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My analsysis of Mauricio's trailing arm kit breakages

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  • My analsysis of Mauricio's trailing arm kit breakages

    So as most of you know there was a kerfuffle mid-2016 about the trailing arm kit failures, or more specifically the turnbuckle failures, and a lot of bullshit has been spread by people giddy to hurt me or my business, I aim to clear up both what happened and what I was thinking... because I believe I know the problem having had the second best seat in the house for the raw information. Also as a side note, Mauricio had driven his car with the trailing arm setup for something like 9 months prior to this sequence of events, and had no issues during that time, others had driven the kit even longer (and harder) like Omron, again without issue.

    Firstly, there have been 3 confirmed owners (of the original blue hardware) who suffered breakages, one was the result of hitting a barrier, another was actual track usage fatigue (culminating in a high-g sustained load skidpad event), as such both these cases can be ignored as outside of expectations. There's nothing we can do about accidents, and the Enduro hardware is meant precisely for enduring track events. This isn't to say the regular kits haven't held up during track events, there are at least twelve confirmed owners who routinely drift and auto-x, which have reported everything from reverse entries to track jumps with zero failures since the kits were released. This means we have to examine the oddball, the one case where a mundane car driven on the street would suffer a half dozen failures.

    As a preface, Mauricio's first breakage was on the highway hitting a pothole. As a courtesy new parts were sent to replace the broken pivot, including clamping plate and rodend just to be safe. The second breakage happened on the same arm on the other pivot position, the most logical but inconclusive deduction is they were related, that the inner was merely damaged during the pothole strike but held on as best it could until fatigue killed whatever strength it had left. There was no evidence that anything other than what I described happened, despite what some might have asserted.

    The problem should have ended there but it didn't, the same vehicle managed to break another and another and another. Finding out the circumstances for this chain of events was not as simple as it sounds, and I don't want to lay blame here, I wouldn't expect anyone to keep track of pertinent details when angry or frustrated, nor do I expect someone to even think to mention many relevant details that could have helped sort out the issue. Needless to say I was the second most frustrated by the whole ordeal, I needed an answer, I needed facts, but all I got was attacks and some awful photographs with minimal story details.

    This made the investigation long and winding, and I'll be honest, it seemed like there wasn't going to be a way to find out based on how things progressed. The photos showed that some turnbuckles broke upward, some downward, which directly contradicts the people who said they can't handle sideloads, the failure was not sideload at all. One major possible culprit for breaking was the rodends being tightened to the trailing arm before their position on the subframe had settled, putting them into binding stress, but again the breakage was vertical, that stress would have been horizontal. Likewise the turnbuckles eventually broke on both sides of the car, which eliminated any relation to accidents or body structure, and further limited the potential of user error, yet it couldn't be ruled out entirely.

    I had limited facts to work with, but the one that kept coming back is some steep driveway Mauricio frequented, I received no pictures of it only that it was steep enough to require entry (and presumably exit) on an angle. How this related wouldn't be clear until recently, but it seemed to be the best lead or biggest factor in all this since I learned of it. Other facts included the use of coilovers, and new bushings, standard stuff, nothing that has caused or should cause any problem, pretty much every other owner has done the same or more. The ride height also didn't seem to be extreme in any case, lower than stock I believe it was, but pretty close to it.

    So as things stagnated, no new evidence came forward, and no other unusual happenings among the rest of the owners, it was settled that Mauricio would get the Enduro hardware and conclude whatever remained of the discussion. That included no more requests for free parts, no more criticism on public forums, and so on. The episode would ride or die on the Enduro hardware. Shortly after he had an accident.

    I had surmised that the only way to break the turnbuckles in this fashion was to lever against them, but that's not possible unless the trailing arm hits something, the coilover would have moved before transfering the bending load. I had asked for photos of the underside of the car, around both pivots, especially after another owner Josh had complained his trailing gets very close to the brake lines adjusting out camber. The photos I got showed damage and impact, but nothing unexpected for the accident he had, or the sudden breakages at low speed contacting afterwards. There appeared to be nothing visible that indicated the arm levered against the body anywhere. The seemingly impossible problem of why inners and outers were breaking randomly made this intractable, if it was levering anywhere, it would always break closest to that, that's how physics works.

    The conclusion was actually prompted by Mauricio's videos on the topic, specifically his video where he talks about the Enduro parts and how impressed he is with them. There are two key points, one is he shows the car's ride height, which actually appears higher than I had seen it previously, and he mentions he has helper springs, a detail I was unaware of. That was the missing link, this was the final piece. I can now firmly say this vehicle suffered from a combination of choices and activities I had not predicted, and which as far as I can tell, didn't seem to apply to anyone else.

    The first factor is the extreme travel range of his suspension, the helper springs on his coilovers added extra droop, which wouldn't be a problem if it wasn't for the driveway pushing one wheel up as high as possible allowing the other side to droop. This maximal change from one side to the other also wouldn't be possible without the helper springs, the far side coilover would have bottomed and the car would instead have tilted more. Effectively neither would have been an issue in isolation, but together they created the right conditions.

