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Triangular four link Question

Discussion in 'The Hokey Ass Message Board' started by No_Respect, Mar 16, 2006.

  1. No_Respect
    Joined: Jul 27, 2005
    Posts: 1,169

    No_Respect
    Member
    from So-Cal

    I searched but mostly all i found were four bar set ups My question is what angle do you mount the Links at and how close do i go to the pumkin i dont want them binding and my last question is where do you mount the upper links do i mount them on a kustom made crossmember? pictures would be help full I'm mounting this on elwoodblues's 59 apachie with air bags thanks for your help

    Jared
     
  2. No_Respect
    Joined: Jul 27, 2005
    Posts: 1,169

    No_Respect
    Member
    from So-Cal

  3. I think I saw some drawings awhile back. Maybe on here as I don't go anyplace else very often.

    Looks like I'm going to have to triangulate the 4 link on my roadster because of lack of room. But you won't want to copy mine it'll be a concoction/one off piece.

    My top links will mount somewhere close to the punkin and angle toward the middle and my lowers will be outside and parallel with the chassis. At least that's what I'm thinkin today.
     
  4. 392_hemi
    Joined: Jun 16, 2004
    Posts: 1,737

    392_hemi
    Member

    Should be some photos of these on the Art Morrison web site. He does later model chassis, but the link setup is the same.
     
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  5. jerry
    Joined: Mar 2, 2001
    Posts: 3,474

    jerry
    Member

    To get it to work properyl the upper bars need to be at 90* to each other. Elpolacko has done a few of these.


    jerry
     
  6. Blair
    Joined: Jul 28, 2005
    Posts: 361

    Blair
    Member
    from xx

    No they don't. In any four-link the most important thing is that you get the upper bars parallel to the lower bars to keep it from binding (should be obvious). As for how much triangulation you need to run it without a panhard bar, I have never heard of any hard line angle between the two needed. I would just put them as close to the pinion as possible given the physical constraints. You might want to run a sway bar with a triangulated four-link because it will have more body roll than a conventional four-link.
     
  7. Blair, aparently you have never stuck your head under any production vehicle that uses triangulated four link systems.

    ALL and I mean ALL of them use one set of bars mounted 45 degrees to the axle. Usually the top bars, GM style stuff has the bars mounted on top of the differential housing close together and wider at the frame.

    [​IMG]



    [​IMG]

    The FOX chassised Mustang/Fairmont/Thunderbird had a very similar system to this. And if you look closely at this pic you can see the upper control arms are very much 90 Degrees to each other.

    [​IMG]



    The exceptions to the rule are some of the large platform Ford systems where the bars were closer together at the frame and wider at the axle.

    The only cases I have seen the pairs of bars not at 90 degrees is in hot rodding, and I can assure you those systems have a tendency to sway. Even if it is set up on Heim joints you will be able to flex the rear axle/chassis over eachother.

    I see tons of other myths related to the triangulated four link as to the relation of the upper bars over the lower bars. Some say you cannot cross them and have the upper bar mounts outside of the lower bar mounts. Total BS, it can be done without any ill effects.
     
  8. 52pickup
    Joined: Aug 11, 2004
    Posts: 847

    52pickup
    Member
    from Tucson, Az

    no they dont. Setting the bars at different angles set the instant center and anti squat characteristics for the rear suspension.

    the number I remember hearing for the triangulated links is taht each one should be at least 30 deg off of parallel with the chassis centerline, total 60deg between the two. that is minimum.

    i can go farther in depth if you guys want.
     
  9. Bugman
    Joined: Nov 17, 2001
    Posts: 3,483

    Bugman
    Member

    Please do. I'll be building one of these eventually for a supercharged street/strip car.

    Question? If you were to draw a line along the upper control arms, does the point where those lines intersect make any difference? like in the pic below, the red line is where the factory arms are. What would happen if you moved the arms out away from the center of the axle so they followed the blue lines? How would that affect handling? What if you moved them closer together?
     

    Attached Files:

  10. Yes, the convergance point on your triangulated bars is called the Roll Center on this type of system. If you understand Roll Centers and how they affect handling you will understand why it is desired to have the roll center close to the center of the axle in all planes.
     
