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  • What is Shackle Reversal? 4.0L Head Swap Question.

    First off, what is shackle reversal, can someone please enlighten me..

    With a 4.0L head conversion, I know I will need to seal off a couple water passages, and get a different set of headers. What I'm wondering is if the intake will be the same, and if my current exhaust system will mount up exactly where my old headers where, or will I need to modify my entire exhaust system. As of right now I have Headman Headers, if I get another set of Headman Headers for a 4.0L will it be a dirrect swap with no issues?

  • #2
    Shackles are moved from the in front of the front axle to behind it.

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    • #3
      Still confused??

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      • #4
        Originally posted by Alaskanbadfish View Post
        Still confused??
        shackles are the pivot point for your leaf pack. They are somewhere around 5" tall and have bolt that goes horizontal through the shackle and into the frame. Like Joda says they are stock mounted to the front end of the leaf pack (front axle). With the reversal the front of the leaf pack is mounted directly to the frame (with a bracket of course) and the shackle (pivot point) mounts to the rear of the front leaf pack.

        I'm sure some one will post a pic to see

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        • #5
          The idea behind a shackle reversal is to obtain a better ride and possibly improve articulation.

          http://jeep.off-road.com/jeep/articl....jsp?id=260281

          The leaf spring design depends on being able to move, to elongate when being compressed and to shrink when un-compressed ( the axle drops down, taking weight off the springs). To do this, one end of the spring is firmly anchored with just pivot movement and the other end has a shackle, pivoting on two points to allow the spring's movement.

          When the shackle is located at the front of the spring pack, the spring has to elongate forward, carrying the axle forward as well. Any shock received by bumping into an obstacle, pothole etc, is transmitted directly rearward to the frame and thus to the driver's butt as the spring tried to shove the axle and wheels forward, into the pothole or rock, to allow the spring to move.

          Reversing this setup allows the spring to transmit the shock load into the shackle, which then can move and dissipate the energy instead of transferring it to the frame. This allows for a smoother ride and less wandering on the road. It does, however, have a few side effects. Because the shackle is now at the rear, it allows the axle to walk forward on hill climbs and the nose can dive more on deceleration. The nose-dive can be un-nerving I am told, but it can be gotten used to and does not seem to negatively affect anything. The hill climb thing can separate an unmodified front driveshaft though. It is often recommended to install a shaft with a longer slip-yoke to compensate for this. A reversal also often locates the front axle an inch or so forward, stretching the front shaft even more. This does allow more room at the rear of the wheel well to avoid rubbing however, or else the axle could shove the wheel into the rear of the opening as it flexes.

          There is a lot of controversy on the engineering principles and why the OE's built vehicles with the shackle at the front. Most every stock vehicle (Jeep, Toyota FJ40, etc) I have ever seen has this same configuration, so there must be an industry opinion (or legal issue) involved there.

          No clue on the 4.0 conversion. I know it was addressed before, but thats all hiding in the archives and I havent found a way to search them.
          Last edited by Gryphon; 03-09-2010, 01:34 PM. Reason: Found a link to more/better info with pics.

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          • #6
            Originally posted by Alaskanbadfish View Post
            Still confused??
            :facepalm:

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            • #7
              check this out...

              this thread has a few pics and stuff. I have more if you need em'...
              http://jeep-forums.4wd.com/showthrea...l-kit-and-lift

              Between what Gryphon said and that link, you should be able to finger it out...

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              • #8
                Did the head swap on mine awhile back bought the head already remaned with the proper jackets welded up, the fuel injection system I used was for the 4.2 but works fine on the 4.0 head however exhaust is a different story I was told by the folks at HESCO the exhaust had to be for the 4.0 due to larger exhaust ports

                LOL

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                • #9
                  I'm just nervous that I'll put in a lot of time, effort, and money into replacing the head with the 4.0L, get new headers, and they won't match up with my exhaust. Then I'll have a bunch of exhaust work on top of all the head work, I just replaced all my exhaust too.

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                  • #10
                    Gonna bet your old exhaust will not line up perfect you will have to do some mods to it but the 4.0 head is worth it

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