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

[fuse]

CPI #1: I've swapped out all control arms with MC arms, and IMO the DF bushings are as soft, or maybe softer than factory Clevites. At one point I had Currie lowers and factory Clevite uppers. Switching to the MC arms made little to no difference.

I'm running clevite bushings in the axle ends of my LCA's.

Good to know. Now I can scratch that one off the list and save the trouble of messing around with stock control arms.

CPI #2: Adding a MML (Motor Mount Lift) (Motor Mount Lift) made the biggest gains for my particular rainbow unicorn problem. I've since dropped the t-case skid 1/4" at a time with washer down to 3/4" drop with no perceivable gains, adjusting the pinion angle at each change. I've changed the pinion angle all over the place with no luck.

Thanks for the confirmation. That makes me think I don't need to spend any time on this either. I've been through the full range of pinion angles too. I can make the vibrations worse, but not any better than they are now.

 

[bobthetj03]

Good to know. Now I can scratch that one off the list and save the trouble of messing around with stock control arms.


Thanks for the confirmation. That makes me think I don't need to spend any time on this either. I've been through the full range of pinion angles too. I can make the vibrations worse, but not any better than they are now.

Pretty much where I'm at.

 

[1515art]

Initially I’d thought I managed to dodge the vibration bullet on my regearing, but no after sorting out all the other problems I had a definite vibration on both front and back axels. After installing the manual front hub conversion kit my vibration in the front was solved but I was having trouble getting consistent measurement with my digital angle finger off the round driveshaft and round surface of the axel housing at the rear pinion every slight difference in alignment in every direction affecting the reading between the housing and driveshaft measurement.

I tried several different approaches to solve this and finally I used adhesive to attach half of a pvc collar to the bottom of the angle finder and a string level to the end of the angle finder allowing consistent alignment along the housing and driveshaft and degree of level between the top angle measurements, this addition gave me very consistent numbers as I made small adjustments to the driveshaft angle. The addition of the rare earth magnet holds everything solidly in place.

I’m not sure what method others are using to get consistency but if you are having difficulty this worked well for me.

 

[Alex01]

Initially I’d thought I managed to dodge the vibration bullet on my regearing, but no after sorting out all the other problems I had a definite vibration on both front and back axels. After installing the manual front hub conversion kit my vibration in the front was solved but I was having trouble getting consistent measurement with my digital angle finger off the round driveshaft and round surface of the axel housing at the rear pinion every slight difference in alignment in every direction affecting the reading between the housing and driveshaft measurement.

I tried several different approaches to solve this and finally I used adhesive to attach half of a pvc collar to the bottom of the angle finder and a string level to the end of the angle finder allowing consistent alignment along the housing and driveshaft and degree of level between the top angle measurements, this addition gave me very consistent numbers as I made small adjustments to the driveshaft angle. The addition of the rare earth magnet holds everything solidly in place.

I’m not sure what method others are using to get consistency but if you are having difficulty this worked well for me.
View attachment 223301View attachment 223302View attachment 223303

Smart idea, time to sign up for shark tank. I'd buy one.

 

[Pcleaners2]

My vibes are present no matter what gear I'm in, or no gear at all. I can ramp it up to 70mph going down hill put it in neutral, let out the clutch and there is no change. I'll be doing some more testing in a few weeks when I put the hard top back on for winter. Too noisy with the soft top to test.

Tom woods makes a fatter front driveshaft that is supposed to cure this. I get it today. It’s a 2.5” as opposed to 2” diameter. Something about being too long and skinny. Also has to do with the critical mass. This may require me to bend the down pipe a bit bc may hit with articulation. We’ll see what happens tonight. My symptoms exactly mirror @bobthetj03. Here goes nothing ...

