CHECK YOUR DIFFS...

[rjgvt]

When my truck arrived in January, I asked the sales guy if the the service department could check the front and rear diff levels during prep. He said, sure, no problem. When I picked up the truck, sales guy said it was all good.

 

Had an appointment today for an oil change at 1161 miles. Figured I’d burn one of “free” oil changes just after break in miles. Requested that they check the diffs since I did not see any paperwork when I got the truck. I requested no tire rotation due to low miles. 
 

Service document stated that lube oil and filter service was performed. Also stated that they checked front and rear fluids, t-case fluid and trans fluid, all are in spec. Keep in mind that the diff fluid level should be 10mm below the fill hole opening. No problem found.
 

I’ve been running my tire pressures at 55 to 56psi when tires are cold. Tire pressures were at 60/70 psi after service. I waited a few hours after I got home and put them back to 55psi. Will have to request not to change the tire pressures next time! 

[bruceb58]

On 2/14/2024 at 1:29 PM, rjgvt said:

When my truck arrived in January, I asked the sales guy if the the service department could check the front and rear diff levels during prep. He said, sure, no problem. When I picked up the truck, sales guy said it was all good.

 

Had an appointment today for an oil change at 1161 miles. Figured I’d burn one of “free” oil changes just after break in miles. Requested that they check the diffs since I did not see any paperwork when I got the truck. I requested no tire rotation due to low miles. 
 

Service document stated that lube oil and filter service was performed. Also stated that they checked front and rear fluids, t-case fluid and trans fluid, all are in spec. Keep in mind that the diff fluid level should be 10mm below the fill hole opening. No problem found.
 

I’ve been running my tire pressures at 55 to 56psi when tires are cold. Tire pressures were at 60/70 psi after service. I waited a few hours after I got home and put them back to 55psi. Will have to request not to change the tire pressures next time! 

I thought the spec was 0 to 10mm which mean if it's level with the fill hole, it is also good.

[rjgvt]

The spec is 0 to 10mm, I wrote what was on the paperwork. 

[bruceb58]

9 hours ago, rjgvt said:

The spec is 0 to 10mm, I wrote what was on the paperwork. 

OK...I thought you were implying that the correct level was ONLY 10mm down and not a range. Whenever I end up doing mine, I will fill level with the fill hole unless I buy the Banks cover in which I will fill to the middle of the sight glass on it.

[Z45]

Don't know if it was said but some time ago I read service info that said the axle were lube filled at the axle plant, not the final assembly plant.  I am sure they use means to cut costs such as filling to the minimum level and with lube from the lowest bidder.  . 

[64BAwagon]

American axle fills the units then ships them to GM. They are not checked during production unless there is an issue in validation/repair

[Capt Bob]

I checked my diff yesterday and it measured 25mm below the bottom of the fill so I ordered a quart of AC Delco juice to top it off. I’m now going to check the front and the transfer case. For all I know, my 2018 1500 might have been low. I never checked it till I did the first change at 25k. Still, I’m liking this truck a lot but it’s still early.

[Capt Bob]

Rear took a full quart to get it within the 10mm spec. Front took only a small amount  but it was below spec.

I plan on a drain and fill at 5K. Is there any reason not to use 75W90 in both front and back rather than having two different specs. I still have two quarts of Redline 75W90 left and would like to use it up.

[Mike71]

I recently did to rear differential oil changes on my 2020 and 2022 trucks with Amsoil 75-90.  45K and 30K miles.  Owners manual states ask dealer regarding service intervals.  Zero info on what type of oil and quantity needed.

 

#1 2020 Silverado 2500HD with 45K miles Duramax-  Easy peaky drain plug at bottom ant fill plug at top.  Dropped the bottom plug and got about 4.5 quarts into the drain pan. This is about the same amount that went back in to make it dribble out of the fill hole on level ground. Truck is a combo towing vehicle 10K trailer, snow pusher, and soccer mom taxi.  old oil came out looking pretty good.

 

#2 2022 Silverado 3500HD DRW Duramax with 30K miles pulls trailers up to 16K half of these miles.  No drain plug only fill plug on the cover.  Ordered new gasket and pulled rear dif cover.  Only got about 3 quarts of  oil out after I pulled the cover.  The oil was not horrible but definitely brown.  I examined all the seals and found no indication of leakage.  My only thought is that it was shipped low from the factory, because it required 4.5 quarts of 75-90 to make it dripple out of the fill plug hole on level ground.  Would have gladly paid a few extra bucks up front for a drain plug. 

 

Also zero info on rear end bolt tightening pattern and torque specs.   Must be top secret!

 

 

 

Has anyone else had a similar experience??? 

[Black02Silverado]

17 hours ago, Mike71 said:

I recently did to rear differential oil changes on my 2020 and 2022 trucks with Amsoil 75-90.  45K and 30K miles.  Owners manual states ask dealer regarding service intervals.  Zero info on what type of oil and quantity needed.

 

#1 2020 Silverado 2500HD with 45K miles Duramax-  Easy peaky drain plug at bottom ant fill plug at top.  Dropped the bottom plug and got about 4.5 quarts into the drain pan. This is about the same amount that went back in to make it dribble out of the fill hole on level ground. Truck is a combo towing vehicle 10K trailer, snow pusher, and soccer mom taxi.  old oil came out looking pretty good.

