I don't know how the 2210D works, but on my 240D there is a shift fork that engages a drive gear for a drop-box that spins the front drive shaft. I've bent the engagement for the low range on one before, and if the designs are similar, that would do the same for yours. On my 186D I've bent the finger engagement as well.
You can kind of see
what it's like. On the 2000D, the linkage is parts 29 (shifter), 30 (linkage), 31 (bracket thing) and 28 (engagement for the shift fork). It's kind of a complicated arrangement, held together with roll pins and stuff. It's easily conceivable that something bent or broke in there.
When I bent the one on my 186D, it was just the bent finger part of piece number 6
here. You can see a picture of the
bent component after you scroll down through a lot of me blabbing.
The 186D is more straightforward than the 2000D/240D. There is a splined gear with three prongs that engages a corresponding gear on the driveshaft. The shift lever moves a pawl that slides the gear in or out along the splined shaft on the transmission output.
Your 2210D may have a different setup, but if it's similar to either of these, you should be able to figure out where the trouble is with only minor disassembly, if any.
As the others advised, you can isolate the area of the problem by jacking one side of the tractor up, and, in 4wd, trying to spin the lifted tire by hand. If the driveshaft spins, then it isn't engaging with the transmission of the tractor. If it doesn't spin, then the problem is from the driveshaft engagement to the pinion gear or closer to the tire.
Good luck!
