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

[freedom_in_4low]

f the weight of the rubicrawler was an issue, a smaller weight anywhere near the transfer case will probably shift the vibes, especially if it is hung outboard in some fashion like on the side. If I was looking for a place to stick a weight I'd probably attach it to the rear side of the transfer case opposite the front yoke.

Balance wheels on the rear transfer case output did randomly appear on TJs and newer Jeeps did get a totally different front shaft design. These things might point to a more difficult to solve resonance issue especially considering Jeep is now going to be offering 4.88 gears for the first time only after including a disconnect for the front shaft from the factory. It all could just be coincidence.

Yeah. Key to point out that it didn't get rid of it entirely for him, it just got it to where it was smooth with the front shaft out and cleared the way for hubs to fix it. If it was a matter of rigidity or the resonant frequency of the powertrain assembly, I think it would have gone away entirely, but the fact that it just made it so it took both shafts to cause it instead of just one is what makes me think it's just the extra mass reducing the amplitude of the vibration in the powertrain assembly before it hits the frame and tub. I'll have to crawl under there and spend some time brainstorming on the best way to attach weight to the transfer case. Mine is barely more than 1 pound so I don't think it'll do anything there. Also the mounting needs to be pretty rigid so the transfer case can't vibrate within the mount while the extra mass hangs stationary in space. I might rig something up out of angle iron to mount to two of the case half bolts and bolt weight onto that so I can tinker with the amounts.

 

[freedom_in_4low]

Balance wheels on the rear transfer case output did randomly appear on TJs and newer Jeeps did get a totally different front shaft design. These things might point to a more difficult to solve resonance issue especially considering Jeep is now going to be offering 4.88 gears for the first time only after including a disconnect for the front shaft from the factory. It all could just be coincidence.

were those balancers random? I just assumed it was universal on 2003-2006 models. My 05 and 06 LJ's both had one. I've often wished there was some way for me to put it back on with my JB SS SYE.

That disconnect is on the long side axle shaft, right, or is it actually on the front driveshaft? I haven't been through the options but I assume those 4.88 gears are in a Rubicon with a selectable locker? If those gears came with an open or LSD differential, it might be entertaining to watch people learn that installing a lunchbox locker defeats the CAD, at least in the sense that the short side axle shaft will still drive the carrier and the driveshaft back through the locker. Before I installed my Torq locker I thought about un-deleting the CAD in my HP30 and converting it to a cable shifter, as an alternative to buying hubs, but in the end I decided against it because then I'd have had to go to a selectable locker instead of a lunchbox, and the cost would have ended up at least the same, if not more, plus then I'd be subjecting an OEM axle shaft with an already weak disconnect mechanism to 35's and a locker.

 

[pagrey]

That disconnect is on the long side axle shaft, right, or is it actually on the front driveshaft?

Does it matter?

 

[freedom_in_4low]

Does it matter?

Not for us, I'm just curious because historically it's been on the axle shaft. (and as I described, it would matter if somebody installed a lunchbox locker). The driveshaft seems less failure prone because it's 1/4.88th of the torque seen by the axle shaft, but a completely different set of packaging challenges.

 

[eastbloc]

I have successfully got rid of my harmonic vibes... but i don't know what made the difference.
At the same time a new rear axle, rear ds and larger tires were installed.
I don't recall success stories of new drive shafts alone solving this issues, so maybe going from 31.5s to 33's reduced ds rotation enough to not trigger it?
Alternatively, if new rear axle was the solution, there is something about old axles and new gears that does not play well together. But how does that explain effectiveness of front locking hubs, or when engagement of 4wd eliminates the vibration?

