Front Differential Gear Oil Change

[Jacob Szymanski]

Haven’t seen much on the forums or YouTube about front differential service on these trucks so wanted to post about it. Everything I have seen recommended to suck the oil fluid out and refill rather than taking the diff cover off due to lack of room to work. I did not like that route, so I pulled the cover and can report there is plenty of room. Here’s how I did it:

1. Remove skid plates

2. Disconnect battery 

3. Remove locking clips from the 3 connectors on the power steering rack and then disconnect the 3 connectors and move them out of the way (note: top locking clip is white and hard to reach, I used a bent pick)

4. Disconnect the front 4x4 solenoid connector to get the wire out of the way

5. Loosen fill plug (this is critical so you know you can refill it)

6. Remove all except 2 diff cover bolts, a flex head ratchet was useful here and one bolt needed a wrench.

7. Loosen last two bolts, crack the cover seal, and drain.

8. The diff cover comes out with minimal maneuvering, recommend marking the cover and noting gasket position before removal since it’s relatively symmetrical.

9. Wipe everything out and clean the surfaces.

10. New gasket P/N: 84428297 for GM axle, install and torque bolts to 30 ft-lb

11. I used a hose on the end of the gear oil bottle and went though the wheel well with the tire off to fill the diff easier, can fill the same way from underneath with a pump.

12. Rest is reverse from before.

 

Rear diff is the same but easier, gasket P/N 84412728 for GM axle. 
 

I have been using 75W-90 with no LS additive in heavy towing applications with the 3.42 gearset and only have a small amount on the magnet each time with services every 25,000 miles. The rear diff will have clutch material everywhere from the G80 if you use it often so I just wiped that off anywhere I could reach.

 

Lastly, the front diff gear is welded to the carrier, so looks like a regear for our trucks is out of question until the aftermarket makes a front locker/carrier of some kind.

 

[Atlas]

Nice write-up! Easy to follow.

[Black02Silverado]

Thanks for the write-up.  Most don't mess with it because of having to do all the extra just to get the cover off. This explanation make it easier to understand.

[Gangly]

I thought there was a drain plug, guess I was wrong, haha.

[Z45]

The dealers will just vacuum them out.  They have a dedicated machine that does that. Watched the tech do it on my 2021. 

Edited June 27, 2025 by Z45

[Jacob Szymanski]

8 hours ago, Gangly said:

I thought there was a drain plug, guess I was wrong, haha.

The AAM axle may have a drain, the GM does not.

[SilveradoRST]

12 hours ago, Z45 said:

The dealers will just vacuum them out.  They have a dedicated machine that does that. Watched the tech do it on my 2021. 

So then there’s no chance to clean the magnet on the inside of the cover.   That’s disappointing.