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-   -   Tech Discussion: Track Bars (http://www.wranglerforum.com/f274/tech-discussion-track-bars-258716.html)

5150Rubicon 07-27-2013 05:03 PM

Tech Discussion: Track Bars
 
Let's have a technical discussion on Track Bars. I want to avoid getting into "what size lift warrants adjustable track bars, etc". Purely a technical discussion on geometry and how it works.

Here's what I've understood from my research. I'm not stating these as "facts" at all. I know nothing. My goal is to learn (1) because its fun and (2) I want to build my jeep properly. Here is what I think I understand...followed by a few comments/questions.

FRONT TRACK BAR:

One end of it connects to the chassis/frame. The other end connects to the axle. It does a couple of things. It controls the lateral relationship between the Jeep and the front axle (for example, it holds the axle centered under the jeep if set up properly).

If you visualize a "Z" with the top line being the Jeep Frame, The bottom line being the front axle, and the connecting line being the front track bar (looking head on from the front of the Jeep) it become very obvious and easy to understand what happens when we lift a Jeep. When we lift a jeep, in other words, increase the distance between the top line and the bottom line, the track bar acts as a pendulum. In our "Z", we can see that as we increase the distance (lift) between the top and bottom lines, the bottom line will NEED to move to the right relative to the top line. The track bar doesn't change length, so the bottom line (front axle) NEEDS to move to the right relative to the top line (chassis/Jeep).

It then becomes easy to understand where an "Adjustable Track Bar" comes into play. By replacing the stock (static) track bar with an adjustable one, we can lengthen that connecting line in the "Z". When we lengthen that line (track bar), the bottom line (axle) NEEDS to shift to the left relative to the Jeep. Thus, if we adjust it properly, we can recenter the axle after we lift the Jeep.

A centered axle is important for many reasons. Straight tracking, avoiding unneccesary pressure on other components by being shifted, etc. I think its safe to say a centered front axle is the goal (though I understand there may be variances that are within an acceptable range).

So, assuming my thinking is correct, I have questions about the rear track bar.

The rear track bar seems to be the forgotten, ugly twin of the front track bar :rofl: Seriously, seems like it doesn't get addressed and I want to understand why.

For example, even in the AEV kit, they handle the rear track bar by doing a higher tower. However, this simply moves the roll center...and to my knowledge isn't doing anything to compensate for the axle shift the MUST have occurred for the rear axle when we do a lift (remember the Z...same for the rear, but a backwards Z).

How come?

I feel like the right way to do my lift is to have adjustable track bars front and rear. Comments?

Thanks. I hope that the responses/thread will serve to help others too. Just a few short weeks ago...I had no idea what ANY part was called or what it did. But now...I'm hooked and I love it.

County98 07-27-2013 05:07 PM

Interested in learning also!

nwbronco 07-27-2013 05:12 PM

Your thinking is pretty much spot on. Another issue is using the brackets to raise the trac bar mount point. This creates a point of leverage with a higher fulcrum against the stock mounting bracket and can cause the weld to break. I have seen this happen to a few rigs and is the reason I went adjustable front and back.

Not restoring the relationship to the trac bar and drag link can also cause bumpsteer during suspension articulation.

Bob K

5150Rubicon 07-27-2013 05:21 PM

Quote:

Originally Posted by nwbronco (Post 4009805)
Your thinking is pretty much spot on. Another issue is using the brackets to raise the trac bar mount point. This creates a point of leverage with a higher fulcrum against the stock mounting bracket and can cause the weld to break. I have seen this happen to a few rigs and is the reason I went adjustable front and back.

Not restoring the relationship to the trac bar and drag link can also cause bumpsteer during suspension articulation.

Bob K

Thanks Bob,

So all other things being equal (no other "changes")...if we lift a Jeep, adjustable track bars (front and rear) that are mounted to the original mounting spots...is the way to bring the axles back to center (in other words, back to the way they should be for all the other components to work as designed)?

Aeschylus 07-27-2013 05:41 PM

So, a follow up question from someone who is planning out future mods ...

