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A Primer on “Stops” Mod, Bushing & A-arm Theory

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  • A Primer on “Stops” Mod, Bushing & A-arm Theory

    Suspension of Disbelief, Part 1.d.

    Intro: This is a fourth article about a mod to prevent the development of fore/aft travel in stock bushed front type A-arms. Please follow the links back (bottom of post) to read previous, see photos, or to contact author (via the ad may be best) regarding sourcing.

    In my view it is well worth re-examining this up-dated older idea, how one might better employ stock A-arm bushings that with help, can provide both maintenance and performance improvements far beyond what stock alone can provide, for very low additional cost. With this piece I aim to explain the need for and effect of the mod on the bushings and A-arm behaviour; and the success I’ve had with this in the hope that others might also want to try the mod.

    Premise: In Praise of Original Equipment (OE) Bushings.
    Not older bushings, not used bushings, nor recently replaced ones. As this whole concept is about preserving the characteristics of unspoiled “as wrought” new bushings, this next part begins there and is strictly about correctly installed brand new bushings. More specifically the Boge ones, more as to why later. Without stepping into the debate of OE vs. alternatives, I will simply state that there are characteristics of OE bushings that are most suitable for our application here forming the inner hinge-axis of the A-arm as follows:
    a.) Sealed unit with no 'moving parts' that is impervious to water, road grit, etc.;
    b.) Acts as a friction-less, zero-play, silent and maintenance-free hinge-line which provides an excellent basis from which to align the wheels precisely and repeatedly (my alignment tech prefers them over all other types). Laterally, they feel stable and strong enough when driving at the limit; &
    c.) Fits precisely, are relatively low-cost, and are easily available.

    The only real criticism is that while excellent when brand new, they simply do not last. If their “as new” character could be preserved, they’d be near perfect. Like their sister the strut-mount, the main flaw lies in what appears to be missing from beside the bushing in the installed A-arm to the sub-frame, rather than what is present in the bushing alone. Hence “Stops” (re-named "Arm-Stops" post script, and explained later), a mod to buttress OE bushing function for longer bushing life, more accurate fore/aft positioning of the A-arm and other benefits that follow from these two improvements.

    This piece aims to explain how this is achieved. Because this would otherwise be overly long, I’ll add the rest in sections to follow.

    Again, please also see the links going back (parts 1.a., b. & c.) starting with the previous Part 1.c.
    Last edited by Lago Blue; 17 February 2021, 02:14.

  • #2

    S2 Coupe 3B Project


    Ur quattro restoration

    S2 Avant

    Boost is the new rock and roll!
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    • #3
      This sounds interesting.

      96 URS6 plus speck saloon
      96 URS6 plus speck estate
      94 2.6 80 Avant
      99 2.8 final edition Cabriolet

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      • #4
        Any pics to go with the text that, at least for me, is hard to understand?

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        • #5
          Originally posted by quattrostyle View Post
          Any pics to go with the text that, at least for me, is hard to understand?
          Sounds like washers being fitted between the wishbone and the subframe?
          Current-2004 Impreza PPP wagon

          Sold-92 3B coupe-RS2+, 996s, konis, rear torsen, forged rods........
          Sold ABY-stock

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          • #6
            Actually I thought it was something simple like that, but the text around it makes it sound pretty difficult

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            • #7
              Andy is correct. I've gone back and made the existing links to previous texts & photos more obvious.
              Last edited by Lago Blue; 1 December 2015, 23:12. Reason: clarity

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              • #8
                Am I the only one that doesn't understand any of this? Or understand why you wouldn't just take a picture of the mod and say why it's worth doing in normal terms??

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                • #9
                  Just Starting with "Stops"?

