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

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Well, #&@+. It's still doing it
Local driveline shop retubed the rear shaft (out of round) and replaced the slip yoke that was seized on the splines. Picked it up yesterday, swapped it in today and it's still doing exactly the same thing
Stopped by Ujoint Offroad and took the driveline/gear guy there for a ride. He's like "dude that's a driveshaft issue". Then I gave him the backstory and he's at a loss as well
I did pull another tape measure on the wheelbase. Pass side is (approx) 106.75" and driver is 106.25". Front is square measuring from crossmember to LCA bolts and has fixed arms. Caster is 6*. I'm wondering if the rear is out just enough where the locker is doing something weird at speed? Easy enough to roll the pass side back a few turns and see
I'm really at a loss if the WB adjustment doesn't materialize.
UGH!
 
I could maybe see the u joint doing weird things because the pinion isn't in line with the transfer case output. Compound angles and what not, perhaps?

Somebody could probably do the math and figure out the left/right angle of the pinion. Plus, the yoke/u joint are probably close to a foot from the center line of the axle shafts which would pitch it off even further.

I feel like fixing the wheelbase SHOULD cure it.
 
Stupid Jeep. This freaking thing 🤬.
Went back to square one and double checked everything this afternoon.
Driveline angle is 11*, pinion is at 10*. Perfect.
Front is the exact same. Perfect.
Toe in is 1/8". Perfect.
Wheelbase is within 1/32" per side. Good nuff
Set tire pressures, removed front driveshaft, reinstalled it, checked wheel bearings, axle bearings, all the rotational stuff. Tested the Truetrac, it's not bound up. Spartan is gapped right and no wear to be seen Still fn resonates/vibes badly 53-65
Coasting, decel, accel, pop into neutral, whatever you do doesn't change anything. Beyond frustrating
Talked to @zubz a while on the way home. We combined our Rochester NY and Candler NC brains and came up with looking for something in the chassis that may be worn enough to cause the resonance. Couple it with the shell of a unibody ZJ that transfers noise like crazy and *maybe* that'll cause it.
Gonna loosen and retorque the entire suspension this weekend, with it sitting on its own weight. Hoping for any discernable change to help isolate the cause
We theorized the harmonic balancer as the cause. But engine speed has zero effect. So that rules out the transmission as well. Front drive shaft out rules out the t case output.
When I solve this, it's going deep in the memory bank for sure
 
jeepinmatt said:
Just the input, not the output.
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The one that's supported by the transfer case input? I don't see any way for it to vibrate.
The transfer case rear output is a brand new AA SYE kit in the just rebuilt and swapped in 231.
Not being argumentative whatsoever. Purely looking for ideas.
BTW- I nearly called you this afternoon since you're a smart feller. Decided to sulk and drink a beer in my shop instead
 
StretchASU said:
Buy the 35 stickies @Van-go is selling, send that rock missile up some trails, let the new vibrations hide the old vibrations.

I’m here for more bad advice when you need it
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I can always count on you, sweetie
Convince Lisa to do it to HER ZJ and I'll buy you a White Claw in a a yet to be determined wheeling location
 
R Q said:
Doll that ZJ up all nice and shiny and pass it on as you can always do then buy her a Denali Yukon and let her enjoy life in luxury! It's a sweet ride and it ain't gonna vibrate!...unless you push the button for it to.
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She signs my paychecks. She can buy her own Denali 😉
She rocks a 22 Expedition as her DD. The ZJ is a weekend warrior, bike and dog car. Well equipped though!
 
Jody Treadway said:
I can always count on you, sweetie
Convince Lisa to do it to HER ZJ and I'll buy you a White Claw in a a yet to be determined wheeling location
Click to expand...

Haha on a serious note.

I’m assuming you’re measuring the pinion angle static sitting in the shop floor or parking lot. Is there any chance that when the driveline loads up, the rear suspension squats a little or even while it’s going down the road causing that angle to change for the worst? I know the pinion angle doesn’t change as much in a coil spring suspension like it can with leafs, but we are running out of things to check and these are random things that pop into my head and whilst evacuating the AM grumper.
 
StretchASU said:
Haha on a serious note.

