I just change the diff oil and found something unpleasant. When I took down the drain bolt, I found some black muddy sludge. When I smear it on my finger, I see some very visible metal shavings. My jaw drolpped!!

I used mobil 1 gear oil 75w90. Standard off the shelve Auto Zone stuff.

I want to know if that is a indicator of a soon to be dead diff.

Last time i change the diff oil was about 10 months ago with one track day with 12k on the street.

Help!!!

 

Perhaps the mobil diff oil couldn't handle the heat on track? what did the rest of the oil look like? (color?)

 

What are the miles on the diff? A bit of mud and metallic on the drain magnet can be “normal” if the miles are high, long interval oil changes, or a fresh built rear after break in.

It would be best to change the oil again in a week or so using the Mobli1 75/140 from your auto store or, Amsoil 75/110 75/140 if you have a dealer in your area.

 

The paste on the magnetic plug is normal, I've never seen it come out perfectly clean. I've never seen metallic pieces on it, but it certainly could happen and the magnet is where they will collect. I'm sure you are likely fine, just monitor it in the future.

 

I have seen a few small pieces come out before maybe 1-2mm...and some sludge...got a pic?

 

That's normal

 

Sounds fairly normal if its just sludgy and tiny metallic specs. Larger bits I might be concerned with, but if the particles are as small or smaller than, say, white sugar crystals, then I would call it normal wear. Did you clean the plug off the last time you changed the diff oil? Cause if not, most of that is probably just held over from the last change.

 

^^This...seems normal as long as it just tiny specs. Do another diff change and see if the results are the same so soon after a change.

 

The diff have 52K total.

The Old oil is dark yellow/brownish looking.

The metal sheavings is very tiny, a little larger than sand. But still visable to naked eye.

The duration of the oil in the diff was about 12K miles in 10 months old.

 

sounds like an over-reaction OP