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Definitive Adjustable Trailing Arm Thread

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  • MFalcon
    replied
    Ara- I finally worked out my coolant issues (not the head gasket, thank g), so haven't done this yet. I'll update this thread when I do.

    M

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  • Ara.
    replied
    Originally posted by anaphe View Post
    I am thinking about adapting something like the 911 RSR camber box into my subframe build. Any thoughts?

    Keep us posted on that !

    Mark, any updates?........or havent gotten around to it yet?

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  • LeeVuong
    replied
    If you use big rod ends on the trailing arms, then you can make adjustments with a threaded rod that goes thru the floorpan for easy access. My advice if you go to rod ends is to use rear coil-overs in replacement of the separate coil spring. That is because if the big seprate spring stacks, all the stress will be on the rod ends, and chances are that they are less strong than a stack of coils... I experimented such system on a friend's car and we kept on breaking rod ends until we found the culprit.

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  • anaphe
    replied
    I am thinking about adapting something like the 911 RSR camber box into my subframe build. Any thoughts?


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  • TR-Spider
    replied
    http://www.s14.net/forums/showthread.php?t=30111&page=3

    post #37 ff
    That are the BMW parts, which I think are also in the IE-kit (Ireland Engineering) which most of the US owners use.

    And no, it "didn't pay off"...but you can learn from trying...

    Thomas

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  • Larsen-Racing
    replied
    Oh, thanks dude! So the work does not pay off after all?

    Tell me about the E39 parts you are talking about please!

    Bjorn

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  • TR-Spider
    replied
    Hi Björn

    have you figured out a way to cut 12mm of the poly bushings?
    No, but I tried something else.
    The big washer placed above the bushing (see the picture in previous post #123) is thicker on the outside than inside. The inside cutout is big enough to allow the rotation of the washer. Therefore one can shift the polybushing (and the subframe) additional 5 mm up by adding a additional 5 mm thick washer under the bushing (like the yellow part in picture) . I simply didnt bother to remove the poly and have another 2 mm grinded of in the workshop, but it is possible.

    So far so good: yes it is possible to move the subframe 12 mm up with a modified polybushing.

    Now the bad news: my camber did not change more than 0.1° really...
    How can that be?
    Well, if we look at Gustaves graph showing the change in camber vs wheel movement, it says the camber will go 0.9° more negative per 1 inch wheel upward movement. Recalculated to metrics thats 0.035° neg camber per mm wheel movement.
    In a first aproximation raising the subframe has the same effect as lowering the wheel.
    So raising the the subframe by 5 mm reduces camber by 0.178°.
    And raising the the subframe by 12 mm reduces camber by 0.42°.
    In reality, if one compensates the suspension height it may be a small bit more, maybe -0.5°
    If one starts from a worn-out rubber bushing, it may be another -0.2°.

    I think I will mount the E39 parts during wintertime and have camber then really adjustable, but starting from a raised subframe.

    Thomas
    Last edited by TR-Spider; 11-13-2009, 06:46 AM.

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  • Larsen-Racing
    replied
    Thomas, have you figured out a way to cut 12mm of the poly bushings?

    Bjorn

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  • Ara.
    replied
    <<<< smiling because this guy doesnt have to drop the subframe, get the IE plates, mess up 13 times trying to weld those suckers in place!

    Lee da man

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  • LeeVuong
    replied
    Hey Thomas

    Raising the subrame by 12mm will change the angle of the trailing arms, which in return will remove some of the camber and toe in associated to a lowered car. And in most cases, it will remove enough so that adding adjustable devices is not required anymore.

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  • TR-Spider
    replied
    Definitive Adjustable Trailing Arm Thread

    Just a thought, maybe its time to open a "Rear Subframe Height Alteration Thread" ?
    Just because we are discussing neither "Trailing Arm" nor "adjustable" anymore...
    Or shall we leave it here because its all about getting the rear wheels into a reasonable position towards the road?

    Thomas
    Last edited by TR-Spider; 10-16-2009, 10:17 PM.

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  • LeeVuong
    replied
    The subframe mounts should be shortened by 12mm on top. It works quite well with solid aluminum bushings or self made units with steel caps and hollow tube. A set of 12mm shims must be placed under the subframe mount to make up for the upper travel, while the retaing plate stays at the same height. Basically, whatever was removed on top,must be added at the bottom.

    A second set of four 12mm shims go between the differential and the subframe.

    So, 6 shims are required and they can simply be M12 bolts that are 12mm thick. Just drill out the threads.

    And please allow me to highlight that you can raise the subframe by 5, 7 10 or 12mm. But never more than 12...

    Lee
    Last edited by LeeVuong; 10-16-2009, 08:30 AM.

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  • MFalcon
    replied
    To clarify Lee's shim method, my understanding is that the rear subframe is mounted to the chassis at the point of the rear subframe bushing sleeves, and also at the differential. The 12mm spacer/shims would go between the chassis mounting bracket and the subframe bushing sleeve, effectively raising the subframe by 12mm. The shims need to straddle the subframe bushing through-bolt. Shimming the differential is self-explanatory.

    The same net effect can be attained using shorter solid subframe bushings with no spacer between the subframe bushing sleeves and the chassis bracket, while still shimming the diff.

    This is my understanding, anyway. Let me know if I'm full of it. I am going to try the former method in a few days.

    M

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  • Larsen-Racing
    replied
    I run 17" now, and going to run 18" next season. So I have to get that camber issue sortet. It feels like the rear end does not follow the front in some corners as well.

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  • TR-Spider
    replied
    I assume the inside tire wear depends also on the tire/rim combo.
    Lower profile tires like 17" or 18" tend to have much stiffer sidewalls and thus will flex less running on camber.
    When BMW designed the suspension, it was for 15" (only later 16" adapted).
    So most likely a stock size tire can handle the stock camber of 2° negative better due to its flexible sidewalls relaxing the pressure on the inside edge.

    I will think of how to modify the poly bushing for 12mm.

    Thomas
    Last edited by TR-Spider; 10-15-2009, 10:27 PM.

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