Why do my front control arms rotate after driving?


freedom_in_4low

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So if the joint moving around is acceptable, then why have the jam nut?

ask teraflex, I think they had some experience in this area 15+ years ago.

seriously though, they tried it, it didn't work that well and the threads wore out in a hurry. My TJ had them when I bought it, they'd been welded solid because the threads were trashed.
 

Wingback73

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The joint is moving on the misalignment ball, not the threads in the arm.
Fair enough, but why is the jam nut there at all then? I can't imagine any manufacturer is dying to increase material costs an additional $1-2 per arm to include a nut that has no purpose. So why are they doing so?
 

Wingback73

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ask teraflex, I think they had some experience in this area 15+ years ago.

seriously though, they tried it, it didn't work that well and the threads wore out in a hurry. My TJ had them when I bought it, they'd been welded solid because the threads were trashed.
Sorry if I'm slow, but doesn't that lead us back where we started? That would imply that the weld nut is there to keep the arm from turning, which in turn means, centered or not, the nut is important to the longevity of the arm, and therefore we should all make sure they are tight, and that the arm is NOT turning under load.

Not trying to be argumentative, but if there is one thing I've learned after 20+ years in automotive, it is that no one is incurring material costs unless absolutely necessary, so trying to understand what I interpreted as implications that the jam nut doesn't matter. Perhaps I just misunderstood the earlier posts...
 
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rasband

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Fair enough, but why is the jam nut there at all then? I can't imagine any manufacturer is dying to increase material costs an additional $1-2 per arm to include a nut that has no purpose. So why are they doing so?
You don't want the arm rotating on the joint threads, that will lead to a failure eventually (the arm will unscrew itself and fall out, leaving you with two joints bolted to the axle/frame without any other connection). The jam nuts mitigate (eliminate, if done correctly) the arm from rotating itself. Instead, the joins can misalign.

Metalcloak joints self-center, so generally you should always seem them as "centered" in the mount. However JJs are free floating - so the joint will be any orientation within the mount. Unless someone installed them wrong they will allow for a good bit of misalignment. The installation should be done with them aligned the direction the jam nut would otherwise push them. Then you tighten each jam nut incrementally to avoid the arm spinning. That way the heads are aligned and allow the maximum movement (30ish degrees each direction).
 

mrblaine

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Fair enough, but why is the jam nut there at all then? I can't imagine any manufacturer is dying to increase material costs an additional $1-2 per arm to include a nut that has no purpose. So why are they doing so?
You don't know how adjustable control arms work. Come back to this and we'll revisit it when you do.
 
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Wingback73

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You don't want the arm rotating on the joint threads, that will lead to a failure eventually (the arm will unscrew itself and fall out, leaving you with two joints bolted to the axle/frame without any other connection). The jam nuts mitigate (eliminate, if done correctly) the arm from rotating itself. Instead, the joins can misalign.

Metalcloak joints self-center, so generally you should always seem them as "centered" in the mount. However JJs are free floating - so the joint will be any orientation within the mount. Unless someone installed them wrong they will allow for a good bit of misalignment. The installation should be done with them aligned the direction the jam nut would otherwise push them. Then you tighten each jam nut incrementally to avoid the arm spinning. That way the heads are aligned and allow the maximum movement (30ish degrees each direction).
The arms can't rotate more than their mounts would allow though anyway, right? No chance of an arm unscrewing for the simple reason that both ends are fixed - that part I get. It seems to me that the whole point of the jam nut is to keep the threaded part from rotating back and forth and wearing out the threads. You also get substantially better load bearing by have the threads fully engaged and avoiding the lash that would otherwise wear them over time.

What I'm unclear on, and trying to sort out is this: If we agree we don't want the arm to move, which I think is what I've read above, then the threaded end needs to be locked in some position. The OP's original position allows substantially more rotation in one direction than another. Is that desirable? I have mine centered since I assume that I want the same amount of rotation in both directions to control both upward and downward articulation of the axle.

But that may be a poor assumption - perhaps we want to allow more range of motion on the suspension downward articulation because the wheel can drop more than it can compress. Is that a true statement? If so, how much/in which direction should they be rotated when locked in place for maximum range of articulation both up and down?

d-
 
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Wingback73

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You don't know how adjustable control arms work. Come back to this and we'll revisit it when you do.
<edited now that I see where this is coming from>

I recognize you are a well-respected member here, and I've learned an awful lot from reading your responses, but I've asked legitimate questions in a fair and respectful fashion, and that post is purely worthless. If you think I need to learn something, then by all means feel free to point me in the direction of the learnings that you think I haven't read. That will be much more useful to people who may need to learn more in order to have an intelligent discussion.
 
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Wingback73

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No, that part you don’t get.
Am I in alternate land right now? The arm can't possibly come unscrewed - there is a bolt going through each end of it that is attached to either the frame or the axle. Unless you somehow managed to rotate the entire axle relative to the frame you will never disconnect the two ends of an adjustable control arm while it is still attached to the vehicle.

I'm wondering if perhaps Mr. Blaine meant to respond to you instead of to me...
 
