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Harmonic vibrations in Jeeps: A new theory (please read!)

Fouledplugs

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Definitely good questions to ponder. Or even an heavy duty conversion like below ... does it work well without the balancer due to the heft of the upgraded components?

http://www.fourwheeler.com/how-to/transmission-drivetrain/1807-super-duty-jeep-transfer-case-conversion/
Morris 4x4 still sells new ones!

https://www.morris4x4center.com/damper-np231-transfer-case-5017819aa.html

Also, wish we could ask @mrblaine his thoughts on the topic.

Tom Wood may also have more information it seems. @bobthetj03 , would you mind writing a note to Tom Wood on this subject? You can just point him to this thread perhaps. Or PM me his email info to me and I will write an email.

View attachment 61296
The article you posted is quoted with, "What’s the difference between heavy duty and super duty? Well, the Tom Wood’s Super-Duty 231 conversion kit comes with the manufacturer’s unique rear output flange that allows the installation of a 1210, 1310, 1330, and 1350 series driveshaft with a conventional two-joint CV (double-Cardan) setup, or a 1410 series
conventional two-joint driveshaft, all without changing the flange.
"

JB Conversions still offers the rear output companion flange yokes (far better than a eared yoke IMO on many fronts) on their 32 spline output shafts for the SYE on both the 231 and24transfercases.
http://www.jbconversions.com/products/yokes_flanges/1966.php
1966-leadin.jpg


Like you pointed out what @mrblaine mentioned on another site, if the factory designed and engineered it, it might be in best interest to keep it or re utilize it. Like I have mentioned before, I am a huge fan of companion flanges over typical eared flanges both on output shafts and pinion shafts.
 
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Fouledplugs

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Great detailed post @RaymondT. I came to post something else, but I simply had to reply to you. The fact that you were able to modulate and actually percieve the change in vibration frequency is a great observation.

Based on my research, your Jeep should have the damper per the manuals (see the FSM for your year). However, Like @ElectricWizard your Jeep could be an inbetweener Jeep and I strongly think you would benefit from having a damper from what I've seen. The fact that you are stock and still have vibrations is a big clue, and a bigger one is that you are able to change it with changes to the skid. You've done good work already and made it better by sharing it here.

The part is $139 brand new from Morris 4x4. You can try it if you don't mind experimenting. Or maybe perhaps borrow @bobthetj03's to test out if he's willing to send it out to you. I think @Chris will agree with what I'm saying. I'll understand if you are skeptical, but it looks like you've already checked everything else including the skid.

If you have questions please ask us here, we are collectively trying to figure it out. @StG58 lit the spark by posting a photo of his stock Jeep without the damper and it really got me going. Your post is lighting the next one.

What started as an idea in my head is slowly getting to be a strong argument. @Chris and I are still discussing this heavily between ourselves before I even post here, trying to poke holes in the model. We need data and proof of concept and your case is very strong to test it.

https://www.morris4x4center.com/damper-np231-transfer-case-5017819aa.html





And now what I actually came to post ...

This is a question for @Chris and @Fouledplugs. I dug up this discussion on a skid made by a company called TKD from @Chris' build thread. Hope you guys recall the discussion. I've somewhat convinced myself the either the skid or the damper or both may need to be changed to curb these post regear harmonic vibrations. We've been talking a lot about the damper, but the TKD skid is actually quite promising not only from clearence viewpoint, but also from vibration standpoint since the design is actually different and well thought out.

$400+shipping is not too bad either. Thoughts on trying a skid like this in the vibration context? Worse case I'll have a nicer skid.

https://wranglertjforum.com/threads/my-2005-jeep-wrangler-tj-rubicon-a-tj-built-for-overlanding-exploring-and-family-fun.8537/page-20#post-137666
A much nicer skid I might add, both on the trail and in the garage.
 

Fouledplugs

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Who knows! Your post now makes me wonder if guys with Atlas transfer cases have these vibration issues after regear.
I am thinking that most folks who run an Atlas will also have the appropriate rear stetch to accomadate the tire size they are running. I feel like this vibe issue mainly effects bolt on lift buyers or folks who are running 35's and under with stock wheel base.

As soon as you streth the wheel base you are going to more often than not, run 1 ton drive shafts, yokes, and axles. Which would play into your heavier driveline theory.

Not without mention, the Atlas which is much shorter than the 231/241 and a rear stretch the longer driveshft is going to play into the vibe resolution. Just a thoery.
 

Fouledplugs

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The back calculation is the way to go at this stage. The whole system is very complex obviously. The design of 241 TC vs 231 T balancers tells me that the frequency numbers are slightly different (ie resonance appears at lower rpms).

