The first component of this transformation
is the shackle reversal. By "shackle reversal" we mean that the pivoting shackle
normally found on the front of the spring is moved to the rear and the fixed
mount normally found on the rear is moved to the front.
Why would we want to do this? Reversing the shackles
provides a much smoother ride and can help steering wander a bit (more on
this issue later). The smoother ride is a result of the movement of the
spring and axle when it compresses over a bump. Normally when driving forward
and the tire encounters a bump, the bump wants to push the tire back and up,
while in the normal configuration as the spring compresses it wants to move the
tire forward because the shackle swings forward (well, to get technical the bump
does not "want" or "push" anything, but you get the picture without complicated
force explanations) - the result is that when you encounter a bump your Jeep
gives you more of a jolt than it has to. This is most pronounced with highly
arched lift springs, which is one big reason why Jeeps with flatter stock
springs have a fairly reasonable ride.
Now when you encounter a bump with a shackle reversal the
bump wants to push up and back and the as the spring compresses it naturally
moves backwards. All is right with the world. The effect is quite noticeable and
it turns what used to be a jarring, tooth rattling ride into a much smoother
more pleasant experience. In addition, an added benefit is that bumps now
increase camber instead of decreasing camber and that helps result in a little
bit more stable steering and less wander over bumps.
Sounds wonderful, why are all Jeeps not made
that way?
Well in short, it is because like all things in life there
are tradeoffs. (In fact some of the military Jeeps did have reversed shackles)
The most noticeable tradeoff with the shackle reversal on the road is that now,
when you brake hard, there is a much more pronounced brake dive. This happens
for all the same reasons it is better going over bumps. The forward mounted
shackle in the normal configuration helps combat brake dive because as the
shackle moves back with braking it tends to fight the compression of the spring
(raises the spring rate). While with the shackle reversal as the shackle moves
back it tends to cause more compression in the spring (lowers the spring rate).
This can be compensated for by using a good firm shock absorber which will damp
the tendency of the system to dive forward and still leave you with a better all
around ride. Because of the more pronounced brake dive I highly recommend that
you DO NOT drive on the street without your sway bar attached.
In lawsuit happy America this reason alone could be why Jeep very early on
switched to it's current shackle configuration.
The other tradeoffs to be aware of are that since the Jeep
was not designed to have the shackles work this way some people may see problems
with fender rub that was not there before and often the front driveshaft must be
modified to avoid pulling it apart under extreme extension (since the axle now
moves in the opposite arc).
Are the trade-offs worth it? For my particular application I
think they were. The ride is now much better than before, both on and off the
trail.
There are tradeoffs for the buggy spring configuration as
well, but before we discuss those lets look at how the system installation
went:
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