View single post by Esprit2
 Posted: 09-27-2017 10:12 pm
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Joined: 05-01-2005
Location: Minneapolis, Minnesota USA
Posts: 343
Use a GL-5. It's specifically formulated for use with hypoid gears, such as those used in the final drive's crown wheel & pinion. It's consistent with the EP requirement.

GL-4 is formulated for manual transmissions, and it's synchro friendly... ie, those yellow metal parts you're concerned about. It is NOT for the hypoid gears commonly used in crown wheel and pinion of rear axle assemblies.

Back in the day, the JH manual recommended the following gear oils for the rear axle:
Shell Spirax 90EP
BP Gear Oil 90EP
Esso Gear Oil GX 90/140
Castrol Hypoy
Fina Pontonic MP SAE 90
Mobil Mobilube HD90
Texaco Multigear Lubricant EP90
Duckhams Hypoid 90

Note that all those oils are decades old and probably no longer available. But you can use them as a starting point to cross-ref to a modern gear oil.

Or, just shop for a GL-5, EP90 gear oil.

Many modern full synthetic gear oils are dual-rated for both GL-4 and GL-5. One of those would be fine as well.

Back in the old days, most GL-5 oils used compounds of sulfur to provide EP protection for hypoid gears. It was those sulfur compounds that would attack brass components. Many modern gear oils have replaced sulfur with other compounds for EP protection. It's that brass compatibility that allows some EP oils to be dual-rated GL-4 & GL-5.

Tim Engel