This is on my 2013 Jeep Wrangler. About a year ago, I had a local off-road shop install Yukon 4.56 gears so I wouldn't have to mess with getting the lash correct, and everything has been great. Over the last month or so, I have noticed that the yoke is wet and the driveshaft is wet also near the U joints. I will include some pictures in this post. I highly doubt it is the pinion seal, since it is dry around the seal. I have done pinion installs in the past, and I remember coating the splines in RTV and putting some RTV on the inside of the nut before installing it. Has anyone had this type of leak happen before? It almost seems like it is coming from inside the yoke itself, and spreading to the end of the driveshaft. It also has slung a little bit on my oil pan and upper driver side control arm. I am certain that its not a leak from above. Its definitely gear oil. Thanks.
***I should mention that the shop will look at it and warranty their work, but with this being my only vehicle, I would have to rent a car, etc. I am just looking for advice on if anyone has had this happen before and give me some ideas so I can just fix it myself.***

 

For the pinion flange to be such a mess, and look like that is what is flinging oil around, seems like it's traveling up through the splines primarily, exiting between where the flange and the DS mate. That looks like a pretty bad leak. I mean, for it to be wet is one thing. For it to be flinging oil over there on the pan is another.

You might remove those 4 bolts holding the DS to the pinion flange and get a look at the pinion nut. I'd bet it's a bit wet down in there.

 

Yeah that's what I will probably do over the weekend, remove the 4 bolts a drop the DS down a bit to see if its soaked with gear oil in there. I did check the fluid levels last week and they were all still perfect, so maybe its just a slow seep. I wwonder if the shop didn't use "enough" RTV (or any) on the splines/pinion nut. It was installed a year ago though, and just popped up in the last month or 2.

 

It’s interesting if it’s leaking from that nut on the pinion yoke. The smooth surface of the nut tightened against the yoke should create a tight enough seal to not allow oil to leak out. Also, some driveshaft install instructions don’t even call for rtv there when replacing the yoke. If it’s leaking from there, I would almost be willing to bet that the nut isn’t tight enough... just a thought.

If you do pull the nut and yoke, go ahead and get a new pinion seal as well as insurance. If you don’t need it then you can return it after the fact.

I recently replaced both front and rear yokes in my Jeep and replaced the seals just for good insurance. However, my seals were 6 years old.

Edit: I wouldn’t coat the splines with rtv. The threads of the nut on the threads of the yoke will create a seal. If you choose to use rtv on the back side of the nut then you’re creating a seal there too. In all the splines flanges I’ve installed on vehicles or aircraft, never have I used rtv on the splines, nor did any service manual call for that. You may be introducing a headache with that extra material there since it’s already somewhat of a close tolerance to get the yoke into the pinion gear end.

Also, with the differential looking wet, my bet is a leaking pinion seal. The seal may look dry or even be somewhat dry since the yoke will sling the oil away from it.

 

When driving forward, the direction of air would push the oil up the joint and yoke a little like the pics show.

 

I was just thinking #1, would have to be a huge leak to make it that far, and #2 if it was traveling up the joint it would get flung off on its way up rather than once at the flange. It seems odd enough oil is getting on that flange to then be flung off. Most leaky seals definitely make a mess at the pumpkin, so this one is indeed pretty interesting. Would be nice to have a go pro down there to see if it could pick up what's happening while in motion.

 

This weekend I plan on dropping the shaft and replacing the pinion seal "just in case" while I am in there, but as both of you are, I am sort of stumped on this one. I rarely post in any forum, unless it really makes me confused. I tried searching for a similar leak and I found 1 thread that had 2 vague replies and no solution at the end. When I pull the shaft this weekend I will at least be able to take a better look around. The plus side is that the fluid level is fine, and easy enough to check so I am not too worried about driving it for the rest of the week until the weekend.

 

If I had a GoPro, I would do that but I don't sadly. This is definitely confusing for sure, and you make some really good points there. I hate being stumped on something, when generally a seal leak will make a certain type of mess and this one is doing the opposite. Would you suggest RTV on the shaft and on the inside on the pinion nut? I know when i did a SYE on my last TJ, the instructions actually called for that...and this is almost the same type of design...a shaft and a nut with a yoke.