Metallic sludge on differential drain plug

[roddy]

I mentioned this in another thread, but thought it would better serve people in this section. For those who have changed their diff fluid once (or those who have seen the pictures) and are concerned about the amount of metallic sludge on the magnet in the drain plug, don't sweat it. This is normal during the break-in of hypoid gears. I initially changed mine last summer at around 1,100 miles and there was quite a bit there. I changed it again last night with over 15,000 miles on the clock and there was very little sludge on the magnet (if I had to guess, I'd say there was about 1/4 of what was on it at 1,100 miles). I used Redline 75W85 GL-5 gear oil both times. This is the grade that is spec'd for the rear end, but not many companies offer it. 75W90 is also acceptable as per the manual, and if you track your car, it may be the better choice. Plus it is more readily available than 75W85.

[chenshuo]

good to know.

I'm going to get my Engine oil, Diff fluid and Transmission fluid changed in two weeks. By then i should have a bit over 4000km on the odo.

[Lonewolf]

Has anyone had an analysis of their diff fluid performed yet?

[FRSRAVEN]

Swapped my diff fluid around 1700 miles. Also noticed a very large amount of metallic buildup on the drain magnet. Just break in wear, nothing all that concerning. I won't perform another swap until 20K.
Used a synthetic 75w-90.

[Rabble]

I want to assume that the black stuff on the diff magnet was grease that they put there on purpose to trap the particles. I.e. the magnet would attract the bits/shavings and the grease would keep it there.

Of course, this is just what I tell myself. I'm just some schmuck on the internet.