4.0, 42RLE, NP241OR High Speed Vibrations After Re-Gear to 4.88 or Deeper

I have a 06 LJ 42RLE and got harmonic vibs after regear. It starts at about 62 and is the worst at 67ish. I have 5.13 Revolution Gears, 4" Currie SA, 1"MML, 1"BL, Tummy Tuck on 35s. I have NEW CV drivelines front and rear.I have had them both rebalanced...it is not the wheels and tires. If I remove the F driveshaft no worries at all. My only issue is with the front driveline in. I have played with the pinion angles over and over again....I have check for rubbing of the drivetrain to the tub, replace the tranny mount, motor mounts are good. I have built race cars and I am supper anal, my CAs are matched to the MM, Trackbars are with in a 1/16 centered on the chassis. I have 'heard' that there is an issue with the 42RLE when both driveshafts are spinning at high speed, although some do not have our issues.....They only thing I can think of to do now is to check the trasfercase yoke for accuracy/run-out and possibly remove the MML. the MML only helps REAR driveshaft angle....it actually HURTS the F. transfercase yoke angle. F driveshaft is at 9 degrees and R driveshaft is at 13 degrees.

The only improvement that I have seen is when I remove the spare tire (weight behind the rear axle). My LJ runs a bit low in the rear as it is :( , but when I remove the spare tire (70 LBS) the LJ does not sag as much in the rear, this actually helps the F transfercase yoke angle.....and I observe less harmonic vibration at same speeds above. This helps my theory on the MML removal to help.....BUT I am so frustrated and tired of chasing this ghost and may end up with hubs as well or just turn up the tunes. FYI, my TJ has way more extreme angles on the driveshafts, a shorter rear shaft and no vibs. Another note, I don't beleive the whole tummy tuck will HELP pinion angles.....someone is going to have to explain that one to me. A Tummy tuck lifts the entire drivetrain, thus increasing the angle down to axles. When most people talk about improving driveshaft angle they are talkin about the rear......WE are talking about the front only, that is the issue here.
 
I read someplace online (that I can no longer find) that the front output bearing for the NV241OR transfer case is rated at a certain rpm and that there is a replacement bearing rated for greater rpm's. The post or article I read even had the part numbes for that bearing. I really wish I could find it now. I'm not confident that it would make any difference in the harmonic/vibration that we are experiencing after a regear to 5.13 or 5.38, but it would be something to try before giving up and/or installing manual hubs.

Has anyone else seen the article or post I am referring to? Have a link per chance?
 
My theory with the TT idea is this, the drivetrain is at a downward angle to the rear end, with the motor mounts being the fulcrum point. By raising the TC skid, you are decreasing the operating angle of the TC front input yoke. Yes, you also are increasing the angle of the rear drive shaft, but the front is the problem, not the rear. Taking the MML out will even further decrease the drivetrain angle and lower that input yoke even more. I think its the TC input that is the culprit. Drive shafts are spinning faster after re-gearing, so something has reached and exceeded a threshold. No TJ/LJ is the same, and some are more sensitive to change than others, as I've come to realize.
 
Bob, thank you for the explanation on the TT. That makes since. I forgot the motor mount is fixed and the rear rotates up with a TT. I should have thought about it more before I posted. None the less at least the rest of you have my set up as an example. Also my set up only has harmonic and not steering wheel vibration. Mine also has a lower F driveshaft angle (9 degrees) then others with this problem which is weird, I would think mine would be higher F DS anglewith the TT ???

Another issue I have, is the F Currie trackbar is hitting the front of the F stock diff cover during articulation. I assume this is because I have been going after 0 pinion angle and not caring about caster rotating the diff cover forward closer to the trackbar. Which is also interesting that Blaine would suggest the F dif angle higher then the F DS angle to get rid of vibration. Not disagreeing with the expert just curious??? Because that should reduce positive caster and decrease trackbar clearance to diff cover right ???

