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Unread 08-23-2013, 11:33 PM   #1
93zjgrand
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anyone who knows control arms

Ok some lifts come with a new lower control arms, my question is do the lower control arms center the axle for that lift. I'm thinking of maybe vying a lift with no control arms, to center the axle do I just need the lower ones or do I need all upper and lower arms.

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Unread 08-23-2013, 11:47 PM   #2
93zjgrand
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I just want the axles center will the lower arms do that by there self
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Unread 08-24-2013, 12:57 AM   #3
dnuccio
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for the rear, you do not want the axle centered. the axle travels up and back when the suspension compresses, so if the axle is centered in the wheel well, the tire will have alot better chance of contacting.
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Unread 08-24-2013, 01:16 AM   #4
kg6mov
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Uppers are more important so you can get the pinion angle set correctly.

As stated you don't want the axle truly centered because a 4 link suspension moves forward and back not vertical like a leaf suspension.
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Unread 08-24-2013, 01:25 AM   #5
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Quote:
Originally Posted by dnuccio View Post
the axle travels up and back when the suspension compresses
It's not just the rear, it's both front and rear. That being said, IMO most lift kit manufacturers spec. their CAs a bit too short.

Quote:
Originally Posted by kg6mov View Post
As stated you don't want the axle truly centered because a 4 link suspension moves forward and back not vertical like a leaf suspension.
Actually, it's just the design fault of the Jeep engineers back in the day when they thought it's a good idea to use such short arms and weird axle travel path A 4-link can be designed with minimal vertical movement if wanted, and also with close to 0* pinion angle change during suspension movement. It requires a lot longer arms though..


For the OP: lowers adjust wheelbase, uppers adjust caster angle/ pinion angle. With only the lowers, you may end up with bad caster/ pinion angle, which in turn makes your Jeep wander all over the the road, may cause DW, and driveline vibes due to incorrect pinion angle.

Depending on your lift height you may be ok with only the lowers, or not. I always suggest buying adjustable uppers and lowers, in the long run you'll be much happier. If you plan on wheeling your Jeep, you want stronger aftermarket arms anyway. As mentioned uppers are more important because of the caster/ pinion angle setup, but lowers get scraped on rocks etc., and they do NOT like it. Thin stamped sheetmetal arms + wheeling = bad idea
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Unread 08-24-2013, 01:40 AM   #6
Climbit
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Quote:
Originally Posted by kg6mov View Post
Uppers are more important so you can get the pinion angle set correctly.
both are important. and both need to be adjusted to keep the axle in the center of the wheel well (at full bump) and the pinion at the proper angle

Quote:
As stated you don't want the axle truly centered because a 4 link suspension moves forward and back not vertical like a leaf suspension.
leaf spring suspension also travel forward and back as the shackle swings.

Quote:
Originally Posted by Timo_90xj View Post
It's not just the rear, it's both front and rear. That being said, IMO most lift kit manufacturers spec. their CAs a bit too short.
on what grounds?



F
Quote:
or the OP: lowers adjust wheelbase, uppers adjust caster angle/ pinion angle.
no. both the lowers and the uppers will change the axle position and the pinion angle. neither of them are mounted in the exact center of the tube. therefore one cannot be adjusted without affecting the other.
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Unread 08-24-2013, 01:27 PM   #7
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Quote:
Originally Posted by Climbit View Post

Quote:
It's not just the rear, it's both front and rear. That being said, IMO most lift kit manufacturers spec. their CAs a bit too short.
on what grounds?
Everyone has their own likings on where to locate the axles and what to look for. Most kits I've seen IMO place the axles too far back on the front, and too far front in the back of the vehicle. Not only does it look stupid, but you will run into clerance issues at the back of the wheelwell in the front, even if you smack in the pinchweld seams. There's not so much to worry about at the back, but I'd still adjust the WB a around 1"-1.5" longer than usually specified for certain lift heights.

