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Single Shear Bolt application, strength info required

  1. Feb 18, 2009 #1
    I have a suspension arm that I am rebuilding, the main reason is to make it adjustable in length, and the other is to replace the ball joint.

    The original equipment is a standard automotive ball joint, greased and the shaft is 1 piece with the ball.

    The new setup would use a 5/8 spherical rod end with a hole ID of 15.87mm (.625")
    I can only use an M12 bolt which would be about 55mm long plus the thread.

    I would need to use 2x stainless steel spacers to mimic the taper on the ball joint stud, and also to space the head of the nut out so that it doesnt interfere with misalignment, it would only be spaced about 3mm or so.

    My question is, will this setup be as strong, stronger or weaker than the original setup?
    To me it looks weaker but I am no expert.
    Any advice on how to mkae it better, or advice on what can be changed etc.

    The Rod end is Chromeolly
    The spacers are stainless (I can use other materials if need be)
    The bolt is eitehr 8.8 or 10.9, both are readily available.

    My next question is, what can be done to stop the bolt undoing over time?
    Standard they use a cotter pin through a castle nut, and the taper helps it stay in place in one direction.

    I dont think I can buy an 8.8 or 10.9 bolt that has a hole in t for a cotter pin, so what can i do?
    Should I use a nyloc nut instead?
    Locking nuts?
    Or can i drill a hole in the bolts without effecting strength? The way i see it the hole would be past where the load is, but I am not sure if this is safe.
    Also are castle nuts even available in a 10.9 grade nut??

    Thank you very much for any help you can give
    My email is cazman@internode.on.net if you have any other specific questions, bu I will keep an eye on this thread, as I am trying to have these parts made within a week.

    Attached Files:

  2. jcsd
  3. Feb 18, 2009 #2
    WHOA! You're planning to stick a 12mm bolt in a 15.87mm hole? In a suspension component?

    Are you familiar with the term "catastrophic failure"? (You will be!)
  4. Feb 18, 2009 #3
    No there are spacers in there, click on the pic to see them.

    The factory joint was an m12 thread but had a large formed taper on it, what I want to know is, is a 12mm bolt through the middle going to be strong enough?

    The hubs have a taper in them that i cant avoid, 12mm is the biggest bolt I can fit in there, maybe 12.7mm if im lucky.
  5. Feb 19, 2009 #4


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    It's tough without really knowing the magnitude of the loading this thing will see. The original design may have a factor of saefty of 5 built in. Who knows? From a strict comparisson standpoint, yes, the smaller bolt will be lower strength than the original. You can't get around the smaller cross sectional area of the new bolt. That being said, now the tough part is will that affect you?

    Out of curiosity, why the restriction to an M12?
  6. Feb 19, 2009 #5
    I could use a large bolt, but it would mean drilling out the cast hub itself, not a difficult task, but when it comes to selling these parts as a "bolt on" item, its not something people will want to do.

    The load the bolt would see is impossible for myself to measure. It is a rear toe arm on a multilink suspension, the car weighs aprox 16-1800kg.

    This arm itself doesnt take as much load as all the others, it is only there to control the toe, but in saying that, I dont really know how much it takes.
  7. Feb 19, 2009 #6
    Oops... Didn't see that. :redface:

    I would say no. In the original part, the taper is taking the active load. The threaded end is merely a retaining device.
  8. Feb 19, 2009 #7
    Thats what i was thinking and fearing.

    Any ideas? I can get some shanks turned up and threaded, and probly in decent steel too. I dont know what grade would be decent though

    The ones you can buy off the shelf look like this, but they all seem to have the wrong size taper and length for me
    http://static.zoovy.com/img/stage3motorsports/-/M/mm5tr_1.jpg [Broken]
    Last edited by a moderator: May 4, 2017
  9. Feb 19, 2009 #8
  10. Mar 5, 2009 #9
    No one has any ideas how to make it stronger?
  11. Mar 5, 2009 #10


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    One of the main questions here is, what is the purpose of the taper? Does a tapered connection somehow reduce the cyclic tensile stress ratio on the threads, more than a highly-preloaded, straight-shank bolt? If so, could someone explain how it works? I don't readily see why it would, although I have not studied this.

