Traction Bars

[MaXJohnson]

I'm going to increase it's angle. The more the traction bar points up, the more anti-squat there will be, so I want to lower the bar on the axle.

Moving the mount in a vertical plane at the axle end won't change the amount of anti-squat. The lever arm that determines the AS% is a line drawn from the axle centerline to the front chassis mount. No matter how you locate the arm at the axle end, the effective link still extends from the axle centerline. To change the amount of anti-squat you can change the length of the arm as you already mentioned or change the height of the forward (chassis) mount.

 

[gearwhine]

ok, let's see. I'm tyring to think of a little test you can do you understand it better. not working.

OK, back to the picture. You have to realize the frame mounts are on bushings, so they can rotate freely by themselves. At the axle, each "link" is mounted solidly (springs are bolted on, tbar is bolted to a welded on bracket). These theoretically will not allow any twist in relation to each other.

With the traction bar, you're trying to keep your springs in their natural shape and working in it's natural "rythm", that's the point of a traction bar, correct? You are trying to keep the spring from bending ways it shouldn't (s-shaped springs).

OK,

Even with the forward end of the traction bar allowed to float for and aft, the radius of the axle movement with a traction bar is changed from how it would move with no traction bar. The difference is taken up in the springs and various bushings, but the difference MUST cause SOME bind.

What jeff said, that's exactly what I'm getting at. I can't really say how much bind it causes, but I would say a considerable amount IMO.

However, there will still be some as without the traction bar, the axle will more or less move straight down since the rear of the spring plays into this. The axle will not rotate in an exact arc from the front spring hanger without a traction bar, but it will with a traction bar. I can see it, but it is hard to explain it via words. Jeff

I completely understand this. The axle does not move in an arc around the front leaf eye, and it does not move in a constant radius'd arc. It actaully pivots about 1/3 of the distance of the front half of the spring behind the front mount but still not in a constant arc due to teh leaf shackle.(wow, I'm a nerd, I actually plotted all this junk down a month or two ago using the chevy power manual diagrams for leaf springs).

But THIS Radius, is what the shackle takes care of, and the only thing it takes care of. It allows the spring to travel in it's own natural arc or "rythym" as I said earlier without the traction bar forcing it to move in a specified radius'd arc. So this should cause no bind at all wheater you ahve a long bar or a short bar, assuming the shackle has enough travel in it.

I think I got a little too in depth here, but I've been messing with this leaf spring stuff for a while now trying to understand them like people understand 4-links. Sorry! Have fun! :wave: _nicko_

 

[Goatman]

What jeff said, that's exactly what I'm getting at. I can't really say how much bind it causes, but I would say a considerable amount IMO.



I completely understand this. The axle does not move in an arc around the front leaf eye, and it does not move in a constant radius'd arc. It actaully pivots about 1/3 of the distance of the front half of the spring behind the front mount but still not in a constant arc due to teh leaf shackle.(wow, I'm a nerd, I actually plotted all this junk down a month or two ago using the chevy power manual diagrams for leaf springs).

But THIS Radius, is what the shackle takes care of, and the only thing it takes care of. It allows the spring to travel in it's own natural arc or "rythym" as I said earlier without the traction bar forcing it to move in a specified radius'd arc. So this should cause no bind at all wheater you ahve a long bar or a short bar, assuming the shackle has enough travel in it.

I think I got a little too in depth here, but I've been messing with this leaf spring stuff for a while now trying to understand them like people understand 4-links. Sorry! Have fun! :wave: _nicko_

So, what are you saying now. Are you saying there is bind, or that there isn't? :dunno:

There is no bind as far as the arc of movement of the axle/leaf springs, as the traction bar exerts no force on it at all. The only action from the traction bar on the springs is some rotation of the pinion as the bar causes the pinion to raise slightly when the suspension is fully drooped. I wouldn't call this binding by any definition of the term, since the only thing that happens is a very slight movement of the leaf spring which it is easily able to absorb and would not effect the performance of the spring in any significant way.

Even with a slight deflection of the spring caused by axle droop, there are two reasons I see this as no problem. One is that when the axle is articulated, the middle of the axle, where the traction bar is located, droops very little so the traction bar is not rotating the pinion up. When the axle is not articulating, but is just fully drooped, is either when you are dropping off of a steep downhill, or when you are at speed and hit dips that cause a full extension of the leaf springs (full droop). In neither of these situations does it matter if the traction bar causes a slight deflection of the springs.

Again, binding is something in the suspension that does not allow the suspension to move freely and so hinders it's travel. The potential slight deflection of the leaf spring that we are talking about here will not resist suspension movement. So, back to the original point, I see no way that this style of traction bar will limit suspension travel through binding.

