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!!! Followup on 3-Link Discussion.....(with PICS) !!!

Discussion in 'Center Of Gravity' started by Greg72, Sep 1, 2003.

  1. Greg72

    Greg72 "Might As Well..." Staff Member Super Moderator

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    OK guys, I'm looking for a little guidance relating to the panhard bar in a front 3-link suspension. I've been collecting lots of data, and photos and studying as much as I can stand in the books....but I'm a "visual" guy, so I decided to do some mock-ups on a front suspension so I could really understand what happens with all the links and how they all affect each other.

    So far, I've come up with a set of 36" lower links that look promising. The axle end of the link attaches almost directly on top of the "old" spring perches on both sides, which gives me a seperation of ~32". The other end of the links goes up inside the framerails with a slight taper. The seperation on that end is around 24". The links are basically even with the lower edge of the framerail. The resulting side view shows the lower links have about an 8* angle on them. (Not bad for anti-squat if I'm interpreting that correctly!) <- (EDIT: That should read "Anti-Dive")

    I haven't attached the upper control link yet (still trying to figure out where to put it) but I have tried a few different panhard bar combinations....starting with some very LONG ones (42"+), and slowly chopping them down to the 24" one that's in the photo below. My objective was to keep the panhard bar parallel to the axletube and to split the 12" of clearance between the axletube and framerails. I built a 6" riser off the axletube, and a 6" drop bracket off the frame. This "looks" nice, but with the longer panhard bars, it smacks the frame on compression of the passengerside tire.

    As I started to understand what was happening, I shortened the panhard, until the bar could "tuck" underneath the PS framerail (which it now does) which gives me more uptravel.

    One thing that I've noticed on ALL of the panhard bar setups (but to a lesser degree on the longer bars) is the centerline of the axle is shifting as the axle articulates. I have indicated the centerline in the pics (in green) so show the effect.

    I'm looking for feedback on the panhard bar design.....should I give up on keeping it parallel to the axletubes (and draglink) and get a longer bar in there, or should I keep it short and just deal with the (increasingly bad) axle shift that's occurring??


    DISCLAIMERS:

    1. There is no upper locating link yet.
    2. I am not an expert
    3. These pictures show an unnatural amount of flex that I can probably not utilize due to other interferences
    4. My engine has no oilpan or crank.....I know this. /forums/images/graemlins/grin.gif
    5. I am having a LOT of fun playing with this, but I am willing to change this design 100 more times until I get it right.


    That being said........onto the pics!


    Here's the passenger side view (pretty decent angle on links):
    [​IMG]


    And here's the front view with the DS stuffed and the PS drooped:
    [​IMG]


    And here's a closeup shot showing the "short" panhard bar, and how it clears the PS framerail:
    [​IMG]




    Ideas and suggestions are now welcome at this time..... /forums/images/graemlins/deal.gif
     
  2. 4X4HIGH

    4X4HIGH 1 ton status Premium Member GMOTM Winner

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    Hey Greg, not sure if it would work or not but in race cars they use either a wishbone style track locator or a diagonal track locator. Just a thought, not even sure if you could make either of these clear everything properly.
     
  3. rodzzilla

    rodzzilla 1/2 ton status

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    That is what I have been considering. Not sure if the steeiring forces will affect it.
     
  4. m j

    m j 1/2 ton status

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  5. Seventy4Blazer

    Seventy4Blazer 3/4 ton status

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    with pass side stuff your axle wants to shift a bit to the pass side as gravity takes its toll right? i know thats what the pan hard bar is, but with the frame flexing, and the axle wanting to move are you sure that what looks like about half an inch will be enough clearance?

    you are no expert, and i am just starting to think about learning stuff for a linked front suspension... so you know LOTS more than i. but these frames as you know flex a lot.
    Grant
     
  6. m j

    m j 1/2 ton status

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  7. BorregoK5

    BorregoK5 1/2 ton status

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    First off, I'd like to thank you for post the pics of the mockup since it does a great job of showing the geometry. It looks like the limitations your running into are a result of having to work around a single fixed variable, the stock frame, and not a lack of knowledge of application on your part. No matter how you arrange your links, your going to end up with axle shift using a panhard bar. Running a longer panhard will reduce the shifting but never eliminate it. I'm not a fan of panhards simply due to dropout shift to one side, like getting airborn would produce whether pulling a wheelie up a hill or jumping a whoop at speed. The articulating shift doesn't bother me because it most likely wouldn't be at speed so the weight shift wouldn't be very evident.

    Oh, and you think you could dirty up that garage a bit, your making the rest of us look bad!!!
     