                  As the title at the top of this thread suggests, this is the 4th article in a series. For those just jumping in here, the link in the above post can be used to view the previous post; and so on. I've gone back -again- and numbered the pre-existing links in two of the previous 3 posts on the subject to help make it even more clear. The installed mod just doesn't photograph well, it is a black "stop"-washer (again, photo is in the first post) installed on a black bushing in a black A-arm into a black sub-frame; under the car. Perhaps the easiest way to illustrate how the "stops" are used is to draw in (see on attached photo) where they will be installed onto the bushing cores just prior to A-arm re-installation into the sub-frame. Does that help?
                  Attached Files
                  Last edited by Lago Blue; 1 December 2018, 18:52.

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                  • #10
                    I think everyone gets where they fit and how they work, it would be good to see them
                    Panthero Coupé quattro 20vt
                    Indigo ABY coupé
                    Imola B6 S4 Avant

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                    • #11
                      Here is a photo from the first post 3 clicks away. As the "stop" faces are quite reflective, it is more difficult to capture. The bushing it is balanced on gives it scale.
                      Attached Files
                      Last edited by Lago Blue; 18 November 2020, 18:02.

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                      • #12
                        Error, I think the exact opposite, but your more than welcome to help me with my questions to follow.

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                        • #13
                          Suspension of Disbelief, Part 1.d. cont’d.

                          Background: An old idea, updated.
                          The first I heard of this mod was back in the mid-nineties from a female participant at an Audi club driving event at Watkins Glen, NY. She was part of the Anderson clan that had driven their cars down from Minnesota for the 3-day event. She drove a lovely A90Q20V sedan. Back in the day, this mod (small bushings only & a less expensive material) was available through them. You can see her husband’s (Keith Anderson) ’83 UrQ Coupe here:

                          Link to: Anderson Motorsports

                          All the few references I can find to this mod’s application today are from happy users of which I am one. However, the scant number of references to be found indicate to me this mod has likely fallen into dis-use and I believe it should be more widely understood and in use. Given my success with this fix, I don’t believe it is necessary to turn away from OE bushings to gain either increased longevity or performance. For those interested, I’ll continue.

                          The updates I have done are to separately accommodate both small and large diameter OE bushings and to fashion the two “Stops” versions from Acetron® GP, a hard and durable material, porosity free and with a very low coefficient of friction.

                          As you may have seen amongst my previous posts on this, I would welcome comments by others particularly those who have done the mod, on the mod itself and perhaps comparisons with the alternatives, particularly WRT $/years of durability.

                          1. What: Have Arms - Will Travel.
                          This divides A-arm travel into two aspects:
                          a.) Primary (the design intent arc travel): up/down by pivoting on the inboard mounts; &
                          b.) Secondary (resulting slide travel and the subject here): front to rear along the hinge-axis of the above mounts.
                          This contends in a newly re-bushed stock A-arm installation, the development of secondary travel is an inevitable and negative consequence of the stock design; and a symptom of early bushing failure which has other deleterious down-stream effects. Given stock installed A-arms can or will shuttle front to rear, and at any given moment owe their fore/aft position to where the force across the tire’s contact patch is driving them to, this argues that condition is not just unhelpful but entirely unacceptable; and with the “Stops” mod, preventable.

                          In all stock installations, this slide travel develops from zero to increasing amounts of fore/aft movement in a range only limited finally by sub-frame bracket spacing and bush flange-face wear. What begins as “sprung” travel from a stiffly held centered position maintained by strong new bushes where the A-arms are powerfully re-centered to, too quickly degrades to “slack” travel where the bushings have become lazy on their long axis and the A-arms don't re-center themselves between the S/F brackets nearly so quickly or powerfully. Beyond the ever increasing shifting geometry, the real performance cost is evidenced by the A-arm’s decreasing ability to resist being displaced front to rear from “on center”; and to not only not spring back quickly to the center-point afterwards, but that the bushings no longer remember where the center-point is.