 

[NOTNSUV]

I'm likely one of few with vibes after re-gear, which were pronounced and nasty, that were eliminated with the (aftermarket) front driveline re-balance. Afterwards was smooth as a baby's bottom with and without the driveshaft with no discernable difference. Even had a pal, who'd never been in my LJ with me for both identical test runs up to 75mph (that I'll never need). He felt/heard nothing.
Returned the unopened Yukon hub kit, saving me the hassle of adjusting wheel backspacing, spacers, etc, etc.
Gonna have the shop check the rear DL for shits & giggles.. why not.

 

[jengland03]

I have an 06 LJ Rubicon. Vibration issues started after regearing to 5.38s. I have noticed that my vibrations essentially disappear when I run the Jeep in 4wd. Vibrations also disappear when I remove the rear drive shaft and drive the Jeep in 4wd. The common factor between both scenarios appears to be applying load to the front drive. Has anyone else attempted to run their jeep in 4wd at highway speeds? Can anyone explain why loading the front drive shaft could cause the vibrations to disappear?

 

[eastbloc]

I have an 06 LJ Rubicon. Vibration issues started after regearing to 5.38s. I have noticed that my vibrations essentially disappear when I run the Jeep in 4wd. Vibrations also disappear when I remove the rear drive shaft and drive the Jeep in 4wd. The common factor between both scenarios appears to be applying load to the front drive. Has anyone else attempted to run their jeep in 4wd at highway speeds? Can anyone explain why loading the front drive shaft could cause the vibrations to disappear?

You are experiencing a typical behavior that many of us have as well.
Why? We have pages and pages of theories on this, but no definite explanation or the solution that would lead to a resolution that can be applied to most of the cases. This is a rabbit hole that you will have to crawl your way through.

Start by playing with pinion angles on front and rear, 2 degrees up and down. Keep in mind that front is typically tolerable to bad angles in both directions, while rear will act up fast when you go above drive shaft. Vibration will change from severe to moderate and from constant to pulsating, Don't give it too much thought, just play with it to see if it goes away or gets better. Take notes, it will get frustrating and confusing fast.

Checking your DSs for balance at local shop is around $100, it is fast and may reveal some imperfections. You have to understand that now your DS is spinning much faster, little imperfections that were tolerable are now pushing things out of whack. If local shop can do high rpm balance, ask for it, but many don't have machines to do that.
Also, check if your front DS has play in TC output, over time a bearing in there wears out and results in a play. By it self it may not cause anything, but when everything adds up, like gear setup that produce specific vibe frequency along with a bit of play in the DS and TC output...

If a shop did your gears, come back and tell them about it. A mechanic explained to me that there is a way to set up gears to accommodate for when vibration happens under load or off load, while still being withing specs of proper set up. I don't know the extent of validity of that statement, im sure experienced guys can validate or debunk it. But, i have heard of shops redoing the job because of regearing vibes.

Welcome to the forum and post regear vibes club !

 

[fuse]

I have run my Jeep at highway speed both in 4WD with both driveshafts, and with the rear driveshaft removed. I wouldn't recommend that you do it on a regular basis, but it should be fine if you want to do it for a few minutes to test things out.

As for how this might affect your particular situation, all I can say is that my vibration symptoms were different. Removing my front driveshaft made my vibrations go away. As @eastbloc said, keep experimenting with things until you find something that works.

 

[jengland03]

I have run my Jeep at highway speed both in 4WD with both driveshafts, and with the rear driveshaft removed. I wouldn't recommend that you do it on a regular basis, but it should be fine if you want to do it for a few minutes to test things out.

As for how this might affect your particular situation, all I can say is that my vibration symptoms were different. Removing my front driveshaft made my vibrations go away. As @eastbloc said, keep experimenting with things until you find something that works.

Maybe I was not clear in my original post. I have already experimented with both scenarios (running the jeep in 4wd with both drive shafts in, with the rear drive shaft removed, and with the front removed). In all cases the vibrations were essentially gone. Did you notice any reduction in vibration when you ran your jeep in 4wd with both drive shafts installed?

