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Old 05-04-2018, 01:05 AM   #1 (permalink)
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Disadvantages of long arm suspension?

I've read about the advantages. What I can't seem to find, are the disadvantages. I'm trying to weigh long arm, vs just keeping the stock stuff on my 1979 CJ7. And I don't want to leave anything out or miss any important detail, that makes me have regrets. So what are the disadvantages of having a long arm suspension on a CJ7?

Perhaps the looks change in some way?
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Old 05-04-2018, 01:41 AM   #2 (permalink)
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This has to be a troll thread.
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Old 05-04-2018, 01:49 AM   #3 (permalink)
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The re long arm kits for the tj and lj make them wildly more flex able but they are not necissarily prime link desings. The rears are a bit long for optimal nuetral squat geometry and can cause some funky actions that could be better handled with shorter links and better angles. But packaging suffers to gain function in a truely ideal suspension.

Ground clearance and flex gained far out weigh the less than perfect geometry
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Old 05-04-2018, 11:27 PM   #4 (permalink)
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The re long arm kits for the tj and lj make them wildly more flex able but they are not necissarily prime link desings. The rears are a bit long for optimal nuetral squat geometry and can cause some funky actions that could be better handled with shorter links and better angles. But packaging suffers to gain function in a truely ideal suspension.

Ground clearance and flex gained far out weigh the less than perfect geometry
I guess I should have started by saying that I'm something of an off roading newb. The CJ7 will see medium difficulty trails at most, never anything beyond that. And probably not usually that, but it will happen at some point. So I'm trying to figure out if long arm is actually useful in my situation. If I should even bother with it.

I was attracted to the long arm setup because everyone says it yields better road manners. I'm all for that. As I'd like to drive it to the trails instead of having to always trailer it. I'm kind of picky about my driving experience and I don't really want it to be miserable. So I was just wanting to know about any overall disadvantages, if there are any. What would I lose, if anything, vs rebuilding the stock suspension.

Is long arm the ultimate upgrade vs stock? All advantages and no disadvantages? Again a newb is asking.
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Old 05-04-2018, 11:56 PM   #5 (permalink)
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If youre picky about ride the last thing you want is a old jeep or a built crawler.

Go buy a jk
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Old 05-05-2018, 12:50 AM   #6 (permalink)
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Op buys 30 year old jeep with metal dash and is worried about driving expierence.

Op link suspension when done correctly do ride better. But a sprung over jeep when built correctly doesn’t ride that bad for a trail rig. Your question lead me to believe this route might be closer to your skill set.
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Old 05-07-2018, 11:59 AM   #7 (permalink)
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Worst issue I see is the break over on the belly. Other than that, it's an improvement. The a well done mid arm is pretty banging.... @Syrings72
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Old 05-07-2018, 12:14 PM   #8 (permalink)
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I've read about the advantages. What I can't seem to find, are the disadvantages. I'm trying to weigh long arm, vs just keeping the stock stuff on my 1979 CJ7. And I don't want to leave anything out or miss any important detail, that makes me have regrets. So what are the disadvantages of having a long arm suspension on a CJ7?

Perhaps the looks change in some way?
A set of QUALITY leaf spring with some QUALITY shocks, will do wonders on a CJ7 and give a very nice, and quite, ride. Not Rancho, but something like Bilstein 7100 series shocks. Yes they're more money, but you'll like them.

Regarding converting to link suspension on a CJ7..... don't.
You're far better off starting with a 97 to 06 Jeep TJ Wrangler. They're already linked. With the money you'll spend converting the CJ over, you're better off selling the CJ.

Regarding long arm, verse, short arm. The primary constraint you should be dealing with is packaging. Trying to fit all the link arms, mounting brackets, including steering arms with the panhard (remember, the CJ has the front axle pumpkin on the wrong side) inside the narrower CJ frame is a giant PITA. Yes. Tons of folks have already done this suspension. But they're not taking on 'intermediate' trails. They build for extreme.
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Old 05-07-2018, 03:59 PM   #9 (permalink)
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A set of QUALITY leaf spring with some QUALITY shocks, will do wonders on a CJ7 and give a very nice, and quite, ride. Not Rancho, but something like Bilstein 7100 series shocks. Yes they're more money, but you'll like them.

Regarding converting to link suspension on a CJ7..... don't.
You're far better off starting with a 97 to 06 Jeep TJ Wrangler. They're already linked. With the money you'll spend converting the CJ over, you're better off selling the CJ.

