Minimum threading of adjustable rear control arms


Knows enough to be dangerous
Supporting Member
Nov 29, 2018
What would you say is the minimum amount of threads I should have from the rear lower control arms when installing a new axle? I was hoping to better center my rear wheels in the wheel wells by pushing the axle back a little, but run out of threads on my adjustable arms before it's perfectly centered. Right now I have about 5 1/4" on the front side of both wheels to the closest point on the wheel well and about 7" on the backside.
They should be centered on the bump stops at full bump.
Got it. I currently have it centered on the bump stops at ride height. So I'll start articulating the rear axle. I currently have 4 full turns threaded on. At what point do I need to worry about too few threads?
Yes. Single side adjustable.

No less than the width of the jam nut. So if the jam nut is 1/2" wide you should have 1/2" engaged in the arm. They won't fail due to thread engagement if you follow that rule. Now, that can lead to some strength issues with impacting offroad since a 1.5" OD arm will be stronger than a 7/8" OD shank on the rod end.
Rule of thumb for minimum thread engagement is 1 x diameter in steel.

a 1/2 bolt should engage in 1/2" of threads, a 1" bolt should engage in 1" of threads, etc...

I wouldn't trust anything less for any sort of critical joint.
Thanks for the input. I have about 9 full turns of thread engagement once I centered the bump stops. Didn't measure it once it was set, but I'd estimate that I have about half the threads in side the control arm.
I'd try and get full thread engagement of the bung. If the bung threads are 1 1/2" deep then I would thread the arm in 1 1/2" minimum. If you have the right arms then this wouldn't be a concern as the amount of exposed thread would be minimal. If you are to the point of counting thread engagement then you should be getting different (longer) arms.
What arms are they?
I went with Trail Logic. They're a newer company but make everything to about the same spec as everyone else. The UCA's are double adjustable. They say it works up to a 4.5" lift and I have a 4" lift.

When I pull the rear out again today to paint I'll measure how much I have threaded in.
If you center the wheel at ride height, you may have tire clearance or trackbar to fuel tank clearance at full stuff. Mine with 35s looks like it needs to extended at ride height, but fills the stock wheel opening at full stuff. You might get away with it with 33.