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Unread 03-18-2012, 01:07 PM   #16
fratis
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clearing up some bad advice. it happens constantly. someone gets on here spouting off bazaar stuff that makes no sense. if this helps the OP spend less time googling "link separation", "radius arm triangulation" or "track bar angle" thats a good thing.

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Unread 03-18-2012, 07:48 PM   #17
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Originally Posted by fratis View Post
thats a bit simplistic. a triangulated system can be very compliant. what he has is a radius system and this is how they work.


without measuring it looks similar to most link systems.



the pic is obviously showing full droop.
Moving the radius arm upper links higher and/or further inboard causes more triangulation. Triangulation keeps things from moving and is not compliant. (insert implied dumbsheet here since that seems to be your m.o.)

In this case the increased inboard triangulation between the upper and lower arms is limiting the axle's ability to move side-to-side. The track bar by nature causes the axle to travel side-to-side, the very direction that the increased triangulation of the upper arms is limiting.

Cut down on the triangulation to within something that the bushings can handle and/or flatten out the track bar angle so the axle isn't forced as far side-to-side for the same amount of travel.
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Unread 03-18-2012, 08:02 PM   #18
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Quote:
Originally Posted by ftgiles View Post
Moving the radius arm upper links higher and/or further inboard causes more triangulation. Triangulation keeps things from moving and is not compliant. (insert implied dumbsheet here since that seems to be your m.o.)

In this case the increased inboard triangulation between the upper and lower arms is limiting the axle's ability to move side-to-side. The track bar by nature causes the axle to travel side-to-side, the very direction that the increased triangulation of the upper arms is limiting.

Cut down on the triangulation to within something that the bushings can handle and/or flatten out the track bar angle so the axle isn't forced as far side-to-side for the same amount of travel.

correct.

IMHO if you are going to run radius arms, just make the upper and lower mounts on the same vertical plane, leave the lateral location to the trackbar.. thats how ford did it.
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Unread 03-18-2012, 09:38 PM   #19
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i like all the thoughts and good ideas. after the tires were on and the truck was sitting there at ride height and steering was hooked up it was quite ovous that the pitman arm steering joint was almost maxed out and the draglink was sitting at 21 deg. i have since ordered full crossover arms and knuckles and i will be moving the trac bar up and making myown and hopefully get this thing on the road soon. with the weight on the truck and back on tires instead of jackstans it did flex better but there is alot of side to side axle movement and i would like to try to lessen that. ill keep pics coming and i do appricate all the good info.
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Unread 03-18-2012, 09:40 PM   #20
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if i do remove uppeer arm and beef up the 2nd one which arm is better to remove? 2 people gave 2 different responses just iin case i do this later on
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Unread 03-18-2012, 09:53 PM   #21
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You guys are talking about two different things. You're both right, though. The problem with this particular suspension setup is that we're looking at two different bind points: the resistance to axle twist in a radius arm system, and the battle for lateral location between the upper links and the track bar.

The latter is actually much less of a concern in this particular setup. There isn't nearly enough triangulation on the upper arms to center the axle very well on their own. This is clearly the case in the third picture, where there's plenty of droop on the passenger side, which is where the lateral bind would be greatest.

Ironically, the lack of upper arm triangulation is what's hurting the articulation. If those uppers were much closer, the anti-twist tendency of radius arms would be greatly reduced. The closer the upper and lower mount points are to vertical, the less this setup will articulate. Yes, that's how Ford did it...and it articulated extremely poorly. The only reason it moved at all was because Ford used huge spongey rubber bushings that allowed all sorts of slop.
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Unread 03-18-2012, 09:54 PM   #22
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Originally Posted by cherokeemudman0 View Post
if i do remove uppeer arm and beef up the 2nd one which arm is better to remove? 2 people gave 2 different responses just iin case i do this later on
Typically, you'd remove the upper arm on the side opposite of the driveshaft. In this case, you'd want to remove the passenger upper. Removing the driver's side upper will produce brutal u-joint angles when the driver's side droops.
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Unread 03-18-2012, 10:55 PM   #23
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If it was just about axle twist then there would be the same binding with or without the track bar connected.
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Unread 03-18-2012, 11:11 PM   #24
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Since you have a driver's side drop axle then leave the driver's side upper link. The side to side axle movement is caused by your trac bar location, in a perfect world you want the trac bar as level as possible at ride height. You also want the trac bar as long as possible. The other major downfall to radius setup is steering geometry and caster angle, you'll go positive to negative caster with the axle cycling up and down, this can make it a little hard to control when driving down the road. I went radius arm for the simplicity and this is my offroad toy, not on the street too often and has full hydro steering to replace all the steering geometry and angle changes.
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Unread 03-19-2012, 12:39 AM   #25
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If it was just about axle twist then there would be the same binding with or without the track bar connected.
The track bar is no doubt binding, but very little of that bind is coming laterally. The uppers just aren't triangulated enough and they have big ol' bushings to allow for a substantial amount of slop. OP even mentions that he has more lateral movement than he expects. There's definitely bind on those track bar mounts, though. As the axle articulates, it's trying to bend the track bar backwards towards the rear of the vehicle and also (and probably the greatest factor) it's trying to twist the mount bushings. A high misalignment rod end at either side would eliminate that problem, but I don't think it's worth it. I'd beef the driver's side mount and remove the passenger upper. That solves both the radius arm bind and the track bar bushing bind. It'll have plenty of articulation after that.

