How Do I Keep Water From Entering the Rear Diff?

When the weep hole of the rear differential of a motorcycle, ATV or side-by-side has an unusually high level of rear diff oil in it, could it be that water has gotten mixed in with it?

Partzilla’s powersports expert John Talley hosts live Q&A sessions on our YouTube channel every Friday at 3pm Eastern. In this session, John was asked what could be replaced on an unspecified powersports machine to prevent water from entering the rear differential.

How to keep water out of rear diff

How to Prevent Water Intrusion in Rear Diff Oil Q&A

My rear diff oil was way above the weep hole. I assume it’s water. What would have to be replaced to stop water from getting into the rear end?

John Talley: It’s more than likely going to be your seals, and it’s going to have three. Two on the output shafts, one on the input shaft. But there’s one other thing you want to take into consideration. There should be a vent line that’s connected to the top of your differential, because as the fluid heats up, it expands and it pressurizes the differential itself. So it has to have a breather hose. And usually that just snakes up around the frame up high enough where hopefully it won’t pull in any water. Now, if you’re constantly running your machine in the water, that can be an issue. Because it’s going to act like a vacuum, especially once it gets hot. You throw a bunch of cold water on it and it’s got cold water at the end of that vent line, it’s going to pull it in. So just make sure that it has a vent line, and that it’s hooked up and routed properly. And if it’s not that, then it’s going to be one of your seals. So if you’re going to go ahead and replace one seal, you might as well do all three. At least I would while I’m in there.