Recently purchased a used 2008 4Runner Sport, V8 with about 108,000 miles which has the full time 4wd. Not many official service records, but it appeared the previous owner had done some work himself. I recently changed the plugs, ATF, rear diff., transfer case, and finally this morning got to the front diff. There was quite a bit of metallic gunk stuck to the magnet in the drain plug (as there was in the rear diff), but I also found this 3 inch thin curly piece of metal in the used fluid. For what it's worth, it appeared the plugs, front, transfer case, rear diff fluids had never been changed. The Toyota Tech who did the ATF said the fluid looked fine with no red flags.

How worried should I be about this? Thanks in advance!

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Dang. A chip like that is usually only formed by a drill bit.

Not sure how it would get in there though. Maybe if the drain was drilled/retapped.

You should be fine if it's still running. It doesn't look bent or mangled like if the gears got to it.

I say run it. I clicked on this thread looking for a busted gear tooth, but since there is no tooth or bearing parts you are good to go.

interesting, a spring from a retractable pen??

Id say send it till it causes an issue. If its fine then great, and if not, there wasn't much you could have done differently anyways

I don't think it's cause for alarm..lost a chunk off the ring gear in my offroad rig years ago and haven't had an issue.

Not a problem. I've seen far worse chunks out of my solid axle diffs and they run like champs.

Thanks gentlemen, the feedback is much appreciated. My level of anxiety is back to a normal state now!

Clearly seems to be a spring judging by the tight coils still intact at the bottom. I'd say it's good that it was stuck to the magnet and as others said, it's likely fine to forget it unless/until you have issues.

did you look at the drain and fill bolts? did the thread look fine? looks like it might come off them.

Helicoil thread repair?

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Good points and good questions. I will say in hindsight I remember thinking wow, the threads in the drain plug housing (the threads within the axle/differential itself) looked especially silvery and shiny compared to the transfer case and rear diff. The fluid in the front transfer case also seemed a bit cleaner than transfer/rear. Maybe it was changed and the threads were repaired at some point in the life of the vehicle. The drain plug was a bear to break loose, but threaded in and out easily by hand after that.

Either way, I'll make sure sure at my next oil change the front diff. fluid level is checked to be sure. I used a new washer and torqued it to specs, so should be solid.

IIRC, the drain plug in front diff is often tough/nearly impossible to remove, so likely the previous owner stripped or damaged it and used helicoil fix.

That looks like the remains of the tiny springs in axel seals. Sometimes they pop off if tapped too hard in the install. A little dap of grease can help prevent them from coming loose during installation.

Thankfully differentials are pretty unforgiving: if there's something going wrong they whine or do weird things like clunk and bang.

If something has gone wrong they just explode.

Because of the immense pressures between the gear teeth in all differentials, and even more so in Toyota hypoid differentials; eh, they're neither shy nor hesitant about informing you know something has gone wrong.