    Entering and exiting the driveway in different directions would mean the full extension and compression on opposing sides would be inconsistent, giving both sides an opportunity to experience the bending loads. This accounts for why both sides suffered breakages but one side suffered more.

    And finally, with this extreme difference in vertical position, there is only one factor that could connect them both, the one thing that could create the bending moment is the swaybar. I could not fathom a 200lb additional force from the swaybar would have had any effect on the trailing arm hardware, and I still believe that is true, what I didn't anticipate was that with such a large differential between sides, the swaybar was being pushed well past double, maybe even triple it's normal bending rotation. For anyone who still hasn't clued in at this point, the swaybar is progressive, what's 200lbs at 1x rotation is now many multiples at 2x or 3x rotation.

    There is very likely 800lbs or more of vertical pressure being applied to the trailing arm by doing what Mauricio did, with his car specifically, something that wasn't happening to any other vehicle. That swaybar was at a certain point of flex becoming an immovable object, a point located between the wheel and each pivot (for which the coilover probably added a bit of twisting load) around which the trailing arm rotated, snapping the turnbuckle. The swaybar broke the kit.

    I should also note that I had asked Mauricio to remove or disconnect his swaybar on two occasions during the investigation phase, but in both cases he refused. Something about needing it for handling, he wouldn't even entertain removing it as a test for some reason. I didn't hammer him on this point because it was just a theory, something to eliminate, and he was not in the best of moods at that point.

    I did everything I could, I proceeded through everything based on facts. I ignored rumours and accusations, especially the self-aggrandizing "told you so's" my detractors had been itching to use against my nearly flawless record.

    I chose to do the right thing as I saw it, I wasn't going to give free replacements forever when the experience of the majority contradicted the experience of the one.

    I wasn't going to jump to conclusions, I needed facts, and facts took time to accumulate, but it was still an isolated case.

    One doesn't make a pattern.

    That is all.
    Last edited by G-E; 02-06-2018, 05:50 PM. Reason: grammar bleh

  • #2
    Thanks for the detailed explanation.

    84 AE/Shiro #683/Shiro #820/84 Turbo


    • #3
      Welcome back G-E, the Z31 front end stuff I've got from you looks to be well designed and of good quality. But I will take issue with you over ignoring circuit use as being a legitimate application for aftermarket suspension parts. From any supplier. In fact parts that improve handling constitute a big race car market, there are corners that my Z tackles where a suspension failure could result in a fatality. So any aftermarket suspension parts that are not intended for race use should carry a prominent warning that they are not fit for high G loadings, suppliers can't have it both ways, either they cater for high stress use and are sold accordingly or they don't.

      Just trying to add some general objectivity and user feedback here, I have no knowledge of the specific parts you refer the above comments are not aimed at them and I have no interest in them anyway.


      • #4
        Originally posted by 260DET View Post
        But I will take issue with you over ignoring circuit use as being a legitimate application for aftermarket suspension parts. From any supplier. In fact parts that improve handling constitute a big race car market, there are corners that my Z tackles where a suspension failure could result in a fatality. So any aftermarket suspension parts that are not intended for race use should carry a prominent warning that they are not fit for high G loadings...
        There was never an issue with high-G per se, in those cases both pivots share the load, and the original kit was designed for ordinary slammed cars not to chew tires or suffer wonky handling from grip loss due to camber. This particular failure scenario required a number of factors to conspire together, any one of which excluded would have prevented it.

        The (original) kit was not designed for serious racing specifically, it was expected the repetitive stresses would shorten the kits lifespan, not just fail outright for exceeding some limit. There was always going to be the followup kit specifically for people with huge tires doing lots of transitions, and given the real world experience matched expectations (in all except this one case) there's nothing to change or apologize for....

        As far as I'm aware no one was hyping them to do anything they couldn't do, and in at least one case, the original version changed hands after over a year of hard street driving, and continues to be driven in different car.
        Last edited by G-E; 02-08-2018, 08:37 PM.


        • #5
          BTW as an aside, of all the people who I ran the design by, and even those who saw it after production, the top two suggested points of failure were the studs breaking or the aluminum clamping plate not being strong enough, the remaining theoretical complaints centered around the choice of rodend or through-bolt used. In short everyone who criticized it was wrong....

          There's a lesson here.


          • #6
            What is the best way to order parts and see the parts that you have to offer


            • #7
              As a general point when using bolts, if they have nuts then where possible use the finer thread option, it's stronger. The one thing that annoys me about metric is the unavailability of fine threaded bolts in the larger sizes. This applies to rod ends too and is one reason why metric rod ends are often not used in an otherwise metric car. All the more important for a race car.


              • #8
                Has the adjustable front control arm kit been used in a track application?

                For those wondering:



                • 260DET
                  260DET commented
                  Editing a comment
                  That kit looks pretty solid to me, I have installed one on the project race car which should be in use later this year. I have no reservations.