                          The further realization that each wheel’s position will at times be pushed around independently of the other; and likely spends little time on the design center-point (with obvious ill effect including dulled and delayed steering signal to and from the driver), should drive home the point that without this travel, the car will act and feel very differently indeed. In fact I suspect said travel is a primary part of the deficiency at the root of complaints some have expressed WRT steering feel. On new bushings, the “Stops” mod prevents this travel from developing in the first place. My experience, of largely stock suspensions with minor enhancements including the “Stops” mod are certainly more satisfying to drive than when the bushings are simply re-placed without the mod.

                          While cruising, the “lift-pause-thump; press-pause-thump” experienced on release and re-application of the throttle, can at least in part be traced back to this slide travel. That there is scope for A-arms to shuttle back & forth can be easily confirmed with a small pry-bar, the car up on a hoist and the weight off the wheels. Seeing that the A-arms are only centered by a force equal to how easily you can displace them front to rear, one can immediately grasp how deficient their inboard mountings may have become.

                          3 questions any of you may be able to help me with:
                          1.) It may be the lengthy radius rods (see in attached) where added to the factory rally Urq’s A-arms to address this same issue, where they?;
                          2.) Did the above works cars use the OE bushes?; &
                          3.) When the above rods first appeared, was it a homologation rule driven mod which allowed only this type of add-on reinforcement and prohibited any substitution or deletion of original equipment, or was it at the entirely free hand of the factory?

                          …to be cont’d.
                          Attached Files
                          Last edited by Lago Blue; 25 February 2020, 06:06.

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                          • #14
                            I dont think these stops are a tough concept to grasp
                            I'm going to add my opinon on your questions
                            The radius rods were used to strengthen the wishbone to prevent / limit damage on the roughest stages.
                            AFAIK the works cars used bespoke bushes (they look different) - regardless undamaged suspension components will have been renewed on a time-served basis long before the bushes degraded.

                            My personal thoughts on this mod to OE bushes are that poly bushes are significantly cheaper & easier to fit.
                            Panthero Coupé quattro 20vt
                            Indigo ABY coupé
                            Imola B6 S4 Avant

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                            • #15
                              Replacing the original bushings is a cheap & easy DIY trick...

                              Thanks Error, however once again I disagree almost entirely, but that's what forums are for and besides, if we all agreed that would really discourage conversation.

                              This is a great mod for beginner or grizzled veteran alike. You can do this on the drive-way with pipe fittings and threaded-rod if need be, but spare A-arms prep'd in advance with a bench-vice makes it go back together even faster & easier, perhaps also an opportunity for up-grading to the forged arms at the same time; and that the Boges can be had on E-bay for 11 to 15 bucks a pop vs £19.72 ea for a Powerflex reinforces my headline above. I think the mod provides, if not a permanent solution; perhaps near enough, as it's proven to work exceptionally well for several years now.

                              Yes, the mod is simple, however the reasons for it may not be to some, and as I am unable to find even one single post on this forum that mentions it, it may be that it is neither widely understood nor in use (save for mine). Clearly, I think it should be. I will even venture to say that I think it ought to be -thee- choice against which others are measured.

                              I am not necessarily writing this for someone who, with their 10K hours into it can correctly intuit the benefit of shipping an otherwise perfectly serviceable steering-rack back and forth across the Atlantic; just to have it altered by thousands of an inch. No, this is not that hard to grasp, it is however a little more fundamental to the basic operation of the vehicle, and for some it may provide an improvement; greater than a modified rack torsion bar. I am writing it for someone who may simply want to read, learn and achieve, like I have, an absolutely excellent result and the reasons why; for very reasonable cost. Newbies stumble by here everyday and even old guys like me can learn new tricks. Having kept the wheels from falling off, they then may decide to move on to sub-frame braces, etc. I hope they do, that's whom I'm writing for.

                              You may be correct about the radius rods, but if I can wreck my OE bushings with one drive down my street, certainly the factory did worse & quicker to them racing; before ever damaging an A-arm. This mod aims to remove that vulnerability.
                              Last edited by Lago Blue; 18 November 2020, 20:12.

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