"Ed Huntress" wrote in message
...

"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

Ford used the Mazda R2 5-speed box in Rangers and F-150s. Mine has 106K on
it and shifts fine. My friend has 300K on his and it shifts fine. Both
trucks have the 300 cube six which belts out 292 lbft of torque. The R2 uses
ATF with a change interval of 60K. A lot of stick shift transmissions now
have needle bearings, which are better lubricated by lighter oils (like ATF
or even 10W-30 motor oil) than good old 80W/90.

-Carl