Rear suspension: Understanding the rear track bar arc and how it binds suspension

[motomick76]

Currently I am in a futile attempt to fuck up my rig and to copy what Dave does to make Sarah handle a bit better. I have my upper mounts tacked in place, checking everything, cycling the suspension, and when I go to articulate the rear suspension, the rear track bar is binding the axle from flexing a couple of inches. either way. It moves up and down ok, when flexing it binds. I am not understanding why the track bar is binding the axle.

How does the track bar affect the articulation of the axle, and what I am I missing?

Does the track bar mount need to be same height or higher than the UCAM? Does it need to be closer to the UCAM?

Pictures are of the axle at ride height, setup is Currie short arms, Artec 8.8 truss kit, and Currie track bar.

 

[Wildman]

I wish I understood more about how all this works so I could help you out. Good luck and keep us posted on how you're doing and what you come up with.

 

[freedom_in_4low]

so to be clear, the entire axle will move up and down freely (like going over a speedbump) but if you try to move one wheel up or down without the other wheel, it only goes an inch or two? It sounds like the sway bar is connected, but I can clearly see in your photo that it's not.

I don't have the answer for you, but as you move a wheel up and down think about which links you might be trying to stretch or compress. With the bolts loose, look at their positions in their holes to see if the arm is trying to push or pull the bolt against the hole. In a stock suspension, the upper links are slightly triangulated so as the axle shifts side to side with the arc of the track bar, the upper links fight each other as one is trying to push the axle back while the other is trying to pull it forward. I haven't experimented with what happens with one wheel stuffed and the other drooped.

 

[Wildman]

To add to what 4Low said I'd take the trackbar out of the equation for now and see if you have binding from the control arms or if it is really the trackbar that is causing issues.

 

[Blackjack]

Height of the track bar dictates what your roll center height is so as high as possible lends itself to greater stability. Dave shoots for 3.5 inches above stock because that does not hit the floor with 2 inches of bump extension and no body lift. From there the bar is either pushing or pulling against the axle depending on its position in the arc. This is why a flatter bar position can be beneficial but is not realistic for us due to packaging restraints. Like Wildman said take the trackbar out of the equation first and make check for bind in the control arms. Because you are running 5 links there is going to be some bind somewhere that is the nature of the beast.

 

[motomick76]

Sway bar is disconnected, and I disconnect the track bar, it flexes fine. All that is hooked up is 4 links and track bar.

 

[1904-06LJR]

I think your answer is above from Black Jack. The trac bar limits the arc....but tell us why you redrilled the holes in the stock lower control arm brackets...?

 

[motomick76]

Thanks everyone. I think I am going to experiment more, detach one UCA and see which way it pushes or pulls.

 

[motomick76]

I think your answer is above from Black Jack. The trac bar limits the arc....but tell us why you redrilled the holes in the stock lower control arm brackets...?

This is part of the Nth degree correction and what Dave does to help short arm lifted rigs handle like stock again.

 

[1904-06LJR]

Hmmm, seems safe.

 

[mrblaine]

Sway bar is disconnected, and I disconnect the track bar, it flexes fine. All that is hooked up is 4 links and track bar.

Alright, this is basic. If you view the arrangement of the control arms from directly above you will note that they describe a very large W. The lowers are wider at the axle than the frame, the uppers are narrower at the axle than the frame. There is almost enough triangulation to not need a trackbar, almost but not quite. The triangulation causes the axle to want to move straight up and down and as soon as you introduce any lateral movement like the trackbar causes, it locks up against the triangulation.

To aid in the cycling, remove the end of one upper arm and that will help a bunch.

 

[Brianj5600]

It is raining/snowing so I'd rather not go out and look at the frame bracket. Can the frame end of the track bar be lowered? If so, how much? Would it help or create another problem?

 

[mrblaine]

It is raining/snowing so I'd rather not go out and look at the frame bracket. Can the frame end of the track bar be lowered? If so, how much? Would it help or create another problem?

You would have to rework the exhaust and there is a limited amount of space inside the spring before the mount moves the trackbar back into the gas tank. Forward runs into the spring, down runs into the exhaust and there is the problem of the right side upper control arm moving up if you try to sneak it forward. It lives in a fairly small but well defined space now. It would not be hard to screw that up. If you recall, the bolt for the trackbar frame side just about runs into the spring if you stand the spring straight up and down.

 

[BuildBreakRepeat]

Where in the trackbar is your bind occurring? One side? Both? Pictures of the bind?

 

[mrblaine]

Where in the trackbar is your bind occurring? One side? Both? Pictures of the bind?

Left side never drops as far as the right side.

 

[Blackjack]

Hmmm, seems safe.

Why would it not be safe?

 

[motomick76]

Where in the trackbar is your bind occurring? One side? Both? Pictures of the bind?

Ok, so I can see what is going on. I am taking the axle to full bump, axle cups are centered with frame cups, and everyone is happy there, 4 control arms and track bar connected. If I even lower it to ride height. there is heavy bind. So at full bump I remove the passenger axle UCA bolt, and just have the driver upper, both lower, and track bar connected. I take it to ride height, and the axle is still centered with the spring buckets. But when I take it to full shock length, it is pulling the axle hard into the passenger side. It pulls it so far that the driver LCA is almost straight.

