I just changed my oil yesterday and decided to check the fluid level in my rear diff, i just replaced the fliud in the rear diff about 5500 KMs ago when i checked it its black with a metallic tinge to it, does this mean i got water into it or is something burning up? or do i need to take the diff cover off and clean? i dont know but the fluid in the front diff which hasnt been changed since new still looks golden , i was planning on pulling both covers in a month what should i look for? do i need to do the rear NOW where the fluid looks like that? i did notice a tiny bit of seepage around my rear diff cover but not enough to drip just enough to make it a little wet.Any insight would be helpful

 

Water contamination usually gives a milky appearance. And the rears tend to be "dirtier", probably from mostly using 2 hi.

Sounds like you eventually want to pull the cover spray down everything with a can of brake cleaner and replace the RTV to seal it up well (or get the gaskets called lube lockers).

You say you just changed the 5500 km ago; why are you changing so often? Do you wheel a lot or tow? or cross water? Have you ever pulled off the covers?

It doesn't sound like anything urgent that can't wait a few weeks.

 

I was still half asleep when i posted the last one so i try this again, i just changed my rear differential fluid 5500km ago when i did that the fluid was black i mean black, figured it hadnt been changed since new and wasnt anything to worry about mabye a little burnt, but i just checked my levels because i noticed it seeping around the diff cover not enough to drip just make it moist and when i did the fluid is black again, wondering what would make the fluid go from a nice golden color to pitch black in 5500kms?

 

just noticed your reply.....im not changing it that often i did it back when the manual said to do so at 50 000 km and i was just checking the levels yesterday when i noticed the seepage......its not really milky more pitch black with like a hint of a silver metallic color........so when i spray down with brake cleaner should i wipe out the excess really good to keep from contaminating?


i planned on redoing the diff this summer because when i changed the fluid at the 50000km mark it was winter and i didnt take the covers off to do the real good cleaning because i dont have a garage to do it so i figured i would just change the fluid and do the covers off cleaning and change when its warmer out.

 

Like Jiblet said. Because you didn't pull the cover to do the change last time and spray out all the extra crap with brake cleaner, I'm not surprised it's black again. Sounds perfectly normal. How did the drain plug look?? It's normal to have a marble or so size ball of shavings glued to it...too much more and you might wanna look into it. You don't need to worry about contamination and wiping things down after brake cleaner...it is designed to evaporate completely and leave no film or residue, if you wanna wipe and scrub some stuff down go for it, or if you get a puddle of brake cleaner in the bottum of the pumpkin just sop it up...try using the shamwow for that...and don't be so concerned about a little seepage around the diff cover, no biggie, if it's dripping like a pig then worry.
Make sense? If you have the time now, go ahead and pull the cover, spray things down and fill up. Dont compare the front colour to the back, unless your always in 4wd.

 

thanks jiblet and blacknorthern answered all my questions awesome

 

I attribute it to Limited slip clutch wear (assuming you have LSD). Only other reason would be some difference between the Dana 30 vs 40 differentials (I don't have a Rubicon), but I doubt it. I wouldn't think being in 2WD vs 4WD would make any difference since the diff always spins on a jeep since the front axle is splined to the hub due to the unit bearing construction.

 

and some of the black is likely caused by shearing of the oil under the heat/pressure of the gears. some oxidation, too.