“ See your dealer” for advice on GM truck rear diff lubricant

[Snagglefoot]

Around 2019 the owners manuals for GM 1500 and 2500/3500 trucks changed from advising using 75w90 synthetic differential fluid to simply saying “ See your Dealer” So want’s going on? I assume they mean “ see your service writer” or see the mechanic who happens to walk over to the parts department to chat with the good looking parts girl ( or guy).

It sounds somewhat negligent to me. The manufacturer should have a stated recommendation for diff fluid. Leaving it up to their staff leaves the consumer hanging in the wind. Also, diff fluid changes are no longer a recommended maintenance technique for normal service. Maybe that’s why you should “ see your dealer” about. Does anyone have the true GM sanctioned story about “seeing your dealer? Thanks. End of rant.

P.S. Edit: If they just read it off the computer based on the VIN and don’t try to give a personalized Thickie Love opinion, then I’m satisfied.

 

[Snagglefoot]

Here is a screen print from the owners manual of a 2024 Silverado 2500.

 

[Snagglefoot]

And here is the maintenance recommendations for a 2024 Silverado 2500. Rear diff fluid changes are not listed, even for severe service.

 

[Snagglefoot]

Here is the recommendation from a 2008 owner manual. It’s 75w90 synthetic for the rear diff.

 

[MrHorspwer]

Around 2019 the owners manuals for GM 1500 and 2500/3500 trucks changed from advising using 75w90 synthetic differential fluid to simply saying “ See your Dealer” So want’s going on? I assume they mean “ see your service writer” or see the mechanic who happens to walk over to the parts department to chat with the good looking parts girl ( or guy).

It sounds somewhat negligent to me. The manufacturer should have a stated recommendation for diff fluid. Leaving it up to their staff leaves the consumer hanging in the wind. Also, diff fluid changes are no longer a recommended maintenance technique for normal service. Maybe that’s why you should “ see your dealer” about. Does anyone have the true GM sanctioned story about “seeing your dealer? Thanks. End of rant.

It's because there are three different possible axles for both the front and the rear:

Rear axle may be an 8.6 in or a 9.5 in and for the 9.5 in, it may have been manufactured by AAM or by GMCH (RPOs SU7 and SU8)

Front axle may be an 8.0 in, from AAM or GMCH (RPOs SU4 and SU5), or an 8.6 in.

To know which fluid to use, you need to know both the axle size and who manufactured it.

Using the VIN, a dealer parts department is the one who can decode and determine which axle your truck uses and which fluid should be poured in.

My 2020 Silverado had an AAM (RPO SU7) 9.5. The spec oil for it was p/n 19300457, which is a 75w85. I had a pinion leak and wanted some fluid on-hand before I could get it in for warranty service in case it needed to be topped up. Never checked what fluid the front axle used.

 

[SumGuy]

See this:

https://www.gm-trucks.com/forums/topic/234858-differential-fluids/

Does it explain what you're seeing?

 

[CorvairGeek]

Sadly, I'm sure whatever bulk oils a GM dealer gets at a discount, will happen to be just what yours needs!

 

[Snagglefoot]

See this:

https://www.gm-trucks.com/forums/topic/234858-differential-fluids/

Does it explain what you're seeing?

I think so. Our diff fluid post are certainly well advanced at Bitog, with sililiar comments. I would believe that non- Bittoggers would not have enough energy to change their diff fluid, especially when its not even a recommendation in their owners manual so I agree it might be wasted space in the manual ( too much information.) They are now too busy with the infotainment Center.
Thanks for your post.

 

[Snagglefoot]

I wonder if anyone with a 2000 and newer GM truck has had the dealer run their vin. Did they just print out the one line answer or was there any other recommendation based on towing etc. And for the record, I have a 10.5 - GM 14 bolt and their recommendation was 75w90 synthetic. No discussion on towing. I might photo a VIN off a new 2024 and see what the gal at the Chevy parts department says.

 

[AZjeff]

Encountered this when I wanted to change rear diff fluid at 10K in the '21 HD. Service writer looked it up no drama.

 

[gman2304]

My 2020 Silverado had an AAM (RPO SU7) 9.5. The spec oil for it was p/n 19300457, which is a 75w85.

My new to me 2019 Silverado has the AAM RPO SU7 as well. Mine is an open diff and I changed it last week and used Mobil Delvac1 75w90. Now I’m second guessing my choice. Do I have any reason to be concerned?

 

[I<3oil]

Encountered this when I wanted to change rear diff fluid at 10K in the '21 HD. Service writer looked it up no drama.

What was it

 

[AZjeff]

What was it

75w-90. HPL went in.

 

[redhat]

My new to me 2019 Silverado has the AAM RPO SU7 as well. Mine is an open diff and I changed it last week and used Mobil Delvac1 75w90. Now I’m second guessing my choice. Do I have any reason to be concerned?

I wouldn't be worried in the least bit. IMO if it were my truck... even if it called for 75w85 I'd probably just put 75w90, and I'd do the same even if it called for 80w90.

Unless there was some big compelling reason and tons of supporting information not to.

You used Mobil Delvac 1 which is a very very good gear oil.

 

[CorvairGeek]

I had found out about the difference a while ago, but wasn't aware of a different lube spec. I had saved pics to compare to my 2019 Yukon, as I have no idea which it has. I intend to change the gear oil at 30K.

 

[Snagglefoot]

I had found out about the difference a while ago, but wasn't aware of a different lube spec. I had saved pics to compare to my 2019 Yukon, as I have no idea which it has. I intend to change the gear oil at 30K.

View attachment 227827

View attachment 227828

You can add the 14 bolt 10.5 inch GM rear end. I believe the 2500’s went to a 11.5” 14 bolt AAM for the gas 6.6 in 2020.

 

[Snagglefoot]

Here are the horsepower and torque ratings in the latest version of Chevy pickups.

The 6.6 liter gas engine has 464 lb ft of torque. This may have caused the 2500 to get a 11.5 inch 14 bolt AAM instead of the 10.5 inch 14 bolt GM rear end with the 6.0 with 383 lb ft of torque that was used in the 2500 in the years previous to 2020.

 

[4WD]

Here is the recommendation from a 2008 owner manual. It’s 75w90 synthetic for the rear diff.

View attachment 227771

Talking to a guy at the dealership (and no official position) - there is more in the OM from lawyers than engineers …
Blame that on an out of control legal system … and 45% for those “caring folks” in nice suits - and a gullible jury …
I’m going to put 75W90 Delvac 1 in the ‘22 Tahoe … still have to figure out the transfer case …

 

[4WD]

Here are the horsepower and torque ratings in the latest version of Chevy pickups.

The 6.6 liter gas engine has 464 lb ft of torque. This may have caused the 2500 to get a 11.5 inch 14 bolt AAM instead of the 10.5 inch 14 bolt GM rear end with the 6.0 with 383 lb ft of torque that was used in the 2500 in the years previous to 2020.

View attachment 227839

And the Ally 10 speed ?

 

[4WD]

Here are the horsepower and torque ratings in the latest version of Chevy pickups.

The 6.6 liter gas engine has 464 lb ft of torque. This may have caused the 2500 to get a 11.5 inch 14 bolt AAM instead of the 10.5 inch 14 bolt GM rear end with the 6.0 with 383 lb ft of torque that was used in the 2500 in the years previous to 2020.

View attachment 227839

Is that right ?
Geez - the 5.3L has 383 torque …