On Dec 21, 3:19 pm, "Ed Huntress" wrote:
"Ivan Vegvary" wrote in message

news:yPUaj.12$ML6.5@trndny04...



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

You'll probably get better answers to this, but you may be interested that
my '87 Mazda 626 with manual gearbox specified *either* a heavy gear oil
*or* ATF for the gearbox. That one really threw me when I read it in the
factory shop manual. I used both at different times and the gearbox
definitely was quieter with the heavy lube. However, the synchro was also
much slower to work in cold weather.

That transmission, BTW, was one of the worst corruptions the Japanese ever
built. It was just that year -- 1987. I had it rebuilt twice, and I'm easy
on gears.

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.

--
Ed Huntress

My '85 Volvo DL also had ATF in the manual tranny....very nice on
those -35 F mornings.

Wolfgang