Any idea what causes this?

Only 15 years of operating a company shop!! I have always stressed during a post-trip (or any stop and exit of the cab) to also use you nose as well, if you smell hot gear oil, engine oil, tranny fluid, etc. It has to come from somewhere. Identifying it early will save time and money. At least know where it’s coming from so you can watch it and keep it from the extreme failure.

As others have mentioned, water shouldn’t just show up in a differential. Humidity and sitting on the back row a long time can cause it naturally. But, if you flushed and changed the fluid in the last 6 months then that’s not enough time for “natural” build up). If you already had this problem either you have water entering the housing through a crack, other failure, or it wasn’t properly cleaned when it was done ( it is time and resource consuming to do it without pulling the diff). So you DO need to check for cracks in your housing and/or a plugged vent/hose.

But if it was a young mechanic doing the work 6 months ago, it’s more than likely he was doing just what he was told and didn’t know what he needed to look for when he was doing it or how to do it properly (there are some old guys still in the game that are to proud to ask or to lazy to do it right as well!!!). So check for places for water to intrude. If there’s none, find a better mechanic or put the fear of god in the one you have and make them do it right.

Losing a wheel end is unacceptable in today’s world. You’ve had it happen twice.
I’m not saying there aren’t people in my own company that can’t meet that standard, but I do and my shop does..... and my drivers don’t like me when they prove me wrong in this instance. It usually involves a good cop/bad cop scenario where there’s a lot of yelling, apologizing, blaming, hooting & hollering, and the eventual “think of the others on the road”.

This is a serious issue, get to the bottom of it, get it fixed, and do what you can to keep it from happening again. (Which is what your doing here)

 

Now that would be interesting. I didnt catch that part.

 

I know I am getting here late. But..is it same person that installed the bearings? They need to be "set" properly. When you check your hub oil level..most if not all the time moisture will create a milky foam. A small amount on the plug won't do that. Not bragging but I have installed many many wheel bearings and never had a failure.(yet lol) It would take a lot of moisture to cause what you have experienced. Have had cracked rearend housings that seeped oil. Welded the crack..it never let in water. Or at least not enough to take out any bearings. Last..do you park at home, or a secure area? Mayby someone is screwing with you equipment?