Vibration remains unsolved

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JMendez
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Vibration remains unsolved

Post by JMendez »

I have been having a MF of a time trying to solve my persistent driveshaft vibration.

I have a 83 Wagoneer with an LS swap, backed by a New AX15 with a rebuilt NP208 transfer case.
Its running 32x11.50 tires on original alloy wheels, axles are newly rebuilt with all new bearings and 4.10 gears. (Dana 44 front, AMC 20 rear)

As stated it has a persistent vibration beginning at 60 and is most severe at 75, which translates to roughly 2500 rpms.

If I remove the rear shaft entirely and drive (in 4x4) only on the front wheels, the vibrations go away.

So far we have done the following:
front lockable hubs
rebalanced the shafts 2 twice by two different shops
new 3” diameter Tom Woods rear CV shaft with 3-deg leaf spring wedges
changed the bearings in the rear AMC20
reset the pinion preload w/ new crush sleeves
replaced both transfer case and axle pinion yokes

This has done nothing to eliminate the vibration, it will still show up at anything over 60mph wether under load or coasting down a hill.

The only way to stop the vibration is to remove the rear shaft entirely.


We are out of options. Anyone have any ideas?


Jon
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Stuka
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Re: Vibration remains unsolved

Post by Stuka »

I am sure you have tried/checked these, but I didn't see them mentioned above.

1: Are the u-joints in phase with each other? Meaning, the slip yoke can come off, and depending on how many spines it has, can be slide on in many ways. But it MUST be slid on so that the u-joint is in phase with the other u-joint. See image below, even if one spline off, it can cause some nasty vibrations.
Image

2: You did mention having a CV and shims in back. So does this mean the rear u-joint is at roughly zero degrees, and the CV is taking up all the angle?

Assuming the top two items are not the issue. If it was me, I would stick my GoPro under there, probably on three trips, pointing it at different spots, and set it to the highest frame rate it can do, so I can easily play it back in slow motion. I have solved many issues with this method before.
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letank
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Re: Vibration remains unsolved

Post by letank »

a good shop should have the vibration detection software... yes a bit hitech for our riggs... NVH, noise, vibration and harshness detection

https://www.picoauto.com/products/noise ... h-overview
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ghcoe
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Re: Vibration remains unsolved

Post by ghcoe »

You may have a issue with the yokes. A lot of people think pointing the yolk to the transfer case/transmission helps. https://hotrodders.com/gallery/data/500 ... s.jpg?9028
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JMendez
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Re: Vibration remains unsolved

Post by JMendez »

STUKA: Im currently running a 3" Tom Woods CV shaft. My angles are really good with only a 2" lift. Rear pinion is within 0.5 degrees of the shaft angle. I would love to use a Go-Pro even if it doesn't help. The video would still look really cool in my opinion. But currently due to all the part buying, my bank is slightly strained have strained, and if I spend the money on something like that I would like to get the high speed model with the image stabilization.

LETANK: I would love to do something like that high speed vibration software detection system, but I doubt there is a dealer/vendor within 200 miles of my location. I'll take a look.

GHCOE: My angles are good. To eliminate the possibility of bad yokes, we have tried out two different yokes. Both at the t- case and axle ends, still vibrates.

In the mean time.

I have an email out to Tom Woods 4xshafts.com.

Asking if they could build a larger diameter shaft. My current Tom Woods 3" shaft (from 2018) begins to vibrate at 60 to 70 mph. The original 2.5" shaft would vibrate at 45mph or so.

The larger diameter shaft seemed to have shifted the vibration up a few mph. Stands to reason an even larger diameter shaft would eliminate or at least shift it beyond my cruising speed of 75 to 85mph.

I will post what Toms Woods response is, maybe I'll get a deal. Doesn't hurt to ask.
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Re: Vibration remains unsolved

Post by Stuka »

A larger diameter shaft may hide the vibes better as they balance better, but it doesn't solve the issue. I am starting to think you may have a bent output shaft at the t-case (assuming its not a slip yoke GM/Dodge version, if it is a slip yoke, I bet its your issue). Or perhaps even a bent pinion on the rear axle.
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JMendez
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Re: Vibration remains unsolved

Post by JMendez »

STUKA: I can't speak for the T-case other than it has been rebuilt. As for the pinion, these are new gears with about 4000miles on them. When I asked my shop to re set the piñon preload they didnt notice anything being bent. Though they did mention the pinion gear could be out of balance but couldn't recall ever seeing one.