The 55Hz number we know for the 231TC, so let's starts with that. Let's assume someone with a 5spd and 33s/4.88s sees resonance vibrations at 65mph. Grimmjeeper should tell us the engine rpms.

Now assume a mass of x for the balancer (I am seeing 2.27kg as the weight online, perhaps we can get an approx weight from @bobthetj03 ) . Let's assume the very basic freq inversely proportional to sqrt(m). How much do we need to change the mass to push the resonance freq to say 80mph? That's the question to answer.

Or use @jjvw's real world numbers that he posted in the previous page. BTW, @jjvw did you go see if you still have the two parts of the balancer in your Jeep? I confirmed that mine does even with the aftermarket driveshaft. This is mine (@Chris cleverly screenshotted it from a video that Dave sent).
View attachment 61379
Just to calify the brown/bronze looking "damper" closest to the actual transfer case is the actual damper pictured here:
https://www.morris4x4center.com/damper-np231-transfer-case-5017819aa.html

The brwon/bronze "dampner" looking part that sits behind it and closer to the driveshaft is the transfer case output companion flange that is not part of the damper at all. All Rubicon 241's came with compantion flanges.

Also the damper is two parts in one. A rubber isolator and a metal body. The rubber is vulcanized to the metal body. They are one single part and serviced as one. If they seperate, it needs to replaced as a whole unit. Just FYI
 

bobthetj03

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The companion flange idea is interesting. In essence, couldn't you make one to fit the rear output, and actually make it tuneable/balanceable? Wouldn't it also allow for a bit longer ds? And, if there is enough clearance from the tc linkage up front, maybe another companion flange for that location?
 
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psrivats

psrivats

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Just to calify the brown/bronze looking "damper" closest to the actual transfer case is the actual damper pictured here:
https://www.morris4x4center.com/damper-np231-transfer-case-5017819aa.html

The brwon/bronze "dampner" looking part that sits behind it and closer to the driveshaft is the transfer case output companion flange that is not part of the damper at all. All Rubicon 241's came with compantion flanges.

Also the damper is two parts in one. A rubber isolator and a metal body. The rubber is vulcanized to the metal body. They are one single part and serviced as one. If they seperate, it needs to replaced as a whole unit. Just FYI

I'm aware. For the TJ Rubicon, the flange and the damper are listed together as one part and you can only get them together.

@bobthetj03 I suspect the damper itself is the same design and weight between 231 and 241 and the flange does what you are saying (adding weight to the system, in essence "tuning"). I actually requested Dave to take apart mine and weigh it, and show me photos of 231 damper and 241 damper+ flange side by side (@Chris is cc'd in the conversation). I'll remind them Monday when I talk to them.
 
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Jeepers-n-Creepers

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Grateful for this thread; I had previously thought I was losing my mind, when, during a 2400 mile 'round-trip several years back, in my TJ, I was certain that the vibratory harmonics I was experiencing were that which actually sounded much like a human droning, or even a chant of some sort.

It was not long ago that I met with an incredulous discovery--the very sound I was hearing during this 2400 mile trip. It is captured, remarkably, in this brief video clip:

 
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Chris

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Grateful for this thread; I had previously thought I was losing my mind, when, during a 2400 mile 'round-trip several years back, in my TJ, I was certain that the vibratory harmonics I was experiencing where that which actually sounded much like a human droning, or even a chant of some sort.

It was not long ago that I met with an incredulous discovery--the very sound I was hearing during this 2400 mile trip. It is captured, remarkably, in this brief video clip:

You're not alone, trust me. A number of us have it. Somehow or another, one of us will fix it and share the remedy with everyone else. I'm just shocked that with as long as the TJ has been around, NO ONE has solved it. Or if they have, they aren't sharing the solution.
 

Jeepers-n-Creepers

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You're not alone, trust me. A number of us have it. Somehow or another, one of us will fix it and share the remedy with everyone else. I'm just shocked that with as long as the TJ has been around, NO ONE has solved it. Or if they have, they aren't sharing the solution.
I tend to think there's an eccentric recluse, not unlike the ballistics expert in the movie, "The Shooter" (who knew some fascinating stuff); and who happens to have the answer for us.

Question is, how do we draw him out?

 
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Chris

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I tend to think there's an eccentric recluse, not unlike the ballistics expert in the movie, "The Shooter" (who knew some fascinating stuff); and who happens to have the answer for us.

Question is, how do we draw him out?

