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Unread 06-25-2013, 11:28 PM   #46
J03_TJ
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Quote:
Originally Posted by Necko2529
J03_TJ, think about the stock spring and the way it sits, single rate spring. With the bow in it the leading edge of the spring is already more compressed than the back end and its already "harder". The back end of the spring is more relaxed and softer giving you impression of a dual rate spring. At least that's the way I understand it when I look at it.
Yep, that's my basic understanding of it too. I just thought it was a cost effective way for it to not behave as a linear spring.

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Unread 06-26-2013, 05:06 AM   #47
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Quote:
Originally Posted by mrblaine View Post

You, I, We, as in, in general, nothing personal.

A note though, changing to poly only changes the stiffness if the poly is stiffer than what it replaced. Poly is not inherently stiffer.
So, kind of like the "Royal 'We'"?

The poly I put in (Energy Suspension) did seem like a softer poly was used on the CA bushings than what they used on the TB bushings and sway bar mounts. Not sure how it compares to the stock clevite rubber. Just the fact that it takes up more space than the rubber would give it less 'flex' though. Of course, if you ask most folks on this forum, though, they'll say not to use poly because it will rip your mounts off due to its stiffness. Anyway, my point is there was a definite change in behavior by changing the bushings (and nothing else).
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Unread 06-26-2013, 05:50 AM   #48
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While patting the Chrysler engineers on the back, let's not forget that they also allowed the DW to manifest in the first place.

Take the track bar, for instance. Great idea, poor implementation. For an elastomer (rubber, polyurethane, matters not) to effectively provide damping, it needs to be preloaded and worked in shear. This is the most effective use for these materials as a damper.
The trackbar bushing is designed with a heavy preload, they got that much right. But the direction of the motion is entirely radial (WRT to preload)...in other words, the track bar would better dissipate energy (and hence provide damping) if it were to move in line with the mounting bolt!

In that fashion, the compressive preload is provided by the sleeve, and the damping would be provided best by motion in line with the bushing centerline --- in shear.

To best take advantage of the available damping from the track bar bushing, the bushing should be mounted 90 degrees from its current orientation.

Has anyone developed such a track bar configuration yet?
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Unread 06-26-2013, 07:55 AM   #49
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Quote:
Originally Posted by stripperguy View Post
While patting the Chrysler engineers on the back, let's not forget that they also allowed the DW to manifest in the first place.

Take the track bar, for instance. Great idea, poor implementation. For an elastomer (rubber, polyurethane, matters not) to effectively provide damping, it needs to be preloaded and worked in shear. This is the most effective use for these materials as a damper.
The trackbar bushing is designed with a heavy preload, they got that much right. But the direction of the motion is entirely radial (WRT to preload)...in other words, the track bar would better dissipate energy (and hence provide damping) if it were to move in line with the mounting bolt!

In that fashion, the compressive preload is provided by the sleeve, and the damping would be provided best by motion in line with the bushing centerline --- in shear.

To best take advantage of the available damping from the track bar bushing, the bushing should be mounted 90 degrees from its current orientation.

Has anyone developed such a track bar configuration yet?
If im reading this correctly it sounds like no different than having it mounted solid on there and bushing would have no dampening effect.

Edit to add: It would also bind really bad at any kind of travel.
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Unread 06-26-2013, 07:55 AM   #50
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Quote:
Originally Posted by JEK3 View Post
So, kind of like the "Royal 'We'"?

The poly I put in (Energy Suspension) did seem like a softer poly was used on the CA bushings than what they used on the TB bushings and sway bar mounts. Not sure how it compares to the stock clevite rubber. Just the fact that it takes up more space than the rubber would give it less 'flex' though. Of course, if you ask most folks on this forum, though, they'll say not to use poly because it will rip your mounts off due to its stiffness. Anyway, my point is there was a definite change in behavior by changing the bushings (and nothing else).
I had some poly control arm bushings many years ago I wound up with in a trade. There is no question if they didn't self destruct first, they would have readily ripped mounts off or bent the arms.

If you put a bolt upright in a vise and set the end of a stock arm and the poly ones over it, you could put your full body weight on the end of the arm and it would deflect less than an inch, the OEM moves further with 10 lbs of force.
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Unread 06-26-2013, 07:57 AM   #51
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Originally Posted by J03_TJ View Post
Yep, that's my basic understanding of it too. I just thought it was a cost effective way for it to not behave as a linear spring.
I used to think it was cost effective until I studied the spring some.
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Unread 06-26-2013, 07:59 AM   #52
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Quote:
Originally Posted by stripperguy View Post
While patting the Chrysler engineers on the back, let's not forget that they also allowed the DW to manifest in the first place.

Take the track bar, for instance. Great idea, poor implementation. For an elastomer (rubber, polyurethane, matters not) to effectively provide damping, it needs to be preloaded and worked in shear. This is the most effective use for these materials as a damper.
The trackbar bushing is designed with a heavy preload, they got that much right. But the direction of the motion is entirely radial (WRT to preload)...in other words, the track bar would better dissipate energy (and hence provide damping) if it were to move in line with the mounting bolt!

In that fashion, the compressive preload is provided by the sleeve, and the damping would be provided best by motion in line with the bushing centerline --- in shear.

