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Triangulated 4 link question/help

Discussion in 'The Hokey Ass Message Board' started by pottsie454, Nov 11, 2011.

  1. The bushings have to allow the axle to articulate (twist) as well as move straight up and down. Mounting the ends parallel to the axle is a common mistake made on a lot of mini trucks. The upper arm ends will twist on the threads (or bend) rather than twist in the bushings. Not good.
     
  2. pottsie454
    Joined: Feb 12, 2011
    Posts: 399

    pottsie454
    Member

    dontlift, I will have to try your test after I reinstall the rear end. I will let you know how it goes. But you are probably right... and if you are it will be a lesson learned that I am sure not to forget. I appreciate you bringing the issues to my attention, but using the excel spread sheet and moving the upper control arm to a larger separation degree I would run out of room on the frame rail to mount it.. OR I could have mounted it on the frame rail but i would have had -40% anti squat.

    If this doesnt work then my next step will be back halfing the truck and build the frame rail with the suspension geometry in mind.

    Thanks again.
     
  3. nobby
    Joined: Jan 8, 2006
    Posts: 620

    nobby
    Member

    why not a 94-99 31 spline posi equipped mustang 8.8'' axle
    it will have factory ears cast into it, where you want them, i.e where you can't weld on that iron centre.
    = higher, simply move your lower links up to the chassis, as the top links on the axle are higher, they go up to - you have room there!!

    p.s get factory discs, with enclosed park brake. -

    [​IMG]

    they even have the offset for the centering of the pinion and all that jazz, plus 3 inch tubeing - i.e. the factory cast ears and their forgiving rubber bushing/their angle is factory, you simply apply that angle

    or use a 12 bolt with ears, but the ford might be closer in width, esp- seeing as you aren't narrowing, you don't need worry about c-clip elimination, as you will keep the shafts stock width

    as soon as some one casts up a fake bolt on 8.8'' quick-change finned............
     
    Last edited: Nov 15, 2011
  4. pottsie454
    Joined: Feb 12, 2011
    Posts: 399

    pottsie454
    Member

    I consider that too nooby, since I am buying a new posi unit anyway.. but as sometimes I always do, I bought all the things I needed at once and now have all the parts for this rear end. Over $900 in parts to boot. I dont know of any cars that had an 8.5 with 4 link?? Its hard to throw that kind of money at something and then start over. Well none the less, what I got is what I am going to try, if it doesnt work then I will do it right the second time? lol.
     
  5. nobby
    Joined: Jan 8, 2006
    Posts: 620

    nobby
    Member

    Last edited: Nov 15, 2011
  6. lakeroadster
    Joined: Nov 6, 2008
    Posts: 604

    lakeroadster
    Member
    from *

    Here is a photo that explains exwestracers point. When the rear axle twists, imagine one tire up and one tire down, imagine the torsional loads on the front mount. In this case something will bend and eventually break, assuming the truck is ever driven. And it will more than likely be the front mounts where they attach to the square tubing crossmember. :eek:
    [​IMG]
     
  7. Haha that's a GOOD example! I'm keeping it for my suspension lecture.;)
     
  8. wsdad
    Joined: Dec 31, 2005
    Posts: 1,258

    wsdad
    Member

    Thanks for all the explanations, including the one above.

    I see what you're saying. The front mount would try to twist when one side of the axle goes up and the other side goes down. However, if it were separated into two separate mounts instead of the one, and they were at the same angle as the upper links, wouldn't they try to twist if the axle went straight up and down?

    It seems like you have your choice. When the mount is mounted parallel to the rear axle, it would twist when the axle twists, but not when it goes straight up and down.

    However, if the mounts were mounted at the same angle as the upper links, they would not twist when the axle twists, but they would when the axle goes straight up and down.

    It seems like it will try to twist either way you mount it.

    Is it better for some reason to twist the mounts when both sides of the axle go up and down together?

    Perhaps mounting them at an angle is a better compromise for some other reason - such as when the car goes around a corner and the axle tries to move to the side (horizontally)?

    Some of the newer V8 mustangs have triangulated 4 link suspensions, and they mount thier's as pottsie454 did - at an angle. So I'm sure that's the correct way to do it. I'm just trying to understand why. They seem to use narrower mounts, though, which seems like it would allow the rubber to twist easier, not placing as much stress on the welded mounting tabs.

    Sorry to hijack your thread, pottsie454. If you'd rather we discuss this in another thread, please let me know and I'll create one.
     
