ricky racer wrote:Pulled from the internet:
. . .
What Ricky said pretty well covers it. I think the deactivated sulfur approach is why they initially though that GL-5 could be backfit to places that used GL-4. That didn't work out so well. Today you can run across oils that are labeled GL4/GL-5. A lot of the observations/rumors suggest they are really GL-5 and not totally trustworthy for a GL-4 application. I always thought, but have no proof, that gear oil odor is mostly from sulfur.
HY-Tran, and I believe the compatibles, conform to GL-4. Viscosity Oil Company has advertising that goes to great lengths to talk about how safe it is with yellow metals. Other high quality hydraulic/transmission oils probably are as well but I have not checked.