97 expy 4x4 97 F-150 4x4 question

[SEA Capt.]

Hello all of you. This form has been of great help. I think this is my first post. The expy in question is a 97 4x4 with 5.4, XLT, 4 wheel load leveling, towing package and 3:73 gearing. The electric shift **** on the dash has the following options 2H, AWD, 4H, and 4L. With the expy on the rack in 2H I can spin the front wheels and they are engaged into the front diff. They turn the front drive shaft going into the transfer case. I find this strange. In AWD I see the same thing except the transfer case is in AWD mode this is normal. In 4H I also see the same thing except the transfer case is in 4H and in 4L the same except the transfer case is in 4L I fine all modes except 2H to be normal. On my 97 F-150 4x4 5.4 XLT with 3:55 gearing the electric shift **** on the dash has the following options 2H, 4H,and 4L when the truck is on the rack I can spin the front wheels and it IS NOT engaged into the front diff, the front drive shaft going into the transfer case doesn't turn. The way I understand this is when the dash **** on the truck is turned from 2H to 4H the front end is engaged via vacuum and the transfer case is also engaged thus 4 wheel drive. Using this logic when the expy is in 2H the front end should be disengaged and "free wheeling." When AWD is selected on the dash ****. The front end is engaged via vacuum and the transfer case is put into AWD mode. My question is why is the front end on the expy engaged all the time?? Is this normal and if so why? I thank Yall very much for your help.

[Wino]

its awd. the front end does not dissengage. like the f150 has a vac motor on the front end. awd is totaly diff sys. it uses wheel speed sensors. to engage tranfer case when needed.

[SEA Capt.]

Thanks Wino for your reply. I guess Iam having problems getting this straight in my head. Logic would tell me in 2H power comes from the engine thru the trans into the transfer case and to the rear diff only. There is no connection to the front drive shaft. Then why wouldn't a vacuum motor also disengage the front wheels from the front diff as on any other ford 4x4 in 2H? I guess this means that 2H isn't a complete 2H. The way I understand AWD is the front diff is always engaged and the transfer case is selected to AWD and engine power is divided between the front diff and the rear diff (as needed) via some sort of load sensing clutch packs. In my head when you switch from AWD to 2H the vacuum motor would disengage the front diff. The transfer case would move to 2H ( no power to the front drive shaft) My question is has FORD left out a step by not disengaging the front diff in 2H? Or do I have a problem with my Expy vacuum motor not disengaging the front diff in 2H Iam sure this is having an effect on my gas milage any help would be appreciated