8 lug 14 bolt semi float

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White96k2500

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So i have a leaking rear riff, 8lug 14 bolt semi float with 4.10 gears and g80. What kind of fluid goes in the rear diff? And does the g80 require a additive?
 
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df2x4

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GL5 rated 80W-90, NO additive. That last part is important. If you put any additive or friction modifier in with a G80 it's not going to work correctly. Make sure you don't use a gear oil with additive already in it either (like Amsoil). Here's a link to what I use, ACDelco 10-4051. This is exactly what GM recommends.

https://www.amazon.com/ACDelco-10-4051-GL-5-80W-90-Axle/dp/B007Q10F3S
 

Supercharged111

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How would a friction modifier affect a locker's performance? It's centrifugally operated.
 

df2x4

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How would a friction modifier affect a locker's performance? It's centrifugally operated.

I'm not going to pretend to know the answer to that, but I have experienced it first hand. I had the diff oil changed in my red truck (10 bolt G80) and my mechanic added some friction modifier. It was super unpredictable after that, much more so than usual. Drained it and refilled with the GL5 80W-90 I linked above and it was back to normal. GM has a TSB on this confirming exactly what I experienced:

https://www.chevytalk.org/fusionbb/showtopic.php?tid/256237

You and I (and a few others) have actually discussed this previously in a different thread.

https://www.gmt400.com/threads/differentials-75w-90-vs-75w-110.43445/
 

White96k2500

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I'm not going to pretend to know the answer to that, but I have experienced it first hand. I had the diff oil changed in my red truck (10 bolt G80) and my mechanic added some friction modifier. It was super unpredictable after that, much more so than usual. Drained it and refilled with the GL5 80W-90 I linked above and it was back to normal. GM has a TSB on this confirming exactly what I experienced:

https://www.chevytalk.org/fusionbb/showtopic.php?tid/256237

You and I (and a few others) have actually discussed this previously in a different thread.

https://www.gmt400.com/threads/differentials-75w-90-vs-75w-110.43445/

so should i go with 75w-90 or 80w-90?
 

Supercharged111

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I know not to use the additive, just weird to me it causes issues. Then again, I've never put additive into my locker rears. And please don't rely on my memory, I suffer badly from CRS.
 

White96k2500

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I use the ACDelco GL5 80W-90 that I linked above. That's what I would recommend.
Yes i saw but i was gonna try to find something a little cheaper as I'm about to start a full front end rebuild then have to get an alignment then buy some tires so i was gonna try to find something cheaper or use some fluid my father in law has but i believe it has the additive, do you know any other products that would be cheaper?
 

df2x4

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Yes i saw but i was gonna try to find something a little cheaper as I'm about to start a full front end rebuild then have to get an alignment then buy some tires so i was gonna try to find something cheaper or use some fluid my father in law has but i believe it has the additive, do you know any other products that would be cheaper?

I do not, sorry. It seems like most of the off the shelf options have the additive in them already.
 

White96k2500

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I do not, sorry. It seems like most of the off the shelf options have the additive in them already.
That’s the problem i am running into everything i can find has it, sorry for the question as i am not very knowledgeable about this kind of stuff but what is the difference between 75w-90 and 80w-90? Is the 80w-90 just thicker?
 
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