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Posted by D Sherman [72.47.9.228] on Sunday, April 03, 2011 at 18:59:17 :
In Reply to: Gear Box Lube posted by gmharris [71.105.178.157] on Sunday, April 03, 2011 at 18:12:08 :
As I understand it, the sulfur is added to "extreme pressure" (aka "hypoid") gear oil for the same reason it's added to thread-cutting oil -- as an "anti-flux" to prevent galling when you have metal-to-metal contact which is bound to happen from time to time. It's in the form of elemental sulfur dissolved in the oil, which is also how oil comes up out of the ground and why old-fashioned diesel oil is fairly high in sulfur. I'm don't think it corrodes the bronze by becoming sulfuric acid, because if it did, it would corrode the steel even faster. Look at what battery acid fumes do to battery boxes and hold-down bolts, while bronze battery cable clamps hold up pretty well.
I suspect the sulfur reacts with the copper in the bronze directly. For a "Mr. Science" moment, heat a sheet of copper red hot and drop a lump of sulfur on it. It will react violently and burn a hole right through the copper. Best not do it in the kitchen. The same reaction probably happens more slowly at lower temperatures.
I don't know that it's a matter of "better brands" so much as using the right oil for the job. Just as you wouldn't use thread-cutting oil as engine lubricant or the best motor oil in a winch gearbox, an oil for use with bronze bushings is formulated for that purpose no matter who makes it. On the other hand, no matter what the application, any oil is better than no oil, so if you're out in the boonies and discover your engine oil ran out of a crack in the pan, or your gear oil ran out through a bad seal, it's better to put gear oil in the engine or motor oil in the gearbox than to try to get back to civilization with no oil at all. In a pinch, you could probably drain half the oil out of a gearbox and put it in the engine or vice versa.
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