4.0, 42RLE, NP241OR High Speed Vibrations After Re-Gear to 4.88 or Deeper

I'm going to add one comment- it just seems that any component in the driveline would only have to be out a minute amount to cause the vibration issue , and it would most likely be in the ring and pinion and carry up the shaft if not the shaft .

I regeared my O3 Rubicon to 4:56 and did a crappy job basically - got a vibe at 63 mph that disappeared when I yanked the front shaft .

It's in the shop now - getting guess what - new gears by a professional.

The head guy contacted me and told me my ring and pinion was hammered .

I bet when I get it back , that vibe is gone as well as my other issues .

I know so little I probably shouldn't be on here throwing out guesses , but in my opinion these are likely coming from the differentials , and anything else you do just alters or mask it .
 
Chris said:
Someone who actually has the time to test these things really ought to. Dave for some reason was reluctant to do half the tests on Sri's list. It could have been very telling if he had.
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I would be reluctant for likely very similar reasons. It is hard to spend large amounts of time working on a problem without a known solution without knowing who is footing the bill. Sometimes we do it for the knowledge and learning experience but that is a only if you have the luxury of excess time to toss at it. If you don't and you are trying to keep the doors open, then someone has to pay and without the expert knowledge of the precise solution, that gets into an area where discomfort starts. How much is the customer willing to spend to make this go away without a known path of resolution? Without that path, there is an insidious rabbit hole one can head down where the money spent is ineffective for the sake of experimentation and learning.
 
AndyG said:
I'm going to add one comment- it just seems that any component in the driveline would only have to be out a minute amount to cause the vibration issue , and it would most likely be in the ring and pinion and carry up the shaft if not the shaft .

I regeared my O3 Rubicon to 4:56 and did a crappy job basically - got a vibe at 63 mph that disappeared when I yanked the front shaft .

It's in the shop now - getting guess what - new gears by a professional.

The head guy contacted me and told me my ring and pinion was hammered .

I bet when I get it back , that vibe is gone as well as my other issues .

I know so little I probably shouldn't be on here throwing out guesses , but in my opinion these are likely coming from the differentials , and anything else you do just alters or mask it .
Click to expand...
If it were that simple, it would be that simple to solve and it isn't. It is a harmonic caused by the aligning and misaligning of the resonant frequencies of various components all having to do with the firing order of the 4.0.

In other words, stuff vibrates at a certain frequency. In this case, it doesn't matter what the frequency is high or low, what matters is when one thing vibes at a certain frequency, another thing does, they get in tune with each other and then feed each other off of their individual frequencies that combine and the sum is worse than either. This isn't the type of vibe that can be fixed wholly by making sure stuff is balanced, it is more like how a speaker works.
 
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That is exactly what I posted a while back.

I am a contractor , and I love to learn, but there are also jobs where you are just getting sucked in , and you can't get done , get paid and move on .

I love being able to solve problems , but when you aren't sure if you can solve them and when , you are going to have some other problems if you aren't careful- namely financial.
 
mrblaine said:
If it were that simple, it would be that simple to solve and it isn't. It is a harmonic caused by the aligning and misaligning of the resonant frequencies of various components all having to do with the firing order of the 4.0.

In other words, stuff vibrates at a certain frequency. In this case, it doesn't matter what the frequency is high or low, what matters is when one thing vibes at a certain frequency, another thing does, they get in tune with each other and then feed each other off of their individual frequencies that combine and the sum is worse than either. This isn't the type of vibe that can be fixed wholly by making sure stuff is balanced, it is more like how a speaker works.
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Cool, I didn't think of it like that . I keep thinking of it like a single source .
 
This will help some. Pay attention and imagine how the tub, skid plate, frame, etc. all have various resonant frequencies as well as the engine. Now you have many spinning components and when the frequencies add energy to each other, we get the problem.
 
AndyG said:
Cool, I didn't think of it like that . I keep thinking of it like a single source .
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My explanation was derived from my osmotic knowledge, limited as it is. In other words, I have taken a few key points from folks far smarter than myself and used that to come up with what I perceive as happening. I only found that video a few minutes ago and it shows far more clearly what I was trying to say based on my very limited knowledge. But, I am a bit more learned now for having found it.
 
mrblaine said:
This will help some. Pay attention and imagine how the tub, skid plate, frame, etc. all have various resonant frequencies as well as the engine. Now you have many spinning components and when the frequencies add energy to each other, we get the problem.
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Got it .

