Re: 4 Wheel Drive
The 4x4 for quadra trac or quadra drive is taken care of by the same T-case, the NV247. The progressive coupling inside the T-case will be automatically activated if there is a speed difference between the front and rear propeller shaft, transferring torque to the front wheels. Did you try 4Lo, to see if 4x4 is working then? Did you check the T-case fluid level and color? The progressive coupler could be shot.
The only difference between quadra trac and quadra drive are the varilock differentials (quadra trac has open diffs). They will lock both wheels on the same axle, when a speed difference between those 2 wheels exists. With quadra drive you could (worst case) have 3 wheels spinning free and only one wheel which could transfer all the torque to the ground. With quadra trac or both rear wheels, or both front wheels will have to transfer the torque. If for example 1 rear wheel slips, the other side wheel could stand completely still without any torque transfer.