control arm question

Some one had told me my control arms were to short and if my axle dropped all the way down it could cause my drive shaft to bust my transfer case and we dont want that so im looking for adjustable arms.



i have a 4.5 rough country kit with fixed lca and i kept the stock uca and i just came across this web site http://www.yuccaman.com/jeep/re_db.html which says the length for the lca should be 16.5 and uppers 15". i meet both of those measurements with fixed lca and stock uppers. so now im wondering if i should replace them or not or if i do get adjustable would adding another half inch or so add to my flex and handling or would that addition harm it.

i hope this makes sense im in a rush to go to work now but il be back on later tonight.

your friend needs an education :moon:

Your friend needs an education and you need a tape measure.

Adjustables are good for setting your caster for better steering characteristics, or adjusting wheelbase slightly, but you are very likely fine. If you want to find out for sure, droop the axle completely (wheels off the ground, supported by jackstands on frame) and try to disconnect the driveshaft from the pinion yoke. If you can compress the driveshaft enough to unseat the U-joint a bit you are good to go.

kastein said:

Your friend needs an education and you need a tape measure.

Adjustables are good for setting your caster for better steering characteristics, or adjusting wheelbase slightly, but you are very likely fine. If you want to find out for sure, droop the axle completely (wheels off the ground, supported by jackstands on frame) and try to disconnect the driveshaft from the pinion yoke. If you can compress the driveshaft enough to unseat the U-joint a bit you are good to go.

Click to expand...

^^^ This

scott96 said:

Some one had told me my control arms were to short and if my axle dropped all the way down it could cause my drive shaft to bust my transfer case and we dont want that so im looking for adjustable arms.



i have a 4.5 rough country kit with fixed lca and i kept the stock uca and i just came across this web site http://www.yuccaman.com/jeep/re_db.html which says the length for the lca should be 16.5 and uppers 15". i meet both of those measurements with fixed lca and stock uppers. so now im wondering if i should replace them or not or if i do get adjustable would adding another half inch or so add to my flex and handling or would that addition harm it.

i hope this makes sense im in a rush to go to work now but il be back on later tonight.

Click to expand...

Yuccaman's measurements aren't "one size fits all". It a good starting point but not what you should be set on. You need to measure wheelbase, caster, and pinion angle in order to know how long you need your arms.

I'm pretty sure your shocks will limit your droop before any harm is caused to the shaft. If not the shock, then the arms (if they are straight) will bind on the shock bracket.

kastein said:

Your friend needs an education and you need a tape measure.

Adjustables are good for setting your caster for better steering characteristics, or adjusting wheelbase slightly, but you are very likely fine. If you want to find out for sure, droop the axle completely (wheels off the ground, supported by jackstands on frame) and try to disconnect the driveshaft from the pinion yoke. If you can compress the driveshaft enough to unseat the U-joint a bit you are good to go.

Click to expand...

i measured the eye to eye on the control arms if thats what your talking about. this guy who told me that it my transfer case could crack because of it had the my jeep on a lift and the axle completely dropped.

muddeprived said:

Yuccaman's measurements aren't "one size fits all". It a good starting point but not what you should be set on. You need to measure wheelbase, caster, and pinion angle in order to know how long you need your arms.

I'm pretty sure your shocks will limit your droop before any harm is caused to the shaft. If not the shock, then the arms (if they are straight) will bind on the shock bracket.

Click to expand...

how exactly do i measure the caster and what should the pinion angle be? i have fixed bent arms and im adding more bump stop soon with longer shocks so i dont really want to count on my shock limiting this problem.

scott96 said:

i measured the eye to eye on the control arms if thats what your talking about. this guy who told me that it my transfer case could crack because of it had the my jeep on a lift and the axle completely dropped.



how exactly do i measure the caster and what should the pinion angle be? i have fixed bent arms and im adding more bump stop soon with longer shocks so i dont really want to count on my shock limiting this problem.

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You gotta limit it somewhere. Most of the time the shocks limit droop but if you have bent arms and LONG shocks then you should really get some limiting straps cuz you'll risk stressing the control arm mounts, especially if you don't have any type of flex joint on those arms. It'll also stress the stock steering joints, if that's what you run, and probably the shaft too.