 

[Pcleaners2]

It helped some but didn’t eliminate . Vibes at around 72-73 mph better than 69-70.
I guess I’ll take what I can get ...!

if I could get it to where the vibes start at 80 I’d be happy

 

[freedom_in_4low]

Tom woods makes a fatter front driveshaft that is supposed to cure this. I get it today. It’s a 2.5” as opposed to 2” diameter. Something about being too long and skinny. Also has to do with the critical mass. This may require me to bend the down pipe a bit bc may hit with articulation. We’ll see what happens tonight. My symptoms exactly mirror @bobthetj03. Here goes nothing ...

I wonder if this might be related to the vibes I'm getting with the TW rear shaft I had lengthened by a local shop to use on my LJ.

Before:

After:

I hadn't really even considered that the diameter would play into anything beyond how much torque it could transmit without twisting. But it does seem to have a skinny looking "aspect ratio" looking at it. I think I'm gonna give TW a call and see if adding 10" to an 18-3/8" shaft that spins 4000rpm @ 75mph would have invited a recommendation to replace it with a larger tube.

Mine is giving me the pulses without even having a front driveshaft installed. Happens accel, coast, decel, neutral, clutch in, regardless of engine speed, just starting to be perceptible at 65 and going pretty good by 75. This is with 32/4.88/6 speed, so 75mph corresponds to 3377rpm at the engine and 4020rpm at the shaft. I've been wanting to pull it and test with just a front shaft but having 4.56 in the front instead of 4.88 would not have made a valid comparison (hence not having the front shaft installed). I just dropped it off at the shop this morning to get the front regeared so I hope to get some testing with the front shaft later this week.

 

[bobthetj03]

I wonder if this might be related to the vibes I'm getting with the TW rear shaft I had lengthened by a local shop to use on my LJ.

Before:
View attachment 228367

After:

View attachment 228364

I hadn't really even considered that the diameter would play into anything beyond how much torque it could transmit without twisting. But it does seem to have a skinny looking "aspect ratio" looking at it. I think I'm gonna give TW a call and see if adding 10" to an 18-3/8" shaft that spins 4000rpm @ 75mph would have invited a recommendation to replace it with a larger tube.

Mine is giving me the pulses without even having a front driveshaft installed. Happens accel, coast, decel, neutral, clutch in, regardless of engine speed, just starting to be perceptible at 65 and going pretty good by 75. This is with 32/4.88/6 speed, so 75mph corresponds to 3377rpm at the engine and 4020rpm at the shaft. I've been wanting to pull it and test with just a front shaft but having 4.56 in the front instead of 4.88 would not have made a valid comparison (hence not having the front shaft installed). I just dropped it off at the shop this morning to get the front regeared so I hope to get some testing with the front shaft later this week.

Similar scenario with my TJ. I've been thru 4 different rear drive shafts. 70 mph and up I get a pretty good butt massage.

 

[freedom_in_4low]

There are some free apps available on Android that might be useful for investigations. They might be on Apple too, but I have no idea.

View attachment 194791

This one uses the accelerometers in your phone to measure vibration and give you a plot of level vs. frequency. If you have harmonic vibrations, this might help you dial in their frequency.

View attachment 194792

This one does basically the same thing, but uses the microphone to capture airborne sound. It has a live display that you can pause to capture the spectrum at a moment in time and look for frequency spikes created by any pure tones or harmonics. This could be useful if you can hear certain tones when the vibes happen.

This is an interesting topic to me since 1) I just developed vibes after re-gearing and 2) I work in noise and acoustics. I'm a long way from an NVH engineer though. My work is all related to buildings and environmental noise and vibration, but the same physics and instrumentation applies.

I actually did some experimentation with these apps this weekend. The Spectrum Analyzer I haven't really figured out how to interpret. I generally get how the graphic works, but I can't point to anything obvious that corresponds to what I'm hearing. The left half is at 75mph, then I paused recording, and finished at 65mph. Other than that lower band at 65mph just looking less noisy in general, I'm not sure I can match the visual to what I'm hearing. There is a somewhat defined line that shows p better on the right half that seemed to correspond to engine speed as it would shift up and down. But since my noise is pretty dominant to the rest of the noises I'm hearing, I would have expected a more defined line to show up to represent that on the left side.

