Best mineral based gear lubes

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Jun 10, 2002
Cordelia, CA
I've got a question on another forum. This person is installing an Eaton limited slip differential, and "Eaton strongly recommends utilizing an API-GL5 approved Mineral-Based 80W-90 Axle Lubricant and one 4-oz bottle of Limited Slip Additive (GM or Ford)." I know many "synthetics" are group III. What are they, and where can you get them? Thanks, Wayne
Gosh, I cannot imagine why they would recommend mineral vs. synthetic when Eaton has an extended warranty that is based on the use of synthetic GL-5 75W-90 lubricant! Anyway, the Mobil 1 75W-90 synthetic (Group IV) in quart bottles is GL-5 and already has the limited slip additization so you don't have to worry about getting the proper amount in. Using a full synthetic in a rear end is a total win/win in terms of minimizing througput HP loss, reduced heat, reduced wear, etc. etc.. I realize I am answering a question you did not ask but I can't believe the question!! :-) George Morrison, STLE CLS
I have an Eaton Posi (w/ 400lb springs in the clutches) in my '96 Impala SS. Both Eaton and the person I bought it from recommened 80W90 GM gear lube and GM posi additive. I questioned Eaton on this via email and they told me that they don't recommend synthetics because some synthetics cause the clutches to chatter. I did 500 miles on Chevron 80W90 dino oil, I drained and refilled with Lubrication Engineers 75W140 full synthetic and I used one bottle of GM posi friction modifier both times. I haven't heard a peep out of the clutches with the LE 75W140. The Eaton posi is a super piece. I really works very well.
This is the reply to an e-mail I sent to Eaton, so Is Valvoline Synthetic a Group III based? Wayne: Hello there! How are you? Fine, I hope! We strongly recommend utilizing a mineral based lube with the limited slip additive based on the fact history has indicated synthetic gear oils have a higher propensity to produce the phenomemon known as chatter. All of our internal testing was completed with the GM Mineral Based 80W-90 gear oil and GM limited slip additive (available at any GM parts counter). We obtained excellent results with this lube combination. I must inform you that you have been misinformed in regards to Eaton offering an extended warranty for the use of synthetic gear oil. We do not!!! Thanks for your inquiry and have a blessed day! Wayne Brantley Business Unit Manager Eaton PSCO/TCPD Aftermarket Team
I do know Eaton offered extended warranties for their industial axles if one used full synthetics. Maybe their aftermarket group doesn't, but their industrial group did. For a dino gear lube, I prefer Pennzoil or Chrvron's lubes.
I guess it's the sames as with the stock Impala Auburn. Synthetics in the differential are always a crapshoot. They may or may not chatter. Chatter is probably not an issue in the industrial market. I'd like to run a Group III "synthetic," as that is the highest quality mineral based, but I guess a Group II+ like Pennzoil would do. I e-mailed Valvoline, but have not received a response.
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