Why do my front control arms rotate after driving?

[rasband]

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...

You are. The threads on DA arms are reverse threaded when compared to the other (one right hand, one left hand). Meaning if you turn the arm one way you’re moving up the threads on both joints, reverse the way you’re going and you’re moving the threads down both joints. This is why they’re valuable, else you need to remove a joint from the rig to adjust them.

If you screw the arm long enough you’re either going to reach the joint housing and can’t tighten any further or fully unscrew them when the arm and the joints are now separate. The jam nuts keeps this from happening by working together to block motion either direction. A single jam nut won’t work nor will no jam nuts.

You conjuring @mrblaine doesn't change your misunderstanding.

 

[rasband]

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.

Sounds like your jam nuts are loose in this case. Ideally When you tighten them, they’ll both be oriented toward the side you’re turning, alternate one and the other until each is tight and can’t turn the threaded arm. You’ll need two wrenches to make this work with the clevite end.

 

[mrblaine]

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-

You are not getting the jam nut tight if the threaded end is moving. You need to lock it down with the JJ in the same orientation as the bushing end. There is no reason to do it other than that way.

 

[qslim]

I though you recalibrated your control arm mount for that rotation in Moab.

Yeah lots of stuff likes to rotate down there, especially when I'M driving.

 

[AndyG]

They know you too well.

Proves my theory- normal people are the ones you dont know well.