Anti-wrap bar shackle mount discussion/debate

[Stumpalama]

I've read through tons of threads regarding antiwrap bars and have picked up a lot of great ideas and, unfortunately, a few more questions.

I understand you want the bar as flat as possible and the connection as low as possible to minimize anti-squat. So, with that in mind, my questions center around the front bar mount shackle orientation.

My question: Does the wrap bar want to push forward into the t-case at droop and rearward under compression? Or vice versa?

I am a ludite when it comes to this and have just enough engineering background to make me think I understand, but I also know that it gets me into trouble as well.

Thanks for your help and let the debate begin!

 

[chicago]

I set the front of my wrap bar on a shackle w/ a heim joint and angled the shackle toward the front of the rig, like this /.
So during up travel it'll move forward and down travel, obviously, it'll move back.

Hope that makes sense....

 

[Stumpalama]

It does, Thanks.
I found a thread where there is one instance of someone stating the axle moves forward during droop, but I wonder if the forward movement distance is overcome by the downward movement.

 

[Fast Eddy]

My question: Does the wrap bar want to push forward into the t-case at droop and rearward under compression? Or vice versa?

Giant topic that I'm tired of preaching about. I belive that most people's anti-wrap bar design will bind. There are some posts about it in my after thread, and Decker has a good write-up that is the inspiration for my thoughts on the subject.

The reader's digest version is that the bar needs to be able to telescope. Looking at it from the side of the rig,,, when the front is not connected it would draw a line that is about straight up and down (actually an arc segment of a really big circle), but when connected to a shackle, it is forced in a little circle.

In many or even most wheeling situations, this is not a problem because the center of the axle doesn't move much when articulating. The problem comes when the whole rig comes up, like boosting up over a rise, or comes down, like bottoming out in a gully. I believe it is binding in these situations when wrap bars break.

Decker's description: http://www.deckersonline.com/fj40_traction_bar

I believe my design works better than his, but his geometry explanation is spot on.

 

[Stumpalama]

Yes, I read your posts and agree that a telescoping design is ideal. I am thinking of using some HDPE attached to a sliding inner section. But if a shackle will be the 90% solution, then I might try that 1st.

 

[Stumpalama]

Does the shackle push forward during droop, or rearward?

 

[chicago]

Does the shackle push forward during droop, or rearward?

Rearward on droop.
Built two wrap bars the same way and never an issue w/ either of them...

 

[Fast Eddy]

Does the shackle push forward during droop, or rearward?

Rearward on droop.

With a triangulated bar the tip of the bar will go a little backwards, but also downwards almost as much as the droop, if it's not constrained by a shackle. My axle will droop about 6.5". The tip of the bar goes down about 5.5" and back about 2".

If your heim joint is fixed the trac bar will not allow your axle to droop through it's full travel if the front end is connected to the shackle. Try it.

Even my design needs some give from the big rubber bushings in this case.

 

[Stumpalama]

So, if the axle increases distance from the shackle mount point (wants to stretch the bar) wouldn't you want the shackle anchored at the bottom to allow the shackle to follow the arc and account for the increased distance?

However, if the bar attaches below the anchor point (shackle hanging down) the shackle reaches it lowest point when it is perpendicular to the ground, then it begins to arc back upward and away from the axle and creating tension in the spring between the eye and axle. Correct?

For reference, my truck is SOA using FJ60 rear springs and 1" longer than stock shackles. I have around 40" between the axle and the t-case skid plate which is made from 1.5" DOM tube and 1/8" plate (an adaptation of Poser's design), which should make for a nice long bar.

In designing my bar I've decided to use the JK design, mostly due to my truck being a late model FJ40 with the fuel tank under the bed and space being a premium. I will be using the ruffstuff axle mount with 2"x1/4" square tube for the bar.

 

[chicago]

My 40 is similar. I've built a tank and mounted it under the rig and I'm using 60 series springs and axles.
I should have clarified... My wrap bar shackle hangs DOWN and I DID eliminate the stock, rear fj40 x member and re made another using 1 1/4x 1/4 wall Dom.
I'm guessing, as I don't remember the angle, but the shackle is set at around. 20 or 25 deg toward the front of the rig.
So I welded a shackle mount to the x member w/ a shackle bushing, used stock length cruiser shackles (ruff stuff) and used a heim on the end of the wrap bar and shackle tubes and bushings at the axle end of the wrap bar.
So the shackle will move UP and FORWARD (in my set up) when cycling the suspension UP and the shackle will move DOWN and BACK when drooping. Essentially, just like the spring shackles will when cycling the suspension.

 

[chicago]

Here's a few pics of what I have...
The shackle angle actually looks more like 15-20 deg....

 

[Stumpalama]

Very cool. Thank you for the pics. Nice truck too. Your truck is way clean underneath.

 

[chicago]

Very cool. Thank you for the pics. Nice truck too. Your truck is way clean underneath.

Lol... It's not so clean any more. Only reason it was that clean was because it was being built.
Originally, I was chasing down the info just as you re the wrap bars... One thing I will caution on re the design... At the shackle end of the wrap bar ( if you use a triangular design like mine) leave as little over hang as possible. In other words, you have the upper and lower tubes.... Try and build it so they converge at the end where your shackle mount will be.
Reason being, these things ARE subjected to a great deal of force and if there is a lot of overhang... That is a point that really can fail. I've seen it first hand and it resulted in a broken pinon shaft. In that instance, the top tube had about 3-4 in of overhang beyond where the lower tube was attached.