This is a UOA from my 2018 Chevy HD 3500 Duramax with 13,000 miles on unit and gear lube. 4,000 miles of non-towing and 9,000 miles of towing a roughly 8,000 pound trailer. The sodium cannot have come from road salt, as the truck has never been driven when there is salt on the roads. The iron seems a bit high for 13,000 miles? This differential was underfilled about 1.5 qts from the factory. Disappointed that there was no particle count, is this an extra that I have to request?
Rear Differential UOA 2018 3500 Chevy HD Duramax 13000 miles
- Thread starter wwillson
- Start date
- Status
Originally Posted by wwillson
This differential was underfilled about 1.5 qts from the factory.
Say what now? I wouldn't be very happy about that.
This differential was underfilled about 1.5 qts from the factory.
Say what now? I wouldn't be very happy about that.
Originally Posted by Throt
Originally Posted by wwillson
This differential was underfilled about 1.5 qts from the factory.
Say what now? I wouldn't be very happy about that.
No, I'm not very happy about both GM and the dealer not properly filling the differential, but there is no recourse. My guess is the differential is just fine and will last for hundreds of thousands of miles. Still not happy about it.
Originally Posted by wwillson
This differential was underfilled about 1.5 qts from the factory.
Say what now? I wouldn't be very happy about that.
No, I'm not very happy about both GM and the dealer not properly filling the differential, but there is no recourse. My guess is the differential is just fine and will last for hundreds of thousands of miles. Still not happy about it.
I know my C2500 HD with a limited slip differential had a ton of metal in it at my first change at around 11k miles (I missed the interval recommendation of 5k miles for the first change). The next change at the 50k point was visually pretty clear.
Considering this was the first change with lots of break in metal in the oil, combined with the underfilling impact (who knows how much that affected rear end temperature) I would not make any changes based upon this report. I think another sample at perhaps half the recommended change interval would be warranted to see if a higher weight oil is needed.
Considering this was the first change with lots of break in metal in the oil, combined with the underfilling impact (who knows how much that affected rear end temperature) I would not make any changes based upon this report. I think another sample at perhaps half the recommended change interval would be warranted to see if a higher weight oil is needed.
dnewton3
Staff member
For many years now the AAM 11.5 has been known to be under-filled from the factory; it was a topic even back in 2006 (13 years ago) when I bought my Dmax!
Generally these are robust units except for the "gov-lock" (aka gov-bomb) feature. As long as they are treated easily, they hold up fine. Wayne is not likely to abuse his, so it will be just fine.
The GM fluid is known as "grape juice" due to it's odd factory odor. The only thing this diff needs is any quality GL-5 lube with a friction modifier. GM has a statement out from long ago saying not to add FM to the lube, but that is because the GM already has FM in it, and adding "more" would be adverse to the unit's clutch pack. Despite it being called a "locker", it's actually just a glorified clutch-biased limited slip device. Because it has a clutch pack, it needs the FM or it will chatter badly upon an OCI.
Get any lube that has GL-5 approval; either choose one with FM or add in the supplement if needed. Fill it with 4 full quarts. No issues after that.
As for the UOA itself; it's fine. This is FF; lots of Fe expected. Now that the ring/pinion are broken in, the wear will be fine. Fill it and leave it alone for 50k miles (dino) or 100k miles (quality syn).
Generally these are robust units except for the "gov-lock" (aka gov-bomb) feature. As long as they are treated easily, they hold up fine. Wayne is not likely to abuse his, so it will be just fine.
The GM fluid is known as "grape juice" due to it's odd factory odor. The only thing this diff needs is any quality GL-5 lube with a friction modifier. GM has a statement out from long ago saying not to add FM to the lube, but that is because the GM already has FM in it, and adding "more" would be adverse to the unit's clutch pack. Despite it being called a "locker", it's actually just a glorified clutch-biased limited slip device. Because it has a clutch pack, it needs the FM or it will chatter badly upon an OCI.
Get any lube that has GL-5 approval; either choose one with FM or add in the supplement if needed. Fill it with 4 full quarts. No issues after that.
As for the UOA itself; it's fine. This is FF; lots of Fe expected. Now that the ring/pinion are broken in, the wear will be fine. Fill it and leave it alone for 50k miles (dino) or 100k miles (quality syn).
Last edited:
If the dealer had done a proper PDI it would have been topped off b4 delivery. I did PDI for almost 15 years and the things left low ,loose ,missing from the factory would surprise most people.
- Status
Similar threads
