The Dreaded Post-Re-Gear Vibes

[HuskerJeep]

Last week I picked up my jeep following a regear, and now I'm getting constant vibrations (not harmonic) that start around 68 MPH and intensify as I get up to 75 MPH (I haven't gone over that). Hoping that the brain trust here can provide some advice. Here is what I can tell you:

• It's a '98 on H&R 1" springs (I initially got 1.5" out of it). No other lifts. No MML.
• Control arms are brand new OEM style replacements (Crown)
• I do have cam bolts on the front, and they are maxed out as long as they'll go
• I used to have a small harmonic vibration in the high 60's MPH, but after installing my Gobi rack, that went away. My thought was that the drive line angles came into their comfort zone with the added weight. It was quite smooth at 75 MPH before the regear.
• The regear was done by a reputable shop that does a lot of Jeep work
• I went from 3.07 to 4.10 with an Eaton E-Locker in the front and a Detroit True-Trac in the rear (Dana 30-Dana 35).
• Since the vibes started, here is what I've done to troubleshoot:
  • I verified the lug nuts were torqued correctly (they were all good)
  • Lowered my transfer case about 1/2" (no change to vibes)
  • Removed front driveshaft (vibes were completely gone after doing this)
  • Thinking something may have been out of spec with the front driveshaft (I just rebuilt it a couple months ago with the Denny's kit) I took it to a driveline shop to test for balance and see if it was bent. It was out of balance, so they removed the factory weights and rebalanced it. I installed it last night and on the test drive, the vibes were still there, although it seemed like they may have started a couple mph later. Still strong at 75 MPH though.
• Here are my rear driveline angles:
  • Rear Pinion Oper angle = 1.0*
  • Rear TC Oper Angle = 0.4*
• Here are my front driveline angles:
  • Front Pinion Oper angle = 1.5*
  • Front TC Oper Angle = 2.5*

• 

• 

Questions:

• Shouldn't the front pinion be parallel to the front shaft? Seems like mine is off, but I don't get why - it's only an 1.5" lift, I'm really surprised I'm having these kinds of issues.
• Thoughts on the rear shaft angles?
• Is there anything else to check that I'm not considering? I intend to take it back to the shop at 800 miles for them to check the pattern anyway, so if I can't figure out anything by then, I'll have them check deeper too.

Thanks for the help.

 

[eastbloc]

You know about the dreaded post regear vibes that many of us ran into, how is your example different from the lengthy threads that we have on this matter?
There is a list of things you can try, past that most will say it is a wast of money, and point you directly to a locking hubs

 

[bobthetj03]

If the front ds is the culprit, you could try some adjustable uppers for the front so you can play with the pinion angle. From what I've read, the front shaft seems happier with the pinion angle slightly higher than the ds angle. Keep in mind, the drive shafts are now spinning faster with the regear. If you are doing 75, the shafts think you are doing 90, well there is a formula for that, but that is over my pay grade.

 

[HornedToad]

That is a pretty mild lift and hardly a regear. Rubicons came stock with 4.10’s. Do your drive shafts still have the original u-joints? I’m not saying this will for sure work but a rebuild of the rear driveshaft with sealed spicer u-joints totally solved some vibration issues I was having at one time.

 

[HuskerJeep]

If the front ds is the culprit, you could try some adjustable uppers for the front so you can play with the pinion angle. From what I've read, the front shaft seems happier with the pinion angle slightly higher than the ds angle. Keep in mind, the drive shafts are now spinning faster with the regear. If you are doing 75, the shafts think you are doing 90, well there is a formula for that, but that is over my pay grade.

Thanks Bob, appreciate the response - It may come to that; at this point I'm still trying to determine if it is indeed angle related, or if there could be something else going on. Does 1.5* of operating angle on the front pinion seem high to you? I know you've worked though yours quite a bit. Just how parallel does that need to be?

That is a pretty mild lift and hardly a regear. Rubicons came stock with 4.10’s. Do your drive shafts still have the original u-joints? I’m not saying this will for sure work but a rebuild of the rear driveshaft with sealed spicer u-joints totally solved some vibration issues I was having at one time.

I agree, the mild lift and mild regear were intentional in an attempt to avoid these issues. Seems to me there may be something else going on since the angles are so close to stock in the first place. On the rear shaft - I recently replaced those u-joints with the Spicer sealed units as well.

 

[HuskerJeep]

To adjust the front pinion - if I’m only going to have 1 set of adjustable arms, is it better to adjust upper or lower? Seems like my pinion needs to point down more, so the lowers seem to make more sense in my head.

And yes, I know it’s best to have both.

 

[eastbloc]

@L J
What is thumb down for?
Other than measuring angles, I still don't understand to what extent OP went to alleviate the issue.

 

[Rob L.]

@L J
What is thumb down for?
Other than measuring angles, I still don't understand to what extent OP went to alleviate the issue.

I think @L J was referring to the overall non-helpful nature of your reply or the condescending tone.

My opinion is it's both

 

[HuskerJeep]

Some follow-up here, and hoping for some advice.

In a nutshell, I'm experiencing a steady vibration starting at 70 MPH following a regear. I've had both front & rear driveshafts balanced and removing the front shaft completely eliminates the vibration.

No transfer case drop - I feel like the next logical place to focus in the front pinion angle. I re-measured and am getting 6.6* on the flat spot on the front of the housing, and 3.9* on the driveshaft (pinion pointed up compared to shaft). That gives me a working angle of 2.7* - and this should be close to 0*, or maybe 0.5* high (correct?).

So my question to you guys - am I missing something thinking that my next course of action is to get some adjustable arms and adjust the pinion down?

 

[Dino76033]

I have the same issue after putting in 5:13’s. I pulled my front drive shaft and it went away completely so I ordered a new Tom Woods shaft. Installed the new drive shaft and it still vibes. I have decided to do lock outs and be done with it.

 

[97JadeTJ]

Same scenario here… no vibes before regear, vibes after… no vibes with front ds removed… I’m going to try a 1” tc drop hopefully this weekend… vibes start at approx 60mph..

 

[HuskerJeep]

I have the same issue after putting in 5:13’s. I pulled my front drive shaft and it went away completely so I ordered a new Tom Woods shaft. Installed the new drive shaft and it still vibes. I have decided to do lock outs and be done with it.

Same scenario here… no vibes before regear, vibes after… no vibes with front ds removed… I’m going to try a 1” tc drop hopefully this weekend… vibes start at approx 60mph..

What are your front pinion operating angles? I think mine should be fine, but it's 2.7* with the pinion pointed up and from what I've read, that should be closer to 0.5* to 1*.

I know others are working through similar issues, so I'm just spit-balling on commonalities.

 

[HuskerJeep]

Problem Solved!!

For those who read this later - my issue was that the nut on the front output yoke on the transfer case was not torqued properly and was allowing some up/down movement. I posted a couple videos in this thread: https://wranglertjforum.com/threads/up-and-down-play-on-front-transfer-case-yoke.54815/#post-956884

Thanks for all the help and answering my questions for those of you who took the time and helped with some ideas.