conditions most torque is applied to rear axles but when slippage is detected a georotor pump engages a disc clutch to route power to the front axles. When coupled with Jeeps Vari-Loc axles the entire system is called Quadra-Drive instead of Quadra-Trac II. Uses Dexron III ATF fluid.

This full time four wheel drive system offers a neutral and low range (2.72:1).4WD Full-time, Neutral & 4WD Low.

Quadra-Trac Features:

• Either Fulltime 4 Wheel High or Fulltime 4 Wheel Low ranges
• Split power to front & rear on demand as slip occurs
• Available on ZJ as Quadra-Trac; and WJ Grand Cherokee as Quadra-Trac II.

The NV 249 can be problematic and expensive to repair and is not one of the most popular transfer cases. Many times Jeepers prefer to replace this with either a NP242 or NP231

Viscous Coupling Failure:

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.

Since the VC is a sealed unit and does NOT operate using the fluids withing the transfer case, changing the fluids within the case will NOT fix the problem. 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 do 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