The Official Jeep Wrangler TJ "Vibrations After Re-Gear" Thread

it's premature to break out the champagne flutes, but I did have my LJ up to 71 after installing the UCF Extra clearance (1/4" steel) skid without discernible vibration. Being that it was coming in around 67 beforehand, I'm optimistic. I need to spend some time on a real highway to know for sure.

Since I changed my rear driveshaft angle by about 4 degrees (set the pinion back to half deg below driveshaft), and changed the front driveshaft by about 3 degrees without changing the pinion angle (now about 3 degrees below driveshaft), I can't for certain say it's the weight or stiffness of the skid vs just blindly stumbling my way into the right combination of angles...but if the vibes are gone at least up to 75, I'll take it. If they're gone up to 80, I'll buy lunch for the first forum member that's had this issue that finds themselves in the same metropolitan statistical area with me.
Congratulations! I love it!

That skid plate has been on my wish list. However, after enjoying a couple of days of highway driving with my front driveshaft out (which makes the vibes go away), I gave in and ordered locking hubs.

Wish me luck with that upgrade!
 
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Congratulations! I love it!

That skid plate has been on my wish list. However, after enjoying a couple of days of highway driving with my front driveshaft out (which makes the vibes go away), I gave in and ordered locking hubs.

Wish me luck with that upgrade!

if your vibes go away without the front shaft, I think the hub kit is the right way to go. Mine were still there with only the rear shaft...the only different the front shaft made was making them a little more intense and moving the onset from 70 to 67mph.

To be honest, I was kindof excited about the idea of having locking hubs. It would allow me to use a lunchbox locker up front instead of a selectable, and would let me have low range in 2WD when I'm stuck in traffic and would like to just idle along.
 
Just randomly discovered this thread so put it on WATCH. Yup, a new victim of 5.13 regear and the cycling vibe.. first I heard of it, naturally, other than when driving it the other day; didn't know it was a 'thing'.
Gonna read the whole thread and give it all a shot, step by step. So far lots of what I've seen makes sense. All I know for sure is the shop put new u-joints in both driveshafts along with gears and axles. And mine is manual transmission. Definitely the vibration (like a heartbeat) that Chris describes in post #1.

All prior to the regear and no vibrations noticed:

Tummy Tuck
1.25" BL
MML
5" lift.
 
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Yeah, you can add me to the list too. I re-geared to 4:88s, and that's when I felt it. It's worse with a hard top. I read through this as well, I did everything the previous people on this thread like chasing pinion angles, balance wheels, and wheel bearings. I couldn't drive it over 65 without a precessing vibration. I took off my front driveshaft and it went away. I Could take it up to 75 no issues. So I had the front driveshaft rebuilt by a driveshaft shop. They said it was slightly imbalanced. Stuck it back on and it was back. I ended up dropping 1300$ on the Yukon manual hubs. That was painful but I Haven't had a problem since.
 
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Yeah, you can add me to the list too. I re-geared to 4:88s, and that's when I felt it. It's worse with a hard top. I read through this as well, I did everything the previous people on this thread like chasing pinion angles, balance wheels, and wheel bearings. I couldn't drive it over 65 without a precessing vibration. I took off my front driveshaft and it went away. I Could take it up to 75 no issues. So I had the front driveshaft rebuilt by a driveshaft shop. They said it was slightly imbalanced. Stuck it back on and it was back. I ended up dropping 1300$ on the Yukon manual hubs. That was painful but I Haven't had a problem since.
I LOVE the hubs on my XJ and had pondered doing them on the LJ until I saw the price tag these days (upwards of $2k I've read here). But, if after experimentation, first up will be drop the front DS, I'll spend the coin and get it done.
Of course, I have to be part of the outlier group sporting the 6spd that 'less likely' to have this experience. :cautious:
It IS good to hear that hubs might be the cure.
 