I had my lower F CAs (Currie) as long as possible but shorten them 3/8” due to the rubbing on the front of the F diff cover but still get a slight rub. If I can’t figure out the harmonic issue, I am going to lengthen the F lower CAs back out again (slightly helping DS angle and wheel base) set the caster (decreasing diff angle helping front diff cover clearance) and live with the harmonic for a while then consider the hubs and new wheels with 5.5 pattern for narrower track width.

I also have interference on the front sway bar links (Currie) and the tie rods (Currie )at droop ???? Still have not figured that out.
 
White Shadow 99 said:
Bob, thank you for the explanation on the TT. That makes since. I forgot the motor mount is fixed and the rear rotates up with a TT. I should have thought about it more before I posted. None the less at least the rest of you have my set up as an example. Also my set up only has harmonic and not steering wheel vibration. Mine also has a lower F driveshaft angle (9 degrees) then others with this problem which is weird, I would think mine would be higher F DS anglewith the TT ???

Another issue I have, is the F Currie trackbar is hitting the front of the F stock diff cover during articulation. I assume this is because I have been going after 0 pinion angle and not caring about caster rotating the diff cover forward closer to the trackbar. Which is also interesting that Blaine would suggest the F dif angle higher then the F DS angle to get rid of vibration. Not disagreeing with the expert just curious??? Because that should reduce positive caster and decrease trackbar clearance to diff cover right ???

I had my lower F CAs (Currie) as long as possible but shorten them 3/8” due to the rubbing on the front of the F diff cover but still get a slight rub. If I can’t figure out the harmonic issue, I am going to lengthen the F lower CAs back out again (slightly helping DS angle and wheel base) set the caster (decreasing diff angle helping front diff cover clearance) and live with the harmonic for a while then consider the hubs and new wheels with 5.5 pattern for narrower track width.

I also have interference on the front sway bar links (Currie) and the tie rods (Currie )at droop ???? Still have not figured that out.
Click to expand...

Wouldn't the TT actually lower the front DS angle? Keeping with my theory that the front input yoke will lower its angle in relation to parallel, the DS angle should lower as well. I guess it depends what is happening at the cardan joint to know for sure.
 
Just think... if we had high pinion axles to begin with, the driveline angles would be so much better :risas3:
 
Yes Chris that would be nice. I thought about going to HP Dana 30....but hard to find one in a yard that is not bent.

Bob, IMHO and going with and I agree with your theory, the TT would help F transfer case yoke angle(and/or removable of MML) but raise DS angle due to increased height relative to diff. I also think that the harmonic is potentially due to F transfer case yoke angle and the CV compensating since my/your DS angle relative to F diff pinion angle does not solve issue at 0,- or + pinion angle.
 
  • Like
Reactions: bobthetj03
@David Kishpaugh

Do you have any thoughts here of a fix other than locking hubs?

I'd like to have you regear my ride, but when I click the OD off I have harmonic vibs (in 3rd) at cruising speed.

Thank you in advance.
 
  • Like
Reactions: Chris
Anyone yank a front drive shaft and see if that stops it? Seems he was smooth when waiting on one .
 
White Shadow 99 said:
Hey Chris, maybe you can get Blaine to chime in here since he is a expert and has solved and seen many of these issues and built many, many, many jeeps.
Click to expand...

Blaine left because he was upset that I allowed Metalcloak to sponsor the ride of the month contest. I don't want to discuss that anymore than what I just said (not publicly at least), but you're right, it would be nice to have an expert opinion here.

@David Kishpaugh may or may not have some ideas.
 
There is a lot going on with these type systems where the everything moves up to the transfer case .
 
  • Like
Reactions: Chris
Okay guys, I lied... I hadn't had my Jeep up to highway speeds (60 mph and up) since having it re-geared. After taking the Jeep to @David Kishpaugh at Jeep West this past weekend, that meant I had to do about 40 miles on the highway at 70 mph the entire way.