To best take advantage of the available damping from the track bar bushing, the bushing should be mounted 90 degrees from its current orientation.

Has anyone developed such a track bar configuration yet?
I wonder how long it will take before everyone figures out that like the control arms that need some isolation to slow down the transmission of NVH, so do the trackbars?
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Unread 06-26-2013, 08:00 AM   #53
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Quote:
Originally Posted by stripperguy View Post
While patting the Chrysler engineers on the back, let's not forget that they also allowed the DW to manifest in the first place.

Take the track bar, for instance. Great idea, poor implementation. For an elastomer (rubber, polyurethane, matters not) to effectively provide damping, it needs to be preloaded and worked in shear. This is the most effective use for these materials as a damper.
The trackbar bushing is designed with a heavy preload, they got that much right. But the direction of the motion is entirely radial (WRT to preload)...in other words, the track bar would better dissipate energy (and hence provide damping) if it were to move in line with the mounting bolt!

In that fashion, the compressive preload is provided by the sleeve, and the damping would be provided best by motion in line with the bushing centerline --- in shear.

To best take advantage of the available damping from the track bar bushing, the bushing should be mounted 90 degrees from its current orientation.

Has anyone developed such a track bar configuration yet?
Who says a track bar has to provide damping?
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Unread 06-26-2013, 08:02 AM   #54
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Originally Posted by mrblaine View Post
I wonder how long it will take before everyone figures out that like the control arms that need some isolation to slow down the transmission of NVH, so do the trackbars?
This is my thinking and why I said no different than mounting it "solid" as in with no bushing. Fastened or welded.
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Unread 06-26-2013, 08:06 AM   #55
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Quote:
Originally Posted by mrblaine View Post
I wonder how long it will take before everyone figures out that like the control arms that need some isolation to slow down the transmission of NVH, so do the trackbars?
This is understood. But purely in terms of keeping the axle in place, there doesn't 'need' to be any isolation. Is that incorrect?
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Unread 06-26-2013, 08:32 AM   #56
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This is becoming a good read I'm glad the bickering has stoped and an educated discussion has arisen.
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Unread 06-26-2013, 08:34 AM   #57
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Quote:
Originally Posted by mrblaine View Post
Actually I don't know that. I've been around far too many cases of it where the cause and effect were too tenuous to readily define.

I know what the root cause is but from there the causation and exhibited symptoms are too varied. I also strongly believe there is a correlation between damping from the shocks and instances of DW that hasn't been explored nearly enough.

Whatever.

I say we know nothing because what works on one rig doesn't work on another even though both exhibit the same symptoms. It doesn't matter how acutely you try and dig into the nuance of the equipment either because that information is typically filtered by the mechanical aptitude of the owner.

When faced with trying to distill information down into a hypothetical, I run at it from the other direction and I've done that many times to prove or disprove DW theories.

It's touted a bunch that toe settings affect DW. I've taken several rigs and set the toe on them to many angles and attempted to induce DW. If you can induce something and then make it go away, it is very easy at that point to make statements of certainty. Until then, it's all speculation.
I'm good with most of this. "too tenuous to readily define"? I didn't say readily....you've got wheels, tie-rod, draglink, trackbar and control arms, stabilizer, etc.... it's a finite system. I know one guy that just said **** it, replaced EVERYTHING in the finite system, D/W solved.

That's fine if that's how you run your science, from the theory back to hypothesis, maybe things have changed since I learned empirical process.

To your last point, my experience: after hanving replaced almost everything, including things that weren't broken...removed front lift, no D/W, put front lift back on, yes D/W, removed front lift, no D/W. New HD control arms, no D/W since.
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Unread 06-26-2013, 08:42 AM   #58
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This is understood. But purely in terms of keeping the axle in place, there doesn't 'need' to be any isolation. Is that incorrect?
I don't think it is as understood as you are stating. If it is, there are certainly some products that don't fit that philosophy.

Of course there isn't a "need" for it to have isolation unless you are promoting a system as having less NVH transmission.

Skyjacker certainly has no issues with their double rod end control arms working to control the axle.
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Unread 06-26-2013, 08:52 AM   #59
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Originally Posted by SlackJaw View Post
I'm good with most of this. "too tenuous to readily define"? I didn't say readily....you've got wheels, tie-rod, draglink, trackbar and control arms, stabilizer, etc.... it's a finite system. I know one guy that just said **** it, replaced EVERYTHING in the finite system, D/W solved.

That's fine if that's how you run your science, from the theory back to hypothesis, maybe things have changed since I learned empirical process.

To your last point, my experience: after hanving replaced almost everything, including things that weren't broken...removed front lift, no D/W, put front lift back on, yes D/W, removed front lift, no D/W. New HD control arms, no D/W since.
I'm made my points to show why I believe the way I do. If I have a friend who parks his rig due to a near DW out of control shimmy simply due to inclination and air temp and now it's fine with no other changes, we know nothing, or if we do, which part do I swap?

I am unfamiliar with empirical process, I only have simple tools to work with.
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Unread 06-26-2013, 08:54 AM   #60
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Quote:
Originally Posted by mrblaine

I used to think it was cost effective until I studied the spring some.
Is it the forming and flattening of the little pigtails at the end that drive the cost up, or is there something else?
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