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Unread 12-09-2012, 06:36 AM   #1
Climbit
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short arm 3-link?

so here is my dilemma:

I need more height. I need to get some more air under the belly. AND I need to get rid of the factory 4link+panhard

I am currently running currie 4.5" coils that give me about 4" of lift over stock. the plan is to sell them and put in a set of synergy suspension (polyperf) 6" coils.

once I have the 6" coils in, I will need to deal with the fact that my CAs will be at an extremely steep angle. right now, the arms are at a pretty good angle, not too steep. I really like my short arms, they travel just fine, I can easily travel a 12" shock with them and they are never hung up on anything. the bigger problem is the inherent bind in the factory suspension.

the answer is a 3-link.

the upper link is easy: cut the factory passenger side mount off the axle, grab a 8" link tower from Ruffstuff or the like, weld on, plate the inside of the unibody and weld on a link bracket. make a link with a pair of 2.5" JJs and be done.

the lowers are another story.

I've been thinking about this a lot recently, and an Idea popped into my brain.
why not cut the LCA mounts off the axle, and move them up flush with the tube and keep the frame side mounts where they are?

that will do a couple things for me:
it will lessen the angle of the CAs with the extra lift height, which is good
since my shock mounts are attached to the lower CA mount it will move them up~2" giving me back the same travel numbers I started with (5"up,6.5"down)
it means I don't have to weld on new lower mounts and make new lower arms, it keeps my arms short so that I don't get hung up on them.
more ground clearance at axle.


some notes:
I will be stepping up to 35"s as well and this will give me the extra fender room I need without loosing any travel.
this must be a streetable rig still, its not a daily driver anymore but it still will see a lot of road miles
this rig will stay full-bodied

so am I retarded or what? thoughts?

here are a few pics of what I currently have for perspective.
LCA mount and shock mount, well below the tube


CA angle at ride height


max droop


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Unread 12-09-2012, 09:24 AM   #2
ArticRubi
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Someone a good bit more tech savvy than me will jump on this soon, but here's the problem as I see it: the reason the LCA brackets are below the tube is they provide anti-rotational stability (insert correct term here.) When you have both upper and lower brackets above the axis of rotation (axle shafts) the axle will want to rotate rather than transfer the power to the ground.

Everyone would love to have the extra clearance of having their LCA brackets above the tube, this is the reason no one does it.
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Unread 12-09-2012, 09:57 AM   #3
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Quote:
Originally Posted by ArticRubi View Post
Someone a good bit more tech savvy than me will jump on this soon, but here's the problem as I see it: the reason the LCA brackets are below the tube is they provide anti-rotational stability (insert correct term here.) When you have both upper and lower brackets above the axis of rotation (axle shafts) the axle will want to rotate rather than transfer the power to the ground.

Everyone would love to have the extra clearance of having their LCA brackets above the tube, this is the reason no one does it.
That's incorrect. The lower control arms will do their job even if they're above the axle centerline. As long as the upper is above the lower, the axle will be constrained. I think you were on the right track in regards to the leverage the control arms have over the rotational forces acting on the housing. The further the mounts are from the centerline, the more leverage the arms have on the housing. The less leverage the arms have, the more stresses are placed on the joints so you've got to use good stuff. Currie joints can handle it just fine.

Climbit, as long as you have more separation at the axle than at the frame, you'll be fine. With the lowers mounted flush with the centerline, the upper will need to be a couple inches higher than they currently are. I run my lowers flush at both ends with about 8" of vertical separation at the axles and 6" at the frame. Obviously you shouldn't just rely on general numbers like that but a 75% ratio is a good ballpark number to shoot for. Build the mounts strong and use good ends and you'll wind up being very happy with it. Feel free to keep the discussion going, it's a good topic.
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Unread 12-09-2012, 01:00 PM   #4
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Quote:
Originally Posted by Imped View Post
That's incorrect. The lower control arms will do their job even if they're above the axle centerline. As long as the upper is above the lower, the axle will be constrained. I think you were on the right track in regards to the leverage the control arms have over the rotational forces acting on the housing. The further the mounts are from the centerline, the more leverage the arms have on the housing. The less leverage the arms have, the more stresses are placed on the joints so you've got to use good stuff. Currie joints can handle it just fine.

Climbit, as long as you have more separation at the axle than at the frame, you'll be fine. With the lowers mounted flush with the centerline, the upper will need to be a couple inches higher than they currently are. I run my lowers flush at both ends with about 8" of vertical separation at the axles and 6" at the frame. Obviously you shouldn't just rely on general numbers like that but a 75% ratio is a good ballpark number to shoot for. Build the mounts strong and use good ends and you'll wind up being very happy with it. Feel free to keep the discussion going, it's a good topic.
I was hoping you'd chime in.

I would use an 8" link tower to get the axle separation.

if I stick with short arms, 6" of separation at the frame shouldn't be an issue, since I can plate over where the existing upper mount is and run the mount from there.

