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A few thoughts here David,
<<Brian, you've got it all backwards.>>
True!
<<4wd Part time is the original system, used on the jeeps in ww2 (and
I think 1 as well, but i'm not a history buff). It locks all 4 wheels
to go the same speed all the time, which is great for off reading,
because you'll never be stuck with 1 spinning wheel and being unable
to move.>>
Could be, but I'm not sure... I think the old Willeys were a true 4WD
system that would not be considered part-time... Worked more like the
lockers that are sold aftermarket today or perhaps even more rigid?
<<However, on dry pavement, it adds a lot of stress to the driveline,
as the outside wheels need to turn faster when taking a corner and
cannot with 4pt.>>
This is kinda' true but not with the standard (or open) diffs most
4X4's come with... The tension or "winding up" of a part-time system
comes from the fact that the torque provided to each axle is equal
and, therefore, does not let the axles turn at different speeds in
high traction conditions (on the road). This is what causes wear and
expensive repair bills with part-time systems with open diffs!
<<4wd full time is a system that has 3 differentials (pt has only 1,
the standard rwd unit), so all 4 wheels can turn at different speeds
as conditions require. This is perfectly suited to dry and wet road
conditions, but can cause a loss of traction in severe conditions
(stuck in mud, etc).>>
True... But each axle has a diff so the part-time system has 2 diffs.
While all 4 wheels can spin at different speeds with open diffs on
each axle, the keynote here is that the full-time system has a diff
type system in the transfer case which allows the axles to turn at
different speeds.
<<This is why manufacturers often include either an automatic or
manual locking center differential, which prevents all the engine's
power from going to one spinning wheel.>>
I think we are mixing things here... Shift on the fly is basically a
convenience item to engage the front axle... The only way to prevent
wheels from spinning is to lock the differentials on the axles...
Great for off-road -- very bad for street.
<<AWD, or all-wheel drive, is a lot like 4ft except you cannot turn it
off. often times these systems are designed EXCLUSIVELY for road use
and are far less suitable for off-roading.>>
Basically true but I've heard that Mercedes (I think) puts out an
impressive AWD rig that uses the ABS brake system to keep power coming
to wheels with traction... So they keep open diffs for great highway
performance/manners while maintaining off-road traction that would put
alot of 4x4's (including my Kota) to shame!
T.
This archive was generated by hypermail 2b29 : Fri Jun 20 2003 - 12:09:57 EDT