Mystery! Rear Differential gained fluid?

[cowboywildbill]

I was pulling maintance on our 3500 today and when I removed the rear diff fill plug to check the level, synthetic gear oil started dribbling out of the fill plug hole. It drained until about 30 cc's came out. I got a soda cup and pulled the lower drain plug just enough to drain about another 1/8 of a pint out and tightened it back up. Then I checked the fill level and it was down about an 1/8 inch from the bottom of the fill hole,this is where it was when I originally filled it. The fluid from the bottom was a little "darker" than the fluid that came from the top fill plug "green". It wasn't foamy and the truck was sitting for a couple days and not moved before I did the check. The truck was level when I filled it a year ago and level this time when I checked it. The truck has not been in any high water or situation that would allow any thing to get into the rear housing. The seals are good and no leaks any where, including wheel bearing seals or rear axel seals. I wonder how I gained the extra volume? Anybody have any idea's or simular experience? I'm scatching my head.

[redrider#1]

Since you say the truck was level both times you checked it, the only variable I can come up with is the truck sitting for 2 days this time. There may have been some residual oil in the left and right tubes of the housing and in the wheel bearings when you did your oil change a year ago that now has slowly drained into the main housing over the course of the truck sitting 2 days.

[cowboywildbill]

That might be it, My front diff was the same way. I guess the darker fluid at the bottom of the rear is normal and it wasn't milky. I might just change it again and make sure no metal comes out , I didn't pull the drain plug completley out when I checked it, just held it enough to let it drain a littleto bring the level down and have a look at the fluid. So I didn't get to see if there were any shavings on the plug. Thanks for the reply.