Just randomly discovered this thread so put it on WATCH. Yup, a new victim of 5.13 regear and the cycling vibe.. first I heard of it, naturally, other than when driving it the other day; didn't know it was a 'thing'.
Gonna read the whole thread and give it all a shot, step by step. So far lots of what I've seen makes sense. All I know for sure is the shop put new u-joints in both driveshafts along with gears and axles. And mine is manual transmission. Definitely the vibration (like a heartbeat) that Chris describes in post #1.

All prior to the regear and no vibrations noticed:

Tummy Tuck
1.25" BL
MML
5" lift.

bummer. pull the front shaft and see if it goes away. I just disconnected the axle end and hung it from the frame with a bungee cord and went for a test drive.
 
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bummer. pull the front shaft and see if it goes away. I just disconnected the axle end and hung it from the frame with a bungee cord and went for a test drive.
I'm in the middle of my Locker switch install and was going to move on to rear LCA skids but now DS drop is first up. I read the whole thread, skipping some of the more technical stuff you guys have gone through :oops: - impressive.
I'd (somewhat) gladly spring for lockout hubs to avoid all the tweaking you've gone through.. if only I'm that lucky.

If vibes are gone with the front DS out do you suppose first step might be getting the DS checked/re-balanced, then consider hubs? Naturally, I'll be picking brains for the 'go-to' hub kit.

After noticing the throbbing vibes, I had been thinking about things that were different than before the gear swap. All I could come up with, before finding this thread, was the Centramatics on all 4 so thought of pulling them off to test.
 
Hope it's your front DS 60. If it's the rear, all is lost. :(
My normal would be - I ain't that lucky. 50/50 generally gets me 80% chance of a negative outcome. Glass half empty - nope - lots of experience.

So, is this just an irritant or is shit gonna come undone one day? I'll test this afternoon and document, but my recollection is the hum was at 60mph, the normal speed driving home from town. And with 5.13 my intended cruise speed was gonna be 65.
My wife was with me so I kept my mouth shut but I got a little squeamish.

An aside: my installer said that "Motive gears might be noisier than RGA". I didn't pursue it at the time for a description of the noise of which he spoke. :rolleyes:
 
Will the 15/16" BBK and it's new knuckles matter with my choice of hub kits? Please say no.

Jumping the gun, but could this be it:

https://www.4wheelparts.com/p/yukon...g-hub-conversion-kit-yawu-07/_/R-FDHC-YAWU-07
With the BBK, you'll need Blaine to do some work for you to make the hub kit work, I think. After 2+ years chasing my tail on this, I've succumbed to it being a minor irritant anything above 60 mph. Like you said earlier, the hard top makes it worse. I've tried Noico on the entire tub floor, but haven't tried sound deadening the hardtop yet. It's barely noticeable with the soft top, or no top, but I can still feel it just a little in the seat. I've had the rear pinion anywhere from +4* high to -4* low, and everything in between. Made an adjustment yesterday just for shits-n-giggles and brought it from it's current -3* to -2.5*. I can't even tell anymore if it's changed or not anymore.
 
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With the BBK, you'll need Blaine to do some work for you to make the hub kit work, I think.
I'll wait for my test results to ask Blaine about that. For S&G I posted the question at 4WheelParts just now. Asked if I could forgo the complete kit since all my junk upfront is brand new (knuckles, etc.).

I'm thankful you guys did all this testing, I'm afraid I'd get lost in the wash of all the tweaks that have been tried, not withstanding the math.
I did the Hotheads floor liner and Bedrug right at the jump after buying the LJ and still feel/hear the vibe. Have yet to do the hardtop liner and might not, since I plan to go topless in summer and no long hauls expected.
 
But, if after experimentation, first up will be drop the front DS, I'll spend the coin and get it done.
If vibes go away with the front shaft removed that absolutely does not isolate the problem to the front shaft. It is very common for either the front or rear shaft to eliminate the vibes. Don't get excited when removing the front shaft kills the vibes, it could mean the shaft is out of balance but it could also mean the front and rear are working together which is what this is really all about.
 