I'm 100% certain you're right about that too. I have a very hard time believing that with all the TJs out there, someone hasn't figured this out. I know for sure someone has, they just aren't sharing it with the rest of us, or they just aren't an internet person to begin with.
 
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Jeepers-n-Creepers

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I'm 100% certain you're right about that too. I have a very hard time believing that with all the TJs out there, someone hasn't figured this out. I know for sure someone has, they just aren't sharing it with the rest of us, or they just aren't an internet person to begin with.
Likely a gnome-looking hermit - in the deep woods of Alaska - who's never been on the "interweb" :)
 
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AndyG

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Why can’t someone get Centramatic to make a small balancer for the tranny end of the shafts?

My gut tells me gears could contribute as well to the issue.
 
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psrivats

psrivats

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Any new news over here?
Sorry just saw this.

Got the rear driveshaft (high speed) balanced. Note that it's pretty new (Adams, from earlier in the summer, less than 1k miles on it, no "wheeling" other than few FS roads). I'm told vibes improved a little bit but still very loud and noticeable at 65.

Figuring out details of the skid mods to try next. Talked to Dave about methods to stiffen the skid. He suggested considering the option of Rokmen skid (pic below) that is heavier and has a stiffening crossmember built in (install will be with a 3" drop and a 0.5" body lift).

If the solution to these vibes were as simple as small BL + Rokmen skid, I suppose we'd know that by now. @Chris' Jeep has the Rokmen and it still has the same vibe issue so it's not a guarantee it will work. However his vibes were somewhat milder than mine so there is some merit to the idea. Maybe we need even more stiffening.

So still thinking this suggestion through.

bp14_1.jpg


DSC03587_01.jpg


@jeepndogs and @Ranger_b0b have suggested first trying out a custom tubular crossmember like GenRight's but made for stock TC heights to see if makes an impact on the vibes at all, since it would be stiffer and being tubular, less area to resonate.

I talked to Dave via text about this, and Dave said he can easily build his own crossmember, but he is worried about increased overall NVH due to limited choices in bushings (i.e trading one problem for another). He sent me a photo of one of his designs (pic below).

So I'm thinking though this idea as well.

I'll have to talk to Dave tomorrow to figure out best course of action. Details are not simple as you can see. I want to give the skid mods a try first before I turn my attention to the damper (and I have a feeling we'll get there soon).


GenRight:

https://genright.com/products/universal-transmission-crossmember-kit.html


Dave's custom:

Resized_20181127_125827.jpg
 
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psrivats

psrivats

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Why can’t someone get Centramatic to make a small balancer for the tranny end of the shafts?

My gut tells me gears could contribute as well to the issue.
Andy, those already exist, see link below (uses liquid Mercury filled in a tube, see videos on website homepage).

http://store.balancemasters.com/osCommerce/index.php?cPath=28&osCsid=45228e5c93bc22a2b115a4e0130718fa

Note that there is a difference between a balancer and a damper. I've been very loose in using these words interchangeably, totally my fault.

A balancer will help to balance an imperfect driveshaft .. in the case of centramatics or similar, by using the centripetal force of rotating counterweights. Their action is not specific to cancel one particular resonance frequency.

A damper is particularly and precisely designed to absorb and mitigate resonance vibrations in a specific frequency range. They may be stationary (tuned mass dampers, like you see in very tall skyscrapers to resist heavy wind deflections, or weights attached to heavy machinery like huge generators and motors and pumos) or rotating (like on crankshafts and our t-cases output).

These are examples of stationary tuned mass dampers.

Underneath a bridge:

Infinity_Bridge_tuned_mass_damper_on_small_arch-1632.jpg


Attached to a generator:

tmdhighfig3.png


Inside one of the world's tallest buildings (Taipei 101) weighing a massive 660 metric tons!

595240ed2dc84.jpg


The early JKs also had a stationary tuned mass damper attached directly to the 241 transfer case ( it went away after Jeep moved to the newer Benz automatic transmission from what I could gather online). It's the hunk of weight near the fill hole in the photo below. I learnt about these from @mrblaine.

Interestingly, these early JKs don't seem to have a rear tcase output damper like our TJs.

Early JKs:

DSC08424 (1).jpg


TJ vs JK comparison:

TJ 241 (rear output on the left side)

_56A4826.jpg


Early JK (note lack of damper near output, only the flange is there).


1DSC096581 (1).jpg



Late JKs went back to similar design as TJs:


IMG_20181127_235850_01.png



Not that there exist designs that straddle both ends of the spectrum as well, but in general a balancer and damper perform related but different functions.

My gears have been checked and been deemed OK. The shop is quite experienced in gear installs and I trust their word.
 
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