I have a 2001 F250 7.3 with ZF6 and manual transfer case. I was driving to work and after driving over a railroad track, a horrible grinding sound was happening and I had no power (like being in neutral). I put it in neutral and coasted to the side of the road, and it was not grinding while in neutral. I checked 1st,2nd and 3rd and all the gears grinded so I don't believe my transmission is the issue. I locked the hubs and put it in 4x4 and it still grinded and wouldn't move so I believe that would rule out the rear end exploding. I looked under the truck and i noticed the transfer case had started unbolting (but it was not separated) from the trans. This happened last year but it had completely unbolted itself but still drove "perfectly."

I believe its possible that while the transfer case was a little loose and mixed with the hitting of the rail road track, that maybe it bumped it into a position between neutral and 2wd. Is it possible that the transfer case grenaded itself? could I get lucky and its an easy fix? Am I completely wrong and it probably isn't the transfer case at all? Any input I would appreciate. Does anybody know the torque specs for the bolts connecting the tcase to the trans? clearly the 45ftlbs that I had read somewhere didn't hold up over the course of a year (and only about 5k miles).

EDIT:
For those that don't want to read through the whole chain:
When the transfer case came unbolted it started wearing the splines on the output shaft of the transmission and the input shaft of the transfercase. It then became loose without my knowledge and wore the splines even more to the point that the splines were rounded so badly that any slight amount of torque caused them to spin. This now requires a full tear down of the transmission and the transfer case. If you hear any unnecessary clunking like gear lash in the rear end or the slip joint clunk, make sure that your transfer case if fully tightened down as I thought my clunking was from the slip joint and rear diff. it was so much worse.

 

tighten it up and see if it goes

I would be taking it off and inspecting the splines.

 

Back in 2005 or 6, right after I bought my truck from the original owner, I was out on our first trip with it pulling the 5th wheel. Coming down off the top of Mt. Rainier in Washinton state, the truck dropped to neutral without any warning sounds whatsoever. It didn't take long for me to narrow it down to the transfer case quit on us and I had to find a tow truck.
It's an easy repair if you are confident with opening up the case. What happened on mine is the smaller of the two shift forks had the teeth ground completely away due to lack of lubrication while 2wd was engaged. The rebuild kit had a new input shaft with an oiling galley where the original one did not. Also some updated thrust bearings for the shift fork itself made out of metal instead of plastic.
Here's some pictures that I took of that repair.

Note the old shift fork with no teeth below the larger one on top

 

​​​​​​​are you meaning the splines on the input shaft from the external part of the case? or splitting it open and inspecting the splines on the insde?

 

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I have never opened a Tcase before but I have wrenched on enough stuff to feel that I can't mess it up too bad. If it is something that is internal, Ill probably just get a full rebuild kit for it. Are there things that aren't included in a rebuild kit that I should get like a case saver? or should I just replace whatever is broken along with any bearings/seals since I am already in it.

 

It's easy. Hardest part is getting the two halves separated after all the bolts are removed.

 

I have been looking all over for the same rebuild kit that I got when mine went out and cannot find one. None of them today have the smaller shift fork included that I can see.

 

Well that's a shame, I appreciate you looking though. is there anything I should be looking for specifically in a rebuild? I won't know what's wrong with mine until I split it, but any common wear components that some kits have that others don't?

 

My one and only experience with transfer case repair is the one I did on my own. Once I got it apart, and that was in 2005, it was pretty easy. They used so heavy duty silicome to glue the two halves together at the factory and it took and air chisle to get it apart. Stood it up on the input side and everything laid in there, super easy to reassemble. Just clean the mating surfaces down to bare metal and silicone it back together.

 

In case you need a reference for how it all works together:
https://www.ford-trucks.com/forums/1...e-curious.html

 

I finally got some time to do a little bit of investigative work. I tightened the case back up to the transmission and the grinding changed sounds but still happened. I confirmed that 2wd, 4wd, and 4 low all grind and the grinding sound speed is dependent on the input side as putting the truck in different gears changes the sound but it sounds the same in 4hi and 4 low. (silent in neutral). I dropped the rear drive shaft and with the truck in gear I can still spin the output shaft and all it does is spin (with some mild clunking like a ratchet). In 4wd, the output shaft and forward driveshaft still move together. I will be picking up some tools and materials today and try to drop it to investigate further what the issue is. I'm thinking as of now that it might be the shift fork or the retaining rings on the input shaft. I will update with my findings.

For anyone with a similar issue (very rare as I'm learning), some things that happened prior to this failure that could have lead to it as the 271 is a very robust transfer case
- transfer case completely separated from trans while driving (bolts rattled out)
- front axle u joint failed which then lead to the hub bearing to also fail ( probably drove 1k miles with ALOT of vibrations, stupid I know but it was my only vehicle at the time and I was working 7 days a week)
- I didn't abuse it like my old f150 on the dirt roads but I most likely drove it a bit harder on the dirt roads/two tracks of Michigan than most people would

 

Jeepers! I wish I would have seen this thread earlier. Thank you for taking us along it’s definitely helping me out.

I recently lost the range fork in mine and posted up about it. Six mounting bolts all rattled loose as well. Working on getting a parts list

 

I just read through your post and it seems we might have gotten very unlucky at the same time. you're a little ahead of me on disassembly but I have a feeling we might be having the same issues. do you know what lead up to the cause of yours? do you use 4x4 alot?

 

Not in my case. Mostly highway miles, pulling a 5th wheel RV in 2wd. I bought the truck at 49k miles from someone who owned an even bigger trailer than mine and then he went and bought a medium duty truck to pull his with because the 550 wasn't enough truck for his liking. The failure on mine was a design flaw that didn't provide enough oiling for the smaller fork and over time always ran dry which ate the contact areas away.

 

I think you’re right—dang the bad luck! Yes I use 4wd fairly often. I drive backroads exploring around Utah and Idaho as often as I can. Mine gave zero warning that it was on its way out it’s like it just popped into neutral and that’s all she wrote lol