I have asked the question before and not received a definitive answer from a
tech or someone with equivalent qualifications.
I have an 01 Jimmy 55,000 mile on it. When the road is wet from steady rain
am I going to do any damage by putting the transfer case in Auto 4WD? If it
ok when the road wet from rain what about under dry conditions ? I must also
say that I am not worried about reducing gas mileage because it stinks as it
is now when I keep it in HI 2. I only get 13-14 in city driving with a VERY
light touch on the gas peddle.
I run our 01 Z71 in auto anytime the roads are slick be it rain or ice
(don't see much ice in AZ, but it does happen). It is actually good to
run it in 4WD as it keeps everything lubed. As far as dry conditions,
won't really matter as it won't lock into 4WD unless you get tire
slippage on any of the current drive wheels. Open diffs keep damage
from occuring. Now if you had the front/rearend locked/spooled then it
would be a different story and you could do some damage. So run it in
auto all you like.
Why would you need to run in 4x4 when in the rain? Unless you are out in
muddy, dirt road style conditions, being in 4x4 won't help you on a rainy
asphalt or concrete road.
My personal feeling is that you should not use auto4hi unless you are in
low traction conditions like snow, ice. There is no real reason to.
By the way, running in auto4hi does not "keep things lubed" anymore then
running in 2hi. Even in 2hi, the auto t/case applies 5-10% torque to the
front diff and so the front driveshaft and front diff internals are still
The only thing not connected is the right front axle in the extension tube.
it is still being turned by the right axle anyway.
Ian (gm dealer tech for over 25 years now)
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