I got some pretty interesting results from the Vibration Isolator just setting it on top of my center console lid. This was at ~65mph, where my pulsing vibration just barely becomes perceptible.

The 60Hz peaks correspond with my estimated driveshaft speed at 67.2mph and I was just going off the speedometer needle, so that's probably what that is. Not sure which one is ACTUALLY the shaft or why there's 2 peaks so close together (maybe my vehicle speed changed that much while recording the sample and it just recorded both?) No idea what 20.43Hz is, 'cause between the engine, shaft, and axle there's nothing that lines up cleanly with that. It's comparatively low acceleration and it doesn't make the top 3 at the speeds I'm concerned about so I'm just gonna let it go.

The 75mph one is interesting. The 67.38Hz peak again lines up with the driveshaft speed at 75.4mph. It's curious that it recorded less acceleration at 75mph than 65mph. What's also curious is the much larger peak that shows up at 13.67Hz...which is equal to 67.38Hz divided by 4.92...implying that it's pretty close to wheel rpm resulting from my 4.88 gears.

 

[Pcleaners2]

Yeah it didn’t change mine too
Much getting the fatter shaft
. They did it for free so was worth a shot
Next thing is maybe I’ll just use 35 in tires since I have the 4.88. Less revolutions maybe won’t vibrate until 80mph ?

 

[freedom_in_4low]

Yeah it didn’t change mine too
Much getting the fatter shaft
. They did it for free so was worth a shot
Next thing is maybe I’ll just use 35 in tires since I have the 4.88. Less revolutions maybe won’t vibrate until 80mph ?

That's the one bit of comfort I have about this, is that when I get 35's installed, my current 65mph will move up to 71mph, and my current 75mph will move up to 82mph, which I very rarely get to (and usually not on purpose).

 

[freedom_in_4low]

Similar scenario with my TJ. I've been thru 4 different rear drive shafts. 70 mph and up I get a pretty good butt massage.

I'm sure by this point you've considered this...but is there anything in particular stopping you from just buying another TJ and swapping your whole build over to it? I think I'd reach that point having gone through everything you have trying to get rid of it.

 

[bobthetj03]

I'm sure by this point you've considered this...but is there anything in particular stopping you from just buying another TJ and swapping your whole build over to it? I think I'd reach that point having gone through everything you have trying to get rid of it.

It's crossed my mind more than once. With all that I have invested in this one it would be hard to recoop. For now the vibes are tolerable enough to not drive me completely batshit crazy, so I'm living with it. Might make a call to Denny's Driveshafts and pick his brain a little. I hear they balance their drive shafts to a higher RPM than TW and Adams. The ds diameter has me thinking too.

 

[freedom_in_4low]

It's crossed my mind more than once. With all that I have invested in this one it would be hard to recoop. For now the vibes are tolerable enough to not drive me completely batshit crazy, so I'm living with it. Might make a call to Denny's Driveshafts and pick his brain a little. I hear they balance their drive shafts to a higher RPM than TW and Adams. The ds diameter has me thinking too.

having just moved my build from a TJ to an LJ, I can attest to it being a ton of work. And there will be things that don't swap very well, are infuriating to undo because they don't feel worth the effort (motor mount lift), and modifications that aren't easily reversed (like drilled out track bar mounts or holes in the tub to mount sliders).

I'm currently dealing with driveline vibes on both of my rigs. I didn't remove the MML from the TJ because it was too much work for $60, but with only 1.5" suspension lift and stock control arms my pinion is 1/2-1 degree too high so I'm probably going to have to pull the motor mount lift and possibly put in a small transfer case drop instead before I feel good about selling it to someone.

 

[Pcleaners2]

having just moved my build from a TJ to an LJ, I can attest to it being a ton of work. And there will be things that don't swap very well, are infuriating to undo because they don't feel worth the effort (motor mount lift), and modifications that aren't easily reversed (like drilled out track bar mounts or holes in the tub to mount sliders).

