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Definitive Adjustable Trailing Arm Thread

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  • 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
    Mark

    "She'll hold together. Hear me, baby? Hold together!" -- Han

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    • 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.


      [email protected]

      1969 2002 racecar
      1989 M3 racecar
      e39 Touring

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      • 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.
        sigpic

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        • 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.


          [email protected]

          1969 2002 racecar
          1989 M3 racecar
          e39 Touring

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          • <<<< 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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            • Thomas, have you figured out a way to cut 12mm of the poly bushings?

              Bjorn
              1987 BMW M3 E30

              S50B32 swap thread http://www.s14.net/forums/showthread.php?t=43515

              Comment


              • 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.
                sigpic

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

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

                  Bjorn
                  1987 BMW M3 E30

                  S50B32 swap thread http://www.s14.net/forums/showthread.php?t=43515

                  Comment


                  • 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
                    sigpic

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


                      Comment


                      • 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.


                        [email protected]

                        1969 2002 racecar
                        1989 M3 racecar
                        e39 Touring

                        Comment


                        • 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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                          • 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
                            Mark

                            "She'll hold together. Hear me, baby? Hold together!" -- Han

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