 

[Goatman]

Moving the mount in a vertical plane at the axle end won't change the amount of anti-squat. The lever arm that determines the AS% is a line drawn from the axle centerline to the front chassis mount. No matter how you locate the arm at the axle end, the effective link still extends from the axle centerline. To change the amount of anti-squat you can change the length of the arm as you already mentioned or change the height of the forward (chassis) mount.

This question about traction bars and anti-squat is a good one, and one that I certainly don't fully understand. Can you explain more why you figure that the important angle is a line from the axle tube to the front traction bar mount?

The reason I figured I might gain some AS is that my bar is not connected to the axle tube at this time. Both bushings at the axle end of the traction bar are above the axle center line, in fact above the top of the tube. The reason it's not as effective as it should be is because the two bushings are too close together and so bushing deflection allows too much twisting of the axle, which the traction bar is supposed to not allow. I need to move the bottom bushing to even with the axle tube which would spread the distance between the two bushings. I also assumed that this would effectively increase the angle of the bar.

Here's a pic of my current, wishful thinking, poorly designed traction bar. I was determined to use that cool mounting pad at the top and not have to weld to the tubes. It also nicely centers the bar.

 

[gearwhine]

haha, I'm saying the longer one will bind, while the shorter one will not, or at least the longer one will bind a considerable amount more than a shorter one. Can't say the shorter one doesn't bind at all.

One is that when the axle is articulated, the middle of the axle, where the traction bar is located, droops very little so the traction bar is not rotating the pinion up. When the axle is not articulating, but is just fully drooped, is either when you are dropping off of a steep downhill, or when you are at speed and hit dips that cause a full extension of the leaf springs (full droop). In neither of these situations does it matter if the traction bar causes a slight deflection of the springs.

This is it. OK, I'm still sticking to my guns here about the longer one binding, but I neglected this part of it. Under flex, there is not a ton of up-down movement of the center of the axle (where the traction bar is located as you said). The bind will be a ton less because of this, and maybe negligible for how much articulation we might get, but it's still there.
Just as a thought..... If you moved your traction bar all the way to the end of your axle housing, would you say the same thing about it not binding? I would with the shorter one, but with a longer one....that's gonna bind.

NOW, when BOTH springs are compressed or drooped, that's where the bind of the long bar will show. So maybe for something like Jeepspeed this will matter much more.

 

[Goatman]

OK, I give up. We just disagree.......or we have a total different concept of what binding is.



One more thing......if the suspension articulates/flexes and travels the same with or without the traction bar, would you still say that the bar causes binding?

Based on your theory, a shorter bar would bind (it won't bind, but based on your idea ) more than a longer bar because the shorter bar would cause the pinion to raise more than a longer bar as the suspension droops. If the pinion raises more, the spring will be bent more, resulting in more binding (again, your idea of binding). So, based on your analysis, the longer bar would be better.

 

[MaXJohnson]

Can you explain more why you figure that the important angle is a line from the axle tube to the front traction bar mount?

I need to move the bottom bushing to even with the axle tube which would spread the distance between the two bushings. I also assumed that this would effectively increase the angle of the bar.

Since the bar is rigidly attached to the axle tube, it behaves like a radius arm. Even if the bar were bent into a "C" shape or "Z" shape it would still be treated as a point-to-point bar(axle center to chassis mount pivot center). This makes your instance center the chassis mount pivot as well. Anti-squat ends up being asymetrical because you have the bar on the left side defining AS% and the leaf spring on the right side trying to do the same thing. Since the bar is rigid and the leaf is not, the bar wins the battle. You also have engine torque trying to induce body roll. The traction bar, being mounted on the left side, adds to this roll moment.

There was a bar shown on PBB that mounted diagonally on the axle with the lower mount being on the tube and the upper being on the pumpkin. I thought that was an excellent idea since it mounts to the pumkin for strength. This should eliminate any worry of twisting an axle tube. You could copy that design and keep the pumpkin mount. For bushing seperation, measure from the ground to the tube mount and from the ground to the pumpkin mount. The difference would be the effective seperation rather that the diagonal distance between the two bushings.

By the way, that twin heim mount is great. I wish I would have done mine that way instead of the shackle. I would prefer to have a rubber or poly bushing at that end, but you can't beat the rotational freedom that yours has.

 

[MaXJohnson]

haha, I'm saying the longer one will bind, while the shorter one will not, or at least the longer one will bind a considerable amount more than a shorter one. If you moved your traction bar all the way to the end of your axle housing, would you say the same thing about it not binding? I would with the shorter one, but with a longer one....that's gonna bind.

