Rear End Fluid - GL-4 Vs Gl-5?
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Posts: 2,325
From: BC
Rear End Fluid - GL-4 Vs Gl-5?
Went to the dealership to get some new rear end fluid (ACDelco 80W90 PN #89021672). I've previously used synthetic. Looking at the bottle it says it "exceeds API GL-4 requirements", but the book calls for API GL-5 fluid.
The dealership said thats what they use (plus the additive), and the additive is what "makes it" GL-5.
Can anyone shed some light on this?
More info:
http://home.earthlink.net/~cmcguffey...l/lubebsk8.htm
The additive however only mentions that tends to limit excess clutch plate friction. Nothing about "EP" or anything like that 
The dealership said thats what they use (plus the additive), and the additive is what "makes it" GL-5.
Can anyone shed some light on this?
More info:
http://home.earthlink.net/~cmcguffey...l/lubebsk8.htm
Basically, an API GL-5 product has approximately twice the amount of EP (extreme pressure) additive than that of an API GL-4 product. If a GL-5 gear oil is used in a GL-4 application which has yellow metals (brass, bronze, etc.), chemical corrosion may develop between the EP additive and the yellow metals causing damage to certain parts. Likewise, if an GL-4 gear lubricant is used in a GL-5 application, severe gear wear may occur due to the lack of enough EP additive.
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Joined: Mar 2002
Posts: 422
From: Louisville, KY, USA
Re: Rear End Fluid - GL-4 Vs Gl-5?
All the additive does is add friction modifier to make the GL4 stuff GL5. Most everything you buy now is GL5 anyways. Just use the modifier with your gm or any regular name brand gear oil and don't worry about it.
GL4 is typically used in gearboxes where EP additives will make it too slippery and the synchro's won't work right. GL4 is actually hard to come by.
GL4 is typically used in gearboxes where EP additives will make it too slippery and the synchro's won't work right. GL4 is actually hard to come by.
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