My father-in-law has a '43 Willys MB that he bought in the late
forties. He drives it in Colorado every year, generally logging
hundreds to thousands of miles of mostly off-road, mostly 4WD driving.
The old MB now has several hundred thousand miles on it, and I don't
think the driveline has been overhauled more than a couple of times.
I've known him since the late seventies, and I know he hasn't
overhauled the driveline in the MB during the time I've known him.
(Although, I think he may have done a minor overhaul of the engine
once during that time.)
No, he doesn't lock in the hubs (okay, that's not original equipment)
until just before he gets to the seriously steep or slippery stuff.
He never drives over 45mph in 2WD high range (I'm certain of this
number), and not over 20-ish (I'm guessing on this one) in 4WD
regardless of whether it's in high-range or low-range.
Also, he upshifts early. Way early. I used to worry about this,
since I was always told it was easier on the engine to wind it up a
bit before shifting. I had forgotten about the long piston stroke
relative to diameter in the early engines. Also, it's easier for the
transmission synchronizers if you shift at lower speeds. (This is an
observation I've made while shifting some of my later model vehicles
without a clutch. Yes, if you get the engine rpm's just right it can
be done, but don't try this at home, and you definitely don't want to
try it on a valuable antique transmission.)
I try to engage the 4WD on my vehicles once a month, and run them for
one to three miles that way. I also put them in low range for about
an eighth of a mile. If you install lock-out hubs (called
free-wheeling hubs in some areas I think) you can engage the four
wheel drive on pavement by leaving the hubs in free-wheeling mode, and
exercise the 4WD components that way. However, I'm fairly sure my
father-in-law doesn't use the 4WD on his MB at all for 8 or 9 months
at a time. (But, he lives in a climate where things don't rust much.)
Frequent gear oil changes are probably as important as regular
exercise, though. I think you should change gear oil at least
annually in the axles, transfer case, and transmission. I used to do
this, and never had any trouble. It was when I quit for about three
years that the whole driveline began failing. (That's on my 1982 Jeep
CJ5 with 150,000 miles.)
A vehicle's longevity while off-roading can depend on how it's driven
off-road. If you off-road an old vehicle, use low-range, and go easy
on it. You can still go virtually anywhere you want, you just can't
throw sand and rocks and mud as far. And, if you're a responsible
off-roader, you should try not to do that anyway. That's the kind of
stuff that has resulted in a lot of my favorite off-road trails being
closed to vehicles.
So, the upshot is, go ahead and off-road, but be careful with it. It
won't hurt the engine. That's what it was designed for. But, keep
the rpm's low, use low-range, and drive smoothly and slowly,
especially when the going gets rough. And, change the gear oil every
time you sneeze, or at least once a year. Actually, I think twice a
year, using synthetic gear oil would be more appropriate for an older
vehicle that is still driven regularly.
That's the formula that's worked for my father-in-law with his MB for
the last 50 or so years. (Well, the frequency of gear oil changes and
use of synthetics is my formula, not his.)
By the way, my father-in-law also has a nicely restored GPW that he's
selling along with a collection of spare parts. Details and digitized
photos are available upon request.
Lee
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