Differential fluid for 14-bolt 10.5" gear with G80 Eaton Locker

[MartyW]

Our 1997 K2500 GMC Suburban has a 14-bolt rear differential with G80 locker.

I would like clarification from folks familiar with this differential as to what fluids can be used.

As I understand, this same exact differential has been used in many year models, and is still in use, and some of those year models recommend synthetic fluid, and some year models recommend standard non-synthetic fluid.

I asked our local Chevy dealership recently to do a differential service filling with synthetic fluid, but they would only use standard fluid.

Can someone speak to the reasoning why synthetic fluid might be viewed by a GM dealership as being incorrect or harmful for this 1997 14-bolt G80 differential?

 

[someotherguy]

No harm in going with either one, but factory fill on your '97 would be non-synthetic. The main thing to pay attention to is that you don't add any posi type additives to it. It uses straight gear oil just like an open differential, believe that.

Richard

 

[MartyW]

Thanks Richard,

Right on about the no additive. I got quite an education on that. This one is the Eaton mechanical centrifugal locker. When we first got it we got all the fluids changed and the Valvoline folks added the additive. We just got that straightened out at the GM dealership and they put in new diff fluid, without the additive, but they wouldn't put synthetic in. The "reason" they used for not adding synthetic is that the synthetic would eat the RTV since no gasket from the factory. I mentioned the lube locker and felpro gaskets to them but they wouldn't install one. I'm thinking that they just did what was written for the 1997 year model, but that question is the reason for this thread and question. I also called a local 4wd shop and they recommended leaving non-synthetic in it due to age. We got this truck for pulling our camper and wanted to put synthetic in it if possible, but if not I'm thinking that regular fluid has pulled some mighty heavy loads since this diff also went into the 1-ton trucks too.
Marty

 

[Jorge6.5]

Correct, synthetic gear oil is not compatible with the RTV on the diff cover and where the axles meet the hubs. Gm makes gaskets for these.

 

[someotherguy]

My bad, overlooked he was 10.5" FF, dunno why I thought 9.5". Yep gotta watch out for the RTV as typically synthetics will attack it and you'll end up with leaks.

Richard

 

[MartyW]

I've read that other folks have used a gasket for the diff cover (lube locker or felpro) to handle the synthetic.

So, if a gasket is used for the diff cover, would leaks possibly come from the pinion seal and/or end of axle seals on this FF axle when using synthetic?