Just had my 4.30 gear removed and my 4.10 gear reinstalled. Never seen a gear rust while installed in a rear end (dana 60). Can this gear still be used?

I would try soaking it in some rust remover for several days and look at it again before deciding
Those rust pits may store gear oil in them better than the rest of the teeth do

Cab, have you ever seen a gear come out of a rear housing rusted like that. I'm skeptical I did not get my gear back from the shop that preformed the work. The old switcharoo. It is a Strange/US gear and is not labeled any where.

I've seen that many times. Transmission gears too. Especially when they sit and you have weird weather changes. Some oils don't actually stay on the gears as well as others and when they sweat, the oil works off the gears and then the rust sets in.

Sitting in a box on the shelf and that will happen too.

just went through a rear for a 58 chevy that was like that. the car had a 3:55 in it and my buddy wanted to use a 3:36 that he had rebuilt because the 3:55 was leaking at the pinion seal and was a tad noisy.
the 3:36 had several gears that had some slight pitting, and he was worried they might "sing".
put that rear in, works great, no noise, and decreased highway RPM as a bonus. this car is a cruiser and will not be raced, but his rear [pun intended ] will last for a long time.

Rust pits storing oil ? ....couldn’t have said it bester!!

I picked up a 8 3/4 pig some years ago .... a bit rusty on the ring gear ...., cleaned it up with some 600 and it was good to go !

Ok, thanks guys. The 4.10 I just had put back in is a 20+ year old gear and has never rusted. Sits just as much as the 4.30 I just had removed. The 4.10 is a Richmond gear. Well, if anyone is interested this 4.30 has less than 400 miles on it and will be in the for sale section for $50.

If the vehicle sat for a long time outside then rust could've formed on the part that wasn't covered in oil. There is a vent on the housing so moist air will get in there and rust everything eventually. Or that gear could've been rusted before it was installed or perhaps you did get a rusty gear back and the shop kept your good gears. Those are all plausible theories.

A USGear, Richmond or any other decent aftermarket gear will have marks on it identifying who made it and/or the part number. The only gear I've ever seen without it was some cheapo Chinese junk. Unless it sat for a loooong time, it shouldn't have been rusted. Did you drive it to the shop?

Car is stored in my non heated garage. Yes I drove it to the shop. Bought gear from DR.Diff brand new, so gear was brand new when installed. Called US gear and although bar code matches up, their is no serial number on gear to prove its my gear. Could be my gear, but just seems odd that the 4.10 gear that's back in it is 20+ years old, gets stored for long periods of time just like the 4.30 gear did and it has not rusted yet. Cant prove anything so I give up at this point. Maybe I can get $50 out of it.

This is a GM 7.5 part#75-529 gear set, 37 & 7 teeth on the ring and pinion gears, Made In USA, and the little street sign with a "G" symbol is US Gear. If the ring gear didn't have that type of marks, and you were sure of what was in it, I'd go to see the fellows and make them aware of their mistake. But that's me.

Those pits are deeper than the heat treatment. Every time that tooth is loaded hard, a tiny piece flakes off the edge of the pit.
That tooth will fail across the pits earlier than a virgin tooth.
Will it happen later today, or 20 years? Who knows.

This gear has that.