 

#2 2022 Silverado 3500HD DRW Duramax with 30K miles pulls trailers up to 16K half of these miles.  No drain plug only fill plug on the cover.  Ordered new gasket and pulled rear dif cover.  Only got about 3 quarts of  oil out after I pulled the cover.  The oil was not horrible but definitely brown.  I examined all the seals and found no indication of leakage.  My only thought is that it was shipped low from the factory, because it required 4.5 quarts of 75-90 to make it dripple out of the fill plug hole on level ground.  Would have gladly paid a few extra bucks up front for a drain plug. 

 

Also zero info on rear end bolt tightening pattern and torque specs.   Must be top secret!

 

 

 

Has anyone else had a similar experience??? 

I know it is all due to money, but it would be nice to have a drain plug.  I change mine over to AMSOIL at 500 miles, then go 100k, I sent a sample in on my 2002 at 100k and the oil showed still good and very low wear.

[Pryme]

1 hour ago, Black02Silverado said:

I know it is all due to money, but it would be nice to have a drain plug.  I change mine over to AMSOIL at 500 miles, then go 100k, I sent a sample in on my 2002 at 100k and the oil showed still good and very low wear.

I also did amsoil but for me 100k miles would take 20 years since I have been driving my truck only 5k a year so I’ll probably do it again by 50k if I still have the truck. 
 

im also running amsoil in my bike the 10w40 metric and put it in at the recommended 600mi first service and am going to change it again in spring it will only have 1800ish miles on the oil after winter storage and I know that oil will be good still and it’s going right in the mower. 

Edited September 16, 2024 by Pryme

[dieselfan1]

Looks like the trend continues for 2026.

I just did my first oil change at 800 miles , 6.6 gas.

Oil drain plug not much better than finger tight.

Rear differential was a over a pint low. Front was a half pint low.

T case was full.

Sad.

 

Edited October 19, 2025 by dieselfan1

[Chuck FB]

On 2/9/2024 at 9:36 AM, newdude said:

 

 

1 - 88900401 is the GM gear lube 75w90.  Do NOT add any additives to that p/n.  If you filled it to where it ran out, let it come to a slow drip or no drip to get to the 0" range of the spec.

 

2 - All GM HD trucks are the Eaton G80 auto mechanical locker except the ZR2.  ZR2 has an electronic locking diff.  GM calls for no modifiers when using GM's oil.

 

3 - 11.5" on all gas.  

 

4 - Transfer case is spec'd out in the manual.  Page 390.  Dexron VI ATF.  Rear diff is 88900401 75w90, front diff is 19300457 75w85.  

 

5 - Fill plug gasket is re-usable unless damaged.  

I went through this thread from the beginning hoping I might find answers to some questions I have but they were not to be found and was hoping you could shed some light with torque specs. When I do change the oil in the diffs I want to be able to pull the covers and clean off the magnetic strips ( very unfortunate they went away from the drain plug and presuming a magnetic drain plug back in the day ? ). Also I assume its recommended to use loctite on the cover bolts if indeed the torque value is not that high to retain the bolts from backing out ?

 

The rear diff I know has the reusable gasket and a replacement in Canada is 50.00 something dollars. What is the torque value for the rear cover bolts ?  

 

The front diff gasket seems to be the mystery item, its insanely expensive in Canada at 160.00 for that gasket and the dealer did not stock them nor was sure if they were reusable or not as they claimed they typically sucked the oil out of the front diff to avoid taking the cover off. If I need to purchase a gasket then I will have to but no point in ordering one and having it around if I don't require it. And again as per what torque spec the front diff cover bolts are and if they also recommend to have loctite. 

[Pryme]

On 11/3/2025 at 6:03 PM, Chuck FB said:

I went through this thread from the beginning hoping I might find answers to some questions I have but they were not to be found and was hoping you could shed some light with torque specs. When I do change the oil in the diffs I want to be able to pull the covers and clean off the magnetic strips ( very unfortunate they went away from the drain plug and presuming a magnetic drain plug back in the day ? ). Also I assume its recommended to use loctite on the cover bolts if indeed the torque value is not that high to retain the bolts from backing out ?

 

The rear diff I know has the reusable gasket and a replacement in Canada is 50.00 something dollars. What is the torque value for the rear cover bolts ?  

 

The front diff gasket seems to be the mystery item, its insanely expensive in Canada at 160.00 for that gasket and the dealer did not stock them nor was sure if they were reusable or not as they claimed they typically sucked the oil out of the front diff to avoid taking the cover off. If I need to purchase a gasket then I will have to but no point in ordering one and having it around if I don't require it. And again as per what torque spec the front diff cover bolts are and if they also recommend to have loctite. 

If I recall, the rear bolt was magnetic. 
can’t help with specs. Newdude should be able to though. 

[Chuck FB]

6 minutes ago, Pryme said:

If I recall, the rear bolt was magnetic. 
can’t help with specs. Newdude should be able to though. 

I don't have a manual and not sure of any other source to get even simple tech information from. I've seen it mentioned in the past that there is some site one can buy an online manual for an affordable price.