However, I did email Tom Woods and they responded this morning.
Prompt response, but after reading it I wasn't too thrilled.

Troy (from Tom Woods), responded back to my email, saying, "if I thought the vibration was from the front shaft."

He asked if I would call him back, which I did today.

In our phone conversation, Troy preceded to speak over me while I was attempting to explain all the troubleshooting we had done. Then he suggested if it couldn't be a t-case or pinion yoke. Clearly he did not read the email in full. When I tried to explain that we had changed out both yokes and even tried two different axle shafts, he then started to explain how axle shafts don't spin fast enough to warrant them being balanced. Clearly he did not understand that Im grasping at straws and trying to not to leave anything un checked in my attempt to fix this vibration issue.

In the end, he said to ship their drive shaft back so they could take a closer look, because they think it may need rebalancing......
I then tried to talk over his lecture trying to let him know we had two independent local shops rebalance it.

Paid $35 dollars for a UPS label (which just showed up at 4:30pm). We will see if they can find anything wrong with their shaft.

They wouldn't even entertain the idea of a larger diameter shaft. And I felt annoyed and frustrated that Troy didnt even throughly read my email and proceeded to suggest items I had already done.

Very unimpressed with their handling of this. But I will ship it back to them to see what can be done with it. In the mean time I think after work Im treating myself to a steak and beer....before I have to pay my credit card off.
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Re: Vibration remains unsolved

Post by Stuka »

Thats unfortunate. My dealings with them has been pretty good. But I have never had to try and trouble shoot an issue like yours.
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JMendez
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Re: Vibration remains unsolved

Post by JMendez »

Stuka: I agree! I have heard from many quite the opposite, that their customer service is impeccable. Not sure what kind of day Troy was having, we're all human.

But the shaft is in UPS's hands and we will see what Tom Woods finds out about their shaft. In the mean time I placed the original Non-CV 2.5" shaft back in, along with its original yoke and something funny happened.
The vibration is less than with the Tom Woods shaft. It's not gone by any means but it doesn't shake the rear view mirror like Tom's would. Hmm.... I think I will place an AMC Gremlin badge on the tail gate. instead of Wagoneer!
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Re: Vibration remains unsolved

Post by carnuck »

Sounds to me like a bad trans mount and/or the input pinion of the axle twisted.
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JMendez
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Re: Vibration remains unsolved

Post by JMendez »

What follows should be a typical FSJ result.


My mechanic had left the original drive shaft in the jeep so i could drive it home while the Tom Woods shaft is mailed out.

I went out to the garage and double checked his work, I found he had left in the Tom Woods spring wedges which rotate the pinion up for their CV shaft. My old shaft does not have a CV joint and doesn't need them. Thinking this may have something to do with the persistent vibration I removed them.

Then I took it out for a spin.....Nothing, no vibs until you hit 85 or so and even then its nothing what it used to be.

After coming home from the drive I checked if anything else was different, I noticed that the pinion yoke was the new one we had tried.

Im guessing vibration problem was that rear pinion yoke. It has been the one constant; with the old shaft, with Tom Woods shaft and since my mechanic had left in the wedges the angles were all wrong for a shaft with no CV joint so it would have vibrated even if it was balanced.

Im thinking after all this madness it was the yoke which was wrong. The bad yoke came on the replacement axle when I got the lockers and new gears installed. It should have been new, but even new ones are not guaranteed to be right.

Anyway, not sure what to do now with the Tom Woods shaft once i get it back. Im not pulling anything off the jeep now, it runs fine. Guess I will have a spare shaft...
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Stuka
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Re: Vibration remains unsolved

Post by Stuka »

Glad you got it figured out. I think I mentioned above that it could be a bad yoke. But when a bunch of things change at once, it can be tough to track down what the cause is.
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Topic author
JMendez
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Re: Vibration remains unsolved

Post by JMendez »

Suka: Very true. Unless your methodical on your diagnosis. You can end up chasing your tail, so to speak. I would have loved to do all the work myself, but having no knowledge on setting up gears I left it to the professionals. I can do most everything else, just getting the right pattern scares me.
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