Now I've done it (NP231 problems)

[shelbyluvv]

Lower the transfer a half inch and see if that helps.

 

[kootenayXJ]

Actually here is an interesting part of the story.

While I was under the jeep cursing it's name, I had the transfer case in neutral and was slowly spinning the rear output shaft to see if I can hear any bearing noises (I didn't hear any noises). I DID, however, notice that the harmonic balancer on the output shaft is wobbling around like a drunk sailor.

This part, only found on some newer XJ's and most newer TJ's, has around 1/2" to 3/4" runout when spun slowly, I can't imagine it came like this from the factory and it's demise may have simply come at the same time as the lift. I noticed the rubber is cracked in a few spots which lead me to take a closer look and notice the runout.

The head scratcher (and I'm no engineer so this might be simple for someone else) is that with the rear DS pulled and running in "front wheel drive", there is no vibration at all. With the rear driveshaft in, I am getting terrible, rattle my teeth type vibrations above 35mph. If the bad harmonic dampener is to blame, why is it only showing up with the rear DS in since the dampener is spinning even in "front wheel" drive? Amplified through the rear DS? I don't know what the term for that is.

I also re-measured to see how much spline engagement I actually have on the stock slip yoke and was surprised to see that I am still getting 2.5" of engagement at static ride height. I figure that at most I have only pulled the stock slip yoke out approx 3/8" more than it was sitting before the lift and it's not, in fact, dangling off the back like I thought before. I cleaned up the splines on both the output shaft and inside of the slip yoke and ran my fingernail along them to feel for deformations I couldn't see with my eyes and I can't feel a damn thing. With the slip yoke engaged 2.5" like it sits at static height I can't feel any play between the slip yoke and output shaft, only if I pull it most of the way out and only leave 1/2" spline engagement.

For those not familiar with the harmonic dampener I'm talking about, this is what it looks like (photo I found online):

 

[shelbyluvv]

I still think messing with the pinion angle screwed up your driveline angle. There was zero need to mess with the pinion angle on a budget boost. Drop the transfer 1/2" and take it for a ride and see if it makes a difference

 

[kootenayXJ]

I still think messing with the pinion angle screwed up your driveline angle. There was zero need to mess with the pinion angle on a budget boost. Drop the transfer 1/2" and take it for a ride and see if it makes a difference

I'll pull the 1* shims in the next few days and let you know how it goes.

but first the harmonic dampener is coming off..

 

[kootenayXJ]

just to update for anyone who comes across this in a search,

I pulled the harmonic dampener off the TC output shaft, bolted everything back up without it installed and took it for a drive.

Removing the failing harmonic dampener got rid of the violent, tooth rattling "driveshaft coming through the floor" vibrations that started suddenly a week ago. Still some minor vibes but no worse than I was experiencing right after the lift, completely liveable for the time being as I had before.

I see some fairly significant play between the slip yoke and the output shaft, so guessing the slip yoke has in fact worn after being thrashed around by the broken harmonic dampener.

I'm guessing the slight driveline vibes after lifting where enough to slowly throw the failing harmonic dampener off balance after a bit of driving. Over a few days it got worse to the point that it was throwing the driveshaft around and caused some damage to the driveshaft slip yoke.

Thanks for everyone who has helped answer my questions, turns out the bad harmonic dampener was to blame for the sudden terrible vibrations. Hopefully if someone else comes across this thread it saves them a load of hassle.