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Does extra differential fluid cause issues?

Interleukin6
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Interleukin6 Enthusiast

Interleukin6

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Posted (edited)

I just changed the rear differential fluid. My 2022 LTD LT has a GM rear differential supposed to take 2.64 qts but it actually took all 3 qts. I was waiting for a little drip from the fill plug hole to stop while adding new fluid, but again it took all 3 qts. The fluid level was right below the fill hole. Should I take out extra 0.36 qts or I will be okay? Thank you. 

Edited by Interleukin6
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Z45
Z45

FWIW, AMSOIL will have a 75W-85 Gear Oil coming Nov 1. 

Interleukin6
Interleukin6

I checked the level again today. My truck was completely leveled, which was confirmed by the dashboard. No fluid was seeping. The fluid was at the fill hole. Weird.. it is definitely overfilled from 2

Z45
Z45

They been busy expanding into the industrial manf and a grease manf . https://blog.amsoilindustrial.com/2023/05/08/amsoil-inc-acquires-benz-oil-expanding-amsoil-industrial-business-unit/ htt

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newdude Senior Enthusiast

newdude

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Was the truck on a flat level surface?  If you were facing downhill it could have snuck some extra in.  Will it hurt?  Probably not?   

 

The capacity (depending on RPO code axle) is between 2.59-2.75 quarts, but the service manual then states the following:

 

  1. The axle lubricant level should be 0.0 – 20 mm (0.0 – 0.78 in) below the fill plug opening.
Edited by newdude
customboss Senior Enthusiast

customboss

Posted
Posted
2 hours ago, Interleukin6 said:

I used OEM GM gear fluids. To sump up, as long as the fluid does not come out from the fill hole, it should be ok… right?

Was the clean GM GL straw colored? 

customboss Senior Enthusiast

customboss

Posted
Posted

That’s a biobased syn blend. It will not foam easily. If you see fluid coming out fill at seep level then  it will be splashed up into system and not foam in my opinion. 

Interleukin6 Enthusiast

Interleukin6

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Posted (edited)

I checked the level again today. My truck was completely leveled, which was confirmed by the dashboard. No fluid was seeping. The fluid was at the fill hole. Weird.. it is definitely overfilled from 2.64 qts but still meets “0-20 mm below fill hole”

Edited by Interleukin6
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64BAwagon Senior Enthusiast

64BAwagon

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Posted

On the HD models the rear differential is filled by American axle before it is shipped to the assembly plant. I was told by someone with contacts at AA that the fluid is filled by weight rather than volume. Many people here (me included) have noted that their truck took just shy of a full qt to fill to the level prescribed in the service instructions that @newdude is referencing.  

redwngr Senior Enthusiast

redwngr

Posted
Posted
21 hours ago, Interleukin6 said:

I checked the level again today. My truck was completely leveled, which was confirmed by the dashboard. No fluid was seeping. The fluid was at the fill hole. Weird.. it is definitely overfilled from 2.64 qts but still meets “0-20 mm below fill hole”

 

How long was it stationary before checking? 

 

 

 

Z45 Senior Enthusiast

Z45

Posted
Posted

FWIW, AMSOIL will have a 75W-85 Gear Oil coming Nov 1. 

ulv.png

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Z45 Senior Enthusiast

Z45

Posted
Posted (edited)

fwiw, the SU8 axle the OP has is not a AAM axle. 

 

Its termed GM Axle (supplier B in parts I am told) and will be stamped GM on the case.

 

SU4 Front AAM

SU7 Rear AAM

SU5 Front GM

SU8 Rear GM

If anyone recalls, several years ago AAM was hit with some labor problems and GM had to source (front and rear) axles from another supplier who remains anonymous.

Edited by Z45
newdude Senior Enthusiast

newdude

Posted
Posted
1 hour ago, Z45 said:

FWIW, AMSOIL will have a 75W-85 Gear Oil coming Nov 1. 

ulv.png

 

 

Really...I'm actually surprised they didn't make that sooner given many light duty truck OEMs have been using it for some time now.  

64BAwagon Senior Enthusiast

64BAwagon

Posted
Posted (edited)
1 hour ago, Z45 said:

fwiw, the SU8 axle the OP has is not a AAM axle. 

 

Its termed GM Axle (supplier B in parts I am told) and will be stamped GM on the case.

 

SU4 Front AAM

SU7 Rear AAM

SU5 Front GM

SU8 Rear GM

If anyone recalls, several years ago AAM was hit with some labor problems and GM had to source (front and rear) axles from another supplier who remains anonymous.

You noticed I used the axle on the HD as a reference only. I did this because I didnt have info on the ones in the other series of trucks. 

With the side plug fill on many new transmissions that squeeze bag will come in handy. 

Edited by 64BAwagon

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