Hello, I found this site a while back and have pulled some great information from it. Ive browsed for a bit and cant find anything on an issue I am having, I hope someone has delt with something similar and could explain what is causing my current issue:
Truck info 2001 Ford F250 7.3 4x4 with a manual transfer case and an automatic transmission.

I acquired the truck a year or so ago from a family member when he was going to trade it into a dealership for pennies. The guy I got it from is notorious for not doing proper maintenance to it so ive been busy catching up on things. I had the truck in 4wd at the lease the other day due to the road being muddy. When I got back to the main road I turned it back into 2wd, unlocked the hubs and took off. When I took off I noticed a noise coming from what I assumed was a front wheel bearing. I swapped the front wheel hub and the noise was still there. I did some digging and noticed the front drive shaft was spinning as if it was locked in. I did some more reading and jacked up the front of the truck and spun both wheels freely without the driveshaft moving. I assume this eliminates the possibility of a stuck wheel hub. More research and was convinced that the T case was locked in 4 or was about to give up the ghost so I did some digging into that and logic would say that if the T case was the issue, I would not be able to spin the driveshaft by hand due to it being locked. I ran that test a few minutes ago and the driveshaft spun as it should. This would lead me to believe that the T case is not the issue and I cant figure out what to try next. Any suggestions would be much appreciated. I am going to condense story time below so maybe someone just skimming could provide some insight...

Problem:
Front drive shaft seems to be engaged when truck is in 2wd.
Both front wheels spin freely when jacked up without front drive shaft moving
Front drive shaft spins by hand
Loud roaring noise coming from front driveline when truck is being driven

 

If the front drive shaft spins by hand when TC in 2wd, the front drive is free..

If the front is howling and the DL does not spin when you spin the wheels by hand, you need to check the diff fluid, and then the condition of the internals..

 

I do need to look into that again I guess, I just dropped the fluid cleaned the case and put it back together and refilled the lube while I was working on the front wheel bearing. I didn't see anything crazy and only had minor normal metal shavings as I expected to find. Do the internals rotate full time? I was under the impression that if the 4wd was disengaged the internals would all be disengaged.

 

The only way the drive wont spin is if you have vacuum hubs..

 

If you can spin the front driveshaft while in 2WD, then your transfer case is partially OK. Shift into 4H and make sure it locks correctly.

If you can spin the wheels freely in 2WD, then your front locking hubs are releasing correctly.

A very slight amount of drag is normal while in 2WD, which will spin the front driveshaft while in 2WD. Servicing the locking hubs will cut down on the drag, but never eliminate it.

When you say you replaced the hubs, are you talking about the lockout hubs, or the hubs with the unit bearings?

What do the stub axle U-joints look like?

 

If you can rotate the front DS while it sits in 2wd the T case isounds fine. You will/can get a rotating ds from OIL drag in some T cases,, cant say on ours, never looked. If you can jack a wheel up ,make sure the hub is free, and spin the wheel without that inner U joint/axle spinning your hubs are OK as well. You might have in inner axle needle bearing that's wasted on the other side. Its not that uncommon really. ..

 

I replaced the hub unit with the wheel bearings. I had the front axle shaft out on one side to check the u joints, that one seemed to be in working order. They were replaced at some point so I just shot some grease into them and stuck it back together.

 

Also, don’t overlook the brakes as a source of the noise.