I usually use the bottom of the knuckle, right behind the ball joint where there's a flat spot, to measure my caster and get it in the ballpark. You gotta get the pinion happy enough that it doesn't vibe or bind and kinda live with what caster results. The rule of thumb is to sacrifice caster angle for pinion angle cuz no one wants to keep replacing u-joints, pinion bearings, and seals.

kastein said:

Your friend needs an education and you need a tape measure.

Adjustables are good for setting your caster for better steering characteristics, or adjusting wheelbase slightly, but you are very likely fine. If you want to find out for sure, droop the axle completely (wheels off the ground, supported by jackstands on frame) and try to disconnect the driveshaft from the pinion yoke. If you can compress the driveshaft enough to unseat the U-joint a bit you are good to go.

Click to expand...

Nearly every short arm lifted Jeep I've ever had on my lift (hundreds) has "failed" this "test". It's the nature of the beast. No cracked T-cases.

muddeprived said:

Yuccaman's measurements aren't "one size fits all". It a good starting point but not what you should be set on. You need to measure wheelbase, caster, and pinion angle in order to know how long you need your arms.

Click to expand...

Actually, it is "one size fits all". It's basic geometry. Based on OEM suspension geometry and mounting points, if I lift "x" amount (and I want the caster and wheelbase not to change), then my arms need to be "x" long. Period. Yes, you can fine tune it to your personal desires and needs, but then it's not based on OEM caster and wheelbase.

your pinion angle isn't what you need to measure... it will fall were it falls baced on where you put your caster. You need to get an angle finder and have the caster set at 5*-7* negitive... this means the inner C's on the axle are leaned back 5-7 degrees. As for the drive shaft cracking the t-case... I have seen a lot of jeeps with t-case drops have binding problems at full droop. If you end up having this issue a set of limit straps are your friend... you don't need a lot of flex any way. just limit the travel just before the drive shaft bottoms out.

And as for the arms... if you have the money for arms with flex joints buy them. Otherwise just run the fixed arms you have. Adjustable arms will cause the same problems as you have now. The reason your drive shaft would bind is not because the arms are to short but its because the arms are mounted in front of the out put to far. If your arms were 36" and mounted in the same frame side mount it would still cause the same issue. Its because the two move alond differant paths and are two differant lengths.

bobnoxious said:

Nearly every short arm lifted Jeep I've ever had on my lift (hundreds) has "failed" this "test". It's the nature of the beast. No cracked T-cases.


Actually, it is "one size fits all". It's basic geometry. Based on OEM suspension geometry and mounting points, if I lift "x" amount (and I want the caster and wheelbase not to change), then my arms need to be "x" long. Period. Yes, you can fine tune it to your personal desires and needs, but then it's not based on OEM caster and wheelbase.

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What I meant was his measurements were a good starting point but aren't what you should set your arms for and be done with it. For instance, his measurements made my LP30 vibe like mad at 4.5". Yeah my caster was good but wasn't ideal since I'd be going through pinion bearings in no time. It'll be good at setting the caster but caster is only half of the equation. You still gotta tune the pinion.

bobnoxious said:

Nearly every short arm lifted Jeep I've ever had on my lift (hundreds) has "failed" this "test". It's the nature of the beast. No cracked T-cases.

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huh. I never actually tested mine :doh: never broke a case housing either... and you saw how I wheeled that rolling shitpile.

OP - if you aren't happy with your steering / handling characteristics, set your caster to 5-7 degrees, if you get vibrations from the front driveline you need to either adjust the caster till you achieve a decent tradeoff between handling and vibrations, or adjust for zero pinion angle with regard to front driveshaft, then cut loose and rotate the inner Cs on your front axle till your caster is within the 5-7 degree range. You probably don't want to spend your time on that... I'd go for the tradeoff or just leave it how it is if you're OK with it.

I just replaced my control arms when going to 4.5" of lift and got some good advice from a rep at Rusty's. The addition of adjustable arms over fixed gives some benefits you may or may not need, but adds the detriment of an adjustable end which can wear and eventually require replacement. With custom built arms at a fixed length the only thing that wears are bushings. Also, when/if you go any higher you will more than likely be switching to long arms, meaning you won't be able to carry the arms over to the next lift. The logic of that saved me 50 bucks per pair on new arms.