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Thread: Unicorn rear adjustable spring perches

  1. #1
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    Unicorn rear adjustable spring perches

    As mentioned in the other suspension thread, here are pics of the spring perches I've been working on for the E39 Touring. I can't take too much credit for the design since it is based on the existing adjustable perches that is/were in the market. I used the ST and the Fortune Auto rear perches I already had to improve the design - mainly improve the bottom mount of the perch and to allow the use of stand alone coilover spring sets available out there like the ones from Swift.

    A little history so you understand the why. The M5T I built started out with B&G rear springs after the complete SLS was deleted during the build process. The rear B&G spring was ridiculously too soft. It was fired. I sourced a set of ST rear perches and rear spring. The ST rear set up was way too soft too! On top of that, the ST adjustable perch was very very short, only allowing me to use the ST spring because it is very tall. I then purchased from FA their rear kit, because their rear perch was at least twice as tall as the ST perch. The fact that FA offered several spring rates allowed me to fine tune the rear. When I installed the FA perches, I wasn't too happy about the mounting of the bottom base. The stud was too short and there was no way to perfectly center the base on the trailing arm. Was it workable? Yes. But I didn't accept it as a permanent solution. Since there was no other aftermarket support for the E39 specifically addressing this issue, the decision to make my own shit the was next natural step.

    I liked the design of the ST bottom base. There's a centering guide that goes into the hole of the trailing arm. You just tighten the bolt on the underside and done. The threads however were too short. This limited the ST perch to only work with very tall springs. On the FA rear set up, the only thing I really liked was the taller threads, allowing me to use shorter 2.5" OD springs. So I essentially designed my own perches to have both features I liked and none of the features I didn't like. Call it a cleansing of the design lol. Aside from this, I also was generous with the materials, meaning I added (thickened) certain areas of the base and perch to make it indestructible.

    There you have it. Nothing complex about it. And with this, the E39 Tourings finally have a permanent solution to deleting the SLS and allow the use of any aftermarket 2.5" coilover springs.

    I made a production run of 50 pcs. of these perches, and 2 are needed per car, so I have 25 sets available to sell to the community. I'm offering them at $250 shipped within the continental USA.

    Below are pics for reference and comparison:








  2. #2
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    The pics below show the mounting methods of each type on the trailing arm.










  3. #3
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    The pics below show how the FA base is a stud/nut type mounting with no centering guide. The stud basically is swimming in the larger hole of the trailing arm.





  4. #4
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    Pics below show the differences in material added to strengthen design.


















  5. #5
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  6. #6
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    Love it! Will definitely order a set when I get my next check. Spent too much this month. And although I have never had any issues with my mounts, I still like these even better.

  7. #7
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    Pics below show my new perches with a standard 2.5" OD rear coilover spring.






  8. #8
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    Does it still put the spring top off center of the original spring cavity like the FA one? Not that it matters as I never have any issues or noises etc and my spring never moves but just curious.

  9. #9
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    The FA mounts are fine if tightened well, but the thick washer gets pretty kinked and over time can loosen up. It's something so trivial but should be addressed.

  10. #10
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    Yeah mine is kinked but because of that, it always seems to go back to the same position whenever I remove them.

    It also looks like these are probably easier to remove in the car. With the FA's you have to really fight to get the 24mm wrench in there to remove the bottom nut because of the half shaft proximity.

  11. #11
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    Quote Originally Posted by RVAE34 View Post
    Does it still put the spring top off center of the original spring cavity like the FA one? Not that it matters as I never have any issues or noises etc and my spring never moves but just curious.
    I haven't gone through the motion of putting the car down to fully compress the rear suspension and jack it back up to see. Still need to finish cutting the notches for the adjusting wrench. Once that is done, I can install the new perches and set the ride height and then check for that.

  12. #12
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    Quote Originally Posted by RVAE34 View Post
    Yeah mine is kinked but because of that, it always seems to go back to the same position whenever I remove them.

    It also looks like these are probably easier to remove in the car. With the FA's you have to really fight to get the 24mm wrench in there to remove the bottom nut because of the half shaft proximity.
    The mounting bolt for the base will be a 15mm or 17 mm, It will be far easier to torque down with a ratcheting box end wrench. I'm still sourcing the bolt with the proper washer size and getting the adjusting wrench stamped to include it in the kit.

  13. #13
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    Nice work!

  14. #14
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    Finished cutting the adjusting notches. Fits the wrench like a glove!








  15. #15
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    Outstanding work, good sir!!!!

  16. #16
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    Those parts made my day as that wrench does fit like a glove!

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  17. #17
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    Very interested in these, once you're done with all of your testing, I'd like to hear the outcome. With the SLS deletion and using adjustable shocks for the rear, being able to utilize a 2.5" spring is key. Just a question.. is the perch too long by chance? Do you have a side by side with the longest one that was ever made any why do you think they only made it that height. Also the benefit of having such a tall perch for height adjustment.

  18. #18
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    Quote Originally Posted by RVAE34 View Post
    Outstanding work, good sir!!!!
    Thank you Brandon! I appreciate the complement.

  19. #19
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    Quote Originally Posted by speed7 View Post
    Very interested in these, once you're done with all of your testing, I'd like to hear the outcome. With the SLS deletion and using adjustable shocks for the rear, being able to utilize a 2.5" spring is key. Just a question.. is the perch too long by chance? Do you have a side by side with the longest one that was ever made any why do you think they only made it that height. Also the benefit of having such a tall perch for height adjustment.
    Yes will certainly post more info about them after I get some miles on them.

    The perch I made was intentionally longer/taller for 2 reasons:

    1. Added strength because the base is solid billet and not hollow

    2. Having a taller base, you can opt for shorter springs, stiffer rate. My perches open more options for the user as far as spring applications.

    I'll take some close up pics of the perch bases I have to compare the different heights.

  20. #20
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    Adjusting wrenches freshly minted from the water-jet cutter. Will undergo special treatment to make it pretty and rust-proof.






  21. #21
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    Have you put many miles on the setup yet? Anxious to hear the feedback on your setup.

  22. #22
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    I installed a set of these perches on the Pegasus. Simple and straightforward. The centering dowel on the bottom of the perch assured it is dead center and bolt and washer made it easy to secure it. I used M5 half axles on my builds so it was a little tight but still enough room to tighten the 17mm bolt. If you have 540 half axles there will be plenty more room.

    I put some miles on the Pegasus this week, the set up works perfect, no clunking, no knocking. I do have an upper spring pad on top of the coil to isolate it from the chassis. Adjusting ride height is as simple at removing the wheel, and turning the adjuster with the wrench. It helps to use a Sharpie marker to mark the adjuster so you know how many rotations. Mine works out to be about .25" for 2 rotations.

    I'll put a set on the Unicorn next, after the holidays.







  23. #23
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    How does that spring and shock combo feel?

  24. #24
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    If you recall, I bought these springs from you, with the FA perches. With the Koni Sport Adjustable shocks, the combo works well. I would say the spring is still a wee soft, but the Pegasus is not as highly modified as the Unicorn. The Pegasus has a milder set up and this works out just fine. It feels more planted it stable around fast bends, but I'm sure this was also because I have the Dinan RSB at full stiff.

  25. #25
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    Yeah I remember that, more curious how the shock worked with it. When I had Bilsteins with them, it was horrible.

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