I suppose I should plug the numbers in to a calculator... just to see what my A/S would be....
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Unread 12-09-2012, 01:17 PM   #5
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A friend of mine welded my axles up when I did my 3/4 link. I wanted to make the lower arm mounts on the axle even with the axle also. He told me to run them slightly down. His reasoning was more for strength of the mount. They are high enough that they don't really hang up on anything so I am happy. I trust his judgement his builds survive rock and endurance races.
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Unread 12-09-2012, 02:18 PM   #6
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does anyone have the 3link calc numbers for the OEM setup? would save me a ton of time. thanks.
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Unread 12-09-2012, 07:43 PM   #7
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i have seen a couple vehicles with the lower CA mounts even with/ above the tube and they rotated enough to cause damage. on level ground it is fine but with power applied with a good amount of suspension compression it allowed too much rotation. now i have no figures to plug into any calc and i wasnt about to run under there and start measuring but it can happen. im sure the placement of the other mounts had a lot to do with it as well. just keep in mind that a lot more is going on under there when wheeling then is easily imagined while building. mine are 45* down and they are still higher then the dana 60 inner c that they are snugged up to so i dont think im loosing any valuable clearance.

if you are going with a larger tire you can afford a longer control arm with respect to issues of hanging up on things. i personally dont understand the paranoia over having completely flat control arms that has been going around lately particularly in the jk world. there are always compromises to be made and i dont think what it takes to run flat arms is worth what it takes to make it happen.
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Unread 12-09-2012, 09:18 PM   #8
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I run my rear lower link mounts level with the axle centerline with absolutely no issues with the axle twisting or breaking mounts. I run 6.5" of separation at the frame and 8" of separation at the axle. As long as you move the upper CA mount up to maintain roughly 8" of separation you shouldn't have any problems with axle rotation. Build the mounts to handle the increased forces and use joints that can handle the load (I run 1.25" Ruffstuff rod ends, 2.5" JJs will work as well).

It's very nice having nothing hang below the axle tube. Know where your pumpkins are and you very rarely get hung up on the rocks.
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Unread 12-09-2012, 11:08 PM   #9
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Quote:
Originally Posted by fratis View Post
i have seen a couple vehicles with the lower CA mounts even with/ above the tube and they rotated enough to cause damage.
The axle housing can't physically rotate unless the arm bends, the joints deflect or the mounts move.
Quote:
Originally Posted by fratis View Post
on level ground it is fine but with power applied with a good amount of suspension compression it allowed too much rotation.
See above. The only time I've ever had movement was when my old truss (fairly weak design) bent. The mounts, arms and joints were all fine.
Quote:
Originally Posted by fratis View Post
i personally dont understand the paranoia over having completely flat control arms that has been going around lately particularly in the jk world. there are always compromises to be made and i dont think what it takes to run flat arms is worth what it takes to make it happen.
The flatter the arms, generally the more neutral the roll axis angle is. This results in minimal unwanted steering input while articulating. And in theory, the ride quality is optimized but personally, I can't tell a difference between arms sitting at 5 degrees and those sitting at 15 degrees and I consider my senses pretty good at pickup the small differences. All in all, flatter arms perform better than steeper arms. The former is the real advantage to be gained. The latter is what most gullible JK owners worry about. It's really not tough to make it happen--don't jack the rig up to the sky and keep the axle mounts tucked up where they belong.
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Unread 12-09-2012, 11:49 PM   #10
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Quote:
Originally Posted by Imped View Post

See above. The only time I've ever had movement was when my old truss (fairly weak design) bent. The mounts, arms and joints were all fine.
like this one?



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Unread 12-10-2012, 02:05 AM   #11
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i disagree saw it myself. if i remember right the uppers, that had plenty of separation were set straight up and down with a pinion angle of 0 or before the pinion was set. with the pinion set the upper tower had a very large lean equalling a upper link that was pretty long. couple this with a lower link bracket that was high(honestly dont remember if it was even or above axle tubing) and it can happen. ill state again and clarify the placement of the link mounting other then the axle LCA had a lot to do with it. just having enough "separation" at the axle end is not enough. my point was simply to be weary of all the elements and do thorough travel tests.
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Unread 12-10-2012, 06:56 AM   #12
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Well, I've been around plenty of rigs with lower mounts above the axle centerline--most of those are Ultra 4 cars. The housings are held rock solid, as they should be. It makes no logical sense for there to be any movement unless there is that much movement somewhere else in the system. Now in your case, if there wasn't enough triangulation to keep the housing laterally constrained then I can understand what you're describing.

And considering my personal rig has all lower arms at the axle centerline and the housings don't budge....why would I have done that if it wouldn't have prevented the housings from rolling? Take a look at just about any custom suspension--the mounts are normally tucked up. It's a very common practice in order to minimize the angle of the arms and to improve clearance. If there was any decrease in the ability to constrain the housing's rotation, it wouldn't be nearly as common.

Lower mounts above the axle centerline


Think about this--what would happen if you put a jack under the pinion and went to town? It wouldn't rotate anymore than if the lowers were 1" below the axle. It's constrained in that axis exactly the same way.

Lower mounts behind and flush with the axle tube.....
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Unread 12-10-2012, 08:20 AM   #13
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Fratis, are you saying that the upper mounting locations were burned in with no regard to the lower mounting locations?
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Unread 12-10-2012, 08:23 AM   #14
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I'll be watching this. Some good ideas here.
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Unread 12-10-2012, 11:16 AM   #15
Climbit
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Quote:
Originally Posted by fratis View Post
i disagree saw it myself. if i remember right the uppers, that had plenty of separation were set straight up and down with a pinion angle of 0 or before the pinion was set. with the pinion set the upper tower had a very large lean equalling a upper link that was pretty long. couple this with a lower link bracket that was high(honestly dont remember if it was even or above axle tubing) and it can happen. ill state again and clarify the placement of the link mounting other then the axle LCA had a lot to do with it. just having enough "separation" at the axle end is not enough. my point was simply to be weary of all the elements and do thorough travel tests.
methinks that something else is going on in those suspensions. if you have 6-8" of vertical separation, it does not matter where your lowers are located, the upper will control all rotational forces.

now if the upper link fails, or there is too much slop in the joints (why I don't like bushings) then you have problems.
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