Driveshaft operation question

[elrothir]

Hi all. I've got a 1998 Explorer 4x4 and have been getting pretty bad gas mileage. In trying to check it out, I ran across something with the driveshaft that I wasn't sure if it was supposed to work that way or not and thought/hoped someone here might know. I've got the car in Auto 4WD, so I think that means on dry pavement, it should basically be a rear-wheel drive vehicle. So, if I raise the front of the vehicle, the front tire should spin freely, right? If I do this, I notice that the driveshaft turns. This is with one side jacked up, so I don't have both front tires off the ground. Is this normal? I assumed that if the front wheels are not being 'powered' that the driveshaft shouldn't be engaged while in 2WD.
Thanks for any comments. I'm just thinking that if the front wheels are engaged, that might be a reason I'm getting such poor fuel economy.

 

[IZwack]

Unfortunately, the transfer case you have (which is the BW-4405) has some "drag" inside of it which causes the front driveshaft to rotate even in AUTO mode.

Also, with three wheels off the ground, yes you can rotate one wheel because the differntial in the axle allows that one wheel to rotate while the others remain still (this is how a vehicle makes a turn w/o burning its tires off). All that energy you're putting in to rotate the wheel/tire then goes to the driveshaft and into the transfer case.