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Can you help make my triangulated 4 bar work?

Discussion in 'The Hokey Ass Message Board' started by MeanYellowZ, Feb 6, 2011.

  1. newsomtravis
    Joined: Jun 1, 2009
    Posts: 562

    newsomtravis
    Member
    from pville, ca

    why is your driveshaft gonna hit your upper bars...you have an amboid instead of a hypoid?



    rtflmoa..........
     
  2. MeanYellowZ
    Joined: Jan 10, 2007
    Posts: 59

    MeanYellowZ
    Member

    Tinman,

    Bags on the lower bars are very common with these setups. Pretty much makes it like a Mustang with the springs on the lower control arms to improve ride and in this case lift since it obviously uses the lower bar as a lever. KP Components makes some of the most common setups using bag on bar setups, here is an example:

    http://www.kplinks.com/product.php?productid=141&cat=50&page=1

    You can see the type of gussets that my lowers will have to support the load. This also won't be used for towing or hauling of any sort.

    I made a cheesy paint pic to show how the upper bag brackets will be braced...which really doesn't have to do with much since they would be braced and installed well regardless of where the bags were located.



    [​IMG]
     
  3. Da Tinman
    Joined: Dec 29, 2005
    Posts: 4,222

    Da Tinman
    Member

    I'm still not convinced thats the way to go, what is the wall thickness and type of tubing used in those lower arms?

    It may be fine, dont get me wrong,,,, but I still wouldnt do it that way if it were mine.
     
  4. MeanYellowZ
    Joined: Jan 10, 2007
    Posts: 59

    MeanYellowZ
    Member

    They are 1/4" DOM tubing 1.5" diameter. The under bar gussets will be full length and are cut from 1/4" plate.
     
  5. MeanYellowZ
    Joined: Jan 10, 2007
    Posts: 59

    MeanYellowZ
    Member

    Its along the same design as the Mustang stuff....tons of tubular lower bars out there for them and they have the spring on them from the factory.



    [​IMG]
     
  6. Da Tinman
    Joined: Dec 29, 2005
    Posts: 4,222

    Da Tinman
    Member

    correct but those arms are not adjustable, so they arent placing a side load onto a smaller threaded portion.

    think of it like this,, what is the worst that can happen if the bar fails, not the bag. can you live with the consequences, or even survive them?


    not trying to pick a fight just giving you my thoughts.
     
  7. MeanYellowZ
    Joined: Jan 10, 2007
    Posts: 59

    MeanYellowZ
    Member

    Well it is the way they are done often but your point is well taken. Instead of an under bar gusset maybe a set of 2"x2" square lower bars that are non adjustable would be a good upgrade?
     
    Last edited: Feb 7, 2011
  8. Da Tinman
    Joined: Dec 29, 2005
    Posts: 4,222

    Da Tinman
    Member

    now your talkin, I was just thinkin along those lines.. Good call!!
     
  9. MeanYellowZ
    Joined: Jan 10, 2007
    Posts: 59

    MeanYellowZ
    Member

    I will build it all with the round bars and once its done and all adjusted for wheelbase I will use the final length of the lowers to make square non adjustable ones before it hits the road.
     
  10. langy
    Joined: Apr 27, 2006
    Posts: 5,730

    langy
    Member Emeritus

    You need to rethink that setup, how is it going to articulate ???



     
  11. LaidoutRivi63
    Joined: Apr 21, 2009
    Posts: 193

    LaidoutRivi63
    Member

    ok, you should try and run outwards from the center of the pumpkin out. truss the rearend like this or similar, so you have a weldable section to fasten your link ends to.

    [​IMG]

    And im sure you can pull the angle you need to keep the side to side motion to a min if you shorten your uppers. as long as you are close to your goal of the 70% length, you will be fine, and your usable travel will be likely less than you think. you aren't realistically going to use 10" in a driving situation, because it will be much too stiff or soft somewhere in the actual 10" you have. So honestly, if you pinion angles a bit radically, as long as it doesnt cause your driveshaft to pull to far, you wont have to worry about it, cause a radical pinion angle isnt gonna pose issues when you lift to a height to pass over a speed bump at 10mph or less. so try and get all your ducks in a row with the triangulation and upper bar length, and since you will be replacing the lower bars, you have the opportunity to back track a bit and change the lower lenghts to correct the geometry of the changed upper lengths.

    Some food for thought.

    [​IMG]
     
  12. rlsteel
    Joined: Apr 10, 2005
    Posts: 513

    rlsteel
    Member

    Tinman is right panyard bar.My Anglia is set up with a triagulated 4 bar and it had rear sway problems so I am in the process of puting a panyard bar on to cure it (I hope) RLS
     
  13. Ned Ludd
    Joined: May 15, 2009
    Posts: 5,025

    Ned Ludd
    Member

    For what it's worth, here's how to find the roll centre on a triangulated 4-bar:

    Project the lines of the angled bars to their intersection. Construct a line parallel to the parallel bars, running through that intersection. Your roll centre is where this line intersects the vertical plane of the axle.