Question - do vibration s cause these or do these cause /feel like vibrations ?

Mine "felt" like a vibration -and kind of a Jaws theme like pulse .
 
AndyG said:
Got it .

Question - do vibration s cause these or do these cause /feel like vibrations ?

Mine "felt" like a vibration -and kind of a Jaws theme like pulse .
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Think of the sheet metal in the tub like a big speaker. Once the harmonic gets going, the tub sort of turns into a giant speaker and we can feel the vibrations from even a mediocre subwoofer. Yes, they are felt, heard, and sensed.
 
One thing I wanted to eliminate was engine vibrations adding to the mix. I had sent out my flywheel and pressure plate to a shop for balancing together but they sat on it for almost a month. They finally admitted they didn't have an adapter nor the time to make one so I just installed it. Wish I would have sent them to another shop. You never know.

I've got a list as long as your arm on things I've done with little affect. Not only have I removed the front drive shaft but I also converted it to 2wd by removing the inner front axles and the carrier. Drive-shafts balanced, new mounts, etc. About the only thing that did help somewhat was installing the better Moog rear upper control arms. The bushings in the "CK" series are Clevite and 12mm I/D with internal bumps to center on the bolt exactly like Mopar ones. The Moog Clevite bushings that I had installed a year or earlier were 10mm that fit the bolt diameter exactly and the vibrations were worse. I'm not suggesting the bushing I/D had anything to do with it, but perhaps the rubber composition was different. The better ones had "Silent" molded into the rubber.

I also cut it down a bit when I went with all-season Firestones for the winter. I wish I could have access to a decent tire balancer and do the job myself. I've had a number of different shops have a go at my tires and discussions with the operators have been disappointing. The last shop had a Hunter Road Force GSP-9700 (the one with the pressure wheel) and when I asked "Bubba" to see the print out, I got told it was never hooked up. When I questioned him on checking the wheel and tire for high spots and minimizing the difference, I got a blank look. So I can't be absolutely sure the tires aren't causing a little bit of the vibration. I've probably spent over $400 on balancing on two different sets of tires and it gets lame quick.

When it warms up, I'll strip the floor and do the insulation thing. Mines not that bad but that fix is cheap.
 
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mrblaine said:
Think of the sheet metal in the tub like a big speaker. Once the harmonic gets going, the tub sort of turns into a giant speaker and we can feel the vibrations from even a mediocre subwoofer. Yes, they are felt, heard, and sensed.
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I guess it's a chicken vs. egg question ...I thought something vibrated and you felt it , but it seems a lot of frequencies end up causing a vibration .

I've noticed discord tuning a guitar to itself .

That explains why adjusting some components may remove some but not all of it .

I can imagine that's frustrating to chase down .
 
RaymondT said:
One thing I wanted to eliminate was engine vibrations adding to the mix. I had sent out my flywheel and pressure plate to a shop for balancing together but they sat on it for almost a month. They finally admitted they didn't have an adapter nor the time to make one so I just installed it. Wish I would have sent them to another shop. You never know.

I've got a list as long as your arm on things I've done with little affect. Not only have I removed the front drive shaft but I also converted it to 2wd by removing the inner front axles and the carrier. Drive-shafts balanced, new mounts, etc. About the only thing that did help somewhat was installing the better Moog rear upper control arms. The bushings in the "CK" series are Clevite and 12mm I/D with internal bumps to center on the bolt exactly like Mopar ones. The Moog Clevite bushings that I had installed a year or earlier were 10mm that fit the bolt diameter exactly and the vibrations were worse. I'm not suggesting the bushing I/D had anything to do with it, but perhaps the rubber composition was different. The better ones had "Silent" molded into the rubber.

I also cut it down a bit when I went with all-season Firestones for the winter. I wish I could have access to a decent tire balancer and do the job myself. I've had a number of different shops have a go at my tires and discussions with the operators have been disappointing. The last shop had a Hunter Road Force GSP-9700 (the one with the pressure wheel) and when I asked "Bubba" to see the print out, I got told it was never hooked up. When I questioned him on checking the wheel and tire for high spots and minimizing the difference, I got a blank look. So I can't be absolutely sure the tires aren't causing a little bit of the vibration. I've probably spent over $400 on balancing on two different sets of tires and it gets lame quick.