I have been dealing with these vibrations for a long time. I have done a fair amount of research on this issue over the last few years. I doubt there are many threads that I haven't skimmed some point. I have tried the common proposed solutions (new/balanced front driveshaft, played with the pinion angle, etc.) Every couple of months, I hit a google to see if anyone has discovered a magical solution.

I have known that my vibrations disappeared when the front drive shaft was removed for awhile. It wasn't until recently that I realized that the vibrations disappeared when I ran the Jeep in 4wd (both driveshafts installed). Its been awhile since I have read every post I could find on this topic in its entirety, but I do not recall anyone discussing the vibrations disappearing while running the jeep in 4wd (both driveshafts installed). I hoped that someone educated in the field of mechanics/vibrations/sound waves/resonance etc. would see this and make sense of why putting the front drive shaft "under load" causes the vibrations to go away.

 

[eastbloc]

but I do not recall anyone discussing the vibrations disappearing while running the jeep in 4wd (both driveshafts installed).

It is common for vibes to go away in 4wd, drives like butter as if nothing was ever there.
No explanation, only guessing and hypothesis based on testing data.

 

[JMT]

Maybe I was not clear in my original post. I have already experimented with both scenarios (running the jeep in 4wd with both drive shafts in, with the rear drive shaft removed, and with the front removed). In all cases the vibrations were essentially gone. Did you notice any reduction in vibration when you ran your jeep in 4wd with both drive shafts installed?

I have been dealing with these vibrations for a long time. I have done a fair amount of research on this issue over the last few years. I doubt there are many threads that I haven't skimmed some point. I have tried the common proposed solutions (new/balanced front driveshaft, played with the pinion angle, etc.) Every couple of months, I hit a google to see if anyone has discovered a magical solution.

I have known that my vibrations disappeared when the front drive shaft was removed for awhile. It wasn't until recently that I realized that the vibrations disappeared when I ran the Jeep in 4wd (both driveshafts installed). Its been awhile since I have read every post I could find on this topic in its entirety, but I do not recall anyone discussing the vibrations disappearing while running the jeep in 4wd (both driveshafts installed). I hoped that someone educated in the field of mechanics/vibrations/sound waves/resonance etc. would see this and make sense of why putting the front drive shaft "under load" causes the vibrations to go away.

Most people get oscilllating vibes at 60mph+. I don’t recall anyone running in 4H at those speeds. It might help to reveal the speeds these vibes onset. Also, what kind of vibes? Static or oscillating?

The common solution is front hubs.

As Shawn at Tom Wood’s also ponts out, driveshaft speeds over 3000rpm’s can’t be balanced for. With gearing at 5.38 that shaft will be well above that when you get somewhere in the 60+mph zone (I didn’t go do the calculation). They have a calculator on their website. I think the balance of the axle coupled with the speed of the shaft are the issue for oscillating vibes.

 

[tworley]

As Shawn at Tom Wood’s also ponts out, driveshaft speeds over 3000rpm’s can’t be balanced for. With gearing at 5.38 that shaft will be well above that when you get somewhere in the 60+mph zone (I didn’t go do the calculation). They have a calculator on their website. I think the balance of the axle coupled with the speed of the shaft are the issue for oscillating vibes.

Interesting. I get an oscillating vibe at 65+ with 5.13s. Its fairly faint and I dont think passengers can feel it, but I certainly can when behind the wheel. With that calculator my driveshaft is at 3202 RPM

 

[DickD1911]

This group is great!

Once Again, the information available is spot on for making my LJ better.
I too had driveline vibration after going to 4.88 gears with the auto trans.
I installed a set of yukon free spinning hubs and problem solved. 70mph and no vibration.

We just got back from a Jeep Jamboree in Arkansas with 1150 highway miles round trip pulling our small popup camper.
When on the trail we did all three BoH and was in 4lo for 29 miles over two days.
Then Unlocked the hubs and hit the road home with no problems.

This forum is my go to source for accurate information and advice.