  8. m j

    m j 1/2 ton status

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  9. Greg72

    Greg72 "Might As Well..." Staff Member Super Moderator

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    [ QUOTE ]
    looks like having those 2 links as uppers will allow the lower to run in the very centre of the dif to the tranny crossmember area.

    I would look to having a double draglink using an idler arm back at the ds upper link frame mount
    Mr Watson stated he had tire to steering box interference that precluded that being done
    doing it that way would open up your axle location possibilities
    you could run a watts link with the pivot frame mounted, or any length PHB you could fit

    beautiful work you are doing there

    [/ QUOTE ]



    I'm intrigued by the "idler arm" comment. This is something I don't fully understand....

    Are you talking about this little beauty?:


    [​IMG]


    Watson's front suspension confuses me due to the steering box being so oddly placed. Now when I look at the jumble of tubing there I can't really detect what is there as a result of the new steering box location vs. parts for a conventional 3-link!!! /forums/images/graemlins/grin.gif

    From what I can gather though, you seem to be indicating that the idler arm creates an "association" between the steering draglink and a conventional panhard bar?? It would appear that the ability of that idler arm to pivot, could allow for it to correct the "misalignment" of the axle from a pure PHB implementation....???

    I will try to find some additional pics of the idler arm stuff and maybe build an 1/8" scale model before trying it "full scale" under the frame.

    Please keep the insights coming...!!! /forums/images/graemlins/thumb.gif
     
  10. Greg72

    Greg72 "Might As Well..." Staff Member Super Moderator

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    [ QUOTE ]
    [ QUOTE ]
    Oh, and you think you could dirty up that garage a bit, your making the rest of us look bad!!!

    [/ QUOTE ]

    THANK YOU!

    my wife saw these images!

    [/ QUOTE ]


    The garage DOES get dirty....I just clean it before snapping pics. /forums/images/graemlins/grin.gif Plus, the more clutter there is, the more difficult the "backgrounds" are in my photos....it tends to make things hard to decipher.


    BTW -> In case you haven't already figured it out, I'm a virgo..... that should explain a LOT! /forums/images/graemlins/rotfl.gif
     
  11. BorregoK5

    BorregoK5 1/2 ton status

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    Now I wouldn't have said anything, but you went so far as to face all the cans and evenly space them, and even align the spray bottles heads perfectly.. heck, you even aligned the jackstands equal but opposite.. if I'm not mistaken, each spec of dirt on that floor is exactly 3 centimeters apart from each other!!! /forums/images/graemlins/thumb.gif I have a feeling choas theory doesn't apply to you - so just build it, how could it go wrong! /forums/images/graemlins/rotfl.gif
     
  12. 4X4HIGH

    4X4HIGH 1 ton status Premium Member GMOTM Winner

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    Hey Greg, another thing I overlooked the first time I replied, you would need some kind of link going towards the rear of the truck to keep the housing from rotating the pinion since you will no longer have a solid mounting point such as your leaf springs from keeping it from rotating. This is why a wishbone set-up would work best, it would not allow the movement I am speaking of and also it would locate the axle between the frame rails. /forums/images/graemlins/thumb.gif
     
  13. m j

    m j 1/2 ton status

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  14. Greg72

    Greg72 "Might As Well..." Staff Member Super Moderator

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    Scott,

    I will refer you back to "Disclaimer #1"... /forums/images/graemlins/grin.gif

    I've been talking with Triaged quite a bit about some possible designs (wishbones, radius arms, etc) and a lot of the suspension styles that are considered 4-link type solutions, tend to bind and fight each other during articulation..... Dan described it as "your axletube basically starts acting like a 3.5" swaybar..." With all parallel links (4 link) I can remove the binding, but I still need to locate the axle laterally.... (hello link #5!) and that starts to look like a real "tube farm" under the front end....especially with crossover steering and a tie rod and a driveshaft to fit into the mix. /forums/images/graemlins/blush.gif

    The more I do projects like this.....the more I'm amazed by what Stephen has designed and built. This is NOT easy stuff.... /forums/images/graemlins/1zhelp.gif
     
  15. 4X4HIGH

    4X4HIGH 1 ton status Premium Member GMOTM Winner

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    Like I said, a wishbone would accomplish both problems at once, it will locate the axle under the frame and also keep the pinion pointed in the right direction. A TRUE 3 link set-up. You should try to mock that up and see how it works with all the articulation that you want.
     
