Traction Bar Question...

[uncc civilengineer]

Does a traction bar need to be mounted with a shackle at the frame end?

If so, what's the reasoning behind it?

 

[MarsFab]

With leaf springs you're axle will travel relatively vertical through its range of travel. A traction bar is mounted at a pivot point on the frame. As it swings up and down with the axle the end of it draws a radius as it cycles. Without a shackle on the frame end that radius that the arm moves in would fight the verticle movement of the axle. So the shackle lets the frame end float so it doesn't bind with the leaves.

 

[wrangler00]

With leaf springs you're axle will travel relatively vertical through its range of travel. A traction bar is mounted at a pivot point on the frame. As it swings up and down with the axle the end of it draws a radius as it cycles. Without a shackle on the frame end that radius that the arm moves in would fight the verticle movement of the axle. So the shackle lets the frame end float so it doesn't bind with the leaves.

great answer!

 

[sweetk30]

leaf spring + flex + soft ride = shackle at frame end.

leaf spring + no flex + stiff ride = no shackle at frame end.

thats as far as i can help.

 

[WARRIORWELDING]

also killing the purpose of mounting the traction bar. think about it if it is allowed to pivot at its mounting point movement is again put back into the equation. A traction bar is mounted to control axle wrap, by allowing it to travel forward and backward at either fixed end motion is again added back to the cycle. It would only be limited by the lenght of the shackle and its allowable cycle or arc. Traction bars rob suspension of vertical travel because of the job they are trying to preform. To combat this robbing nature be sure to mount the pivots points as close to the same locations as the stock fixed end of the leaves and the center line of the axle. This is so they travel in nearly identical arcs. This also works best with very flat packs so the elongation of the pack isn't nearly as great a factor. The best way to combat axle wrap is by designing packs that are full of long supple leaves rather than several short stiff ones. The wrapping nature is then transfered along the whole packs lenght. Shocks at all sorts of angles have been tried and usually don't gain much control. A properly weighted pack will control wrap and most wheel hop, you can make packs entirely to light which leads to alot of these issues, however way big tires and horsepower is usually best controlled with a well designed link based suspension.

 

[uncc civilengineer]

With leaf springs you're axle will travel relatively vertical through its range of travel. A traction bar is mounted at a pivot point on the frame. As it swings up and down with the axle the end of it draws a radius as it cycles. Without a shackle on the frame end that radius that the arm moves in would fight the verticle movement of the axle. So the shackle lets the frame end float so it doesn't bind with the leaves.

Makes sense... i'm going to try to run some numbers tomorrow to see exactly how much it moves through it's radius..

also killing the purpose of mounting the traction bar. think about it if it is allowed to pivot at its mounting point movement is again put back into the equation. A traction bar is mounted to control axle wrap, by allowing it to travel forward and backward at either fixed end motion is again added back to the cycle. It would only be limited by the lenght of the shackle and its allowable cycle or arc. Traction bars rob suspension of vertical travel because of the job they are trying to preform. To combat this robbing nature be sure to mount the pivots points as close to the same locations as the stock fixed end of the leaves and the center line of the axle. This is so they travel in nearly identical arcs. This also works best with very flat packs so the elongation of the pack isn't nearly as great a factor. The best way to combat axle wrap is by designing packs that are full of long supple leaves rather than several short stiff ones. The wrapping nature is then transfered along the whole packs lenght. Shocks at all sorts of angles have been tried and usually don't gain much control. A properly weighted pack will control wrap and most wheel hop, you can make packs entirely to light which leads to alot of these issues, however way big tires and horsepower is usually best controlled with a well designed link based suspension.

The leaf pack I built is pretty much just like you described mostly flat, mostly longer leafs.

The traction bar is mounted as follows:

My "pivot" point (Jonny Joint) is mounted in the same vertical plane with respect to the fixed spring hanger bolt @ 22.5" vertical. It is approximately 3" inboard of it and is approximately 14" forward (towards the front axle) of the spring hanger bolt.

The axle end is also mounted exactly along the center line (@ 17" vertical)...



I guess i'll play around with it in CAD tomorrow.. but basically what's more important -or- more benefitial.... allowing movement into the system for the sake of less binding -or- no movement and some binding?

 

[WARRIORWELDING]

I whole heartedly agree that the shackle based traction bar would allow for more suspension travel but from what i've seen and studied on the idea follows as thus... axle wrapping in very severe forms breaks all sorts of stuff, including transfercases, axle wrapping in mild forms leads to premature u joint failure and in the long term bearing damage at either end of what the drive shaft is connected to. The most annoying thing about axle wrap it almost imediately leads to wheel hop and a complete loss of traction which blows in all sorts of wheeling senerios. I'd honestly rather carry a tire in the air and have the other firmly planted and digging steady rather than have a rearend bucking around hunting for traction. So if I had to choose I'd go with a limited amount of controlled travel, at least it will be predictable.

 

[uncc civilengineer]

I took the X out for it's maiden voyage to Callalantee this weekend... While I really didnt notice much loss in travel I defintely noticed that I never once had wheel hop.. I guess i'll leave it "fixed" for now...

Thanks for the info...

 

[WARRIORWELDING]

remember when you plot it out in cad that the pack naturally elongates during its cycle, that's the whole reason for the shackle and the biggest reason why traction bars fight the suspension travel. If u can facter that in....i wouldn't know how other than knowing the lenght along the radius in relation to the center line of travel. It doesn't simply move in an arc so thats what creates some of the binding. good luck. I'd love to see a post of your cad work. Be neat to see.

