Help me out here if you can

[partsman]

Have a 1996 GMC K2500 4X4 auto trans, G80 diff which is a limited slip type, and I was going to change the diff fluid front and rear, fellow at work used to work at GM dealer, brings me fluid still sealed he says he had kicking around and will be good for the truck, part numbers 10950849 and 89021672 they are both SAE 80W-90 GL4 rated, but I think I am supposed to use something with a GL5 rating, plus some type of additive.
Any input?

 

[Steve S]

Yes on the GL5.

 

[mechtech2]

That GL4 will actually work decently.
IF the truck is lightly used with light loads .
GL4 is not a death sentence. It just won't hold up to severe conditions like GL5.

That said, this is not an emergency and you have no need to use the incorrect fluid. It is not smart when you have a choice.
So gt the GL5 in your favorite brand.

 

[partsman]

I do tow a 23 foot fifth wheel in the summer, so I think I will grab the GL5 just have to see how much additive it takes for the rear diff, and obviously add it first and then fill the rest with the 80W-90

 

[Rand]

that was probably meant for a manual transmission not your rear end.

Just get the right stuff.

A 75w140 or 75w110 syn would be good also if you tow the trailer often. or for extended distances in heat.

 

[oilboy123]

GL-5 or nothing.

 

[Whitewolf]

is it a plate diff?

 

[Eric24]

for my 08 and 09 Silverado with G80s don't call for any additive but I not sure on a 96

 

[xxch4osxx]

My '04 Silverado didnt need any additive either.

 

[oilboy123]

I just put Amsoil Severe Gear in a 92 Dodge and needed no Friction modifier. The old lube was Series 2000 gear lube and non needed with it either. It's a limited slip Dana 60.