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    Default 1986 35mm fork tubes vs 1983 35mm 4' over tubes. Can I make this work?

    So I recently bought some 4 over fork tubes that are for years 1979-1983 because I couldnt get a straight answer on why they wouldnt work for my year(1986 sportster) if they are both 35mm. Anyways, now I know why. The bottom bushing appears to be different. My fork lowers are Showa and my question is If I buy a lower bushing for the 1979-1983 forks will they work in my lowers? Has anyone done this before? I've tried looking at previous posts and I cant find a definitive answer. Am I SOL and need to sell these and just go back to my original forks? My forks are on the left and the new ones on the right pictured. Click image for larger version. 

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  2. #2
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    Been there done that. The easy solution is to get 1984+ tubes. I have a set of 4" over Forking by Frank tubes in my shop I used for one season on my 1984 FXSB if you are interested. Here is how they looked when they were on the bike. I decided I wasn't about that life so I put the stock length tubes back in.

    Last edited by garystaven88; 05-14-2020 at 2:28 PM.

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    going to send you a message.

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    Quote Originally Posted by garystaven88 View Post
    Been there done that. The easy solution is to get 1984+ tubes. I have a set of 4" over Forking by Frank tubes in my shop I used for one season on my 1984 FXSB if you are interested. Here is how they looked when they were on the bike. I decided I wasn't about that life so I put the stock length tubes back in.

    My account is being weird on here, can you email me? Michaelleejohnson24@gmail.com, I am interested.

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    I'd measure the inside diameter of the fork tube on the area at the cap end below the threads, then turn the bottom ends up and compare the holes for the damper rods.

    Damping function:
    Your existing damper rod must fit through the hole in the new tube steel inner end bushing while the head of the damper rod seals against the inside of the tube or you'll have no dampening which is bad news as dampening controls fork dive. Therefor the tube ID must match within a few thousandths for the damper rod sealing rings to function.

    The steel bushing inside the new tube will also have to permit damper rod installation since the "bolt end" of the damper rod you have may not be compatible. The lower stop must not wedge in the new fork tube bushing or it may stick when the fork bottoms out.

    (For those not familiar, fork tubes slide inside the top bushing whose position is fixed by the fork slider, while the bottom bushing mounted on the tube slides in the fork slider.)

    I don't have any of the right side style tubes or bushings for same to compare but the nominal diameter of the split bushing for the left side tube (they have some spring to them because the bushing is split to slide over the tube) = 36mm. My samples were off a 1985 FXR and earlier Sporty or Shovel (I put all my 35mm shit in one bucket).

    What is the inside diameter of your sliders measured at the "running" area further in than the top bushing?

    If your damper rods fit inside the new tubes and the slider ID is 36mm then the lower bushing may solve the problem.

    http://sportsterpedia.com/doku.php/techtalk:evo:susp01

    The bottom bushing for the earlier forks will not fit your new tubes. Note the different width of the machined step where the bushings ride on the tube. If the bushing OD for the later tubes is 36mm it could work but I don't have one of those forks apart to check.

    It makes more sense to get the tubes off GaryStaven88 and sell your new ones
    but if the ID of your sliders is 36mm I'm the curious type so I'd check to see what fits for giggles even if I bought the correct parts.

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