Front and Rear differential fluid change ??

[DWTahoe]

Sorry if I missed this somewhere else. The threads I found were old, so I wasn't sure if it should be asked again.

I'm going to change the front and rear diff fluid. One asks for 75w-90 (front I think), rear 75-w85. The 85 is harder to find and more expensive. Does anyone have any info about using the 75w-90 in the front and rear? The way I understand it is the 85 oil may provide better fuel economy but probably not enough for me to bother with. I just want to make sure it will not ruin anything else?

The second part is, does the rear need a fluid with the limited slip additive or does it matter. The local store has the -90 but it says it has the additive, do I need this one, or one without it? Or maybe it doesn't really matter. I know it was an issue in my 01 Grand Cherokee with front and rear limited slip diffs. If you didn't have enough additive it would chatter and make horrible noises, if you had too much it wouldn't engage properly.

Mine is a 2015 Tahoe w/ the G80, 100k miles. Thanks in advance.

 

[AJMBLAZER]

You won't need any LS additive as you don't have the limited slip. The Gov-Lock locker doesn't require it.


You should be fine with 75w90 so long as it DOESN'T have the GL5 additive in it.

 

[Bob2C]

I changed mine out at 24k to the Amsoil Severe gear 75w-90 for both. No issues to report at about 7k miles of usage.


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[DWTahoe]

Thank you both for the responses. I guess I need to do some more research. I'm not sure what the difference is between the Gov-lock and a limited slip. I assumed the G80 was a limited slip differential.

I was just looking at what was available at the store that I could use. It looks like the mobil-1 75w-90 and the other brands there all have some sort of LSlip additive when you read the tech specs on the fluid.

If I'm reading correctly, I should be able to put 75w-90 in both diffs and I need to make sure they do NOT have any LS additive? TIA.

 

[AJMBLAZER]

Front wouldn't matter, but the rear locker doesn't need the additive. It can actually make it engage more harshly.

 

[DWTahoe]

I'm not as familiar with IFS. Does the front have any sort of limited slip feature?

 

[AJMBLAZER]

No. Open diff.

 

[DWTahoe]

That's what I figured, but thought I would ask just in case. Thanks for the info.

 

[OR VietVet]

I have the G80 limited slip in my rig. I recently changed the fluids. Front diff calls for, in my 2005 Z71, 80w-90 and I use the GM brands. The front number is 89021669

The rear diff calls for 75w-90 and that GM number is 88900401.

My transfer case called for Auto Trak II fluid and that number is 12378508

 

[DWTahoe]

I'm going to add this info here as well in case others searching for it need the specs.

100k miles...changed the front and rear diff fluid. I settled on 75w-90 in both. It has the Limited Slip in it, which I don't think it needs, but everyone seemed to agree it will be good.

Just for info purposes, in case others look for it. All fill and drain plugs seem to want to be torqued to 24 ft. lbs. The rear diff cover, 12 bolt, 20 ft. lbs on each bolt in a star or criss cross pattern. If someone knows that's wrong, please let me know. Otherwise, it's here now in case others go searching for torque specs.

 

[AJMBLAZER]

If it has the G80 Gov Lock locker in the rear you don't want that additive. It will make it engage harsher. Operation will be more noticeable.

 

[RobDenali]

Can anyone confirm that when changing your drive train fluids, do you fill until it starts to come out of the fill plug? I am horrible at measuring liquids

Thanks

 

[AJMBLAZER]

That's what most people do.

 

[mb1500]

This.

That's what most people do.

 

[wjburken]

That's what most people do.

x2

 

[Bob2C]

Can anyone confirm that when changing your drive train fluids, do you fill until it starts to come out of the fill plug? I am horrible at measuring liquids

Thanks

That’s what I have always done. No issues.


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[wjburken]

Can anyone confirm that when changing your drive train fluids, do you fill until it starts to come out of the fill plug? I am horrible at measuring liquids

Thanks

Make sure on the front differential that you can get the fill plug out before you pull the drain plug. Otherwise you could end up with an empty differential and no easy way to refill it.