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Thread: Potential for failure in rod end adjuster nuts

  1. #1
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    Potential for failure in rod end adjuster nuts

    Terry has been good enough to bring to our attention that there is a potential risk for failure in the adjuster nuts on the suspension arms. On the Brammo made Atom's, these are the adjuster nuts use to change camber and toe without having the remove the rod end. The part was custom made by Brammo so no off the shelf part is a replacement. There are 6 on the car total.

    It turns out that the rod end isnt nearly long enough to fit very far into the suspension arm which puts more force on the adjuster nut. If you just screw the rod end in further, it messes up the alignment. There has been 1 perhaps 2 failures and one person noted cracks when when they were magnafluxed.

    Here are the pics of one of mine (there are 6 on the car)





    As you can see by the third pic, the rod end shaft ends before the suspension arm starts. As seen by this diagram, this puts a lot of force on the adjuster nut where the green line is



    Now the problem.... the ideal solution would be a longer rod end. But this would be a complete custom part and we are needing to order like 50-100 minimum. 6 per car at somewhere between $70 and $170 (this is really up in the air right now)

    I've also asked around for quotes on a stronger adjuster nut and have a place that will make me them out of 4130 alloy at $22 each. Not an idea solution and it comes with no official strength testing.

    I have another place that gave me a quote of $135 each for 4150 alloy.

    So we need input from other owners on how to proceed, especially if we need to order parts

    Terry has done a lot of the leg work looking into this, so I appreciate all his help


    EDIT:
    These are now available at $22 each

    Last edited by bolus; November 22, 2011 at 09:15 AM.

  2. #2
    Neutrino MadMaxAtom's Avatar
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    I run my cars with a lot of camber,so the adjuster nut is not quite as stressed (unsupported) as a street alignment setting would place them,but I do see the need to improve the setup. $22 for a better sleeve would be tolerable..but $135 is outrageous.Why isn't the 4130 alternative acceptable? Isn't that a chromoly alloy,of pretty high strength?
    The power of an Atom is a terrible thing to waste! Atom owner/operator since 2007. The more you chase perfection,the faster it becomes. John Force for President! (I asked him once in person...he laughed)

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    The quote from the place that said $135 started the phone call with "just a warning, we only do small runs of custom parts, so we are the most expensive place in town" They do mostly high end parts for robotics and custom parts for antique cars. The guy there suggested 4150. The other place said they only do 4130 which are both chromoly.

    I ordered a set of the $22 ones. we'll see.

    I think a good idea for anyone tracking their cars would be to get these magnafluxed at some point
    Last edited by bolus; November 7, 2011 at 05:07 PM.

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    Neutrino MadMaxAtom's Avatar
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    If you track your car,and are using racing tires,you should also be running a lot of negative camber (I run 5 out back)..so the rod end will be deeper into the adjuster nut and control arm.The stress on the toe adjuster out back are very minimal,so no serious concern. The stresses up front on the top rod end are not as great as the rears,but the camber settings would be closer to 2-3 degrees (I run 2.5) so there would be a potential for stress cracks at the adjuster sleeve after enough flex cycles. I will be watching this thread for developments. The $22 per unit fix would be ideal.
    The power of an Atom is a terrible thing to waste! Atom owner/operator since 2007. The more you chase perfection,the faster it becomes. John Force for President! (I asked him once in person...he laughed)

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    Proton Terry Kennedy's Avatar
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    Quote Originally Posted by MadMaxAtom View Post
    ... running a lot of negative camber (I run 5 out back)..so the rod end will be deeper into the adjuster nut and control arm. The stress on the toe adjuster out back are very minimal,so no serious concern. The stresses up front on the top rod end are not as great as the rears,but the camber settings would be closer to 2-3 degrees (I run 2.5) so there would be a potential for stress cracks at the adjuster sleeve after enough flex cycles.
    In the cases I know of, the cracks were in a thimble on the front (top - no lower thimble on the front as toe is adjusted with the steering pushrods).

    The normal engineering rule is that you want 1.0x to 1.5x the major diameter (5/8" in the case of these rod ends) of thread engagement. That's something like 10 to 15 rotations of the rod end (18TPI thread). I'm not sure you can get 1.0x engagement even with extreme camber.

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    Neutrino MadMaxAtom's Avatar
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    I don't believe there will be an issue on the thimbles when camber is adjusted for race tires as the rod ends are almost bottomed out in the rear,and about 1/2" of overlap engagement in the front.

    My rear camber adjuster (5 degrees negative):



    My front camber adjuster (2.5 degrees negative):



    As can be seen,the rears are well supported. The fronts have about 1/2" of overlap on the rod end threads. If Bolus is satisfied with the 4130 units,I will buy a few to have as replacements.Sorry about the dirt in the photos Bolus..it rained the last time I used the car and I have not polished it yet...
    Last edited by MadMaxAtom; November 8, 2011 at 05:21 AM.
    The power of an Atom is a terrible thing to waste! Atom owner/operator since 2007. The more you chase perfection,the faster it becomes. John Force for President! (I asked him once in person...he laughed)

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    Holy camber dude! Yeah I think that rear is fine

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    Neutrino MadMaxAtom's Avatar
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    Yea..the FA tires like a lot of camber to wear evenly and put down the traction. I've tried less,but have always gone back to the numbers that work. I can get about 10 track days out of a set of rears IF I watch pressures and flip them every other event. I do love my traction!

    Keep us posted on the new thimbles. I wonder if TMI would be interested at all in your findings? They do seem to be supporting all Atoms the best they can. Good people..
    The power of an Atom is a terrible thing to waste! Atom owner/operator since 2007. The more you chase perfection,the faster it becomes. John Force for President! (I asked him once in person...he laughed)

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    I need a way to inexpensively test breaking on these when I get one. I am not going to pay $300 to get an independent lab to break test them. My physics is rusty, how would one test one with a long lever until breaking an calculate the force it takes to break one?

  10. #10
    Neutrino MadMaxAtom's Avatar
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    ^Good question.All I can think of..short of paying someone to do it "professionally",would be to place an old thimble and a new thimble in a heavy shop press,one on top of each other(probably laying on their sides) and squash them together to see which one gives out first.It won't give you any hard numbers,but it would tell you how much more durable the 4130 alloy units are over the brammo units.
    Another thought I had..what if the rod ends threaded stock diameter was reduced to 1/2" (I believe they are 5/8" currently) and correspondingly machined thimbles were made,so the wall thickness of the new thimbles would be greater? 1/2" rod stock would still be an overkill for strength in the Atoms application. If you were making new thimbles anyway,and the 1/2" shank rod ends were available,this should be adequate insurance against a weak link.
    The power of an Atom is a terrible thing to waste! Atom owner/operator since 2007. The more you chase perfection,the faster it becomes. John Force for President! (I asked him once in person...he laughed)

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