I am posting this so I can get educated. Just finished taking apart an
automatic transaxle (1990 Nissan Maxima) for entertainment and "artsy"
parts. From the bearings and races I see a welding positioner in my future!

Anyway, the planetary gears are amazing as is the differential gear setup.
All of this runs in a transmission fluid bath, which makes me wonder, why
we use heavy gear oils for similar applications when not unitized with an
automatic tranny? Granted this unit was not as heavy duty as would be
required for a rear end of a truck, but, I am sure there are trucks with
front wheel drive automatic transaxles. (Maybe not?).

Educate me why heavy oils are used in gear boxes.

Thanks,

Ivan Vegvary