DIY: Rear diff fluid change - 2018 Sierra 5.3L 4x4

[YYC-SIERRA]

I changed my rear diff fluid in the Spring but didn't get around to posting a write-up until now.

 

2018 Sierra 5.3L auto, 4x4, approx 30,000 kms / 18500 miles

 

This is a fairly easy job, the 2 interesting points I found were how dark the gear oil was after only 30k kms, and how little quantity the factory fluid fill is, vs what it actually takes to drip out of the drain hole.

 

1. Find the tire iron under your rear seat

2. Use your key and pop out the tire lock mechanism from the rear bumper

3. Insert the tire iron into the bumper and crank down the spare tire, then set aside the tire.

4. If you're interested to see what rear diff you have (mine's a 9.5) look just behind the diff on the passenger side.

4. Remove the drain plug

5. Start cracking the pan bolts until fluid starts leaking.

6. Once most of the fluid is out, fully remove the pan bolts and brake cable hardware and set it aside.

7. Wipe off the internal magnet at the bottom center area of the diff to remove any debris.

8. Inspect your gasket, clean the gasket, the pan, and the mating surface of the rear diff as required.

9. Put the gasket and pan back on, and tighten the bolts in a star pattern. 

10. Grab your favorite gear oil and pump it in

11. When oil starts dripping out of the drain hole, put the plug back in and tighten.

 

I bought a couple cheap containers and measuring cups from the Dollar store and tried to measure exactly how much came out and went in.

 

It was approximately 2150 ml of old gear oil I drained out, and about 2650 ml of new Amsoil that I put back in until it started dripping from the drain hole.

 

So almost a half quart more fluid went in then what the factory filled it to! I think that'd be reason enough to get your factory fluids out of the diffs sooner than later. 

 

 

 

Edited October 3, 2020 by YYC-SIERRA

[MY164X4]

Thanks

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[gone_fishing]

Nice write up. Curious why you removed the spare tire? I did this on my 14 Sierra and never removed the spare.

 

Thanks

[davester]

Note, that extra oil (vs the original fill) may be due to it being slightly overfilled, as depending on the diff, I've seen fill specs anywhere from to the fill hole to 1" below it.    And having more fluid in them doesn't necessarily mean it's better, as it gets more aerated, reducing it's ability to lubricate.

[Bob2C]

I changed my rear diff fluid in the Spring but didn't get around to posting a write-up until now.
  2018 Sierra 5.3L auto, 4x4, approx 30,000 kms / 18500 miles   This is a fairly easy job, the 2 interesting points I found were how dark the gear oil was after only 30k kms, and how little quantity the factory fluid fill is, vs what it actually takes to drip out of the drain hole.   1. Find the tire iron under your rear seat 2. Use your key and pop out the tire lock mechanism from the rear bumper 3. Insert the tire iron into the bumper and crank down the spare tire, then set aside the tire. 4. If you're interested to see what rear diff you have (mine's a 9.5) look just behind the diff on the passenger side. 4. Remove the drain plug 5. Start cracking the pan bolts until fluid starts leaking. 6. Once most of the fluid is out, fully remove the pan bolts and brake cable hardware and set it aside. 7. Wipe off the internal magnet at the bottom center area of the diff to remove any debris. 8. Inspect your gasket, clean the gasket, the pan, and the mating surface of the rear diff as required. 9. Put the gasket and pan back on, and tighten the bolts in a star pattern.  10. Grab your favorite gear oil and pump it in 11. When oil starts dripping out of the drain hole, put the plug back in and tighten.   I bought a couple cheap containers and measuring cups from the Dollar store and tried to measure exactly how much came out and went in.   It was approximately 2150 ml of old gear oil I drained out, and about 2650 ml of new Amsoil that I put back in until it started dripping from the drain hole.   So almost a half quart more fluid went in then what the factory filled it to! I think that'd be reason enough to get your factory fluids out of the diffs sooner than later. 




