This may be a dumb question but here it goes

I have a 4x4 dak with the nv231 part time transfer case. I have noticed that even on 2wd mode the front shaft is spinning. How does the truck manages to be in 2wd even if the front driveshaft is givin power to the front axle?

 

The disconnect occurs in the transfer case instead of having manual hubs or a CAD. If you put it in 2wd and get all 4 tires off the ground, you'll notice that front and rear driveshafts spin independently.

 

in other words, the front driveshaft is engaged to the axle 100% of the time, but to the transfer case only when you tell it to. A full time case (SEE: NP205 vs NP203 IIRC?), the disconnect occurs at the locking hub rather than the case.