Regarding long arm, verse, short arm. The primary constraint you should be dealing with is packaging. Trying to fit all the link arms, mounting brackets, including steering arms with the panhard (remember, the CJ has the front axle pumpkin on the wrong side) inside the narrower CJ frame is a giant PITA. Yes. Tons of folks have already done this suspension. But they're not taking on 'intermediate' trails. They build for extreme.
I have to agree with all of this, having just linked the rear of my CJ. Very expensive to the point of cost prohibitive and the CJ frame is not bent in a way to maximize link geometry. You better have a very good reason for needing to be linked other than articulation. Waggy springs yield a ton of articulation and a great ride. My main reason for rear links is 400hp 400ft lb of torque and really tired of band aiding spring wrap/wheel hop issues. I don't believe I'll be doing it again ever though. I'll get better at band-aiding instead. The cost and work involved was full retard.
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Old 05-08-2018, 10:22 AM   #10 (permalink)
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Your CJ-7 will go amazing places in stock form. No need to get all Four Wheeler Magazine to run some easy to moderate trails. Get some knobby tires, go on a few trail rides, keep your eyes open. Then decide what to change bit by bit.

I recommend minimal lift and cutting the body to fit big tires. Spend your money on a cage and axles. I'm not sure if Holbrook Specialties still sells their long leaf springs, but I ran them for years and loved them, sort of like old school long arm suspension for leaf spring vehicles
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Old 05-08-2018, 11:29 AM   #11 (permalink)
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Sell the CJ and buy a JK.
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Old 05-08-2018, 11:41 AM   #12 (permalink)
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The main disadvantage of a long arm suspension, is all the work involved when your intended use doesn't require a long arm suspension.
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Old 05-08-2018, 11:48 AM   #13 (permalink)
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Surprised no one has mentioned it yet.

The primary disadvantage for any long arm conversion is always gonna be cost. $$$$$$$$$$$$

Beyond that I can't think of any other disadvantages.

Having talked to a jeep engineer they would go longarm from the factory if the bean counters weren't involved.

Kevin
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Old 05-08-2018, 11:53 AM   #14 (permalink)
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...

Having talked to a jeep engineer they would go longarm from the factory if the bean counters weren't involved.

Kevin
What would be the benefit on a factory spec Wrangler to go with longer arms?

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Old 05-08-2018, 05:20 PM   #15 (permalink)
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What would be the benefit on a factory spec Wrangler to go with longer arms?

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longer arms will do everything better, both on and offroad
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Old 05-08-2018, 06:22 PM   #16 (permalink)
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The biggest problem I had with mine was trying to fit a decent size muffler inside the body and keep up travel once I triangulated the uppers.

Oh and my SOA CJ7 Had better manners cruising down the road.
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Old 05-08-2018, 08:25 PM   #17 (permalink)
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RockKrawler long arm that copies the nth degree style....aka, the high clearance bent arms, are the way to get around the breakover clearance issue

I think the only disadvantage you might see would be a bit "tippy" feeling since the control arms are able to do what they are designed. However this is such a minor issue and can be fixed with sway bars.

Going to a 5, 4 or 3 link system on a CJ can only be beneficial.
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Old 05-08-2018, 08:31 PM   #18 (permalink)
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longer arms will do everything better, both on and offroad
Regardless of geometry concerns like instant centers and antisquat/antidive? How will they do everything better? Is it because of arm length or do the mount locations matter?

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Old 05-08-2018, 08:33 PM   #19 (permalink)
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Surprised no one has mentioned it yet.



The primary disadvantage for any long arm conversion is always gonna be cost. $$$$$$$$$$$$



Beyond that I can't think of any other disadvantages.



Having talked to a jeep engineer they would go longarm from the factory if the bean counters weren't involved.



Kevin


Your drunk!!!!!
They designed the suspension to do what 99% of TJ’s would be doing......
1% trail and the rest pavement!!!!!
And they did a pretty good Fkn job I think!!!!


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Old 05-08-2018, 08:43 PM   #20 (permalink)
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Regardless of geometry concerns like instant centers and antisquat/antidive? How will they do everything better? Is it because of arm length or do the mount locations matter?

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It is a matter of force vectors. Short arms have a higher ratio of impact energy pushing into the frame vs long arms, which are at an (ideally) horizontal position. This allows the arm to move instead of jolt into the control arm mount.

simply, Force * Sin(resultant angle from axle side mount to frame mount)= force into frame.
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Old 05-08-2018, 08:56 PM   #21 (permalink)
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It is a matter of force vectors. Short arms have a higher ratio of impact energy pushing into the frame vs long arms, which are at an (ideally) horizontal position. This allows the arm to move instead of jolt into the control arm mount.

simply, Force * Sin(resultant angle from axle side mount to frame mount)= force into frame.
What angle is too much? I'm suspicious that the control arm angles seen on a reasonably lifted TJ (the closest coil/linked relative to the CJ7) on stock axles and wheelbase is going to see much noticable "impact" from too steep of a control arm angle. There must be other reasons to change arm length.