I've always gotten way better suspension chasrasteristics by slightly extending the WB - and better clearance on both my XJs and on the ZJ. If you're gonna run 33s or 35s, you gotta do some fender and wheelwell clearancing anyways (unless running a crazy high lift)


Quote:
Originally Posted by Climbit View Post
Quote:
For the OP: lowers adjust wheelbase, uppers adjust caster angle/ pinion angle. With only the lowers, you may end up with bad caster/ pinion angle, which in turn makes your Jeep wander all over the the road, may cause DW, and driveline vibes due to incorrect pinion angle.

F no. both the lowers and the uppers will change the axle position and the pinion angle. neither of them are mounted in the exact center of the tube. therefore one cannot be adjusted without affecting the other.
I guess I need to be even more specific then:

You adjust the lower control arms based on where you want the axle to be located lengthwise inside the wheelwell. After doing that, you adjust the upper control arms to the length required to get the pinion and caster angle you're shooting for. Changing the length of the uppers by ie +/-1" does not change your WB by even close to one inch. Adjusting LCAs by +/-1" you will get very close to 1" difference in WB But, of course if you adjust the lowers you must also adjust the uppers to get the angles you want.


Try using a 4-link or 3- link calculator and you get the point on what does what and what changes affect what charasteristics of the suspension
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1990 XJ Limited (4-door), 4.0 I6, AW4, NP242, ***rolled and totalled @ 165k miles***

***Under construction***
1990 XJ (4-door), 4.0 I6, AW4, NP242, PBR 42" tires, Unimog 404 portal axles, 110" WB, full cage + uniframe completely rebuilt, front 3-link + panhard / double triangulated 4-link rear,... ***SOLD***
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Unread 08-25-2013, 01:14 AM   #8
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Quote:
Originally Posted by Timo_90xj View Post
Everyone has their own likings on where to locate the axles and what to look for. Most kits I've seen IMO place the axles too far back on the front, and too far front in the back of the vehicle. Not only does it look stupid, but you will run into clerance issues at the back of the wheelwell in the front, even if you smack in the pinchweld seams. There's not so much to worry about at the back, but I'd still adjust the WB a around 1"-1.5" longer than usually specified for certain lift heights.
you should be centering the tire in the wheel well at full bump. if that means 1" extra wheel base then so be it

Quote:
I've always gotten way better suspension chasrasteristics by slightly extending the WB - and better clearance on both my XJs and on the ZJ. If you're gonna run 33s or 35s, you gotta do some fender and wheelwell clearancing anyways (unless running a crazy high lift)
1" of wheel base will change almost nothing in how a vehicle performs. there are too many variables at play with different rigs/suspesions/tire/etc combos to point at that one thing.




Quote:
guess I need to be even more specific then:

You adjust the lower control arms based on where you want the axle to be located lengthwise inside the wheelwell. After doing that, you adjust the upper control arms to the length required to get the pinion and caster angle you're shooting for. Changing the length of the uppers by ie +/-1" does not change your WB by even close to one inch. Adjusting LCAs by +/-1" you will get very close to 1" difference in WB But, of course if you adjust the lowers you must also adjust the uppers to get the angles you want.
you will change the pinion angle with the lowers, and you will change the location of the axle with the uppers. you should be adjusting both to get the axle in the right spot.
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Unread 08-25-2013, 05:34 AM   #9
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Quote:
Originally Posted by Climbit View Post
you should be centering the tire in the wheel well at full bump. if that means 1" extra wheel base then so be it
Why should you center the axle at full bump? That's just plain stupid. You want to locate the axle so that you get what you're aiming for. I prefer adjusting the WB so that at full bump the coil plate will touch the bumpstops, but not necessarily dead-center. It's only important for the bumpstop to touch the coil plate, nothing more. By centering the axle at full bump on short arms you may run the risk of hitting the coils with the coil tower; I've had that exact problem on every Jeep I've owned if I've adjusted CAs to manufacturers specs. So, IMO, manufacturers spec. their CA lengths wrong.

