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National Guard guy
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Discussion Starter · #1 ·
Okay, I've been reading up a bit, and a longarm conversion seems to be one of the more popular mods for an XJ.
However, just how long do the arms need to be, and is longer better?
I've had some experience building rearend suspension on lowered trucks with air ride, so I'm familiar with 4-links and such.

Is there any problem with running an adjustable triangulated 4-link on the front axle, with the triangulated bars mounted on the bottom, and straight bars on top?

If I can get to a bandsaw, drill press, welder, and grinder, I should be able to fabricate any custom crossmembers I'd need, and I know a good place to order the links from already.
(they use greasable super pivot joints, and include all the necessary brackets cut from either 3/16" or 1/4" plate)

*puts on flame suit for the newb questions*
 

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5,080 Posts
This isn't really a newb question, most people just buy kits. Props to you for wanting to fabricate it.

Most XJ long arms systems aren't triangulated because there's isn't enough room for the uppers to clear the oil pan and such IIRC.

Many people run either a 3-link(2 lowers, and a drivers side upper) or a y-link suspension, which I'm sure you know of as well.

The two most popular XJ long arm kits seem to be TNT Customs and Rock Krawler(although everyone other than XJ guys hates RK.)

Also, search around NAXJA.org and pirate4x4.com in the Cherokee section, there's alot of fab info there if you look hard enough.
 

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Low Range Drifter
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8,435 Posts
>> just how long do the arms need to be, and is longer better?

There is a middle ground, too long and they are rock magnets, too short and they aren't worth the hassle. I'd say around 36" +/- 4" or so.

>> Is there any problem with running an adjustable triangulated 4-link on the front axle, with the triangulated bars mounted on the bottom, and straight bars on top?

In my opinion, no. There are some who will go on and on about bump steer on this setup if not using full hydro. My take is that sure, that can happen if the geometry is bad, but if you can keep a relatively flat roll axis then bump steer will be minimal. I believe this type of setup is great for the front axle.

>> I know a good place to order the links from already.

Since you mentioned that you've done this on lowered trucks, I would be sure that they use materials suitable for a offroad vehicle. Unless you plan on making it street only, the lowers will make contact with large immovable objects, and must be built to handle the stresses. I would recommend no less than 1.5"x0.25" wall DOM for lowers, with many going with heavier materials.
 

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National Guard guy
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1,063 Posts
Discussion Starter · #4 ·
Most XJ long arms systems aren't triangulated because there's isn't enough room for the uppers to clear the oil pan and such IIRC.

Many people run either a 3-link(2 lowers, and a drivers side upper) or a y-link suspension, which I'm sure you know of as well.
That's why my triangulated arms would be the lower bars, since they'd be approximately 5-6" lower than the upper bars, which would be parallel to the frame rails. Since the bars will be hanging lower, and the truck would (obviously) be lifted, that gives me even more room for flexing, assuming I don't jump the thing and make a hard landing.

And I've seen people using the 3-link, and Y-link, but I personally would rather have more bars holding the front axle in place, and not allowing it to flex left to right, yet still allowing up and down flex.
I'm assuming this is what you mean, by a Y-link, correct? http://www.suicidedoors.com/S103-LinkKit.php# I know that's for dropping an S-10, but the same basic principles apply.


JohnnyJ said:
I would be sure that they use materials suitable for a offroad vehicle. Unless you plan on making it street only, the lowers will make contact with large immovable objects, and must be built to handle the stresses. I would recommend no less than 1.5"x0.25" wall DOM for lowers, with many going with heavier materials.
These http://www.suicidedoors.com/4-LinkRoundAdjBarwithSuperPivot.php are the 4-link bars I'd be using, and as suggested, 1.5" DOM with .25" wall thickness. The kits are cheaper than their individual parts, but that's the best way I could show you the bars themselves.

Their frame brackets are made from .25" steel, as well.
 

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Premium Member
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A single triangulated setup will invite roll steer... no real way around that with the dimensions you have to work with. You can do you best to minimize it though.

Building it and designing it properly are going to take about the same amount of time. You want it to be stout and more importantly drive well, since this is a steering axle you will want to do your homework if this is a street driver :thumb:

Since your working with your stock link mounts on the axle I assume, all your adjustments for drive ability will have to be done at the cross member.

Go to the local bookstore and grab a book about suspension design... this will help you wade through the internet BS and you can decide for yourself what matters and what doesn't.
 

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Low Range Drifter
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8,435 Posts
A single triangulated setup will invite roll steer... no real way around that with the dimensions you have to work with. You can do you best to minimize it though.
If he builds it reasonably, the triangulated lowers and parallel uppers can have quite a low roll axis. It's not uncommon for that setup to have negligible amounts. Going the opposite route of triangulated uppers and parallel lowers is a whole different story.

From what I've seen, the triangulation of the lowers plays a major role in the roll steer that a suspension exhibits.

I would also say that playing with the 4-link calculator (and the 3-link calc) after you've done some reading on link suspensions can also help to demonstrate effects on AS% and roll centers. Also, try and find people who have built different setups and see how they work. Try and identify where their links are and what you liked about it, eventually you can see a trend of what works.

http://www.pirate4x4.com/forum/showthread.php?t=204893
 

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National Guard guy
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1,063 Posts
Discussion Starter · #7 ·
Since your working with your stock link mounts on the axle I assume, all your adjustments for drive ability will have to be done at the cross member.
I really haven't had a chance to examine a completely stock XJ, to know what I've actually got to work with. I was planning to have the lower triangulated bars converge back on the crossmember, however.
 

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National Guard guy
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1,063 Posts
Discussion Starter · #9 ·
I just built my long arm but went the radius arm route. It's a simple build wich a lot of the after market uses.

http://www.greatlakes4x4.com/showthread.php?t=57121

And i though this guys idea was interesting

http://www.phatserver.net/~twiek/longarm/index.html
That makes no sense to me, to have the lower link bars twice as long as the upper bars. They won't have the same arc, and that would only increase any pinion change. I've always been told that the bars should be of equal length from front to back, to keep the pinion change to a minimum.
 

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newbie
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That makes no sense to me, to have the lower link bars twice as long as the upper bars. They won't have the same arc, and that would only increase any pinion change. I've always been told that the bars should be of equal length from front to back, to keep the pinion change to a minimum.
do more research, there are a lot of ways to design suspensions. lots of times packaging it in the truck dictates 90% of the geometry.



for what its worth, my rear 4 link has paralell to eachother UPPER links and triangulated lowers. my roll axis is at 28" on 37" tires and the axis is within 1 degree of flat :chauncy:

edited the word UPPER to clarify what i ment
 

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do more research, there are a lot of ways to design suspensions. lots of times packaging it in the truck dictates 90% of the geometry.



for what its worth, my rear 4 link has paralell to eachother links and triangulated lowers. my roll axis is at 28" on 37" tires and the axis is within 1 degree of flat :chauncy:
X2
there are no absolutes in building a suspension.
Ive built three three dif. ways. taking your time and figuring out your geometry is what counts no matter how you do it
 
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