    Last edited: Nov 28, 2011
  9. Ned Ludd
    Joined: May 15, 2009
    Posts: 4,201

    Ned Ludd
    Member

    Perhaps we should get a bit of perspective. What sort of roll-deflection angle do we need to accommodate?

    There have been a few threads on suspension travel, the upshot of which is that there is generally only about 3" worth of suspension travel happening in either direction - often less. Now, if we assume a spring base of, say, 36", we have a worst-case extreme single-wheel-bump situation where the axle is sitting at 9.6° from horizontal. That places one rear wheel over 9" higher than the other: in how many cases is there actually enough room for the wheels to move that far without something in the suspension fouling on something?

    Note that this is everything to do with single-wheel-bump situations and nothing to do with roll at the limit. The maximum roll angle at the limit of adhesion should be much less than 9.6°; hopefully considerably less than half of that.

    I'd say that it's improbable that we'd see more than about 5° of axle displacement in normal driving. So, whatever method of location we use has to be articulated or compliant enough to handle the axle sitting at 5° from horizontal quite often, and perhaps a bit more on occasion. Will the typical urethane or rubber bushing do that?

    The whole thing becomes moot if one end of each bar has a spherical joint, be it a heim, a steering tie-rod end, or something concocted out of an ifs ball-joint. If we want compliance we need only have it in one place along the "chain". Though twist is thereby not eliminated entirely it is very much less than otherwise.
     
  10. Wsdad,
    That's why they use large rubber bushings in the factory link bars. If the mounts are in line with the bar (angled), they will undergo a small amount of rotational "twist" as the axle moves up and down. If they are aligned with the axle (square), the rubber is trying to twist the entire amount of the axle roll, and will very rapidly run out of compliance, transferring more of the twist (bind) into the bar itself.
     
  11. abbe
    Joined: Sep 21, 2010
    Posts: 61

    abbe
    Member
    from sweden

    What if you put a uniball there insted od the robber buching??
    I meen at the sqere x menber
     
  12. Some builders use Heims or spherical bearings (uniballs), but they will only allow as much roll as the ball can twist on the bolt.

    A ball and socket will allow any amount of roll, but isn't a good idea; as the acceleration force is trying to rip the ball out of the socket.
     
  13. lakeroadster
    Joined: Nov 6, 2008
    Posts: 604

    lakeroadster
    Member
    from *

  14. Ned Ludd
    Joined: May 15, 2009
    Posts: 4,201

    Ned Ludd
    Member

    Such joints should be installed so that the forces acting on them are substantially perpendicular to the pin. In the case of the above A-bracket that is vertical. While the greatest anticipated rotation is not in the plane in which 360° rotation is possible we're not looking at 360° rotation or anything remotely like it anyway: the "misalignment" capacity of the joint should be ample for the anticipated vertical rotation.
     
  15. pottsie454
    Joined: Feb 12, 2011
    Posts: 399

    pottsie454
    Member

    No problems wsdad.. I am learning as well. Glad to see my troubleshooting can benefit you as well!

    As for an update. I installed everything the other day with it fully welding. I then grabbed the frame rail and put both feet on the axle and pused as hard as I could with very little movement. It did move some, but it was actually pushing the opposite side of the axle towards the floor and raising the side I was pushing. I think it had something to do with the way I had my feet on the axle.

    Here are some pictures!

    [​IMG]

    [​IMG]

    [​IMG]
     
  16. wsdad
    Joined: Dec 31, 2005
    Posts: 1,258

    wsdad
    Member

    Looking good! I hope mine turns out that professional-looking!


    Good point.
     
  17. You're absolutely right about the limited amount of roll we can expect on a street rod, Dawie. I tend to explain this stuff in it's purest form, just like I teach it... We do a lot of off-road stuff here, too; so we are seeing some roll angles that are extreme, to say the least! :eek:
     
  18. pottsie454
    Joined: Feb 12, 2011
    Posts: 399

    pottsie454
    Member

    I ran acrossed my own thread while I was researching for another triangulated 4 link setup, I figured I would give an update as to how well the rear end has worked out for me in the truck... My last post on this thread was 4 years ago and I have driven the hell out of this little truck with absolutely no problems thus far. The angle of my upper bars were questionable, but in my case it worked out fine with no noticeable side to side deflection.

    Im putting a triangulated 4 link under a 53 Chevy car right now, I may post some pictures... I am alot more proud of this one. ;)
     

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