NOW, when BOTH springs are compressed or drooped, that's where the bind of the long bar will show. So maybe for something like Jeepspeed this will matter much more.

Just for kicks, I did some rough calculations on your "bind" assuming a 36" traction bar and 25" from the axle centerline to the spring eye(just a guess for an example).

The typical traction bar is mounted about half way between the tire and the vehicle centerline so 10" of droop at the tire would equate to 5" at the traction bar mount. With the example above, the difference in axle tube rotation between the 36" bar and the 25" leaf amounts to only 1° for 5" of droop at the mount or 10" at the tire. 1° would mean next to nothing for the leaf spring; and don't forget the traction bar may have rubber or poly bushings to absorb part of this rotation as well.

Don't forget that even without a traction bar, the axle tube is trying to twist when articulated. The leafs have to react to this twist which is of much greater magnitude that the 1° provided by the traction bar example.

 

[MrShoeBoy]

MaXJohnson how did you calculate that? Is there a formula you could post or direct me to a site where I can learn how to do this?

Thanks,

AARON

 

[gearwhine]

haha...goatman, you're getting frustrated with me aren't you, hiding it with the smiles....I do the same thing sometimes. quite all right. (non- frustrated smiles)

I've based some of my info off these posts, and I thought about it, looked at it, thought some more, and beleived it.

http://www.pirate4x4.com/forum/showthread.php? s=&threadid=187954&highlight=traction+bar+bind

and this one

http://www.pirate4x4.com/forum/showthread.php?s=&threadid=158480&highlight=traction+bar+bind

They're short threads, so read them, and let me know waht you think. There are some others as well, but these two are fine. I'm seeing problems with the short set-up as well, but it seems to me, I'm never going to get my "perfect" traction bar . I'll have to settle with what I've started with, and go from there and see how I like it.

 

[Goatman]

haha...goatman, you're getting frustrated with me aren't you, hiding it with the smiles....I do the same thing sometimes. quite all right. (non- frustrated smiles)

I've based some of my info off these posts, and I thought about it, looked at it, thought some more, and beleived it.

http://www.pirate4x4.com/forum/showthread.php? s=&threadid=187954&highlight=traction+bar+bind

and this one

http://www.pirate4x4.com/forum/showthread.php?s=&threadid=158480&highlight=traction+bar+bind

They're short threads, so read them, and let me know waht you think. There are some others as well, but these two are fine. I'm seeing problems with the short set-up as well, but it seems to me, I'm never going to get my "perfect" traction bar . I'll have to settle with what I've started with, and go from there and see how I like it.

I'm not getting frustrated, you underestimate me. I sit here with a big smile (or smirk) on my face. You can lead a horse to water, but you can't make him drink. :lecture:

It sounds like you put more weight on the info/discussions that you read on POR than you do on what you see here, which could be a mistake. I'm hard to impress, as I like to figure things out for myself as much as possible. Facts are facts, observation is observation, analysis is analysis, and opinions are just that, opinions. Internet opinions are especially suspect. I read those two threads you asked me to, plus I've read plenty of other ones on POR previously about traction bars. I see nothing new, and nothing to convince me otherwise of my own conclusions. I do understand what's behind your view better, though.

I see that all of this discussion makes virtually no difference on how the traction bar actually works, so it's just fun talk regardless of which opinion we have. The differences we're talking about are so slight that it makes absolutely no difference which viewpoint is correct as far as how the traction bar will work.

I do like the hole in your floor, though, it allows for good ground clearance with the traction bar, and you know I'm into good ground clearance.

 

[Goatman]

There was a bar shown on PBB that mounted diagonally on the axle with the lower mount being on the tube and the upper being on the pumpkin. I thought that was an excellent idea since it mounts to the pumkin for strength. This should eliminate any worry of twisting an axle tube. You could copy that design and keep the pumpkin mount.

By the way, that twin heim mount is great. I wish I would have done mine that way instead of the shackle. I would prefer to have a rubber or poly bushing at that end, but you can't beat the rotational freedom that yours has.

Yeah, I saw that bar on POR, and that's what I'm going to do. Keep the upper axle mount and move the lower one to the tube. I like the dual heim mount since it provides movement on every plane (other than up and down). I was concerned that it might allow too little movement fore and aft since there wasn't enough room to have more distance between the two pivot points on the heims, but I've cycled the suspension and it's not an issue. It can be a little noisy, I occasionally get some clunking on the trail that I attribute to the heim joints.

