Drivetrain vibration disappears when 42RLE transmission is in neutral - anyone experienced this?

psrivats

psrivats

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I have an acquaintance who is not active on the forums and he has a '06 TJ with 42RLE. He has had a high speed drivetrain vibration for a while. A mutual friend who knew my vibration saga told him that I was able to resolve my vibration issues and he reached out to me a few weeks ago to talk about it. I drove his Jeep to get an idea and it felt just like what I had after regear but it came on more gradually and was not as severe. It happens past 67+mph by GPS. It's well felt, heard and seen at 72mph and above. His vehicle is fully stock with stock size tires, only used as a 2nd vehicle for the road only and in good shape with him being the only owner. He chatted with me and I recommended thoroughly checking all the usual stuff that should be checked systematically - wheels/tires, ujoints, axle shafts, driveshafts, yokes, differentials, engine/trans mounts, harmonic balancer on the engine.

His front ds was very slightly out of balance and was fixed by a very good local shop. Everything else was deemed to be in good shape. After everything was checked, new fluids, driveshaft balanced, we noticed that his vibration now goes away when the transmission is put in neutral when driving at speed (this was not the case before). No difference with or without the front ds in place. He has ~86k on the vehicle and otherwise has no transmission related issues. What could explain the vibration going way with the trans in netural? Anyone has any ideas?
 
Putting it in neutral also unloads the driveline. That could be why it goes away.

I have something similar but different. More vibration (say above 60) with OD off (high RPM) than with it on (low RPM). The majority of the driveline is turning the same speed and under load.
 
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LONGJP2 said:
Putting it in neutral also unloads the driveline. That could be why it goes away.

I have something similar but different. More vibration (say above 60) with OD off (high RPM) than with it on (low RPM). The majority of the driveline is turning the same speed and under load.
Click to expand...

Even if the driveline is "unloaded", all the rotating components (wheels/tires/axle shafts/ujoints/ R&P znd whatnot...) are still rotating as much as they did at 70mph just before putting the trans in neutral, no? Doesn't that rule out the problem in those components atleast? If so, then the issue is in either the transmission or the engine?

@bobthetj03 any thoughts on this?
 
I could be wrong, but imagine a bad ujoint that moves around. Out of whack under load and maybe centered while coasting. Just a thought.
 
oldb said:
Old school test for u joint vibration is to unload it. U joint is my guess.

B
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+1↑ Also take a look at the yokes the U-joints mount into. They can be bad. I replaced them on one end and found improvement, (Tom Woods pointed me in this direction) I replaced it on the other end and it got even smoother.
 
⬆ +2 Always know a Ujoint is on it's way out when you get a vibe under load. If it is constant off load then it is normally further down the line
 
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U Joints have been inspected and pronounced good. He's getting them changed currently as we speak just in case. Can't hurt anyway. Will update this thread when that's done in a day or two.
 
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New ujoints in and no change. Engine Harmonic balancer and flex plate inspected and pronounced good. Pinion angles set, checked and rechecked in small increments either way.

I don't understand these vibrations at all.
 
Has he done the 'pull front shaft and test for vibe, reinstall, pull rear shaft go to 4hi and test for vibe' yet?
 
This thread is a couple years old but I think I’m having issues similar to this
LONGJP2 said:
Putting it in neutral also unloads the driveline. That could be why it goes away.

I have something similar but different. More vibration (say above 60) with OD off (high RPM) than with it on (low RPM). The majority of the driveline is turning the same speed and under load.
Click to expand...
My vibration after the engine swap, re gear, transmission replacement, new adams drive shafts, new axels, u-joints, hubs, warn manual front hubs, new shocks and mounts, all savvy dbl adjustable control arms no front cam bolts professional alignment and endless adjusting rear driveshaft angles plus and minus around 1 to 2 degrees, so far I can only chase it around.
the speed range. If I get it much past 1 in any direction the vibration will start as low as in the high 40’s but even shifting it around +/- sub 1 the vibration never really disappears.

ATM my rear angle is now around -.7 and driving on the freeway a slight vibration I can live with starts around 59mph just a tiny vibration in the mid 60 range noticeable and beginning to be annoying after an hour, driving high 60 to low 70 a little more vibration and 79 on up to 85 it goes away. Towing my trailer on flat ground the vibration is less, going up hill towing or not the vibration increases dramatically when the engine rpm’s increase after shifting out of overdrive ive noticed reciently driving mountain passes, it probably has been doing this all along but I’ve been hyper focusing on all the usual suspects now I’m suspecting it is somehow engine related? Downhill coasting at any speed no vibration or it is not enough to overcome typical tire hum.

The increase in vibration intensity is very much in pace with changes in engine rpm more so than drive train load although I imagine there is some difference in torque to the rear wheels when it shifts, I tried switching the overdrive on and off while maintaining steady throttle going up a steep grade and there is a dramatic change in both the intensity and pace (frequency) of the vibration directly in relation to engine RPM? This seems counter intuitive to a drivetrain angle issue only?

So, the elephant in the room has been the engine swap and now I suspect there was something overlooked there when I had it done Judging from all the other issues I had to take care of, most of the engine sensors, missing intake and exhaust manifold bolts and obviously loose manifolds, missing engine ground straps, missing radiator bracket bolts… not that all the work done was bad quite the opposite a lot was really good, just the guy they had doing the odds and ends bolting on the accessory parts and wires was I guess over his head from the things the shop missed.

Now, the question what part possibly overlooked would fit my symptoms? The list I’m guessing is mounts both engine and transmission, harmonic balancer? I think the engine came with a new one but I’ll have to look back in my receipts, torque converter?

Something changed, prior to starting all this after needing to replace the engine I was vibration free at any speed?
 
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