 



 

 

Nice job. Did mine at 24k miles. Wasn’t that dark. Did you have a magnet on the bottom of your housing? Can tell from the photo. Mine did.




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[YYC-SIERRA]

Gone_fishing,

 

I removed the tire purely out of personal preference. I liked the extra room underneath, it allowed me to sit upright. Also wanted to clean out all the underside with a hose when I was done. For sure you can do this without removing the tire.

 

Davester,

 

Thanks for that info. How would you fill it to 1" below the hole when you can't see inside?

 

Bob2c,

 

Yes it has a magnet at the inside bottom, I cleaned it out, it was just a little metal sludge type stuff like what's seen on the drain plug, didn;t see any metal chunks. 

 

Edited October 3, 2020 by YYC-SIERRA

[davester]

..you fill it slowly, and use a small bent dipstick to check how far below the fluid is below the hole.  IMHO, it's totally stupid to spec it this way, vs just getting a cover with the fill hole at the fill height at the factory, but it is what it is...

[Black02Silverado]

Nice write-up.

 

Next time get the Squeeze packs.  Makes adding the fluid a breeze.  

[YYC-SIERRA]

Here's the front diff job, not much different (30000kms / 18500 miles)

 

1. locate the front diff plugs, loosen the top fill plug first, then the bottom drain plug second

2. drain fluid

3. refill with your favorite gear oil (i used Amsoil 75w90, same as the rear diff) 

4. tighten plugs back to spec

 

Some observations:

 

the old fluid was a dark green as opposed to the dark black from the rear diff. I only use the front diff occasionally in the winter with AUTO mode, and very rarely in 4 HI, so that likely explains the colour difference, it's not used as much. I tow a 3000lb and a 5000lb trailer boat about 2000 miles a year. 

 

I drained approximately 1200 ml out, and refilled with 1600 ml back in. 

[YYC-SIERRA]

I also changed the transfer case fluid in the same manner as above, using ACDelco Dexron 6 ATF, not much to report other than the look of the drain plug magnet.

 

Apparently this is normal from the break-in of the timing chain. 

Edited October 4, 2020 by YYC-SIERRA

[Granite7]

I’m due for this very soon. Thanks for posting. Will you be posting the T case also?

[Bob2C]

Here's the front diff job, not much different (30000kms / 18500 miles)
 
1. locate the front diff plugs, loosen the top fill plug first, then the bottom drain plug second
2. drain fluid
3. refill with your favorite gear oil (i used Amsoil 75w90, same as the rear diff) 
4. tighten plugs back to spec
 
Some observations:
 
the old fluid was a dark green as opposed to the dark black from the rear diff. I only use the front diff occasionally in the winter with AUTO mode, and very rarely in 4 HI, so that likely explains the colour difference, it's not used as much. I tow a 3000lb and a 5000lb trailer boat about 2000 miles a year. 
 
I drained approximately 1200 ml out, and refilled with 1600 ml back in. 

I never understood why a steel fill plug is used for the fill hole. I waited too long on my 02 Yukon and couldn’t remove the fill plug. Sold it with 150k miles on original front diff oil. Never any issues. This time everything changed out to AMSOIL like you did. Easy 100k before it needs to be done again.


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[YYC-SIERRA]

35 minutes ago, Granite7 said:

I’m due for this very soon. Thanks for posting. Will you be posting the T case also?

I think I was running low on time so I didn't bother taking pics of the T-case fluid change, but from what I recall, it was easy and straight forward. You'll see a top fill plug, and a bottom drain plug. I can't remember the quantity of Dex 6 I used but it wasn't much, less than 2 quarts. Cheers

[TXGREEK]

Highly recommended replacing the crappy rear Diff cover with a new G2 as it makes replacing the fluid a breeze!



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[Black02Silverado]

What stinks is there is no drain plug on the front differential on the new 2019's.  It is also harder to get to the fill plug. The harness for the power steering is in the way.