While I'm re-doing the traction bar, I might move the front mount a little closer to center, which I have room to do. This would also let me mount the heims differently with more distance between the pivot points, just in case. Use a female heim on top threaded onto the lower heim, and then a bolt through it and into the traction bar. BTW, do you figure the pivot point at the front that determines AS is the top one or the bottom one? I guess that could be another discussion......is the interacting point on the frame the bottom pivot or the top? Is the short link in the front mount a part of the bar or a part of the frame?

 

[MaXJohnson]

MaXJohnson how did you calculate that? Is there a formula you could post or direct me to a site where I can learn how to do this?

Thanks,

AARON

Note that I said "rough calculations". I used the Pythagorean formula (a^2 + b^2 = c^2) to calculate longitudinal displacement for the traction bar at various amounts of droop. Did the same for a 25" link (front of leaf). Both were calculated at 2" increments from 0 to 10" of droop. I subtracted one from the other to determine the delta at each 2" increment. Since the leaf is mounted above the axle tube, I used 5" or 6" as the lever arm from axle centerline to leaf mount to apply the delta measurements. Using the formula for the circumference of a circle (2*pi*r) divided by 360 to determine how much movement at a 5" or 6" radius would equal one degree. It's about .1" This was compared to the mean displacement between the 36" and 25" arms.

There's better math available to figure this, but I was at work and wanted a quick and easy idea of the amount of movement involved.

 

[MaXJohnson]

BTW, do you figure the pivot point at the front that determines AS is the top one or the bottom one? I guess that could be another discussion......is the interacting point on the frame the bottom pivot or the top? Is the short link in the front mount a part of the bar or a part of the frame?

I could be wrong, but I use the pivot at the chassis end of the shackle, not the end attached to the bar. I assume this is correct because when figuring roll center on a leaf spring suspension, you use the chassis end of the shackle. It could be that which end to use might depend on the whether the shackle pulls or pushes, I haven't studied the kinematics to know.

I was looking at your dual heim setup again and it dawned on me that you are putting alot of side load on one of your heims. Do you think it will eventually pull through? There's alot of force at the shackle end of the bar.

 

[gearwhine]

I'm with you on that. No use in arguing it, opinions are opinions and it seems there are so many set-ups and it seems no one has any hard facts on which is the better way to go. Do it your way, and work off that. I'm glad you at least understand my view a bit more clearly. :kissyou:

I definitely don't go for whatever is said on POR, not sure that's what you're saying, but it seems like it's along the lines. I really try not to beleive anything without proof, and myself thinking it through thoroughly. POR is 95% BS, here it seems like it's about ...ehhh 25%.

I do like the hole in your floor, though, it allows for good ground clearance with the traction bar, and you know I'm into good ground clearance.

I like my hole in my floor too, but I'll like it alot better when it's covered up. My mom's been in a bind in last weeks snow, and has been driving it around with that whopping hole. And yeah, I think everyone on this bored thinks you hate them for adding something that hangs more than 1/4" under their frame rail.

BTW, I am looking at your shackle setup and can see a benefit in having that lower heim for kind of a side to side swivel rather than just a twist motion I'll get using an RE joint. If my rubber bushing in the shackle doesn't do enough, I'll add a heim in place of it.

I was planning on doing a truss over top the pumpkin, and have the traction bar mount attached to not worry about tube twisting . My question about this is....which would be your suggestion on how to attach this to the pumpkin. I can attach it to the diff cover bolts, or weld directly to the center section. You can weld to cast if you keep it heated and cool the weld very slowly, correct? Any opinions on that one?

oh and....

You can lead a horse to water, but you can't make him drink.

:huh:

 

[Goatman]

I was looking at your dual heim setup again and it dawned on me that you are putting alot of side load on one of your heims. Do you think it will eventually pull through? There's alot of force at the shackle end of the bar.

Good question. Any way to calculate the approximate force at that point? I just did a quick search for rod end ultimate axial load ratings but didn't come up with anything. I've run that mount for around three years, with 4 to 1 t-case gears, and no problem yet. I don't remember if I changed out the rod ends when I installed the D60 2 years ago or not. Probably, because I sold the old traction bar with the rear end. I think I have chromoly rod ends in there, but don't remember what brand. Moving the mount over slightly to be more centered and providing a little more room to mount the upper rod end vertically rather than horizontaly would eliminate the potential for a problem, if it exists.

 

[Goatman]

I'm glad you at least understand my view a bit more clearly. :kissyou:

BTW, I am looking at your shackle setup and can see a benefit in having that lower heim for kind of a side to side swivel rather than just a twist motion I'll get using an RE joint. If my rubber bushing in the shackle doesn't do enough, I'll add a heim in place of it.