What about instant centers? Does that not matter?

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Old 05-09-2018, 06:28 AM   #22 (permalink)
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What angle is too much? I'm suspicious that the control arm angles seen on a reasonably lifted TJ (the closest coil/linked relative to the CJ7) on stock axles and wheelbase is going to see much noticable "impact" from too steep of a control arm angle. There must be other reasons to change arm length.

What about instant centers? Does that not matter?

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Well, obviously the "too much" factor is subjective as suspension handling characteristics are increasingly hindered the closer the control arms approach vertical...but you will have more issues to deal with far before then (wheel base, driveline, etc). Remember what happens as you push an axle away from the frame (lift), your wheelbase will begin to pucker up and shorten.

stock Axles and wheelbase have less to do with it than length of the control arm and the amount of lift... You can have a 200" wheelbase on Dana 60s with the same control arm setup as a stock TJ and experience the exact same issues.

A beam that is secured with a pivot point on one end and a perpendicular force vector on the other will see nearly zero instantaneous vertical force on the pivot since it will be able to pivot freely. However, take the same setup and now angle that beam 45 degrees into the direction from which the force is being imposed and you will see forces transferred into the pivot since the linear force is being converted into an angular force.
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Old 05-09-2018, 06:45 AM   #23 (permalink)
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Well, obviously the "too much" factor is subjective as suspension handling characteristics are increasingly hindered the closer the control arms approach vertical...but you will have more issues to deal with far before then (wheel base, driveline, etc). Remember what happens as you push an axle away from the frame (lift), your wheelbase will begin to pucker up and shorten.

stock Axles and wheelbase have less to do with it than length of the control arm and the amount of lift... You can have a 200" wheelbase on Dana 60s with the same control arm setup as a stock TJ and experience the exact same issues.

A beam that is secured with a pivot point on one end and a perpendicular force vector on the other will see nearly zero instantaneous vertical force on the pivot since it will be able to pivot freely. However, take the same setup and now angle that beam 45 degrees into the direction from which the force is being imposed and you will see forces transferred into the pivot since the linear force is being converted into an angular force.
Are you capable of talking about any of the other, more important, considerations and nuances of linked suspension design? I've tried to point you in those directions. Can anyone else who is following along care to give the OP some actual knowledge outside of simple marketing hype that only focuses on arm angle?

The arm angles the OP would deal with in this potential build that might contribute to NHV are largely irrelevant.

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Old 05-09-2018, 06:57 AM   #24 (permalink)
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I have touched on multiple issues besides just angle. Wheelbase, driveline, ride quality, etc.

If you are trying to point someone in a direction, why can you not take us there?
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Old 05-09-2018, 08:31 AM   #25 (permalink)
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You are barely scratching the surface.

Instant center, antisquat, antidive, vertical separation, roll center.

OP, if you want to seriously explore linking your CJ7, these are the terms you need to familiarize yourself with. This is the real world of suspension geometry. There are no kits for your application. While the TJ world is full of them, nearly all are garbage because they compromise good geometry for ease of installation. What they do offer is the ability for a bunch of uninformed blow hards to brag about how long their arms are.

Keep this in mind. Control arm length is not the important concern. Longer arms do not create suspension travel. Longer arms do not have a meaningful effect on ride quality. What truly matters are the locations of the control arm mounts and the geometry they create. The length of the arm is simply a by product of the mount locations. A good link design will pay close attention to the vertical separation between mounts at both the frame side and axle side, both for strength and to direct the instant centers to their optimal locations in space. Research the list of terms I mention above.

Since the TJ Wrangler is the closest relative to your CJ7 that was designed with coils and links, it might be helpful to spend some time understanding why a bone stock TJ has very good suspension geometry (Hint- the stock suspension is not even close to being the limitation to it's off road capability). Understand what happens to that geometry when the suspension is lifted, but stop fixating on the arm angles. It won't matter for the vast majority of builds. Understand the criticism that is directed toward the bolt on long arm kits. Research why the so called "mid arm" is the way to build your suspension. Again, mount location is the most important consideration.

I only suggest this because I suspect there has been more intelligent discussion of linked suspension on a traditional Jeep platform in the TJ world than in the CJ world. I know there will be useful information and concepts, particularly with the packaging of the mounts, that will carry over between the similar platforms.

All that being said, coils and links are as simple as they are complicated. Most don't grasp the fundamentals. A well built leaf suspension will out perform a badly designed link suspension. But don't worry. If you end up with a crap linked suspension, just say "it's a Jeep thing" and that will fix everything.

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