The arc of the trackbar is pulling it into the passenger side, and when I try to line up the passenger UCA on the axle of which I removed, it is almost a 1" off.

So, I have room to go up with the track bar on the axle, almost 1.5-2", and if I were to take frame mount down, I would hit the exhaust. I could probably get away with 1" down. Looking at it, I think I am going to have to take all I can get.

I will post some pictures in the morning to show what is going on. Working on the cement all day has killed my knees, and I was even using a promotion pad.

It is raining/snowing so I'd rather not go out and look at the frame bracket. Can the frame end of the track bar be lowered? If so, how much? Would it help or create another problem?

You do not have to look, thank you though.

You would have to rework the exhaust and there is a limited amount of space inside the spring before the mount moves the trackbar back into the gas tank. Forward runs into the spring, down runs into the exhaust and there is the problem of the right side upper control arm moving up if you try to sneak it forward. It lives in a fairly small but well defined space now. It would not be hard to screw that up. If you recall, the bolt for the trackbar frame side just about runs into the spring if you stand the spring straight up and down.

I am glad that bar has that bend in it for clearing the exhaust. I understand the bar has its happy little world and does not like to be bothered. I will see how much more I can mess this up tomorrow. I have alot of adjustment left, as it is almost turned all the way in.

 

[mrblaine]

Ok, so I can see what is going on. I am taking the axle to full bump, axle cups are centered with frame cups, and everyone is happy there, 4 control arms and track bar connected. If I even lower it to ride height. there is heavy bind. So at full bump I remove the passenger axle UCA bolt, and just have the driver upper, both lower, and track bar connected. I take it to ride height, and the axle is still centered with the spring buckets. But when I take it to full shock length, it is pulling the axle hard into the passenger side. It pulls it so far that the driver LCA is almost straight.

The arc of the trackbar is pulling it into the passenger side, and when I try to line up the passenger UCA on the axle of which I removed, it is almost a 1" off.

So, I have room to go up with the track bar on the axle, almost 1.5-2", and if I were to take frame mount down, I would hit the exhaust. I could probably get away with 1" down. Looking at it, I think I am going to have to take all I can get.

I will post some pictures in the morning to show what is going on. Working on the cement all day has killed my knees, and I was even using a promotion pad.


You do not have to look, thank you though.



I am glad that bar has that bend in it for clearing the exhaust. I understand the bar has its happy little world and does not like to be bothered. I will see how much more I can mess this up tomorrow. I have alot of adjustment left, as it is almost turned all the way in.

If you need to turn it in further, cut some off of the threads on the bar.

 

[freedom_in_4low]

Ok, so I can see what is going on. I am taking the axle to full bump, axle cups are centered with frame cups, and everyone is happy there, 4 control arms and track bar connected. If I even lower it to ride height. there is heavy bind. So at full bump I remove the passenger axle UCA bolt, and just have the driver upper, both lower, and track bar connected. I take it to ride height, and the axle is still centered with the spring buckets. But when I take it to full shock length, it is pulling the axle hard into the passenger side. It pulls it so far that the driver LCA is almost straight.

The arc of the trackbar is pulling it into the passenger side, and when I try to line up the passenger UCA on the axle of which I removed, it is almost a 1" off.

So, I have room to go up with the track bar on the axle, almost 1.5-2", and if I were to take frame mount down, I would hit the exhaust. I could probably get away with 1" down. Looking at it, I think I am going to have to take all I can get.

I will post some pictures in the morning to show what is going on. Working on the cement all day has killed my knees, and I was even using a promotion pad.


You do not have to look, thank you though.



I am glad that bar has that bend in it for clearing the exhaust. I understand the bar has its happy little world and does not like to be bothered. I will see how much more I can mess this up tomorrow. I have alot of adjustment left, as it is almost turned all the way in.

RE: the UCA you disconnected - if you're at ride height and try to re-connect it, does the hole line up well enough to easily slide the bolt back in?

This reminds me of the time I learned exactly how well that triangulation works - I was setting up my front end and forgot to reconnect my track bar before starting to set the caster/pinion angle. I kept turning and turning my double adjustable uppers and the pinion angle was barely changing. Turns out I was turning one of them the wrong direction (lengthening one and shortening the other), and instead of raising/lowering the pinion, I was just pushing the frame to one side relative to the axle. It was far enough off that no ratchet strap or Archimedal contraption was ever going to get the axle centered again without going back to those arms and turning them the other way. Since then, I haven't used a ratchet strap to center my axle. I lengthen one UCA and shorten the other until the axle is centered, then I slide the track bar bolt in with zero effort.

 

[motomick76]

If you need to turn it in further, cut some off of the threads on the bar.

Thanks, will keep that in mind. Already had to do damage control on the LCA, cut an inch off to get everything to line up.

RE: the UCA you disconnected - if you're at ride height and try to re-connect it, does the hole line up well enough to easily slide the bolt back in?

No it does not. I found out right away with these arms how you can use the triangulation to center an axle, so I am always measuring the length of each arm as I make any adjustments. I really like these bolts with the zerk, as you can hook to the zerk and measure to the zerk, I also rechecking my measurements on my LCA to the front of the Jeep to ensure the axle stays square. You know something is not right if you turn it and you cannot turn it by hand anymore, stuff is binding and tight. The only part I put a wrench on are the jamb bolts, if I cannot turn them by hand, I start looking at where did I mess up.