I got bad vibes, man- FIXED. Go to page 9

Reading through this thread, everything in my head points to T-case bearings on the output side. You said it was originally vibing around 70. Then switched from 3.73 to 4.56, and the vibes dropped down to the 54-60mph range. 3.73/4.56*70=57mph, dead in the center of the 54-60mph you stated earlier, and the 55-58mph that has been stated more recently. So its at a particular driveshaft rpm zone. That pretty much eliminated anything from the carrier downstream. And this mostly rules out engine and transmission, unless the harmonic just doesn't present itself in the first few gears. One way to eliminate those for sure is pull the front driveshaft, put it in 4low, and drive at about 20-22mph, in OD gear, which should be the same RPM (assuming 2.72 t-case gears). If the vibe is there in 4low at same rpm in top gear, then its transmission output or t-case input. Honestly, could be something as simple as the front bearing on the t-case rear output shaft being worn and allowing some harmonic oscillations, especially since that end is pretty much only supported by another bearing.
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That's the kind of thing that would not show up with a runout check or a low RPM, but would really start to show itself at higher speeds.
 
jeepinmatt said:
Reading through this thread, everything in my head points to T-case bearings on the output side. You said it was originally vibing around 70. Then switched from 3.73 to 4.56, and the vibes dropped down to the 54-60mph range. 3.73/4.56*70=57mph, dead in the center of the 54-60mph you stated earlier, and the 55-58mph that has been stated more recently. So its at a particular driveshaft rpm zone. That pretty much eliminated anything from the carrier downstream. And this mostly rules out engine and transmission, unless the harmonic just doesn't present itself in the first few gears. One way to eliminate those for sure is pull the front driveshaft, put it in 4low, and drive at about 20-22mph, in OD gear, which should be the same RPM (assuming 2.72 t-case gears). If the vibe is there in 4low at same rpm in top gear, then its transmission output or t-case input. Honestly, could be something as simple as the front bearing on the t-case rear output shaft being worn and allowing some harmonic oscillations, especially since that end is pretty much only supported by another bearing.
View attachment 378738

That's the kind of thing that would not show up with a runout check or a low RPM, but would really start to show itself at higher speeds.
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Agreed. However, exact same vibe with the 242 case as well as the just swapped in and 100% rebuilt 231.
I've felt this before and it's always been driveshaft related. But 3 shafts (and the OEM front swapped to the rear as a test) all had the same vibration.
It's like a general, hard resonance throughout the entire Jeep. Like an older leaf spring Jeep that needs a tcase drop/SYE but we were all too poor to afford a fancy kit.
 
Jody Treadway said:
Agreed. However, exact same vibe with the 242 case as well as the just swapped in and 100% rebuilt 231.
I've felt this before and it's always been driveshaft related. But 3 shafts (and the OEM front swapped to the rear as a test) all had the same vibration.
It's like a general, hard resonance throughout the entire Jeep. Like an older leaf spring Jeep that needs a tcase drop/SYE but we were all too poor to afford a fancy kit.
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Then the only other item that would be in that RPM range would be the pinion bearing.
 
jeepinmatt said:
Then the only other item that would be in that RPM range would be the pinion bearing.
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Zero play in the pinion yoke. No diff related noise at all.
Spoke with a buddy that spent a good bit of time in the driveshaft industry, gave me a couple.of things to look for tomorrow. Gonna check them out and report back.
I'm convinced it's in the driveline somehow, somewhere.
 
Transmission output shaft bearing?
 
Jody Treadway said:
Zero play in the pinion yoke. No diff related noise at all.
Spoke with a buddy that spent a good bit of time in the driveshaft industry, gave me a couple.of things to look for tomorrow. Gonna check them out and report back.
I'm convinced it's in the driveline somehow, somewhere.
Click to expand...
Play in the pinion yoke doesn't rule out a bad bearing. But new gears should since the issue was present before and after.
 
I would like to imagine @Jody Treadway could spot a bad pinion bearing....

Never met the guy, but I hear he knows a thing or two about a thing or two :D
 
jeepinmatt said:
He says he can, but 3.5 years ago he said the vibes were gone too 🤷‍♂️
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Touche'.
Jedi mind trick didn't convince my wife it was fixed, lol.
Truth is her DD was at the dealer for a few days due to a recall and she had to drive the ZJ while it was gone.
 
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Ron said:
Transmission output shaft bearing?
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jeepinmatt said:
That's about the only thing left.
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I don't know all the details but the transmission seemed like a logical place to go if it was not anything behind it.
Croatan_Kid said:
I would like to imagine @Jody Treadway could spot a bad pinion bearing....

Never met the guy, but I hear he knows a thing or two about a thing or two :D
Click to expand...
Yea I'm over here watching @Jody Treadway being stumped.... :D
 
My money is also on the trans output. When I first started the thread I immediately thought tcase output, but having see you say swapped, it does rule that out. Assuming the transmission is mount up to snuff...
 
I would be tempted to try a different rear pinion yoke.
 
I'm dropping off the rear drive shaft at a local shop to be lengthened a bit. There is a bit too much slip spline showing at ride height and I *think* it may lead to oscillation and vibes at speed.
The fact I can drive through it, tells me it's a driveline issue as opposed to a bent xyz.
There is about 3" showing and from what I gather, it should be around 1.5". All of the shafts I have are like this.
For the $120 or so, I'll try it
 
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