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jjvw

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@rasband
a83a70923c36ebec103983e90a99673a5e4d5bfc52932383324d21d9a1293603_1.gif
 
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P man

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Fair enough, but why is the jam nut there at all then? I can't imagine any manufacturer is dying to increase material costs an additional $1-2 per arm to include a nut that has no purpose. So why are they doing so
If you were to thread the arms without locknuts and wiggle them you would note movement..over time this will wear the threads and cause damage. Now install the lock nut and try to wiggle the arm..there will be no movement..so in short the lock nut keeps the threads from wearing/galling etc..
 

jjvw

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Does this help?
25DPmpvPzyHcGxsBTJ.gif

Once the link is the desired length, the jam nuts are tightened and nothing else happens to them or to the joint housing.
 
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Wingback73

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Okay, okay, I see what happened here. I missed a sentence early on and have given the impression that I have a lack of understanding of control arms and jam nuts. My apologies for doing so. And my apologies to Mr. Blaine, since I now see where he thought I was just too stupid to understand how a screw and nut worked.

Let me completely re-state my question so it is fully formed:
Unlike the OP, I do NOT have johnny joints on both ends. I have a bushing on one end and a johnny joint on the other. I also, however, find that periodically the johnny joint end will come misaligned from the bushing end. The bushing end, by definition, is always centered (ability to rotate, albeit in a limited fashion, equally one way or the other). The johnny joint end, however, will sometimes look like the OPs. I missed the part where the OP indicated that both ends of his are still aligned.

In my case, they aren't. So the simple question I was trying to ask was this:
When I lock down the jam nut, so that the adjustable control arm doesn't spin, do I want the johnny joint end centered while the vehicle is sitting under its own weight, or do I want it to be biased one way or the other? Centered would necessarily allow the joint to flex equally in either direction, which would be exactly as desired if a suspension were capable of articulating the joint equal amounts when the wheel goes up or down. Is that accurate, however? But are the up travel and down travel actually equal? It would seem not, which might imply that we would NOT want the johnny joint end centered when the vehicle is resting, but rather biased to allow more joint articulation to the down travel since that is generally (I think) greater than up travel.

Hopefully that makes more sense - now you can tell me that I'm an idiot for not understanding suspension travel, but hopefully I've at least demonstrated that I understand the principles of a control arm.

d-
 

Thunderhead

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If a JJ control arm is banging side to side it desperately needs to be rebuilt.
Gracias. I don’t think it’s the JJs then cause I just torqued the bolts and re-centered the JJ’s. Took a pray bar to move them.
I’ve only heard it once or twice in 4L, locked up and steering Driver/Passenger
 

jjvw

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Okay, okay, I see what happened here. I missed a sentence early on and have given the impression that I have a lack of understanding of control arms and jam nuts. My apologies for doing so. And my apologies to Mr. Blaine, since I now see where he thought I was just too stupid to understand how a screw and nut worked.

Let me completely re-state my question so it is fully formed:
Unlike the OP, I do NOT have johnny joints on both ends. I have a bushing on one end and a johnny joint on the other. I also, however, find that periodically the johnny joint end will come misaligned from the bushing end. The bushing end, by definition, is always centered (ability to rotate, albeit in a limited fashion, equally one way or the other). The johnny joint end, however, will sometimes look like the OPs. I missed the part where the OP indicated that both ends of his are still aligned.

In my case, they aren't. So the simple question I was trying to ask was this:
When I lock down the jam nut, so that the adjustable control arm doesn't spin, do I want the johnny joint end centered while the vehicle is sitting under its own weight, or do I want it to be biased one way or the other? Centered would necessarily allow the joint to flex equally in either direction, which would be exactly as desired if a suspension were capable of articulating the joint equal amounts when the wheel goes up or down. Is that accurate, however? But are the up travel and down travel actually equal? It would seem not, which might imply that we would NOT want the johnny joint end centered when the vehicle is resting, but rather biased to allow more joint articulation to the down travel since that is generally (I think) greater than up travel.

Hopefully that makes more sense - now you can tell me that I'm an idiot for not understanding suspension travel, but hopefully I've at least demonstrated that I understand the principles of a control arm.

d-
If there is a bushing on one end of a control arm and a flex joint on the other, the flex joint should be in the middle of its range of motion when the bushing is in it's neutral state.

Any jam nuts ought to be tight and none of the threads should move.
 
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mrblaine

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Am I in alternate land right now? The arm can't possibly come unscrewed - there is a bolt going through each end of it that is attached to either the frame or the axle. Unless you somehow managed to rotate the entire axle relative to the frame you will never disconnect the two ends of an adjustable control arm while it is still attached to the vehicle.

I'm wondering if perhaps Mr. Blaine meant to respond to you instead of to me...
Oh no, it was you and correctly since you are clearly illustrating my point. The double adjustable arms are right and left hand thread. With a bit of patience and fiddling around, it is possible to bolt all 4 lower joints in the mounts and then screw the arm onto them.

The joint rotates on the ball inside the urethane races to provide misalignment. If the joint body rolls over to one side while driving, it is of no consequence. That is how they work and there is absolutely zero detrimental effect except for how much time it takes to teach the ignorant how arms work.
 
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