2000 Prairie 400 4x4. 6000 miles, one owner, me.

Somehow the rear differential is injesting a little water when the water level is above the flooboards.

It is not leaking any diff oil.
The breather hose is clear and routed properly to the battery area.

Upon inspection I saw my speedo pickup sensor housing was cracked. I removed, cleaned and rtv sealed it. Have not had it in water to test if that was source of water leak. Kinda doubt it since it is an electrical sensor connected to a gear shaft and there didnt appear to be any evidence of water entering there. The oring looked good.

The swingarm to engine rubber boot looked good near as I could tell. I snugged up the 2 clamps a smidge but they were not loose.

The brake side drain bolt was removed and no water came out. The multi-lip rubber seal for the brake housing was cleaned and lubricated with grease last year.

The diff cover axle seal was replaced years ago and looks good.
Other possible sources of injestion could be where the diff bolts to swingarm for the driveshaft, or where the right side of diff bolts to swingarm.

Anyone had a similar problem and what did you find?

 

Diffs seem to get water in the oil for no apparent reason. I am rebuilding a Suzuki 400 KQ front at the moment and the oil has water in it. OK, pinion seal has gone but it wasn't leaking much oil from it. They have concertina breathers, so water shouldn't get in there.

Are you sure the breather is ending downwards so rain can't get in and that it isn't split somewhere?

 

Yes, breather tube faces down. It is under seat and machine is always stored in garage.

My theory years ago was that water was being sucked into diff thru the housing cover axle seal when the diff is cooled quickly by water, causing water to be pulled thru a good seal. I rationalized that the oil seal was meant to keep oil in, not water out. I just avoided deep water for years. I have only ridden it probably 400 miles in the last 8 years. My ride last week the diff was cool because the stream crossing was done after riding only about 100 yards of slow riding

2008 June 3754 miles diff cover axle oil seal replaced. 454 hours
2026 May 5972 miles, 738 hours

I will inspect the hose closer to ensure it is open, not cracked and exits downward with little chance of sucking in water.