If vibes go away with the front shaft removed that absolutely does not isolate the problem to the front shaft. It is very common for either the front or rear shaft to eliminate the vibes. Don't get excited when removing the front shaft kills the vibes, it could mean the shaft is out of balance but it could also mean the front and rear are working together which is what this is really all about.
So noted. Will haul it to the shop for balance as a first step I guess.
 
Are the vibrations damaging components? This question is vague, but has anyone seen driveline failure due to the increased driveline speed from re-gearing?
I have the re-gear vibrations that stop when I disconnect the front driveshaft. They start around 44mph, they are not terrible, but annoying. It comes on and off in about a 2 second cycle. The thread (link below) I believe applies to my cycling vibrations is the resonance theory, two shafts rotating at high-speed, cycle to the same frequency and convey the vibration into the vehicle frame. I have tried most of the suggestions to reduce it, but I am resigned to the fact I will need to install front hub disconnects. A big chunk of money not in the immediate Jeep budget.
2004 LJ Sport, auto, soft top, 5.13, 33 inch tires, Savvy TT.

Cheers
Steve

Here are a couple links to other threads-
https://wranglertjforum.com/threads/harmonic-vibrations-in-jeeps-a-new-theory-please-read.15144/https://wranglertjforum.com/threads...tions-after-re-gear-thread.32445/#post-691701
 
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I don't think you're far off, but I suspect it's the rear. We don't seem to hear of this happening on 97-02 rigs (rarely enough that when it happens is could very well be a completely different mechanism), which had a T case skid with an asymmetrical bolt pattern. I've been wondering if the back half of the frame is acting like a tuning fork and 03-06 get the oscillations because the two sides are the same length and vibrating at very similar frequency, whereas the older models had more separation.

If my 1/4" steel skid doesn't dampen any of it out, I may bolt some weight onto one side of the back half, and if that works, I might leave it or i might start thinking about moving the passenger side rear skid nutsert a couple inches forward.

With the 1/4" steel skid moving my vibes up into the mid 70s mph range, I only get up fast enough to hit the vibes about once a month, but I'd still like to solve it if I can, and my next move is to test out my tuning fork theory.

The theory goes that the distance between the rearmost transfer case skid bolt and the next constraint, which would be the next crossmember back, is the same on both sides. This was not the case in 97-02 models because the skid was asymmetrical, putting the rearmost passenger side bolt 3" forward of the driver side. I'm curious if those frame sections are vibrating at a similar, but not quite identical frequency, causing the pulsing interference pattern.

I'm going to make a weight I can bolt on to that frame section. I need to measure the thickness of the frame to finalize the weight but I want to make it approximately equal to 3" of frame length. The frame seems to be roughly 4" tall by 2.25" wide, so that adds up to about 37.5 square inches of bar or sheet of whatever thickness the frame is. As an example, if the frame was 1/8" thick, that would be about 21 ounces.
 
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With the 1/4" steel skid moving my vibes up into the mid 70s mph range, I only get up fast enough to hit the vibes about once a month, but I'd still like to solve it if I can, and my next move is to test out my tuning fork theory.

The theory goes that the distance between the rearmost transfer case skid bolt and the next constraint, which would be the next crossmember back, is the same on both sides. This was not the case in 97-02 models because the skid was asymmetrical, putting the rearmost passenger side bolt 3" forward of the driver side. I'm curious if those frame sections are vibrating at a similar, but not quite identical frequency, causing the pulsing interference pattern.

I'm going to make a weight I can bolt on to that frame section. I need to measure the thickness of the frame to finalize the weight but I want to make it approximately equal to 3" of frame length. The frame seems to be roughly 4" tall by 2.25" wide, so that adds up to about 37.5 square inches of bar or sheet of whatever thickness the frame is. As an example, if the frame was 1/8" thick, that would be about 21 ounces.
Sure glad you're here to do the scientific stuff. I'll be standing by.;)

Is this most common in TJ or TJUR or no difference?