    If you do this exercise for all the permutations of suspension movement you might have, especially when the bags come into play, you'll see that a little bit of suspension movement can cause a lot of roll centre migration, especially if your bars are relatively short. Your handling balance might vary noticeably depending on the ride height you're at at that moment. It argues somewhat for the three-bar plus Panhard some of the guys have been suggesting: there at least the RC stays in the middle of the Panhard.
     
  14. scottybaccus
    Joined: Mar 13, 2006
    Posts: 4,109

    scottybaccus
    Member

    What a train wreck. You have the bags all figured out, but you don't even have the suspension figured out. Your frame is too narrow for your body and the generic links you bought. You're gonna replace nice adjustable bars with nonadjustable just so you can put the bags on them.

    Clearly you went into this with one priority. BAGS.

    I think you need to spend more time studying suspension design requirements and understand the pros and cons of various designs. You seem to be trying to copy something on a budget that wouldn't afford you to actually replicate it. Now you're frustrated with people pitching vague ideas to fix your vague problems. I build for real, for paying customers, things I learned through 20 years of experience and exposure to smarter people. When I have someone in my shop in your situation, I tell them the same thing. STOP. Decided what you really want the car to do. LEARN how best to do that. Start over.
     
  15. MeanYellowZ
    Joined: Jan 10, 2007
    Posts: 59

    MeanYellowZ
    Member

    I think I am going to have to post some pics of what is actually there and why it wont work because either I am not coming across clearly or some of you just are understanding what I am trying to get across which I realize can be hard over the internet.

    First off, I don't know how many times I have said it in this thread but I will again.


    I can NOT weld a piece across the rearend to mount the upper bars closer together above the pumpkin. YES, that would allow me to mount the bars close and send them out to the frame to get the proper angle, BUT the bars would be too high above the pumpkin and would get above my notch, which is where my new bed floor height is. I would also have to ditch the front bridge crossbar which I don't really want to do anyway.

    NEXT, there is not enough room to put the bars out wide on the rear and then come in towards the center to get the proper side angle. I am not just saying this because I think there isn't but because I have tried them and even shorter, to the point of being too short they still don't quite make at least 70 degrees. There just isn't enough frame width.....

    .....and on to the frame width comment....lol. This is the factory 55-59 Chevy truck frame with the factory rearend width. It's not the wrong size frame for the truck unless GM designed it that way. All I have done is add a notch to for rearend clearance.

    I think some of you think I am just trying to hack this together and that's not the case or it would have been together and driving around the block by now. Any monkey can simply connect the rearend to the frame with a series of bars and make it, "work" with no regards to proper angles and bar relationships for it to work right, which is why I am here asking since this particular setup does not lend itself very well to what I am intending for it to do.

    As far as having the bags and mounts figured out, sorry that I have already thought through that process I guess?? That part is a pretty straightforward case of bracing the mounts for their given load. Again, the issue I am having is figuring out the best orientation for the upper mounts in this setup.

    I never said I was on a budget, never said I was trying to do it cheaply or replicate a correct setup for less money. Also there is no time rush here, this truck has been sitting like this in the back of my shop for a long time, it's not like I am trying to hack it together to drive this weekend. As long as it takes to make sure the setup is right is what it will take. This is why I posted here, to see ideas to throw around to make it work.

    I'll take some more pictures and add them showing why certain setups arent working.
     


  16. Can you please elaborate as to why it wont articulate? Thanks...

    Justin
     
  17. Da Tinman
    Joined: Dec 29, 2005
    Posts: 4,222

    Da Tinman
    Member

    all of your bushings are solid mounted to the "y" upper, if you lift one side of the rear end there is no way for the bushings to rotate with it. This tries to twist the arm, and tubing is not good at twisting so it puts a lot of strain on everything. Hard bushings will make it worse.

    I dont like that design either but folks have been getting away with it for a while now so I guess its alright but it still makes me cringe.

    I would for sure keep an eye on the upper rear bushing and the single tube going foward for cracking.
     
  18. Heo
    Joined: Jan 8, 2010
    Posts: 524

    Heo
    Member

    the pumkin is not castiron its cast steel and you can weld it with the right
    welding rod. I dont know the numbers in U.S but in sweden ok 48.00
    And if you dont think thats possible make a bracket and bolt it
    with the rear cover
     

  19. So replacing the rear bushing with a heim joint (or the equivalent) would be better?
     
  20. Da Tinman
    Joined: Dec 29, 2005
    Posts: 4,222

    Da Tinman
    Member


    yes it would help, but putting a sleeved "rotator" in the upper would be much better. Kinda hard to describe, I'll see if I can find pics of the last one I did, if I cant I'll get my crayons out and draw it up and scan it..
     
