Driveline Vibration

dchew

dchew

Active Member
2013 JKUR manual trans, 4.88 w/ 38” Nitto TG’s, RCV’s front, Adams 1350’s front/rear, PR44 / SF60*

I am trying to diagnose a cyclic vibration at 70+ mph. I THINK I’ve ruled out tire balancing but maybe not. It is not a constant shake/shimmy; it is cyclic, so at say 75 mph, the ride will be smooth, and then 10 seconds later it will shake like a tire is out of balance, gear shift shimmy 1-2” each way, then 10 seconds later be gone. Cycle repeats. This is not anything like death wobble; its totally drivable but annoying. History:
  • I’ve had this issue for a few years but did not drive the Jeep much during that time until this year. When I first noticed it, I assumed it was just my 37” Cooper STTPro’s that were difficult to balance.
  • Swapped tires this year to 38” Nitto Trail Grapplers. New tires balanced had the same issue.
  • Last month I put the rear end up on jack stands and ran the Jeep in 1st gear to see if I had a bent flange; couldn’t see anything. Not sure if I would see a bent flange this way?
  • Drove from Ohio to Moab late June. It bugged me enough to have the tires balanced and rotated again at Discount Tire in Grand Junction, CO. That didn’t really change the vibration even with rotating the spare in.
  • Below 70 there is no shimmy, but there is a faint, low-pitched hum/vibration that is also cyclic.
  • When I swapped the axles, I had to shorten the rear driveshaft. They were supposed to rebalance it, but maybe they didn’t or didn’t do a good job.
  • Rear pinion and driveshaft are lined up, both 8 degrees
My guesses:
  1. Have the driveshaft(s) rebalanced.
  2. Check my front CV joints. Do I just feel for play, or is there something else I should look for?
  3. Rear axle shafts?
  4. Get the whole thing up on jackstands and see if there is any vibration with/without wheels. This sounds like a bad idea and could turn into an episode of Darwinism at work.
  5. Stop driving over 70 mph.
Anything else I should investigate? I can't tell if it is front or rear.

Dave

*I know, not the best decision. At the time, I wanted to keep my Huchinson wheels and there was no FF option with 5 lugs, so…
 
I’ve got a similar vibration over 72 mph and it started when I installed the new Adams rear driveshaft. Thought it was tires so I had Discount Tire do a 5 tire rotation and didn’t change a thing. My driveshaft and pinion are within 1degree.

Under 72 mph no vibration. I almost think there is some king of harmonic natural frequency being excited above 72 mph.
 
I had a vibration that seems much like you describe. I did about everything under the sun to get rid of it. I eventually decided it was a resonance issue and found a transfer case vibration dampener they used to put on JK’s and installed it on my 2015. That cleaned it up almost completely. Just something to keep in mind.
 
I have a similar vibration on my 2008 Jk on 37 nitto TG's . I have balanced and rotated a few times and it never really solved it. I can also say that when i put the jeep on a hub dyno it was SUPER smooth. No vibration at all. We did several pulls both 2 and 4x4 . So I'm willing to bet its still your tires. 38's have a lot of mass and i bet discount only balanced them to 50 or 60 mph .


 
Take turns taking the front and rear driveshafts off and drive. I'd bet you'll notice a difference with one or the other.

I had this issue a few years ago and dissapeared my transfer case trying to do 80 in Kansas. Went through all of the rebalancing tires, driveshafts, etc. stuff but never found the issue. It was a weird harmonic noise/sound that only happened at 70 & above. I found another crack in the second case & went really in-depth with everything. What we found was when I swapped the sport tcase with the rubicon case the old yoke nuts were used instead of the rubicon versions - they are different. The rubicon has a larger shoulder and the sport nut wasn't allowing the yoke to be fully tightened. I bought 2 new nuts and the issue went away. 80 is no problem any longer.
 
Remove one driveshaft and drive your Jeep around. If the vibration goes away, that shaft is the problem.

Other things to look at is the track bar, drag link and all ball joints.
 
I have a similar vibration at around 75 ish no noise but it’s just enough to be irritating on long drives. Still haven’t found the cause. It is time for a tire rotation though.
 
Update: Drove it with no doors and I do hear a chirp, like “peepers,” those little frogs. One u joint in the front has a little of the telltale red dust (although I did just come back from Moab). On Thursday, I will take off the front driveshaft and I will replace that u joint. See where we go from there.
 
dchew said:
Update: Drove it with no doors and I do hear a chirp, like “peepers,” those little frogs. One u joint in the front has a little of the telltale red dust (although I did just come back from Moab). On Thursday, I will take off the front driveshaft and I will replace that u joint. See where we go from there.
Click to expand...

If you think you have a bent axle flange it'd be pretty easy to jack the rear up & rig up your own runout gauge to see which one it is. I'd do that before I took a driveshaft off.
And I'm very familiar with that damn chirp - I had the same SF60 rear for awhile until I got sick and tired of the F'er bending a flange every trip I went on.
 
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