Overfilled Transfer cases..

[Colt45ws]

I encounter a surprisingly large number of overfilled transfer cases. Im not talking about a trickle, either; Im talking about you pull the fill plug and it starts gluging because the level is higher than the top of the fill plug. Whats interesting is they are also almost always leaking from the rear output seal as well which you would think equals a possible low fluid condition. I mean, if you see a diff leaking its going to be low unless the owner is aware and keeps it full. No, these units seem to manage to be leaking fluid like a Detroit diesel yet be overfull. Its so common that when I see a leaking transfer case, I EXPECT to drain the fluid out to a more reasonable level rather than needing to fill it.
I have not figured out why this is, though I have a few pet theories.
1. Wizards
2. People are filling them at really odd angles (truck tipped on the nose?)
3. Its bleeding in from the transmission somehow.
The third makes the most sense to me. Its the only logical explanation, but I dont know the mechanism of how that would work. As far as I know, the rear output seal (if it was a 2WD trans) is just splash lubed, usually. I dont know why it would be any different with a t-case adapter. But, I sure Im missing something and Im way of base here.
Any other possible ideas?

 

[Michaelbgone]

I would imagine that it would likely be the case of the factory fill. I have heard from time to time of manufacturing processes that fill components while still on the component line, meaning it has not been installed/horizontal at the time of fill. The other could be fluid expansion, were the TC's cool when you checked them? Factory overfill was a common occurrence on Honda Civic manual transmissions. Other than that I can't imagine why or even how they would/could be overfilled, but it happens.

 

[Roadkingnc]

It is migrating from the trans to the transfer case. I have seen it many times, the transmission output shaft seal has failed

 

[JTK]

There must be not enough fluid movement in them to cause oil to come out the vent line?

That's bad because the next path of least resistance would be to blow out the seals on the T-case. Apparently those over-full ones aren't too sensitive.

Joel

 

[Trav]

Depending on the make and model the seal between the transmission and the transfer car can leak ATF into the transfer case.It will not backwash in the transmission just overfill the transfer case.

Almost like a leaking rear tranny seal if you will but instead of the ground it goes into the T case.
Thermal expansion is another possibility.

 

[Chris142]

Originally Posted By: Roadkingnc
It is migrating from the trans to the transfer case. I have seen it many times, the transmission output shaft seal has failed
x2. Verycommon on the "S" series GM trucks. Our last shop truck was so bad that we had to drain the transfercase every 4k.

If we didn't drain it then it would somehow suck atf into the vacuum lines(it had a vacuum operated TC), make lots of smoke and start running out of the HVAC controls.