1. ATTENTION EXISTING USERS: If this is your first visit to the new forum, you must reset your password. Please go to http://cobrakitcar.net/lost-password to reset your password.

    Dismiss Notice

Failed heim joint

Discussion in 'General Comments and Questions' started by tveazey, Nov 6, 2014.

  1. tveazey

    tveazey New Member

    I was driving my car yesterday and went over some rail road tracks I was going about 2 miles an hour and heard a loud pop in the rear of the car metal on metal. so I came home and today I jacked up the car so I could start going over every nut and bolt with lock tight. Beacause I am tired of the car trying to unscrew it self. and this what I found. a busted heim joint on the driver side upper bar on the axle side. I only have 300 miles on the car. Not sure why it happened but I am thinking I have an alignment issue in the rear. any one have any suggestions how to make sure every thing is aligned right and even. I am open to suggestions.



    Attached files 4758-2661.JPG (28.3 KB)
  2. Luce

    Luce Member

    The 4 link is a finicky animal. If the 4 bars are not equal length and parallel, when the axle rolls (one tire up, one tire down) the thing binds. And with the vector math, it puts a HUGE tension and compression on the links.

    Read up. Jim (barnsnake?) and Rick (Cobra Pilot) and a few of us had a thread disusing it a few years back.

    If I had a 4 link, I would replace the 2 front uppers with a poly joint with a little compliance. But I don't think anyone has done that.
  3. tveazey

    tveazey New Member

    thanks. I will look them up
  4. Luce

    Luce Member


    Here's the thread about the 4 link I was talking about. It starts off more as a discussion about sway bars, but then gets into the 4 link.

    You may find more if you search "4 link bind", but pay no attention to anything you find about 4 links in dirty track cars. Their axles are free to rotate about the mounts and use an extra bar near the pinion to control axle twist about the wheel axle's line.
  5. tveazey

    tveazey New Member

    thanks for that I was looking but not finding anything. but thanks again.

  6. bktlist

    bktlist Member

    I had the same issue several months back. See my thread on the other forum. It is important you do not have the four links in a bind. You need to be able to move all of the links when you have the load on the rear end. Crawl up under the cobra, grab each four link, and you should be able to move each one. If not then they are in a bind and you need to adjust. You also need to check and see what is the metalugury of the heim join. If its regular mild steel I suggest you upgrade to Chrom Moly. I even went up a size in the heim to 5/8 shank.
  7. tveazey

    tveazey New Member

    Ya I have been looking at some better and stronger heims. I just may go up to the 5/8 as well. I think it is money well spent. Thanks
  8. tveazey

    tveazey New Member

    Well I was working on ordering my new parts and I noticed that I already have 5/8 so I am just going to order the Chrome moly Heims, ya the high end ones from FK rod ends. about $60.00 bucks each but I should not have this problem again. and I may not ever have it again with the old ends I do think I caused the break anyway the rear end was in a bind I think so we will see when the new ends come in. I am also going to fab up a nut to go over the bars and weld them in place so making adjustments can be done with a wrench in stead of a pair of channel locks that leave nasty scars on the bars no matter how carful you are. I will post some pics after I het them all done and powder coated.
  9. AggieJack

    AggieJack Member

    Unless you just enjoy welding you could use Afco (or other brand) tie-rod tubes (aluminum or steel) that have a flat on them for a wrench.
    They come in lots of anodized colors and look good. I have them in gold.

  10. tveazey

    tveazey New Member

    I have looked on Jegs site before for one like you are showing with the link and have never seen these. and all the ones I have been finding are like the ones that came with the car just a knurled finish to grab and that is a joke. so yes thanks. I will make my own for now until all my new parts arrive and then I will swap them out. I need to make sure I can get my rear end adjusted right so there is no binding again. once I am satisfied I will change the parts out.


  11. Luce

    Luce Member

    These are the guys I like and buy from. If you call them, they will make radius rods out of aluminum bar stock, end drill and tap, and machine a flat spot for a wrench for a very reasonable price.

    http://stores.ebay.com/qscomponents?_tr ... 7675.l2563

    Another option I haven't seen tried, but I think could eliminate the problem is change 2 of the upper heims to a poly joint. I think it would give you the .005" of compliance needed to eliminate the bind issue.
  12. Luce

    Luce Member

    Check this out...

    http://www.ebay.com/itm/4-bar-end-Left- ... fe&vxp=mtr

    It would require a custom radius rod with 5/8 threads on one side, and 3/4 on the other, but I think the tiny amount of flex in the poly would eliminate the bind that is impossible to tune out with non perfectly parallel, non perfectly equal length 4 links.

    The reason I would put them on the top is they are under less stress. You may think " what do you mean they're under less stress, they're the ones that always break?" Yea, when the 4 arms lever against each other the one in tension fails. If you eliminate the bind, then the lower is under compression and the upper in tension when accelerating, but the lower one is under almost double the compression as the tension in the upper. And the lever action of the links in bind is 10-100 times the force that the engine can put on the joints.
  13. tveazey

    tveazey New Member

    I am glad you brought this up I had been thinking of using the poly ends like these on both uppers and lower bars. How do you think that this would work. and eliminate the heim joints altogether I think that would also eliminate any squeaking from the heim joints that you get over time. what's your thoughts on this.


  14. Luce

    Luce Member

    I'm speaking from a purely theoretical and philosophical point. I sidestepped all of the 4 link issues and made my own IRS instead, but I like the rigidity of the other 6 heims (8 counting the panhard) to prevent wheel hop and better control pinion angle. Also, the poly bushings can't rotate, so not having one hiem in each link may fatigue and break something under body roll.
  15. cobrapilot

    cobrapilot Member

    I'm having the strangest feeling of Deja Vu...

    On that old thread about the 4 links, Jim (barnsnake) posted a great step by step instruction on how to set the 4 links so they're not in a bind. We all just had a long discussion about this in Boerne a few weeks ago. In my case, I had changed to larger wheels and lower profile tires, then lowered the suspension down accordingly. I'm sure my links were in a bind. Same link snapped. Driver's side upper.

    I might actually be beneficial to have a weaker joint on one end of the upper arm, or wherever is the preferred failure point, so that a failure will occur in a relatively safe way. Beefing everything up might cause a more dangerous failure.

    I agree with Luce about the compliant bushings. As the heims have virtually no play in them, binding takes only the slightest misalignment.
  16. tveazey

    tveazey New Member

    well I must say you guys have been great. A lot of good advice and I think I will give the poly upper a try on the axel side just to see what it does. I have a friend of mine that is a big 4x4 guy and he has a rock crawler and he does the same thing on his buggy. but I do want to thank ya'll for all your advice, its guys like you that keep the rest of us moving on with our builds. your experience's and knowledge helps us all.



Share This Page