Beating a deathwobble horse

[Cross-Threaded-06TJ]

Not for nothing but if an alignment cures DW, what specs do I use to cause DW?

17

 

[mrblaine]

17

That is at least as accurate as most the answers in this thread so far, so good on ya' for staying in context.

 

[psrivats]

You don't have to understand precession and angular momentum to visualize what is going on when both tires are spinning the same direction which effectively makes them very large, very heavy and very powerful gyroscopes. The video below needs to be studied at the section where both rotors are spinning the same direction. When the directional input is applied, the immediate reaction is to move one tire up and the other one down. That reverses when the directional input is reversed.

That is why we get the tire oscillation when the locating components are worn, weak, or loose and unable to do their job. In an amongst that is some damping from the shock and overall structure stiffness which helps to keep the harmonics at bay by moving them out of the resonant frequency as much as possible. The point of all of that drivel is it has not a damn thing to do with your description of the trackbar moving up and down and whatever wonky logic you came up with to use that as an example.

Once you extrapolate the forces out to tire sized, it then makes perfect sense why you do not want either of your high force gyros out of balance, not running true and being made to behave by sound component size, strength, and viability. I'm going back to work now so this is the last science lesson you get for awhile. Study the video, you'll be all the better for it.

Outstanding explanation and a great video .. thanks for sharing that one.

 

[mrblaine]

Outstanding explanation and a great video .. thanks for sharing that one.

I'd rather be lucky than good, always.

 

[AndyG]

You don't have to understand precession and angular momentum to visualize what is going on when both tires are spinning the same direction which effectively makes them very large, very heavy and very powerful gyroscopes. The video below needs to be studied at the section where both rotors are spinning the same direction. When the directional input is applied, the immediate reaction is to move one tire up and the other one down. That reverses when the directional input is reversed.

That is why we get the tire oscillation when the locating components are worn, weak, or loose and unable to do their job. In an amongst that is some damping from the shock and overall structure stiffness which helps to keep the harmonics at bay by moving them out of the resonant frequency as much as possible. The point of all of that drivel is it has not a damn thing to do with your description of the trackbar moving up and down and whatever wonky logic you came up with to use that as an example.

Once you extrapolate the forces out to tire sized, it then makes perfect sense why you do not want either of your high force gyros out of balance, not running true and being made to behave by sound component size, strength, and viability. I'm going back to work now so this is the last science lesson you get for awhile. Study the video, you'll be all the better for it.

Well somehow the Johnny joint I put in my upper right front that would get death wobble at 70 when I hit a bump fixed the precession-

I don’t know the science and I’m not gonna pretend to but I know things don’t need to be loose typically-

If he has a bad control arm bushing or mount it isn’t precession, it is the results of it he needs to get under control.

Sorry I can’t type anymore I’m too busy patting myself on the back.

 

[PatMc]

Thanks for the replies…. Yeah it was full on death wobble, I first experienced it in my 04 dodge 3500 after lifting it before I got the alignment dialed in. This was the real deal.

Did have to disconnect my track bar to get the axle to drop low enough to get the springs out and the new ones in… I will recheck the lower bolt is tightened down.

The wheels are bone stock rubi wheels, I do rotate them on a regular basis including the spare. Maybe I’ve rotated a poorly balanced tire onto the front. I will take them to a tire shop ASAP to get them rebalanced.

As far as tires, they are knockoffs that were on there when I bought it. “LAUFENN X Fit AT” 265/75/r16. I bought the jeep at a used car lot, I’m sure it had bad tires and they bought the cheapest thing possible to sell it. That being said, they were brand new and I couldnt see throwing them out when I don’t exactly have money growing on tree’s over here haha. I’ve put roughly 20k miles on them, rotating them roughly every 5000 miles. Still have good tread and tread ware is even.

I wouldn't worry about the tires...Laufenn are made by Hankook. As far as no-name tires go, Laufenn are pretty decent.

 

[mrblaine]

Well somehow the Johnny joint I put in my upper right front that would get death wobble at 70 when I hit a bump fixed the precession-

Perfect. Just get the gent with the problem to do that and when it doesn't fix the problem, I'll let you explain to him as to why it didn't.

 

[AndyG]

Perfect. Just get the gent with the problem to do that and when it doesn't fix the problem, I'll let you explain to him as to why it didn't.

I’m not saying he should I’m saying he should investigate and see if that could be a potential problem. It was actually you that enlightened me to that possibility.

I don’t want anyone to just throw parts at something- And of course we all know that happens often with death wobble.

I know it can’t be pinned down to one thing or solved on a forum with some generic solution- But I do believe there’s die you if people can get a broader view of why it can happen- And even today I believe we both done that, at different planes entirely.

 

[mrblaine]

I’m not saying he should I’m saying he should investigate and see if that could be a potential problem. It was actually you that enlightened me to that possibility.

I don’t want anyone to just throw parts at something- And of course we all know that happens often with death wobble.

I know it can’t be pinned down to one thing or solved on a forum with some generic solution- But I do believe there’s die you if people can get a broader view of why it can happen- And even today I believe we both done that, at different planes entirely.

If you don't want him to throw parts at it, then the very first words out of your pretty little mouf are as follows.
Do not throw parts at it. Do start with known good round and balanced tires. If they are not, make them so.
Look up and learn the steering test with the engine running. If after you do that test and you don't see anything obviously loose or deficient, then to test for worn upper control arm bushings or joints, toe it out 5/8-3/4", take it for a drive where you could previously induce DW and see if it has changed.
If it has, that points to an issue with the upper control arms.

But that's only if you aren't trying to get him to shotgun the parts store at it.

 

[AndyG]

If you don't want him to throw parts at it, then the very first words out of your pretty little mouf are as follows.
Do not throw parts at it. Do start with known good round and balanced tires. If they are not, make them so.
Look up and learn the steering test with the engine running. If after you do that test and you don't see anything obviously loose or deficient, then to test for worn upper control arm bushings or joints, toe it out 5/8-3/4", take it for a drive where you could previously induce DW and see if it has changed.
If it has, that points to an issue with the upper control arms.

But that's only if you aren't trying to get him to shotgun the parts store at it.

Well you started with the seminar on precession, Now 29 post in you are telling me how to post what you could have started with as well.

 

[PatMc]

 

[mrblaine]

Well you started with the seminar on precession, Now 29 post in you are telling me how to post what you could have started with as well.

Read post 11 and try that again.

 

[JEEPCJTJ]

This may or may not apply to this thread, or DW.

"GREAT THINGS ARE DONE BY A SERIES OF
SMALL THINGS BROUGHT TOGETHER."
- VINCENT VAN GOGH

I just happened to see it while looking something else up just moments after leaving this thread.