  21. MeanYellowZ
    Joined: Jan 10, 2007
    Posts: 59

    MeanYellowZ
    Member

    Here are some fresh pictures. Forget about the 10" of travel that has nothing to do with it. At ride height as pictured the upper bars need to be at 65* angle or greater to each other, then the upper bars need to aim down slightly to intersect the lowers.

    In these pics you can see the lower bars, parallel with the frame aiming upwards 3 degrees towards the front at ride height, I'm good with this. Next the lower bars are aiming down at 3 degrees, I'm good with this for roughing it in. However the bars are only at about a 55ish degree angle to each other, this is the problem with this scenario. The bars cant go out any wider at the rearend and cant go any closer at the front crossmember. The upper bar length in these pics is 17.5 inches, which is 70% of the lower bars 25". Even changing the bar length to 15" which is 60% of the lower bar length doesn't get it there. Most don't recommend going much shorter percentage wise of the lower bars and I don't want to go much shorter overall since thats where it will start really moving the rearend and pinion angle at full lift.


    [​IMG]

    [​IMG]

    [​IMG]
     
  22. scottybaccus
    Joined: Mar 13, 2006
    Posts: 4,109

    scottybaccus
    Member

    Much better pictures. For what you are doing, your best bet is to use those bars for a parallel 4-link and add a panhard. This could be friendly with your 10" of travel.

    If that isn't acceptable, the 60* angles can work, but are not ideal. Shorten the upper links and aim for 45*. This will not be friendly with 10" of travel.

    If your priority is 10" of travel on bags, you need to look at a cantilever setup on an air ride forum. Having the links out the rear for the bags and to provide track location would be the right way to go about this.
     
  23. 10" of Travel and a Panhard bar is NOT a good idea as the left to right swinging arc at 10" of travel will be too severe, probably causing tire rub issues.
    A Watts link would be the better way with a parallel 4 link - but i don't think he is going to go that way anyway.
     
  24. MeanYellowZ
    Joined: Jan 10, 2007
    Posts: 59

    MeanYellowZ
    Member

    Well I'm glad the pictures help get my point across. Unfortunately the upper links I can only get to about 60* by shortening them a lot. They can't actually meet in the middle but have to be offset a little because that front crossmember will be humped up to clear the driveshaft and if I mount the bars on the "hump" then they would be too high up front.


    Now, my main question, does anyone see any issues with having a parallel 4 link with the upper bars inside the frame and the lowers outside? The bars would obviously be the same length, just not located in the same spot on the rearend when viewed from above. I can't find many examples of this. It would also obviously have a panhard rod.

    Here is my example.

    [​IMG]

    [​IMG]
     
  25. MeanYellowZ
    Joined: Jan 10, 2007
    Posts: 59

    MeanYellowZ
    Member

    If I go panhard rod it would be as long as possible and parallel to the rearend at ride height. Hopefully the rearend wouldnt move too much with around 5" of ride height change. I can deal with it moving some at full extreme lift. This also will have skinny wheels and whitewalls that have a lot of clearance so I shouldn't have rubbing issue.
     
  26. what about using a watts link in place of a panhard with the links in the place pictured above...
     
  27. Francisco Plumbero
    Joined: May 6, 2010
    Posts: 2,533

    Francisco Plumbero
    Member
    from il.

    Why would you not take the bag set up and install it behind the rear axle much as a set of coil overs would be installed? You would have to remove the rear tube and replace it with square stock. You may need to fab a set of custom mounts to attach to the rear end and work with your upper 4 link brackets. You could then attach a locator or panhard to the right bag mount and left frame at the correct angle. I think your ride would be better and more stable by mounting the bags farther back behind the axle.
     
  28. MeanYellowZ
    Joined: Jan 10, 2007
    Posts: 59

    MeanYellowZ
    Member

    The ride is always better on the lower bars and much less bouncy, that is why so many setups are going to that. It takes less pressure in the bag to get to the same ride height when mounted on the bar versus mounted at the axle.
     
  29. RichFox
    Joined: Dec 3, 2006
    Posts: 10,020

    RichFox
    Member Emeritus

    I tried to do the same thing as you, pretty much. Finially gave up and added a Panhard rod. Been fine since 1980. Guess I won't change it.
     
  30. Francisco Plumbero
    Joined: May 6, 2010
    Posts: 2,533

    Francisco Plumbero
    Member
    from il.

    How did this set up look in a Mustang? It seems you are borrowing a few choice concept components of the Mustang suspension system. How does the rest of the rear suspension work with the bagged lower A Arm concept. It seems that you should almost be able to snap a few pics of the bottom of a bagged Mustang and copy most of it saving you a lot of grief in designing and testing. Are they using the same size of bags?
     

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