If you were going to do mods in an optimal sequence (instead of all at once), and you knew you were going to eventually do a lift / bigger tires / upgrade track bars, is it okay to install the beefier track bars before lifting? Or should that only be done in conjunction with the lift?

nwbronco 07-27-2013 05:43 PM

So for the front it is more of a double Z. Trac bar and Drag Link.

bob K.

nwbronco 07-27-2013 05:49 PM

Quote:

Originally Posted by 5150Rubicon (Post 4009836)
Thanks Bob,

So all other things being equal (no other "changes")...if we lift a Jeep, adjustable track bars (front and rear) that are mounted to the original mounting spots...is the way to bring the axles back to center (in other words, back to the way they should be for all the other components to work as designed)?

Exactly. The axle track and steering geometry need to be in the same relationship after the lift. The steering turnbuckle would need to be adjusted to lengthen the drag link, in relation to the amount of lift gained. It is easier to just drop the drag link during the lift installation.

If using an adjustable trac bar, the axle is placed back on the ground and the axle centered. This is done by finding a common spot to measure, say the frame to the tire, to get the axle centered.


Bob K.

5150Rubicon 07-27-2013 05:49 PM

Quote:

Originally Posted by nwbronco (Post 4009898)
So for the front it is more of a double Z. Trac bar and Drag Link.

bob K.

Yes! You just made me realize...that is exactly why...after even a small lift...the steering wheel usually needs to be recentered. Because....as we move the top/bottom lines of the z further apart (lift)...the drag link also NEEDS to move to the right relative to the Jeep...causing the steering wheel to "turn".

5150Rubicon 07-27-2013 05:51 PM

Quote:

Originally Posted by 5150Rubicon (Post 4009910)
Yes! You just made me realize...that is exactly why...after even a small lift...the steering wheel usually needs to be recentered. Because....as we move the top/bottom lines of the z further apart (lift)...the drag link also NEEDS to move to the right relative to the Jeep...causing the steering wheel to "turn".

So, BoB...if we use adjustable track bars properly...by definition...after a lift, the steering wheel would remain perfectly centered...since the drag link is centered via the centered axle

TDUFF 07-27-2013 05:52 PM

Rear track bar
 
The AEV 2.5 XT kit gives you a new rear track bar to go with the tower bracket. Unless you get the RHD kit.
Great kit - just installed mine last weekend.:dance:

nwbronco 07-27-2013 05:55 PM

Quote:

Originally Posted by Aeschylus (Post 4009887)
So, a follow up question from someone who is planning out future mods ...

If you were going to do mods in an optimal sequence (instead of all at once), and you knew you were going to eventually do a lift / bigger tires / upgrade track bars, is it okay to install the beefier track bars before lifting? Or should that only be done in conjunction with the lift?

Most adjustable trac bars come in a range. 0-3", 3 to 6". You would need to research trac bars and find one that fits your needs. If you are going up in lift, and there is no comparable adjustable, you should get the trac bar(s) first and have them ready when the lift goes in. There is not much of a way to piece meal a lift. They come with springs or pucks, shocks or shock extensions, and probably a trac bar bracket. Also some replacement swaybar links. There is not really a way to piece meal it once you get the taller springs or pucks in. The amount of lift is going to further narrow the piece meal possibility.


Bob K.

5150Rubicon 07-27-2013 05:57 PM

Quote:

Originally Posted by nwbronco (Post 4009909)
Exactly. The axle track and steering geometry need to be in the same relationship after the lift. The steering turnbuckle would need to be adjusted to lengthen the drag link, in relation to the amount of lift gained. It is easier to just drop the drag link during the lift installation.

If using an adjustable trac bar, the axle is placed back on the ground and the axle centered. This is done by finding a common spot to measure, say the frame to the tire, to get the axle centered.


Bob K.

dropping the drag link...that would be a "drop pitman arm" ?

5150Rubicon 07-27-2013 06:00 PM

So the lesson learned here folks....

All these companies selling "Lift kits" are doing just that....selling Lift Kits.

however, to do it correctly...one needs a lift/suspension SYSTEM...

Marketing...its a powerful thing.

nwbronco 07-27-2013 06:00 PM

Quote:

Originally Posted by 5150Rubicon (Post 4009918)
So, BoB...if we use adjustable track bars properly...by definition...after a lift, the steering wheel would remain perfectly centered...since the drag link is centered via the centered axle

No, actually the drag link goes through the same change as the trac bar. It will need to be lengthened once the trac bar is installed. Once you lift the rig the drag link is shortened. The The Z thing again. If the parallel lines, representing the frame and the axle are moved further apart, the diagonal line has to be lengthened to maintain the connection.


