"Bill Schwab" wrote in message
...
Ed,

For any automobile gears, you need a high-pressure lubricant. I don't
know how they got away with ATF for that job. For hypoid and spiral-bevel
gears, as in a rear-axle diff, you also need a lubricant with high shear
strength. That's what heavy rear-end oil is supposed to have.

If by shear strength, you mean viscosity, then ATF might be quite viscous
in low temperatures mentioned elsewhere in the thread. Or, are you
thinking of shear thinning or other non-Newtonian/viscoelastic phenomena?

Bill

I don't think ATF is viscous at any reasonable temperatures, Bill. Somebody
mentioned that it forms a chemical film and that rings a bell with me.

I'm not a tribology expert but when I was studying gears the lubricant
properties differentiated high-pressure capability and shear strength. Shear
strength apparently is a property by which oil can take sliding loads, as in
a hypoid gear, without the film breaking down. I've always thought that
high-pressure lubricants can take a high static pressure but not,
necessarily, high shear loads.

But, like many other things having to do with engineering, I studied that a
very long time ago.

--
Ed Huntress