  11. 48fordnut
    Joined: Nov 4, 2005
    Posts: 3,746

    48fordnut
    ALLIANCE MEMBER

    i have a set of chassis eng triangulated 4 link on my rpu and they work great. i shortened the mt so they would be closer to the frame. works great. launches good.
     
  12. Littleman
    Joined: Aug 25, 2004
    Posts: 2,619

    Littleman
    Alliance Member
    from OHIO, USA

    [​IMG]






    I still want to build in more adjustment on the upper rods, and give it a higher mounting point on the rearend housing...........If I remember my top bars are angled down ..........set up like you would a drag race setup looking for that center of gravity...It has no bind am hoping soon to see if it will all perform.............Littleman
     
  13. Littleman
    Joined: Aug 25, 2004
    Posts: 2,619

    Littleman
    Alliance Member
    from OHIO, USA

  14. The Chevy Power book used to have a decent chassis section.
    ''How to make your car handle' by Fred Puhn is also a good resource.
     
  15. Blair
    Joined: Jul 28, 2005
    Posts: 361

    Blair
    Member
    from xx

    I think you misunderstood me. I am talking parallel from a side view, not from the top. You can set up a four-bar with non-parallel links, but it is by a very small amount, and is effectively still parallel. Anything else and the suspension binds because you have created a triangle in the side view. These side angles do not effect the roll center, which is at the centerline of the axle. Instead it is the angle of the links in a top view (what you were referring to) which effects the roll center and instant centers (which are different). See pic. It's from Gillespie pg260.

    Four-bar.jpg
     
  16. Blair
    Joined: Jul 28, 2005
    Posts: 361

    Blair
    Member
    from xx

    I just re-read my first post and it does sound like I'm talking about it from the top view. Sometimes my thought is ahead of my typing and I leave parts out. Sorry for any confusion.
     
  17. Parralel in the side view is a compromise.
    Not slight angles either. Look under a few Pro Mod cars.
    The angle of the upper and lower bars DOES affect roll center.
    The angle also has a marked effect on weight transfer.
     
  18. Blair
    Joined: Jul 28, 2005
    Posts: 361

    Blair
    Member
    from xx

    Apparently I'm an idiot because I didn't even look at my own drawing, and the side angle does effect the roll center.

    I still say though that you wouldn't want the bars in the side view to be much off of parallel if you plan on having travel at all. Drag suspension is decidedly different than most, bind is used to control the weight transfer like you said. It doesn't sound to me like this guy is building a drag car though.
     
  19. Bugman
    Joined: Nov 17, 2001
    Posts: 3,483

    Bugman
    Member

    What happens if you do something like this, using onle 3 bushings instead of 4 to the rear bushing was exactly in the middle of the axle housing?(assuming you had no bind)?
     

    Attached Files:

  20. mazdaslam
    Joined: Sep 9, 2004
    Posts: 2,525

    mazdaslam
    Member

    Attached Files:

  21. willowbilly3
    Joined: Jun 18, 2004
    Posts: 4,356

    willowbilly3
    Member Emeritus
    from Sturgis

    Or what if you reversed it and made the triagle the opposite direction, more like a wishbone?
    I don't see how it will bind if the upper and lowers aren't parelell from a side view. It will just caust the axle to rotate as it goes through its travel.
     
  22. 38racing
    Joined: Jan 7, 2005
    Posts: 23

    38racing

    what about the relative lengths of the bars in a triangulated (viewed from above) setup?
     
  23. 52pickup
    Joined: Aug 11, 2004
    Posts: 847

    52pickup
    Member
    from Tucson, Az

    If the links are setup so the point is on the chassis its called a satchell setup, or something like that. It'll work that way.

    The length of the bars, as they effect suspension movement, are measured from the side view.(see attachment). Having a shorter(or longer) upper bar will change the pinion angle through the suspension's range of motion, which is not really the best. Equal length links would probably be best, but unequal wont be the end of the world.

    There is a line used for setting the location of your instant center that runs from on the ground directly below the rear axle centerline to directly above the front spindle, at the same height as the vehicles center of gravity(height of the engines camshaft is usually a good guess). If your IC is below this line, your car will squat when you launch hard, if it is above the body will raise up at the rear on launch(best). I didnt put that line on the attachment.

    All that said... my bottom link(the spring) on my 1/4ellip setup is going to be level, and my upper will probably be also, cause its not going on a race car, so its really not that big of a deal.
     

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