When it warms up, I'll strip the floor and do the insulation thing. Mines not that bad but that fix is cheap.
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Friend , I don't know what this world is coming to if people don't get on fire about going to work and doing a great job . I honestly don't . People don't know how to work and how to treat a job .

Sound deadening is great , even if you don't have vibes . It works great simply because TJs have none basically.
 
I'm curious about this - my previously owned 03 X had a hybrid lift, about 2.5", with 31" tires, 3.73 gearing, and the 42RLE with 256k miles on the clock. It had a pretty obnoxious pulsing harmonic vibration at about 55 mph - 65 mph. It was worse after the lift.

My current 04 Rubicon has the same 42RLE transmission, 32" tires, 2" OME lift, 24k miles, 4.10 axles, with a faint pulsing harmonic around 55 mph. If I re-gear to 4.88, am I just asking for trouble, or will the better gearing for somewhat larger tires help rid me of vibrations, however slight? I was always under the impression that the pulsing harmonic was due to the engine lugging due to the .69 o/d, and would be better with more rpm appropriate axle gearing.

I feel like there really is no set answer, other than trying it.
 
AndyG said:
I'm going to add one comment- it just seems that any component in the driveline would only have to be out a minute amount to cause the vibration issue , and it would most likely be in the ring and pinion and carry up the shaft if not the shaft .

I regeared my O3 Rubicon to 4:56 and did a crappy job basically - got a vibe at 63 mph that disappeared when I yanked the front shaft .

It's in the shop now - getting guess what - new gears by a professional.

The head guy contacted me and told me my ring and pinion was hammered .

I bet when I get it back , that vibe is gone as well as my other issues .

I know so little I probably shouldn't be on here throwing out guesses , but in my opinion these are likely coming from the differentials , and anything else you do just alters or mask it .
Click to expand...
I for one am interested in the eventual outcome, post professional re-gear.
 
mrblaine said:
In other words, stuff vibrates at a certain frequency. In this case, it doesn't matter what the frequency is high or low, what matters is when one thing vibes at a certain frequency, another thing does, they get in tune with each other and then feed each other off of their individual frequencies that combine and the sum is worse than either. This isn't the type of vibe that can be fixed wholly by making sure stuff is balanced, it is more like how a speaker works.
Click to expand...


This is exactly why this problem is so difficult. The speaker analogy is actually pretty accurate scientifically. If anyone has ever built a speaker box themselves and studied the frequency response, you'll understand what Blaine is saying here. Blaine, your experience and your way if explaining things is awesome.

I understand what you are saying regarding the shop not wanting to try everything I suggested .. while I was willing to spend time and money, they perhaps thought some of my ideas were not worth pursuing since they perhaps already know it might not do anything, and hence did not want to waste both their time and mine. That's ok. My only issue has been sporadic communication in the beginning, which I was able to amicably resolve after I talked to them about it.

Still wish they had run all the experiments so that my curiosity was fulfilled. Dave did get the vibes lowered with the Noico (and he did recommend it), we were both surprised at how much dampening it took. I wanted to go back to 4.10s a while ago and Dave said it's worth trying a little longer and I was ok to wait. I still may to go 4.10s if the vibes don't go away since I want to be able to drive my Jeep 2-3 hour each way on the hwy to my hiking and camping trails come summer. I wish I had more patience and mechanical knowledge to keep poking at this problem.
 
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glwood said:
l

I feel like there really is no set answer, other than trying it.
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There's the simple reality. I read and read and read and there is no way to 100% know what your rig will do. Though I've had to wait a long time, I've actually learned quite a lot, made some good friends on the forum and actually got to know Dave pretty well. Even I go back to 4.10s, I still come out on top with the experience.
 
jodomcfrodo said:
Might not be a bad idea. I'd maybe try both and see how it turns out. It may be telling about where your vibration is coming from.

This might be completely off base, but are there any 2004 owners that have this problem currently? Just hazarding a complete guess here because Jerry says he doesn't have any vibrations and he has a 2004. You and Chris both have a 2005's. Was something changed between 2004 and 2005 at all?
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Doesn't Jerry have manual hubs?
 
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