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Thread: shock mounting 101

  1. #1
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    shock mounting 101

    I'm in a bit of a debate on another forum about shock mounting. Using the brackets off a stock xj rear sway bar as a BPE is quite a popular mod. When I think about this mod, I see a problem with it. When mounting the bracket on the upper mount, you are changing the upper swivel mount from forward/back to side/side. The lower axle mount is also a side/side swivel mount. When a leaf spring articulates, it moves forward and back a little and the axle mount for the shock moves left to right as well. This would require having one shock mount that can swivel left to right and one that can swivel forward and back (like the stock is set up). Changing the upper mount so it swivels in the same direction as the lower mount would cause stress on the shock and bushing during articulation.

    For the front, it doesn't matter how you mount the lower shock cuz the upper uses a stud that can swivel in any direction.

    Am I thinking right?

  2. #2
    PghOffRoad Forum Addict!
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    It really doesn't matter since a shock bushing has a significant amount of flex in them and the amount of motion the shock will see is fairly minimal.

    If you had a ball and socket joint it might matter, but a poly joint flexes either torsionally or in compression about the same. You only have so much movement untill you rip the poly no matter how it's mounted.

  3. #3
    Less posting, more wheeling! joshs1ofakindxj's Avatar
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    Quote Originally Posted by muddeprived View Post
    Am I thinking right?
    I thought about this issue back when I was making XJ BPE's so I made my own that kept the axis of rotation of the upper and lower shock bushings parallel, instead of using the XJ sway bar mounts and then having the axis of rotation of the upper and lower bushings perpendicular to each other. I think having them perpendicular could contribute to heavy wear and premature failure on the upper shock bushing, but I haven't done any experiments. Common sense tells me enough, that you should have them working together as smoothly as possible.

    Quote Originally Posted by oros35 View Post
    a poly joint flexes either torsionally or in compression about the same. You only have so much movement untill you rip the poly no matter how it's mounted.
    I don't know if I agree with this. The torsion, or bending stress on a bushing resulting from the perpendicular mounting wouldn't see the uniform contact area throughout the bushing that would be experienced during compression and extension that you would see if the bushings were parallel. I think if a bushing only experienced compression, it would have a significantly longer life than a bushing that also experienced torsional/bending stress along with compression stress.

    I think this is one of those arguments were the people who want to use the easy and cheap sway bar end to make a BPE, and possibly don't have the means to fabricate a mount with the correct mounting, will argue it will work fine without really having any proof. No offense to you oros, just my take FWIW.
    Last edited by joshs1ofakindxj; 07-15-2010 at 09:51 AM.

  4. #4
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    Ok i feel like an idiot now cuz I got my TJ and XJ mixed up. I was thinking the XJ upper mounts are mounted horizontally like the TJ's are, but in fact they are mounted the same way the axle stud is. Having changed a godzillion different shocks, I should have known the xj mounts by heart but I guess a traffic jam in my brain caused my memory cells to intersect and screw with my way of thinking.

    I "FAIL" myself here........lol.
    Last edited by muddeprived; 07-15-2010 at 11:38 AM.

  5. #5
    Less posting, more wheeling! joshs1ofakindxj's Avatar
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    *high five* for admitting when your wrong haha

  6. #6
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    Quote Originally Posted by joshs1ofakindxj View Post
    *high five* for admitting when your wrong haha
    It's been happening a bit lately. I think the increased consumption of alcohol has something to do with it. I'm already on #3.......

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