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Unread 06-26-2013, 09:01 AM   #61
SlackJaw
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Quote:
Originally Posted by mrblaine View Post

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.
I understand. We are getting off track and I'm stepping out, but I think even your methodological approach would prove that air temp being the ONLY cause would be fallacy.

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Unread 06-26-2013, 09:03 AM   #62
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Quote:
Originally Posted by mrblaine View Post
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.
Right, just checking my train of thought on the matter -- whether a track bar (or control arm, for that matter) isolates from NVH or not doesn't make or break its ability to control the axle.
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Unread 06-26-2013, 09:21 AM   #63
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Wow...I didn't expect this thread to take off like it did....or go into such detail. I never thought to take into account temperature would affect so many parts. It makes sense, though I don't feel that it should be enough to throw off a working setup, meaning that something else would have to be wrong for reasonable temperature to affect it. I say reasonable temperature because I'm not referring to extreme conditions like arctic or desert

Quote:
Originally Posted by SlackJaw View Post
First, do you have teh shimmy or the Death Wobble?
Oh its Death Wobble. Whole Jeep shakes like I'm in a paint can shaker. Lucky for me I'm actually really calm in intense situations like hitting a patch of ice or DW. Staying calm has kept me out of quite a few accidents over the years. Instead of panicking, its like everything slows down and I have more time than actually passes to figure out how not to die. Its probably all the adrenaline.

Quote:
Originally Posted by J03_TJ View Post
I've used the passenger test to determine I I had DW. Make sure they are only used to driving/riding in cars with good suspension characteristics. Have them ride along on a road that will trigger your wiggle. If they grab the bar above the glove box and look at you really scared, you probably have DW.
Ah-hahah! That's great! My mother was in the the Jeep with me when it first happened. Though after raising me and my brother, nothing scares her anymore. She is a rock.

I'm running what appears to be a 4" RC lift. I didn't put it on so I can't be sure the previous owner didn't take a shortcut somewhere. The DW happened much more frequently before I scrapped the retreads (they were on when I bought it) for actual round 31" BFG A-Ts. Now its intermittent, only once or twice a week. After reading all of your thoughts, I do believe every time its happened since I put good tires on it has been going up a slight to medium grade hill. I do live atop a hill, but I don't reach the magic speed to see if its steep inclines as well. I may have to find a different steep hill to test this theory.
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Unread 06-26-2013, 11:24 AM   #64
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Quote:
Originally Posted by Imped View Post
Who says a track bar has to provide damping?
I say the track bar needs damping!!
The particular mode that is active is a transalatory natural frequency (in line with the front axles), I think we can all agree on that.

As I said upthread, the system is under damped...once the axle begins to oscillate in that transverse mode, there is nothing to stop it...nothing.

If the track bar were to be solidly mounted (nevermind the limits imposed on suspension travel) it would stiffen the system in that plane. All that would do is to push the natural frequency higher up the spectrum. If (and that's a huge word for only two letters), the system could be built stiff enough, there may not be enough energy present to create much motion at all.

The introduction of damping, directly in line with the active mode, will dissipate the energy and control the system. That damping also has an apparent stiffness that varies with frequency, but that term would be minimal in this application.

I deal with under damped systems every day here at work...all that is required to have a healthy log decrement is to have adequate damping, introduced in the proper plane...works every time!!

Take a few minutes to visit my companies website, we have some in depth technical publications that can explain far better than I can during my lunch...

Miti.cc We are the recognized world leader in our technology, and how did we get there?? Well, proper application of damping is one route.
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Unread 06-26-2013, 06:40 PM   #65
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Oh no.....
Did I break this thread??????
It was going so well, I thought.
I didn't mean to step on anyone, just want to show DW in its purest sense.
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Unread 06-26-2013, 07:16 PM   #66
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Quote:
Originally Posted by stripperguy View Post
Oh no.....
Did I break this thread??????
It was going so well, I thought.
I didn't mean to step on anyone, just want to show DW in its purest sense.
Step on brother, they won't buy it when I sell it, but you sir have a chance.
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Unread 06-26-2013, 07:24 PM   #67
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Quote:
Originally Posted by SlackJaw View Post
I understand. We are getting off track and I'm stepping out, but I think even your methodological approach would prove that air temp being the ONLY cause would be fallacy.
What other cause is there if the ONLY changes are direction and temp? He did not touch the rig after parking it due to the wobble. We had many discussions concerning tire size, beadlocks, and what not none of which were acted upon due to time and money constraints.

