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| http://www.4x4wire.com/jeep/reviews/more97/ | Short Cuts | ||||
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by: David Gray
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Page 2 - What's a Shackle Reversal?
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| Reverse Shackle Configuration |
The first component of this transformation is the shackle reversal. By "shackle reversal" we mean that the pivoting shackle normally found connected to the front of the spring is moved to the rear and the fixed mount normally found where the rear of the spring connects to the frame 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 of the big reasons why Jeeps with flatter stock springs (like the Wrangler YJ) have a fairly reasonable ride when compared with there predecessors (the CJs).
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 slightly 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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