I was planning on doing a truss over top the pumpkin, and have the traction bar mount attached to not worry about tube twisting . My question about this is....which would be your suggestion on how to attach this to the pumpkin. I can attach it to the diff cover bolts, or weld directly to the center section. You can weld to cast if you keep it heated and cool the weld very slowly, correct? Any opinions on that one?

Understand your view better? Thanks, but I was being facetious....I understood your view perfectly all along.

I don't think it's an issue because the bushings in the traction bar axle mount will allow for some sideways movement of the bar, so it still shouldn't bind. You can help this by grinding a small bevel just inside of the lip on the poly bushing, which will allow the arm to move sideways easier, which is what I did. I agree that the heim joint setup does allow for easy sideways movement, but it also clanks sometimes.

You can weld to cast, but there is a good chance that it won't be strong enough if not done just right, and there is quite a bit of force on that traction bar at the axle mounts. It also can hurt your axle seals by heating the pumpkin. I've welded to my pumpkin in the front, when I shaved the bottom of the D44 and added a plate to the bottom, but I did it without anything in it. I think you would probably be better off making a truss over the pumpkin and attaching a mount to that, tying into the top diff cover bolts if you want to. I don't know what rear end you have, and a truss might be a good idea anyway, at least it can't hurt. If you're willing to weld to the diff housing anyway, you could just mount the traction bar to the tube and put a few welds on the joint between the tube and the diff housing. Or, put the inside of the mount right up against the diff housing and weld one side of the mount to the diff.

Have fun,

 

[MaXJohnson]

Any way to calculate the approximate force at that point?

Here's how I would calculate mine:

Engine Torque = 225 ft/lb [assumes full throttle at peak torque RPM and sea level]

225 * 3.93 (low gear) = 884.25 ft/lb [your transfercase sees this torque]

* 2.72 (low range) = 2,405.16 ft/lb

/ 2 (4WD torque F/R torque split) = 1,202.58 ft/lb [your driveshafts see this torque]

* 4.11 (rear gear ratio) = 4,942.6 ft/lb [axle shafts see this torque]

*.85 (estimate loss through drive train) = 4,201.21 ft/lb

/ 3 (length of traction bar in feet) = 1,400.4 lbs

You can plug in your 4:1 transfer case, rear gear ratio and traction bar length. .85 is a common figure for loss through the drive train although this could easily be .80. Assuming a 4.0 with 225,000 miles is still developing 225 ft/lbs of torque is a stretch due to the certain loss of cylinder pressure due to ring and valve wear. In 2WD, the torque at the rear axle and traction bar would be double the above figure. For street driving, consider the 2WD torque and eliminate the transfer case ratio from the formula.

 

[marcusguy]

Max-you came up with a number that makes me wonder. You basically figured out the torque applied to the axle shafts and divided by three for the length of the bar. Seems like 1400lbs is still a little high because there was no calculation of how much of that torque is being resisted by the leaf springs. The joint isn't going to all of the force of the multiplied engine torque alone... right? Is that right? It's late here and maybe I'm not thinking clearly.

Marcus

 

[MaXJohnson]

Max-you came up with a number that makes me wonder. You basically figured out the torque applied to the axle shafts and divided by three for the length of the bar. Seems like 1400lbs is still a little high because there was no calculation of how much of that torque is being resisted by the leaf springs. The joint isn't going to all of the force of the multiplied engine torque alone... right? Is that right? It's late here and maybe I'm not thinking clearly.

Marcus

The math so far is pretty straight forward. With the limited math skills available to my brain, your question becomes somewhat subjective. How rigid is the bar? How compliant are the bushings? What is the effective spring rate of the leafs when subjected to the "S" shaped bending loads in this application?

If you assume that the traction bar wold allow for a small amount of deflection in the leafs, say the equivalent of 1/2" of vertical axle travel, then you could reasonably assume that a pair of 200 lb/in springs would store 200 ft/lbs of the available torque. This would still leave 1200 lbs for the traction bar. Double the 1/2" and you still have a lot of force. If you have a transfer case that you can put into 4-LO, the rear axle takes 100% of the available torque.

If you've been reading up on traction bars, you've certainly heard of guys that end up ripping apart under-engineered cross members on their test drives. The 200 ft/lb example is a guess. As is the 15% loss in the drive train and the assumption that all 225 ft/lbs of engine torque is available. You can plug some different assumptions in and get a different answer. The prudent thing to do is build for the worse case scenario. I'd rather build the bar to handle 2,000 lbs of force knowing the potential for 1,400 lbs is there. YMMV