How to identify the source of transfer case leak?

Truck is a 2015 Tacoma Off Road, Automatic, V6, 4x4.

I was crawling around under my truck yesterday and noticed weeping on my transfer case. Look, smells (and tastes) like gear oil, not ATF. I just changed driveline fluids a few thousand miles ago and did not notice any leaking at that time.

I'm pretty darn sure I didn't crack the housing or anything since I avoid the rocks at the mall.

How can I tell it is the transfer case vs input shaft seal vs output shaft seal vs something else?

The weep is on both ends of the transfer case, but worse at the front. Both weeping areas look near where the different parts of the housing bolt together.

Photo of worse spot at front of transfer case (looking from underneath from passenger side).

 

I know that UV dye exists that you can use with a UV light to tell where oil leaks are coming from - I used it with good success on my Miata to diagnose a leak. I suppose you could put some of that dye in the t-case and drive it a bit and see exactly where the leak is coming from.

 

I know it’s coming from the transfer case as it’s gear oil, not ATF.

So without disabling the vehicle in the street by pulling the exhaust, transfer case, cross member, and more, I’m trying to diagnose as much as I can first to ensure that I have parts on hand.

 

If there's gear oil coming from where the trans and t case mate, it's either the seal around the input shaft or the RTV around the cover.


IMO though, it's not worth the effort of dropping the transfer case just for that. Unless it becomes a full-fledged leak, I would just monitor and check the oil level periodically. I've swapped to an FJ transfer case recently so the labor involved is fresh in my mind. It wasn't a fun task.

 

Here's a pic of what I'm talking about. This cover goes over the input shaft to the transfer case and is sealed with RTV. It's the only possible source for a leak on that side.

Though as I write this, there's very clearly a seal right there as well.....so it could be that seal too.

 

Possibly a small amount of gear oil from the breather on top.
Filling the Tcase on an incline or filling past bottom of fill hole will do it.

 

And then driving fast... causing a lot of heat/expansion of the gear oil.

Thanks for the tip, I'll shove the boroscope camera to look around more on the top to see if that could be the issue.

 

That's what I was afraid of. Makes me wish there was a dipstick on the transfer case so I could keep an eye on it easier.

 

My tcase has a steady drip. It's the output seal for the front shaft. The drip becomes more noticeable after 4wd use, but I just check it every couple months and top it off if needed. Gear oil is so thick that it doesn't take much to look like a large seep or drip

 

On level ground if you open the fill plug, it's pretty easy to shine a flashlight in there and see where it's at. Although it's not ideal, it'll help you determine how much of an actual leak you have. If you're not getting any drips forming, then I would just check it every few weeks, then space the checks further out as needed. It may be so slow that you never have to fix it and just do routine oil changes.

 

ya, I have a similar weeping of gear oil going on somewhere on my transmission, been like that for a long time. Every time I check it though, even if it's been a few months, the oil level is always full (still dribbles out the fill plug when I go to check). Weird but as long as the level stays OK and it's not enough of a leak to be problematic I'm not going to worry about it.

 

I have weeps all over my truck and I just leave them be until they get worse. Not worth my time or effort when it's not harming anything and the fluid is staying full. If it gets worse, then I fix it.

 

I've even let this mentality delay my fixing of a leaky CV axle seal even though that one is considerably worse Its just easier to top it off lol.

One of these days I'll get around to attempting to fix it...again