Garner Ames

2019 Chevrolet Express 3500 Extended with 6.0L/6L90E/3.42 HD locking diff (G80)

14 bolt rear diff, not sure if 9.5 or 10.5 ring gear but looking in my owners manual it does not show different part numbers for non G80 vs G80 equipped diffs which almost every other GM car or truck I've owned has shown different part numbers or in the case of the old G80 limited slip diffs, an additive to be used in addition. Also no where in there does it provide a capacity for the rear diff so I have no clue how much to buy.

Curious for anyone who has changed their diff fluid on a new Express/Savana specifically 2500 and 3500 models, what oil did you use and how much. Any issues with the G80 after changing it?

Thanks guys.

mountainmanjoe

Synthetic 75W-85 or 75W-90
They stopped using additive for posi units a while back.

tsoleno

I used Lucas 75W90 , between 3 and 4 quarts. Thinking that I may have had to open my rear axle up und look for damage, I bought the GM synthetic 75W90 in a gallon size.

Garner Ames

In digging deeper, I found an excellent write up about the G80 option in later model GM trucks and in this case is geared towards the HD trucks which I believes applies to us GMT610 2500 and 3500 owners. Really good read with cite references from GM, Amsoil and EATON themselves. The confusing thing is GM says not to add any friction modifier to the differential. What they do not say is the reason they say not to add the FM is because the GM service fluids come with the FM already premixed so you can see how this is confusing.

https://www.dieselplace.com/threads/...umdrum.573369/

tsoleno

What I've determined with mine is I may have a locker problem or an operational issue due to the fluid. Hopefully I can get to this and pull the cover this weekend to do an inspection and fluid change w/ the GM fluid. A couple days back I had a tire spin while turning around on a lawn and I thought it was coming apart. From the great YouTube university, the locker is what I am hearing. Thanks bunches for the link.

dberladyn

I have never changed the rear diff oil on any vehicle I have owned. I have never had a rear differential problem. Anyways, while getting an oil change, they took a look and suggested that I change the fluid. It's not black, but it has lots of black particulate in it. I am at 80,600Km.

I am interested in this thread. I will re-read it again when I am not so worn down.

mountainmanjoe

It's like an engine. The better you look after it , the longer it will last. You may not have a problem ... until you do. And then it's too late. Axles are expensive. Changing the oil out every few years is not. Especially such an easy item. With the reusable gaskets they put on there now it can be done in half an hour.