    It seems to me the purpose of the taper is to create an extremely tight-tolerance shear connection. This would eliminate shear displacement in the connection, preventing impact of the bolt shank against the bolt hole. This would also eliminate bending moment on the threads. A simultaneous reason for the taper might be to resist a higher shear load on the larger-diameter cross section of the tapered shank.

    If the larger-diameter cross section is required to resist the shear force, then your new design will be inadequate. It is logical to assume the larger-diameter cross section (and same material grade) is required to handle the shear load at the active end. Secondly, to meet the requirement of zero bolt hole clearance, your tapered spacer would need to be a slight interference fit on its inside diameter. Regarding locking the nut, I think it is OK to drill a cotter pin hole, if you deburr the hole edges well. I think a property class 10 castellated nut might exist. To machine your own shanks, I think you would need to consult with a materials expert who manufactures bolts; perhaps ask Arp (?).
  12. Mar 6, 2009 #11

    Ranger Mike

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    Couple of things to think about..reason OEM use taper BJs and the like is 1.cost
    2.ease of maintenance, 3. quickness of assembly

    takes line worker no time to slap in the taper BJ and run a nut on it ..no washers to fumble with, no requirement to hold a wrench on the bolt while the air gun runs the nut..easy to shoot grease to the zerk, relatively cheap and durable..
    We run spherical rod end of all links of our cars suspension as does every other racer out there where the rules permit...
    off hand , your application, being the rear of the vehicle that weighs almost 4000 lbs. means roughly 992 pounds is on that corner.. is the auto a front engine car?
    if so, even less weight would be on the back end..

    What ever you do..USE HIGH QUALITY BOLTS.. do not stick a SAE bolt from the hardware store into this application..I hate them..these are friking FARM BOLTS......mass produced crap with terrible thread quality..JUNK!!!

    1. not strong enough, 2. these SAE bolts are typically .0015 to .002 inch UNDER size..when mounted in an AIRCRAFT quality rod end..that had an ID sized to .001" or less, there is too much slop..granted, this slop should be negated by clamping pressure but it is still there
    I would much rather use a hi grade AN bolt and nut in this application..
    NYlock lock nut I ok to use but do not take it off and put it back on more than two times. Will not back off as long as you do this.

    Use High Strength Alloy Rod ends Aurora makes these...

    things to watch for...Suspension Bind..the BJ may permit a lot more motion than the rod end..you can buy High-Misalignment high strength rod ends..check how much travel your application has..disconnect a shock if it helps when checking for bind..but you do not want a link that bind and snaps..even if on the rear end..
    two..you will need to lube the rod end regularly and this must be done...this is the major draw back to using these..we have to tear down our cars suspension frequently to lube the rod ends properly..we race in the rain and rain is a major cause of rust..no way around it...it will ruin the rodend in short time if not lubed..just this is justification in my mind to stick with the crappy OEM BJ..who wants to crawl under the vehicle every month to lube the rod end

    see www.PegasusAutoRacing.com for above bolts, rod ends etc...ask tech desk for help..they are all old racers..good people
    Last edited: Mar 6, 2009
  13. Mar 6, 2009 #12
    Personally, I have had a lot of trouble with heim joints wearing out. I used them in a steering application and ended up replacing with tie rod ends.

    For a steering knuckle, the most durable setup would probably be kingpin style. After that ball joint then heim joint.
  14. Mar 6, 2009 #13

    Ranger Mike

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    your right about king pin steering
    it is totally bullet proof..circa 1910 thur 1960 ..pick up trucks
    basic straight axel wit hbronze sleeve bushing inside..
    ref - racing..which is all i care about in life...
    i beg to differ as high quality rod ends..in certain racing applications are the hot set up
    but considering street scene, daily driving..poor or zero maintneance schedule, cost and ease to grease..Bjs are tops for the street..
    not for racing however..
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