Low and behold, the entire way I felt nothing but a vibration underneath me that kicked in right around 60 mph. This vibration was NOT there before the re-gear, so it has to be related to the re-gear, since nothing was changed other than the new gears, Revolution axle shafts, Currie steering, and that's it.

It looks like my only solution might be manual locking front hubs (does anyone still make these for the TJ?), since Dave said my driveline angles look perfect.

Seems like this is starting to become a very common issue. I just can't understand what it would be about re-gearing that would cause a vibration issue like this.

@psrivats is having the same issue with his after after his re-gear as well.
 
  • Like
Reactions: bobthetj03
Chris said:
Okay guys, I lied... I hadn't had my Jeep up to highway speeds (60 mph and up) since having it re-geared. After taking the Jeep to @David Kishpaugh at Jeep West this past weekend, that meant I had to do about 40 miles on the highway at 70 mph the entire way.

Low and behold, the entire way I felt nothing but a vibration underneath me that kicked in right around 60 mph. This vibration was NOT there before the re-gear, so it has to be related to the re-gear, since nothing was changed other than the new gears, Revolution axle shafts, Currie steering, and that's it.

It looks like my only solution might be manual locking front hubs (does anyone still make these for the TJ?), since Dave said my driveline angles look perfect.

Seems like this is starting to become a very common issue. I just can't understand what it would be about re-gearing that would cause a vibration issue like this.

@psrivats is having the same issue with his after after his re-gear as well.
Click to expand...

When you regear, you increase your driveshaft RPM at a given speed. Increased driveshaft RPM's can lead to vibration (for the same reason driveline vibrations occur at higher speeds). Since your driveshaft is now spinning faster than it did before at a given speed, you're more likely to find a vibration. Driving at 70mph with 5.38's is like driving 91mph with 4.10's when it comes to driveshaft speed (5.38 / 4.10) * (70mph) == 91 mph.

When I go to 35's, I think I might find that my highway vibrations diminish. Right now, I can barely feel a vibration at 75mph. After 35's, my driveshaft will be spinning slower than it is now at 75mph, so I might not find those vibrations.
 
Driveshaft speed and the angle of the front cv joint off the transfer case is causing it. And Yukon gear makes the hub conversion as well as spyntech. Yukon make is in the stock bolt pattern and also the 5x5 5.5. The stock pattern will increase track width by 7/8’s per side, the larger pattern will keep the front track width the same.
 
  • Like
Reactions: lindsey97 and Chris
When I read this , the only thing that came to mind is what changed , and basically a regear means it's pulling more at the same rpm , and likely using less fuel to do it , or using less rpm to pull more basically .

Could replacement carrier gears have balance issues ?

I had a double cardan go crazy in my front after a regear .
 
I am betting @jodomcfrodo is close to the right answer. I am also betting when Tom Woods or Adams balances your driveline at an equivalent of speed of 55 or 60 mph. I wonder if they could turn it faster if they could fix the vibration. I would like someone that has a local driveline shop if they have a way to turn it faster for balancing.

It makes sense to me because what over vehicle on the road runs 5:38 gears at free way speeds.

A good way to test this theory would be if you could borrow some bigger tires that are exactly the same except bigger and see if the vibration lessons. but it will probably be hard to find someone with bigger tires that are balanced perfectly to borrow.

BTW I two have a small vibration after my regear, but my regear was massive in that I replaced the rear end, springs tires. I think some of mine is tires, but it is slightly worse than before with the same tires and the other gears.

Mine is pretty slight but noticeable. it will rock me to sleep if I am not careful haha. I can still play with my suspension and see if I can fix it a bit, but I am betting that it is because my driveline is spinning so fast. BTW I went from 3:73 to 4:88's that is considerable especially when I went from 31's to 33's
 
I never thought about the increased drive line speeds , but makes sense .
 
  • Like
Reactions: ac_
Top Bottom
Back