I’m assuming you’re measuring the pinion angle static sitting in the shop floor or parking lot. Is there any chance that when the driveline loads up, the rear suspension squats a little or even while it’s going down the road causing that angle to change for the worst? I know the pinion angle doesn’t change as much in a coil spring suspension like it can with leafs, but we are running out of things to check and these are random things that pop into my head and whilst evacuating the AM grumper.
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Wut?
You mean you don't set pinion angle with the suspension fully drooped on the lift? 😜
 
Have you tried removing both driveshafts, putting it in gear and “running it up to speed” while sitting still?
Driving with just rear shaft? Driving with just front?
I’m still not convinced it’s not a driveshaft issue.

Hell, take both shafts out and coast down a long hill with no driveshafts till you hit 55-60 and see if it does it.
 
ckruzer said:
This is still where my money is. Trans output shaft/bearing
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Explain how that can cause it. Really not being argumentative, but I don't see how it's possible when the trans output is fully supported in the extension housing as well as the t case input.
 
Van-go said:
Have you tried removing both driveshafts, putting it in gear and “running it up to speed” while sitting still?
Driving with just rear shaft? Driving with just front?
I’m still not convinced it’s not a driveshaft issue.

Hell, take both shafts out and coast down a long hill with no driveshafts till you hit 55-60 and see if it does it.
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Just front, just rear, multiple combos of various known good shafts and no discernable change.
I'm game to drop the shafts off the case and run at speed. It's a free test
Probably gonna work on it tomorrow since it's supposed to rain all day
 
Jody Treadway said:
Explain how that can cause it. Really not being argumentative, but I don't see how it's possible when the trans output is fully supported in the extension housing as well as the t case input.
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Why bother with good bearings in a rearend setup? They are fully supported in the housing. ;)

And I understand not wanting to take everything apart to check that. Have you tried this test I recommended last month:
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.
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I'm getting somewhere, finally.
Put it in stands after work and had my wife run it to 55-65 mph. It does it clear as day, you can hear it and feel it. If you place your hand on the rear diff housing, you can feel the resonance, you also feel it on both uppers as well as the track bar.
Remember the Jeep is stationary, but you put your hand on these parts and it's like being in a washboard road. Crazy
While it was vibing, I side loaded the bushings on each part w/o any change in pitch or feel. You cannot feel it in the hitch, exhaust, gas tank skid, etc. I'm unsure if this is a cause or effect.
Laying under it, when you hit 55 and it starts vibing, you can see the nose of the housing start to go up and down a bit. As you would expect, the axle end of the driveshaft follows the pinion and moves a bit too.
I found a leaking axle seal, so I pulled the locker to access the c clips. Tomorrow, I'll pull the carrier to triple check pinion bearings and such.
Oh, I also removed the crossmember and set the case on a fixed pipe stand in an effort to rule out the tranny mount. No change at all.
Essentially, nothing I pried, moved or touched changed anything. But at least I can 100% replicate it in stands and can feel it.
Thoughts?
 
If you remove the rear drive shaft and repeat the test you could likely eliminate Matt’s theory. Or, as he suggested, retest in low range just for process of elimination
 
Jody Treadway said:
Put it in stands after work and had my wife run it to 55-65 mph. It does it clear as day, you can hear it and feel it. If you place your hand on the rear diff housing, you can feel the resonance, you also feel it on both uppers as well as the track bar.
Remember the Jeep is stationary, but you put your hand on these parts and it's like being in a washboard road. Crazy
While it was vibing, I side loaded the bushings on each part w/o any change in pitch or feel. You cannot feel it in the hitch, exhaust, gas tank skid, etc. I'm unsure if this is a cause or effect.
Laying under it, when you hit 55 and it starts vibing, you can see the nose of the housing start to go up and down a bit. As you would expect, the axle end of the driveshaft follows the pinion and moves a bit too.
I found a leaking axle seal, so I pulled the locker to access the c clips. Tomorrow, I'll pull the carrier to triple check pinion bearings and such.
Oh, I also removed the crossmember and set the case on a fixed pipe stand in an effort to rule out the tranny mount. No change at all.
Essentially, nothing I pried, moved or touched changed anything. But at least I can 100% replicate it in stands and can feel it.
Thoughts?
Click to expand...
Axle shaft bent? Or housing bent?
 
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