I'm currently dealing with driveline vibes on both of my rigs. I didn't remove the MML from the TJ because it was too much work for $60, but with only 1.5" suspension lift and stock control arms my pinion is 1/2-1 degree too high so I'm probably going to have to pull the motor mount lift and possibly put in a small transfer case drop instead before I feel good about selling it to someone.

For now I can go 70 and be comfortable until at about 72 I feel them again. Not sure this is worth any extra time anymore at this point

 

[bobthetj03]

For now I can go 70 and be comfortable until at about 72 I feel them again. Not sure this is worth any extra time anymore at this point

Kinda how I'm feeling. I've invested so much time and money into it, I'm just fed up with it all.

 

[fuse]

It helped some but didn’t eliminate . Vibes at around 72-73 mph better than 69-70.
I guess I’ll take what I can get ...!

if I could get it to where the vibes start at 80 I’d be happy

Every little bit helps.

I've been through my whole driveline from transmission to the ground and managed to squeeze out enough in incremental gains to get from 50 to 65 before the vibrations start.

For now I can go 70 and be comfortable until at about 72 I feel them again. Not sure this is worth any extra time anymore at this point

Yep.

I spent 14 hours on the highway this weekend and just pulled the front driveshaft for the trip and put it back in before hitting the trails. No driveline issues even up to 80, although that was literally downhill with a tailwind. For 15 minutes under the Jeep, I can make the problem go away if I need to.

 

[freedom_in_4low]

So this is bizarre to me. I've been driving with no front shaft since I regeared my rear axle and just had my front done and picked it up today. It still has no front shaft installed but the harmonics are different. They're louder, more intense, and more defined now that the axles match, even though in either case no front shaft is installed. It also becomes apparent in the 60-65 range and disappears around 80.

The spectrum analyzer app showed me a well defined peak that I could actually watch shrink and grow with the harmonic oscillation, which peaks about every 2 seconds, implying 2 sources that are 1/2 Hz or 30rpm apart.

I think the app must have a 5hz resolution or be broken down into bands because I could speed up and slow down enough for the peak to move to 59hz or speed up enough to show 69hz but it wouldn't show in between.

The vibration app is more precise though.

67.33hz corresponds really well to my driveshaft speed at 75mph.

So my next step is going to be getting a new front shaft so I can test without the rear, and if it goes away I'm probably going to have TW rebalance my rear shaft.

 

[fuse]

So this is bizarre to me. I've been driving with no front shaft since I regeared my rear axle and just had my front done and picked it up today. It still has no front shaft installed but the harmonics are different. They're louder, more intense, and more defined now that the axles match, even though in either case no front shaft is installed. It also becomes apparent in the 60-65 range and disappears around 80.

I don't have an explanation for it, but I'm not surprised that regearing the front axle makes a difference. I noticed differences in vibrations when I swapped in my spare front axle shafts. So it's entirely possible that the front axle contributes to the vibrations in some way.

I'll be interested to see what results you get with a new front driveshaft. When I tried using the front driveshaft alone, the vibrations were a little worse than 2HI with both shafts in. Here's hoping you have better luck!

 

[freedom_in_4low]

so I've waited because we got 19" of snow last weekend and I wanted to have 4wd, but I finally pulled the rear shaft and took it for a drive with just the front.

The oscillation is gone, and the vibration seems to need more speed to reach the same intensity, but I was still disappointed in the amount of vibration present at 75mph - not only is it audible but it's blurring my mirrors. I'm gonna call TW tomorrow morning and set up a return shipment to have them balance the rear shaft again, and before I put it back on I'm going to experiment a little with front pinion angle. I can't recall exactly but I'm running somewhere between 1 and 2° operating angle at the front u-joint with 5.5 degrees of caster, so I'm gonna take out about half a degree at a time and see if the vibration improves.