At the point in time where both changed, he was on his way to the tire store to get the tires balanced or checked and it became apparent there was no wobble which then enabled him to take the road trip he had planned. Since that point in time, nothing else has been done and still no wobble.

All I did to it that "caused" the wobble was change out beadlock bolts to ones of a different color and I did them one at a time because I didn't want to affect tire balance or roundness.

You are correct though, air temp is not the cause, the change in temp allowed something to resonate at a different frequency in a range outside of the damping ability of the system in it's current state. With enough control and strength, air temp wouldn't matter.
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Unread 06-26-2013, 07:25 PM   #68
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Step on brother, they won't buy it when I sell it, but you sir have a chance.
Woe is ye.
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Unread 06-26-2013, 09:17 PM   #69
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Quote:
Originally Posted by mrblaine View Post

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.
I hear you. However, I liked my poly bushings on my on-road daily driver Jeep up until the day a month or so ago when I swapped them out for a full set of Currie CAs.
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Unread 06-26-2013, 09:19 PM   #70
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I hear you. However, I liked my poly bushings on my on-road daily driver Jeep up until the day a month or so ago when I swapped them out for a full set of Currie CAs.
Currie JJ's give you the lack of deflection of poly (they use a poly blend for the bushing halves) and the misalignment of rod ends.
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Unread 06-26-2013, 10:50 PM   #71
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Currie JJ's give you the lack of deflection of poly (they use a poly blend for the bushing halves) and the misalignment of rod ends.
If there is lack of deflection then how come the JJ at the frame side of the trackbar exhibits side to side movement when you do the dry steering test?
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Unread 06-27-2013, 12:46 AM   #72
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Here"s one for your catalog blairm...

Breaking in the new brakes tonight.

I KNOW that my passenger upper axle joint is insufficient.

In 4 passes from 50 to 5, I found DW once. On that pass I was actually closer to 60, and GPS would say 69...so the 50 to 5 passes were actually 59...fwiw.

I think importantly I decelerated in gear on this pass.

For whatever that's worth to you or anyone else. No other shimmy or d/w under normal driving, after break in, all is very well.
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Unread 06-28-2013, 10:17 PM   #73
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I had a 97. I sold it because of the DW. Everything in the front end was changed. Some things twice. It would only happen on right turns going down a hill. I've had many Jeeps but this one had me and a few others stumped. I got tired of dumping money into it and sold it. Everytime I put on new parts I thought I had it fixed. maybe 2-3 weeks would go by with no DW. Then when you wasnt ready it would do it's dance.


My completely stock 97 TJ had a "wobble" for years. Every bump at any speed and a bit scary on the freeway. To resolve it on the freeway, I could either accelerate out of it or slow down. I had it to 3 or 4 different shops over the years and got standard responses; ball joints, front track bar, steering stabilizer, even "soft sidewall tires" (BFG Mud Terrains 30x9.5).
I decided to do some repairs and a small mod myself (http://www.jeepforum.com/forum/f9/1-...-lift-1150250/). So I read tons of the great posts on this forum and then crawled under the jeep and looked at and wiggled everything I could see.
My Rear Track bar was loose. I could wiggle it to and fro with my hand. The axle mount (driver side) bolt even wiggled around. This was the jeep parked, sitting normal with the tires on, no jacks.
I took it to my current shop (first time they saw this vehicle) as I thought they would have to drill out a new hole or weld a plate over the bracket. Turns out they had to cut off the rusted bolt. They said the holes the bushings and bar were still in good shape. They installed new grade 8 (12.9) bolts, tightened them down and now the wobble I had for years is gone. Completely gone.
This was just last week. I start my suspension mod this week.

Moral of this story..... Rear Track bar.... don't overlook it.
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Unread 06-28-2013, 10:21 PM   #74
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By the way, The above was my first post. I was responding to the post by kbeitz on page 2.
How do I show the post I am responding to in a "quote" insert like every one else does.
Thanks
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Unread 06-28-2013, 10:23 PM   #75
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Quote:
Originally Posted by daddo View Post
By the way, The above was my first post. I was responding to the post by kbeitz on page 2.
How do I show the post I am responding to in a "quote" insert like every one else does.
Thanks
Hit the "Quote" button in the bottom right of the post.
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