rls82959

A few days ago I noticed some spots on the garage floor under the differential.
The cover had sprung a leak, so I had a little project to take care of.
So I took the lower bolts out and loosened the rest of the bolts and let the fluid drain.
This fluid probably had about 30K miles on it and was put in when the 4.10's were installed.
The fluid was Lucas 75W-140 synthetic with 4oz Ford friction modifier.
According to the book, diff fluid should be changed at 60K miles.
The gears looked fine and are very quiet but this fluid was really black.
Would 4.10's require more frequent fluid changes than 3.31's ?

And btw that fill plug was a bear to get out. With that ledge underneath the plug I had to use a short extension on the ratchet. I laid there and said a prayer and finally got it out.

ghunt

Just because it's black doesn't mean anything...that just happens from contaminates that get into the oil, black is a much better color than brown or any other color because that generally means water or something else is getting into the diff.

Urambo Tauro

If it's an opaque brown (sometimes referred to as "milkshake"), that's water contamination. But axle fluid will turn a translucent brown before turning black (just like engine oil), and that's normal.

I don't know if black fluid @ 30,000 miles indicates premature wear or not. I would assume so, just like engine and transmission oils. But I think I read somewhere that it's normal for differential oil to get extra dark between changes, and that one should be more concerned with finding metal particles at the bottom of the housing.

Since it's undergone a gear change, and the cover has to come off anyway, I suppose it couldn't hurt to take a look at the wear pattern and maybe double-check the backlash too.

rls82959

Yeah it was black. No weird milkshake brown or anything like that.
Didn't see any metal particles. Gears looked fine.
Didn't check backlash, wouldn't know how to do that anyway.
The gears are super quiet, I wouldn't even have thought about
changing the fluid if it hadn't been for the drip.
When I put that fill plug back in I snugged it down but I sure didn't crank it down.
Thanks,