Tracking down vibration issues

[JMark]

I'm trying to track down a highway speed vibration issue that's seemingly coming from the rear end.

This issue occurred both BEFORE and After my Dana 300 build so it's not the tcase at this point to my knowledge.

Accelerating, particularly uphill i get a vibration that seems to level out at 62mph and comes back in the form of a pretty nasty rear shimmy at around 70mph (about as fast as i'll run the jeep). It's more pronounced uphill than downhill.

Here's what I've checked so far:
Wheel bearings are good (one piece AMC20 yukon setup)
Swapped all 3 u-joints on my CV driveshaft.
Popped diff cover, checked carrier bearings and verified no real play in pinion bearing.
Verified axle isn't moving at speed (checked u-bolts, center pins, they're tight)

Thinking either my driveshaft is out of balance completely and evens out at specific speeds or maybe a wheel balance issue?

Tires have a touch of chop to them (35" MTR's with about 3k on them)

Thoughts?

 

[cglax6]

Only asking because you didn't mention it, but are your TC and pinion angles correct for a CV shaft?

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[JMark]

Only asking because you didn't mention it, but are your TC and pinion angles correct for a CV shaft?

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I have 4 degree shims in there. I'm starting to think i have too much pinion angle and it's getting extreme at speed.
'

 

[cglax6]

This is what it should look like if you have a CV drive shaft in there.

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[JMark]

This is what it should look like if you have a CV drive shaft in there. View attachment 26751

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https://photos.app.goo.gl/mZ4cqpNpMwyo4GBG9
https://photos.app.goo.gl/2qsH6uueGadaS4h89
https://photos.app.goo.gl/my9AZMGy3F61Vi4Q8

 

[cglax6]

Can't exactly tell what the angles are like, but you should be fine if the rear pinion points tight at the TC output. If it's off by a few degrees, you're going to get some vibration.

What's up with that shock in the background?

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[JMark]

Can't exactly tell what the angles are like, but you should be fine if the rear pinion points tight at the TC output. If it's off by a few degrees, you're going to get some vibration.

What's up with that shock in the background?

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the shock? that boot popped off, no big deal, shock's good.

 

[caveman]

Don't forget to check for wear in the slip joint.

 

[JMark]

ordered a new rear driveshaft and some 2 degree shims. i'll swap the shaft (i need to do it anyway) then if it continues i'll swap the degree shims from the 4s i have in there now down to 2.

 

[JMark]

Update: Driveshaft replaced, vibration seems to have gone away. old shaft was way out of balance apparently.

 

[Lumpy Grits]

Check the old DS to be sure the front and rear u-joints were in proper alignment.
Gary

 

[JMark]

Check the old DS to be sure the front and rear u-joints were in proper alignment.
Gary

Will do. also going to take a straight edge to it.