Control arm length questions

So I got a set of upper and lower control arm today at a u-pull-it yard. They're in really good shape, barely any rust. The truck seemed to be lifted about 3". The lcas are adjustable and the ucas are fixed at 15.5". I understand that that's about a 1/2 inch to long for my 4.5 lift. What length do you guys think I should make the lcas before I put them all in?

Thank you.
Bob

Were you able to tell if the axle on the Jeep you pulled it from either had the front end pushed forward from stock or had the uca mount relocated? Doesn't seem right that they would be longer than you need when it had less lift. It doesn't matter anyway, that is the beauty of the adjustables. Measure your caster angle at the axle C's as it sits. Take out all the control arms and the coils (making sure everything is supported etc, of course) and put in the new uppers. Get the axle to the caster you desire at the approximate ride height and adjust the lowers as needed to make the holes line up.
Unless you are not using the 'too long' uppers. In that case, just remove the lowers and make the new ones the same length. The length of upper vs. lower arms do not need to fit any kind of formula with eachother. They just need to position the axle where you want it.
Hope that kinda sorta helps arty:

B.Styles said:

So I got a set of upper and lower control arm today at a u-pull-it yard. They're in really good shape, barely any rust. The truck seemed to be lifted about 3". The lcas are adjustable and the ucas are fixed at 15.5". I understand that that's about a 1/2 inch to long for my 4.5 lift. What length do you guys think I should make the lcas before I put them all in?

Thank you.
Bob

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I found this formula a long time ago.

Upper Arms - 14.93(Stock Arm Length)^2 + (Lift - 1.5)^2 = (Arm Length)^2
Lower Arms - 15.73(Stock Arm Length)^2 + (Lift + .75)^2 = (Arm Length)^2

Note: ^2 means "squared".

You could solve the upper arm formula for the lift and then use that for the lower arm length.

just remember that pinion angle is more important than castor if your jeep sees any on road 4x4 use.

Using his formula it calls for 15 1/4" uppers. I bet you could make those work with adjustable lowers.

bdiamond said:

Using his formula it calls for 15 1/4" uppers. I bet you could make those work with adjustable lowers.

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The formula also yields 16.58 for the lower so I would start with 16.75 and then adjust for caster. I would try and shoot for the pinion being about 3-4 degrees above level on Hi Pinion or 6-7 degrees on the Low Pinion D30. (This is the actual pinion angles reference level, not the pinion to drive shaft angle.) This should give fairly good caster without drive line vibration.

Also if you have any alignment shims in the mounts make sure you pull those out as you want the arms as far back in the mounts as you can get with them being extra long.

The truck was already in the air with one of the lowers off, and the other was loose so I couldn't tell how the rear was positioned. But I was curious. How far can I take it moving the front rear forward?

B.Styles said:

The truck was already in the air with one of the lowers off, and the other was loose so I couldn't tell how the rear was positioned. But I was curious. How far can I take it moving the front rear forward?

Click to expand...

I'm having a hard time understanding what you are asking?

Nevermind, I had a really long night last night and that seemed to make sence when I wrote it. But I answer my own question when I reread everything.
Thank you everyone.
Bob