Bob K.

nwbronco 07-27-2013 06:01 PM

Quote:

Originally Posted by 5150Rubicon (Post 4009929)
dropping the drag link...that would be a "drop pitman arm" ?

No drop pitman arm required. The drag link only need be lengthened to restore the correct geometry.

By dropping I meant disconnecting.


Bob K.

Gracey143 07-27-2013 06:12 PM

Great thread. I have a couple of questions. I recently had a Teraflex 3 inch lift installed with a JKS adjustable front track bar. I cannot for the life of me get the Jeep from pulling to the right. It's a gradual pull but noticeable. Shop swears it is aligned and square any ideas?

kjeeper10 07-27-2013 06:26 PM

Yes, ideally you want the roll centers to match or the rear slightly higher.
Lowering the front TB DOES NOTHING for roll center. The only way to "raise" roll center for the front is raising the track bar.
Raising or lowering the TB cant be be done without flipping the drag link or w/ a dropped pitman arm.
A drag link flip can not be done w/ smaller lifts. The drag link will hit the frame during flex. 3" of bumpstop is needed regardless which does limit uptravel.
Flipping the drag link is recommended over dropping the pitman arm because of the stress out on the steering box/sector shaft. I know we are talking about Tb's, but since roll center is involved. It's important to mention.

The purpose of track bar axle brackets and mainly roll center. Centering the axle is a benefit. In some cases a adjustable track bar is still needed.

The front stock TB is pretty weak and any lifted jeep will benefit with a upgrade.

kjeeper10 07-27-2013 06:35 PM

2 Attachment(s)
You want to keep the tower in the rear. I know In my case my axle was over corrected using the higher hole with my TF bracket. A RK adjustable brought it back centered.
I also did a highsteer setup but w/ 3.5" of lift.
My roll centers match and both axles are centered.

5150Rubicon 07-28-2013 03:42 PM

Quote:

Originally Posted by kjeeper10 (Post 4010017)
You want to keep the tower in the rear. I know In my case my axle was over corrected using the higher hole with my TF bracket. A RK adjustable brought it back centered.
I also did a highsteer setup but w/ 3.5" of lift.
My roll centers match and both axles are centered.

Thanks. So if I understand. I will install AEV with the track bar tower in rear (per instructions). It will probably be fine (in terms of axle shift). If the axle is not centered (either by the tower OVER compensating or not enough)...then I can get an adjustable rear track bar...and still use the tower as the attachment point (to keep the benefit of the higher roll center). Do i have it right?

5150Rubicon 07-28-2013 03:43 PM

Quote:

Originally Posted by nwbronco (Post 4009939)
No, actually the drag link goes through the same change as the trac bar. It will need to be lengthened once the trac bar is installed. Once you lift the rig the drag link is shortened. The The Z thing again. If the parallel lines, representing the frame and the axle are moved further apart, the diagonal line has to be lengthened to maintain the connection.


Bob K.

Bob, on the steering/drag link. I've never (with a 2.5 lift) seen anyone talk about changing the drag link length. How would this be accomplished?

kjeeper10 07-28-2013 03:57 PM

Quote:

Originally Posted by 5150Rubicon (Post 4012552)

Thanks. So if I understand. I will install AEV with the track bar tower in rear (per instructions). It will probably be fine (in terms of axle shift). If the axle is not centered (either by the tower OVER compensating or not enough)...then I can get an adjustable rear track bar...and still use the tower as the attachment point (to keep the benefit of the higher roll center). Do i have it right?

Yes sir
The rear is not as important as far as axle shift. It can be off slightly and not cause problems.

kjeeper10 07-28-2013 03:58 PM

Quote:

Originally Posted by 5150Rubicon (Post 4012560)

Bob, on the steering/drag link. I've never (with a 2.5 lift) seen anyone talk about changing the drag link length. How would this be accomplished?

Turnbuckle/centering the steering wheel

5150Rubicon 07-28-2013 04:01 PM

Quote:

Originally Posted by kjeeper10 (Post 4012622)
Turnbuckle/centering the steering wheel

ahhhhhh....so the turnbuckle is centering the steering wheel by actually lengthening the drag link? Cool...learn something new everyday

nwbronco 07-28-2013 04:34 PM

Correct. It is two ends threaded into a collar. So they are shortened or lengthened by turning the sleeve, (turnbuckle).

Bob K.


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