Thread: Verifying front LA length questions

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  1. #1 Verifying front LA length questions 
    Senior Member Grand Slam West Planner Mtn WJ's Avatar
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    I replaced my front drivers side control arm joint on the frame side just before Moab and then had to replace the passenger front control arm joint this past weekend. I ended up having to pull the entire arm off to remove the johnny joint and even bought a ginormous pipe wrench to get the old one off. I think I may have moved the lock nut a bit which means I may have affected the overall length of the CA compared to the drivers arm. These are TNT radius arm style long arms.

    Question is where do you suggest I measure between on each side to verify my axle is plum side to side? I did some basic measurements and it seems ok, but its a 17yr old Jeep with lots of trails behind it, so not sure I am using best method.

    Suggestions appreciated.

    Keith
    Ask not what your country can do for you; but what can you do for your country. JFK Jan 20th, 1961

    TnT Customs Long Arms, 33" BFG KM2s, Magnum 9k winch, Ready Welder, Custom HP 30/30 front with ARB, Currie HP 9 rear with Detroit
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  2. #2 Re: Verifying front LA length questions 
    Senior Member Grand Slam West Planner K2's Avatar
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    I measure from wheel center to wheel center front to rear both sides to make sure wheel base is the same. With cut and dented fenders that is all I trust. Then look at wheel stick out, I have someone drive while I follow to look for dog walk.
    02 WJ, Lift, dents, noise and smoke.
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  3. #3 Re: Verifying front LA length questions 
    Senior Member Grand Slam West Planner Mtn WJ's Avatar
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    Yea, I was thinking of using a string to measure each side wheel to wheel. How do you determine center of the wheel?
    Ask not what your country can do for you; but what can you do for your country. JFK Jan 20th, 1961

    TnT Customs Long Arms, 33" BFG KM2s, Magnum 9k winch, Ready Welder, Custom HP 30/30 front with ARB, Currie HP 9 rear with Detroit
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  4. #4 Re: Verifying front LA length questions 
    Senior Member Ken L's Avatar
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    Keith, I'd measure the distance between the axles as close to the wheel as possible. From the axle tube to axle tube. Don't need a center to center measurement, just inside to inside in a straight line. What you're looking for is a common measurement on each side, and assuming that the axle tubes are straight that dimension will be fine to figure arm length needed to make the Jeep "square"

    I've found it easier to start with the bolt to bolt length on the arms. If they're the same side to side, then, at least for me, the tube to tube length has been the same also.
    Ken L
    '96 ZJ with stuff
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  5. #5 Re: Verifying front LA length questions 
    Senior Member Grand Slam West Planner K2's Avatar
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    Quote Originally Posted by Mtn WJ View Post
    Yea, I was thinking of using a string to measure each side wheel to wheel. How do you determine center of the wheel?
    That could be tough. I had centercaps that had a pattern from the center, and I used a GOOD helper, it was easy. Kens way should work too.
    02 WJ, Lift, dents, noise and smoke.
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  6. #6 Re: Verifying front LA length questions 
    Senior Member Grand Slam West Planner Mtn WJ's Avatar
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    I see, I will play around with different pic points and see what I get, I did measure the arms and they are the same, but that would mean the mounting points on the frame are square with the body etc. 17 yrs of trails etc, not so sure they are. No real evidence they are not, but it stands to reason.
    Ask not what your country can do for you; but what can you do for your country. JFK Jan 20th, 1961

    TnT Customs Long Arms, 33" BFG KM2s, Magnum 9k winch, Ready Welder, Custom HP 30/30 front with ARB, Currie HP 9 rear with Detroit
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  7. #7 Re: Verifying front LA length questions 
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    I like Ken's idea the best, using common points on both sides that are fixed. You could probably even do wheel edge to wheel edge, so you are getting true measure at ride height. Just make sure the steering is straight (and the wheels are, too!)

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  8. #8 Re: Verifying front LA length questions 
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    Could always throw it on an alignment rack?
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  9. #9 Re: Verifying front LA length questions 
    Senior Member Grand Slam West Planner Mtn WJ's Avatar
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    Yea, last time I tried to go to normal shops for alignment I was told they would not adjust anything on the control arms. Only toe in/out. They would tell me if I was off or not but no adjustments beyond standard type on stock Jeeps. So I had to go High Country which is ok, but 3x the price and if it is good anyway I waste money. So that is why I want to verify on my own.
    Ask not what your country can do for you; but what can you do for your country. JFK Jan 20th, 1961

    TnT Customs Long Arms, 33" BFG KM2s, Magnum 9k winch, Ready Welder, Custom HP 30/30 front with ARB, Currie HP 9 rear with Detroit
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  10. #10 Verifying front LA length questions 
    Senior Member Grand Slam West Planner JohnBoulderCO's Avatar
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    This is what I have done for many years and it has always worked for several axle swaps on various rigs.

    More than you asked for, but here goes:

    For front to back, Agreed use common points on the “frame” and measure to the axle tube, in case the control arm brackets are rotated slightly or bent. Adjust LCA’s and measure again.

    For left to right, use a yardstick or similar and set it against one tire vertical. Then using another yardstick or tape measure, measure to the spring perch or common place on the “frame” rail. Repeat on opposite side. Split the difference in the measurements to reposition the axle. Rear-both UCA’s are adjusted. Front-track bar is adjusted. Measure again to confirm.

    Pinion angles would be your last step.
    Angle finder on driveshaft, then on flat spot on pumpkin or better yet the pinion yoke. Adjust UCA’s together to adjust pinion.

    Caster-well there’s the rub. Not easily adjusted. Build your new axle with the inner C’s rotated correctly for pinion and caster. Current Axle - If you have hubs, you can dial in caster and forgo front driveshaft pinion angle. If no hubs (D30) it’s a trade off between front driveshaft vibs and fear of DW for lack of caster.

    Cheers!
    Last edited by JohnBoulderCO; 08-07-2018 at 08:39 PM.
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  11. #11 Re: Verifying front LA length questions 
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    A standard alignment will help with thrust angle and the side to side, but won't address wheelbase differences. It will just adjust the toe to compensate.

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  12. #12 Re: Verifying front LA length questions 
    Senior Member Grand Slam West Planner Mtn WJ's Avatar
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    I am happy with the alignment overall, left to right side by side, toe, the caster was addressed when I built the axle and same with pinion angle. The potential issue is I just changed the frame side joints on the front control arms at different times and may have mistakenly moved the jam nut on the passenger side, so just need to verify the arms are essentially the same length compared to each other. The driver side joint spun off after releasing the jam nut, the passenger one was a bitch to get off and that is where I would bump the the jam nut enough times to question its location.

    I appreciate the feedback. I will spend some more time with a tape measure. Thanks again.
    Ask not what your country can do for you; but what can you do for your country. JFK Jan 20th, 1961

    TnT Customs Long Arms, 33" BFG KM2s, Magnum 9k winch, Ready Welder, Custom HP 30/30 front with ARB, Currie HP 9 rear with Detroit
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