I noticed a small puddle of oil on my shop floor yesterday. It turned out to be rear differential oil. It was coming from the breather tube where it makes a bend before going on up to the bladder. There was not much oil on the tube or on the floor. I removed the diff. fill plug and I could not touch the oil in the housing at all. My diff. does not have a seperate level plug below the fill plug like the book shows. I took it back to the dealer and he put a new breather hose with a larger bladder on it from a Prowler. He said it was a design change they came out with later. He refilled the diff. and it took a lot. He would not fill the diff. to the bottom of the fill plug. He just filled it to about where he thought the level plug would be if it had one. My contention is that the diff. was never full because there was not enough oil anywhere on the underside parts of the machine to justify putting that much oil back in. What do you guys think? The machine only has 10 miles on it.

 

I would obviously suggest getting a service manual for your ride, but in most all cases, the fluid level in a rear diff is supposed to be at the bottom of the threads of the bolt that you removed. It's supposed to be pretty full. It's that way in cars/trucks or atvs.
I had an issue with my Yamaha...the seal on the rear shaft drive was allowing water into the rear diff. Result, excess was coming out the breather tube. Problem fixed, but my manual suggest fluid to the brim basically. I would say yours should be that way also.

 

The only reason I questioned where the oil should be was that the front gear has a level check bolt on it about an inch down from the fill. Some of the later 07's have that also. I checked with ArcticChat and found out that they it works better to have the level about an inch down that is why they put the level bolt on the later ones. Every car, truck or motorcycle that I have ever serviced the level is usually the bottom of the fill plug unless there is a separate level plug.

 

My dealer, which sells Kaw, Yam, Can-am, Suzuki, and Honda confirmed to me yesterday that all of the makes listed here all have the fluid to the bottom of the bolt.

 

The dealer didn't fill up the diff because cat diffs run hot. The diff oil expands as it heats, and you need to allow room for the expansion. Most run half full anyway. Any more and the pressure plus the motion of the oil will blow it out of the breather tube. It took more because there is oil in the bladder too. The diff gearset pushes the oil into the bladder where its cooled, then the cooled oil is pushed back into the diff.

In theory it works well, as long as you don't overfill the diff.

Put a real clamp on that breather tube, and route where it won't get wet; or water will come right down the tube into the diff and pollute the oil. And you will have to change the oil.

Mudders like to extend the breather tubes for the front and rear diffs and the carb and gas tank and run them up underneath the handlebars to the highest point on the machine.