I'm not tjhe one "going-by-the-book", I use my own brain to achieve what I want. If I went by the book, I wouldn't be running OTK steering at just 1.75" of lift, or I wouldn't have overall 3.5" extended WB on my ZJ at that lift height. Yeah, I've done a bunch of other stuff on it too to make that happen, but it has made the Jeep handle and perform a lot better, and achieve things like being able to run 33s without extra bumpstopping, or even 35s with a bit of bumpstopping at 1.75" lift height. Guess I'm doing it wrong then


Quote:
1" of wheel base will change almost nothing in how a vehicle performs. there are too many variables at play with different rigs/suspesions/tire/etc combos to point at that one thing.
BS.

For example 1" wheelbase extension over specified CA lengths straight away gives you the ability to run 2" larger tire size in what goes to certain limitations on the wheelwell opening size. Yeah, you may rub at full bump on the front of the wheelwell but that's another story. I certainly prefer hammering in or cutting & welding the front of the wheelwell (or rear part in the back) rather than going into the front legroom area or rear door.

I tried running the "correct" wheelbase for 1.75" of lift height and about 1.5" of added bumpstopping, slightly trimmed fenders, pinchweld seam swhacked in the back of the front wheelwell, turning 32 x 11.50s -> no luck. They rubber like hell all over the place. Extended front WB by 1.25" and had no problems after that. You can come say 1" does nothing, but IMO then you haven't even tried what it does and what it doesn't. I wouldn't say things like that unless I had some personal experience on the subject.

If you want to go the easy way, go with what the lift kit manufacturers say. If you want good results, think out-of-the-box, do your own research and try different things. You may actually improve the handling, suspension charasteristics and off-road performance of your vehicle. 1" adjustments in suspension world are actually big, not small. Especially so when talking about multi-link suspension systems. As I mentioned, try tapping in some numbers on 4-link calculators and see how much little things can change the behavior of the suspension



Quote:
you will change the pinion angle with the lowers, and you will change the location of the axle with the uppers. you should be adjusting both to get the axle in the right spot.
Yeah, you are absolutely correct that both UCAs and LCAs affect both pinion angle and the wheelbase. You can't adjust only the other without adjusting the other - or you will mess up pinion/ caster angle big time.

But think about it a little deeper:
* LCAs are mounted fairly close to axle centerline -> that's why they affect the most on the wheelbase. You will not even have the uppers mounted when setting up WB, you check the WB with the lowers in and pinion angle eyeballed to being close where you want it
* When the lowers are at the desired length and WB, you set-up the length of the uppers based on the LCA length/ WB you've chosen. Ie. place a floor jack under the pinion and micro-adjust pinion (+caster) angle to where you want it to be.

Doing this, you will notice that when the LCAs and WB are at the length you've chosen, adjusting the UCA length by 1" shorter or longer does NOT affect the WB by even close to 1", it's roughly only a third or quarter of that. But if you have the uppers at whatever length and you adjust the length of the lowers by 1", it will equal to about three quarters of that adjustment on the WB (LCAs being close to axle centerline is what does this). Again, adjusting only either the LCAs or UCAs without touching the other, you will mess up things. So yeah, both always need to be adjusted if you adjust the other. Then again, if you go high enough on short arms, the angle of the CAs off from horizontal also plays a role on how much you need to adjust the CA length to achieve ie. a 1" change on teh WB. But let's not go into that

But the very basic fact on setting up a typical 4-link suspension is that you build the WB around the LCAs, and the length of the uppers follows your decision over the lenth of the LCAs/ WB; you adjust them as much shorter or longer what is needed for the proper pinion angle at the WB you've selected.


Now, try designing and setting up a properly functioning 4- link system on a portal axle so that the lowers are mounted at the axle centerline. That's fun!
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http://www.jeepforum.com/forum/f13/d...s-etc-1222317/


1990 XJ Limited (4-door), 4.0 I6, AW4, NP242, ***rolled and totalled @ 165k miles***

***Under construction***
1990 XJ (4-door), 4.0 I6, AW4, NP242, PBR 42" tires, Unimog 404 portal axles, 110" WB, full cage + uniframe completely rebuilt, front 3-link + panhard / double triangulated 4-link rear,... ***SOLD***
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