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Discussion Starter #1
I want to change the fluid in my rear diff. I have heard unconfirmed reports that because I have a G80 rear end, I MUST use the dealer "grape juice" and that I can't use a quality synthetic like AMSOIL or MObil 1 ? Is this true? What can I use that won't screw up anything or void a warranty?

Thanks,

M
 

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Not sure about the warranty, but ANY reputable full synthetic will work just fine.
 

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Never heard that. I've got Mobil 1 in mine. I hope that's not the case. Did a dealer tell you that?
 

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Of course the dealer will try to "coerce" you to buy his GM grape juice for $28/qt! Any GL-5 rated synthetic gear lube is fine. The Eaton G80 locker does not require any friction additives.
 

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I put grape juice in mine only because it is a KNOWN good quality GL 5 that works in the G80, but the manual only says what specs, NOT what brand. I'd think any good quality lube that meets the spec would be fine.
 

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Dealer also has a synthetic gear oil for your truck that is not the grape juice.
 
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