About a week ago I noticed a slight new noise that sounded like a front wheel bearing starting to make noise. It grew a little louder over a few days, until, about three days ago, it suddenly sounded a lot louder and was harder to determine as to location. I knew something was clearly wrong, so I jacked the truck up and checked the front wheels. Everything was fine.
I had my friend sit in the truck and bring it up to about 15 miles an hour when the whine/howl was very clear. I climbed underneath and tracked the sound to the area just in front of the transfer case and immediately under the 4x4 and gear shift levers. I checked the transmission fluid level and the actual transfer case fluid levels and they seemed fine.
I then removed the square side plate to the passenger side of the housing just under the shift levers, and a tiny amount of oil dripped out and a little water. Above this square plate is what appears to be a typical drain/filler plug, but, when I removed it, it had a spring just inside which used the plug bolt for depression. I also noticed some wear on the front of the teeth of the most front gear behind that square plate.
My questions are:
Shouldn't there be a lot of oil bathing the gears behind that square plate?
What is that area of the drive train called? It seems to be behind the transmission and in front of the transfer case?
If it should have more oil in it, what is the proper filler plug location; is it the plug immediately above the square plate with the spring? And what is the purpose of that spring?
Is the wear on the teeth bad enough to be concerned with?