Quote:
Originally Posted by addicted2dunes View Post
The other major downfall to radius setup is steering geometry and caster angle, you'll go positive to negative caster with the axle cycling up and down, this can make it a little hard to control when driving down the road.
It's not really a downfall. Radius arms tend to be rather long and this particular setup is no exception. With long arms, the caster won't change substantially. Especially on the street, the only time it'll change enough to make a noticeable difference is on high speed dips and bumps that make the suspension fully cycle. Those situations will only change the caster momentarily and most people are driving straight for those situations. If you're going over bumps big enough to fully cycle the suspension while turning hard, radius arms may not be the best application. Jeeps may not be the best application either. Stick to SCORE race trucks for that stuff.
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Unread 03-19-2012, 07:46 AM   #26
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Originally Posted by Cresso View Post
It's not really a downfall. Radius arms tend to be rather long and this particular setup is no exception. With long arms, the caster won't change substantially. Especially on the street, the only time it'll change enough to make a noticeable difference is on high speed dips and bumps that make the suspension fully cycle. Those situations will only change the caster momentarily and most people are driving straight for those situations. If you're going over bumps big enough to fully cycle the suspension while turning hard, radius arms may not be the best application. Jeeps may not be the best application either. Stick to SCORE race trucks for that stuff.
My radius arms are 48" long...... have you ever built a radius setup? Ever driven one that was not factory engineered? I am telling him all of this from experience, not just "I thinks"
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Unread 03-19-2012, 09:18 PM   #27
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my arms are 46" eye to eye. i did cut the c's on my axle and rotate them 12 deg and then set the caster at 7deg at ride height. what is the best joint for the trac bar at both end since im going to make it. heim joints, johnny joints or?
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Unread 03-19-2012, 10:54 PM   #28
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Originally Posted by addicted2dunes View Post
have you ever built a radius setup?
Yes, many.

Quote:
Ever driven one that was not factory engineered?
Nearly every day for well over a decade.

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I am telling him all of this from experience, not just "I thinks"
Maybe you should think. If your radius arm suspension doesn't handle well on the road, you designed it poorly or implemented it poorly. Radius arms handle very well on the road, which is why they've been around since the dawn of cars and continue to be used on factory and custom vehicles.

The longer the radius arm, the less caster change you'll experience through the cycling of the suspension. At 48", your arms are significantly longer than most factory-designed radius arms, and therefore have less caster change than most factory-designed radius arms. We'd need to know more about your setup to be able to fix it.

Quote:
Originally Posted by cherokeemudman0 View Post
my arms are 46" eye to eye. i did cut the c's on my axle and rotate them 12 deg and then set the caster at 7deg at ride height. what is the best joint for the trac bar at both end since im going to make it. heim joints, johnny joints or?
"Best" is a tough term to work with. It doesn't mean the same thing to everyone. For example, a simple heim will allow for more misalignment than a bushing, but it's also more expensive, will wear out sooner, and will transmit a lot more vibration. Bushings are cheap, easy to work with, and will have the least vibration transfer, but it's gonna bind a little. Johnny Joints are a little more expensive, but combine the best parts of bushings and rod ends. They're quite large, though, and can sometimes cause space issues if things are real tight.

Realistically, it won't really matter what you use once you remove that one upper link. I've had radius arm setups using bushings at both ends of the track bar that would max out 14" shocks with plenty of articulation left to go. That was on narrow early bronco stuff, too. If I were you, I'd pull that upper link and do your full articulation test again. I bet you'll be maxing out your shocks right there and can leave everything else as is.
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Unread 03-19-2012, 11:05 PM   #29
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Originally Posted by Cresso View Post
Maybe you should think. If your radius arm suspension doesn't handle well on the road, you designed it poorly or implemented it poorly. Radius arms handle very well on the road, which is why they've been around since the dawn of cars and continue to be used on factory and custom vehicles.
It's hard not to get caster change when you cycle 38"..... The only factory setup now that implements it is Ford, they are also not meant to articulate at any means wanted for crawling.
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Unread 03-19-2012, 11:07 PM   #30
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Quote:
Originally Posted by cherokeemudman0 View Post
my arms are 46" eye to eye. i did cut the c's on my axle and rotate them 12 deg and then set the caster at 7deg at ride height. what is the best joint for the trac bar at both end since im going to make it. heim joints, johnny joints or?
For your trac bar I recommend bushing mount at the frame and high misalignment spacers on a heim at the axle end. I also suggest bushing mounts on your links at the axle side and Johnny Joints at the frame side.
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