  16. m j

    m j 1/2 ton status

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  17. Twiz

    Twiz 1/2 ton status

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    [ QUOTE ]
    I'm looking for feedback on the panhard bar design.....should I give up on keeping it parallel to the axletubes (and draglink) and get a longer bar in there, or should I keep it short and just deal with the (increasingly bad) axle shift that's occurring??


    [/ QUOTE ]

    Looks like the shift (indicated by the green line and plum-bob) is about equal when either side is stuffed. Nice and predictable when articulated. (due primarily to keeping the pan-hard bar horizontal)
    Allthough, it is a different story with vertical travel. I would suspect the body shift would get annoying after the "newness" wears off.

    It deppends on where your priorities are.
    For "street-manners", a longer bar might work out better, even if it has abit of angle on it.
    For "rock-crawling", the short bar would probably be just fine.

    If you could figure out how to run a "Watts-linkage" - that'd be the best of both worlds.
    I remember seeing pictures of a Watts-linkage, run horizontal, on top of the axle. Rather than the normal, vertical style. Seems like that would be the way to go, to me. Figureing out how to clear the oil pan, and steering linkage would be the difficult - to say the least.

    Hmmmm.. now ya' got me thinking.
    I've got way too much to do today. Now, I'm going to preocupied with this allday. Dawg-awn it !




    Watching your progress with alot of interest ! /forums/images/graemlins/grin.gif
     
  18. willyswanter

    willyswanter 1/2 ton status GMOTM Winner

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    Ok, here we go...

    First off, Watsons idler arm there is for the steering and not any part of the panhard bar. What he did is locate his steering box towards the pass. side and used a short link from the pitman over to the idler. What this does is allow the pivot point of the drag link to be in the same location when pointed forward as the frame end of the draglink, and his axle end of the panhard is in roughly the same location as the steering arm end of the drag link. Thus he gets rid of as much bump steer as he possible can since the axle will rotate in an arc around the draglink controlled by the panhard bar. Get it?

    Next, your short panhard bar worries me. I would run the longest possible because with that short bar your going to have tons of side to side axle movement as you mentioned. But your just showing the articulation movement, if your front end droops 12" your axle will be like a foot out one side... Street cars get away with a short panhard due to the 4-6" of suspension travel, not the 12-18" your project could be capable of.

    As far as a triangulated 3 or 4 link, I wouldn't run that either unless you go full hydro steering. With the triangulated system, your axle will move straight up and down when compressing and drooping. Your drag link will travel in an arc getting longer as the axle moves up and shorter as the axle moves down, thus creating tons of bump steer. It's basically the same as what happens with leaf springs but you will have a ton more travel than the leaf springs, unless you limit it and if you do whats the point?

    I wouldn't run a watts link either since you couldn't get the panhard bars long enough for it to work with a super long travel system. It's ideal for the street though.

    I'm going to run a double triangulated 4 link in the front of the willys like this XX but I will run full hydro steering and not have to worry about the steering issues, how come you can't run full hydro? Looks like it's going to be a buggy anyway... You could run a triangulated 3 link with the lower arms being angled in and the upper link being straight and have a vertical motion of compression and droop and not have to worry about steering linkages.

    The ideal setup if I were doing it with mechanical steering would be to do a "wishbone" style setup with the steering box being under the cab with a link running to a idler on the axle so that the drag link from pitman to idler is parallel with your lower 3 link bar and has the same pivot poins, then a short draglink from idler to steering arm. It would be complicated but you would have no bump steer as well as hardly any compression/droop steering since the steering arms always stay the same length in relation to axle position.

    Ok, with what you have setup so far, you were talking about your antisquat, since your working in the front this is actually anti-dive and figured a little differently but basically the same but it does need to be looked into. I'm more interested in where your roll center is and your antidive percentage. What are you using for a center of gravity?

    Oh yeah, I've been working on the design for the willys for over a year now and still haven't gotten it perfect but I'm gettin there /forums/images/graemlins/rotfl.gif
     
  19. m j

    m j 1/2 ton status

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  20. Donovan

    Donovan 1/2 ton status

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    Here is my thought on the front 3 link setup. I would first make the bottom links parallel to the frame. If they are not, as the suspension goes thru its travel the axle moves side ways and the tapered link will get longer and the other side will get shorter which induces axle steer. So if the lower links are parallel as the axle moves side ways thru it travel with the panhard it makes a parallelogram and the lower links will stay the same length. Next I would run a panhard as long as the drag link is and at the same angles. The bottom links would be about 34" long and the tops in the 28-30" range. Oh Greg don't forget about the axle's pumkin hitting the oil pan. It is real close as it is right now I bet. /forums/images/graemlins/thumb.gif
     

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