 

[uncc civilengineer]

remember when you plot it out in cad that the pack naturally elongates during its cycle, that's the whole reason for the shackle and the biggest reason why traction bars fight the suspension travel. If u can facter that in....i wouldn't know how other than knowing the lenght along the radius in relation to the center line of travel. It doesn't simply move in an arc so thats what creates some of the binding. good luck. I'd love to see a post of your cad work. Be neat to see.

I'll do some more measuring when it's daylight tomorrow and try to work something up... I'm guessing it'll probably get much deeper than I have the time to fool with.

 

[MarsFab]

One important thing I think needs to be clarified with this type of traction bar is that it will bind as the axle travels up and down but will mildly effect articulation. Obviously the closer you mount the bar to the center of the axle the better it will be. I have actually seen a .120 DOM crossmember bend up^ where the shackle mounted just from lightly jumping a jeep. Hit the ground under power the suspension compressed and and the pinion didn't give so the crossmember had to. Normally as the suspension compresses the traction bar would be able to just force the pinion down.

 

[hadfield4wd]

You can also do a "slip and twist" traction bar. A shackle is not needed with this. It can be built with 1 bushing. Alot less expensive than than a standard traction bar and just as effective.

If I remeber correctly don't you have an XJ? If so I know a vendor who is currently developing one.

 

[woodkrawler]

Does that little Nissan v6 have enough power to wrap the rear springs?

Really, I'm interested to see your design.

 

[uncc civilengineer]

Does that little Nissan v6 have enough power to wrap the rear springs?
Really, I'm interested to see your design.

Ha, not my design... I think Andy built the bar back in his CRS days... I just moved it around some to avoid using the shackle...

And you're probably right about the power except the rear springs are so soft i think a 2.0 could wrap them...

 

[WARRIORWELDING]

I did some more research through talking with a friend. He clarified to me that mounting the shackle with the bar on top, shakle pointing up, then hard mounting the the axle end either in a "y" configuration or top and bottom fixed points would more or less transform the whole assembly into a torq arm. As the axle tried to rotate the leverage would be transfered to the arm and actually pull up on the shakle more than front to rear. As the suspension cycles the shakle would then accomidate the needed front to rear travel. I see how this works and also see were getting good fitment would be an issue. Like "mars" said a tremendous amount of leverage would be transfered. I was describing a link arm with single pivot points on each end. That was the reasoning behind following the existing geometry and pivot points as closely as you could. By mounting it as parallel as posible and in the midpoint of compression and drop most of the load should be forward and aft and the compounding leverage affect from a very long torq arm should be alot less. The needed movement forward and aft would be limited if mounted to work in the middle of the suspension cycle. This also assumes your not working with superslopy packs with huge amounts of travel. By mounting one link toward the center of the axle the cycle affect might also be lessoned but puts the load on one member.

 

[1983Bronco]

This is similar to what I have, get the kit from RuffStuff in the vendor section, it looks way better than these pics

 

[uncc civilengineer]

I have a traction bar... what I was wondering was about the need for a shackle at the frame end... From looking around it seems to be about 50/50. I guess i'll leave it w/ no shackle until something goes wrong.

 

[Spence]

When you visualize the wheel travel of leaf sprung suspension, there is a good bit of front to back movement inherent in the design. by not allowing your traction bar the freedom of movement that the shackle allows, it will put the hard mounted side of your leaf in a bind. Run one like that long enough, and I would just be waiting for broken leafs, or at the very least broken center pins.

No way I would run one without a shackle on my personal ride, for what thats worth.

 

[1983Bronco]

I have a shackle, had them before without. Flex difference is a good bit. Also use a flex joint(heim) of some sort at the shackle end. Then use poly on the axle, just my experience.

 

[hadfield4wd]

You need the shackle unless you do a slip and twist. As the suspension cycles the axle will move forward and back some. Picture a leave spring in an arc. As is compresses the centerline moves backwards. This is what the shacle allows. This is also why there is a slip in the drive shaft.

 

[upnover]

Picture this:
When your leaf spring flattens out(up travel) the space between the center(point a) of the leaf and the and the spring mount(point b), increases. length area from point a to point b has changed
When your axle droops, curve in spring is more severe, the point a and point b are closer.
If you have a fixed mount at both point a and point b, then the leaf can not compress or extend. Something gives, and as I found out the hard way, you bend a spring. Done this several times before I figured it out.
Run a shackle. When at static load it needs to be vertical and have movement to rotate to the front and to the rear, just as shown on the pics above

 

[hadfield4wd]

BTW here is my traction bar build.

Well I had some bad axle wrap with my custom bastard leaves. Bent my perches.

Had wavy springs. I don’t think they are supposed to be wavy like this.

I bought a new set of BDS springs which I promptly took apart and inserted full length deaver spring liner so I didn’t want to ruin new springs. So I built a traction bar.

To get the dimensions right I had to cut a hole in the floor of the jeep.

Here is the bracket on the cross member.

I covered it with a bread pan. Yep a bread pan works great then I sprayed it with spray on bed liner. Can hardly see it.

 

[hadfield4wd]

Now for the axle side. I had a buddy make me a bracket because I needed it custom fit on the 9”. I also had to get a new muffler. I got the magnaflow you can see in these pics because of its size.

Here you can see it doesn’t hang below the axle so it won’t get caught on anything.

Helps protect the driveshaft.

 

[WARRIORWELDING]

These type traction bars remind me alot of the torq arms made for the rear ends in Mustangs for Drag racing.