I getcha. well crap. I guess this is what I get for lifting and not researching. Thanks for the tips.

Gonna buy some shims and center pins locally.

 

It’s possible you have a bad ujoint. I would get under there and see if there is any play.

 

So in an effort to not strand myself (or wife) with getting the wrong parts and then having to wait for shipping, I took the jeep in. This (different) shop measured and found I only needed a 4º shim. There's been a marked improvement, especially at freeway speed, but there's still a bit of rumble at 30–40 mph. I'm going to chalk it up to just "being a modified Jeep" and move on.

I think I'll still take a look at the u-joints anyway this weekend when I do the disc brake conversion. I'll be surprised if they're bad, as they're only a couple years old Moog joints with no trail hours on them, but you never know.

 

I wonder if there's a window of tolerance, like ±3° offset. I know in most cases the axles rotates a little as you give it gas, so you want to consider that when setting the pinon tilt.

I've had the same attitude- it's a lifted Jeep and the poorly-worn tires probably drown out whatever driveline vibrations I have, but I'd like to correct it to an acceptable angle if known.

 

Well, I got the jeep back and it still vibrates, although arguably not as violently as it did before. 4º shim per the shop I took it to.

I took it back in and they couldn't find anything that would be causing it. He's and XJ owner, too, and said it drives about the same as his does. The other possibility is that the DS is out of balance, but I'm running out of time and patience on this one. It's happy at 55, and a bastard at 70+ and I don't plan on commuting with it anymore anyhow. I'm going to chalk it up to "cost of doing business with a modified jeep" and move on.

 

Well, if it needed 4 deg, and he didn't account for the change in angle from the torque of the engine, that could make it act like it is. You may only have needed a 2 or 3 deg shim.

 

I chased a vibration in my XJ for over a year trying all kinds of things. Driveshaft, wheel bearings, Gears, angle blocks, etc...
When I put my Atlas in, my vibration went away...

Don't rule out a bearing in your transfer case being the culprit. Maybe go with a SYE. You have to remove the tail section and output shaft out of the transfer case and you could likely find a bad bearing.
You'll need to do a new drive shaft also if you go this route.

Just something else to consider.

 

This is where a little learning can go a long way.

If you don't have an SYE, and aren't running a CV Driveshaft (which is unlikely without an SYE), your pinion angle and transfercase output angle should be opposite but equal.

Read through this, and it will give you pretty well all the knowledge you'll need:

https://www.pirate4x4.com/tech/billa...aft/index.html

 

So I finally took some time to get down there (life's been nuts and I get in weird slumps with this stuff) and I haven't bought an angle finder yet, but I think this is what's happening:
Top is what the angles look like right now. I added in the shim direction to the diagram, and it's definitely the thicker end facing back. I think they put the shim in backwards... Of course, I'll need to get an angle finder on it to be certain.
Bottom is what I think it would look like if I just flipped the shims to "correct" direction. The pinion shaft is definitely pointing downward, which, to be opposite but equal to the transfer case, it should be more level that it is now

I checked and there's no play in either rear pinion or the Tcase output shaft.

 

Okay. Now I'm totally flummoxed.

I measured the angles, front, rear, rotate 90* repeat, all the way around and I'm completely lost now.
1) 13, 13 (pinion)
2) 6, 9 (driveshaft)
3) 13, 12 (pinion)
4) 4, 7 (driveshaft)
5 (back to 1) 12, 12 (pinion)

Is my driveshaft bad? it's 3* off each time it seems

 

Is the driveshaft out of sequence?

I'm having the same issue with mine. I repaired my front driveshaft, thought it was the rear causing the vibe but it turned out to be the front.
Now I have a vibe at 70+ like you do. I put in 4* shims in mine as well.

May want to check your front shaft.

Ultimately you'll gonna want to get an SYE and a driveshaft.

 

Well, I took off the rear driveshaft and drove it fwd only. Smooth as an xj should be. No shaking, no vibration.

I'm thinking it might actually be the xfer case, now I'm putting things together:

• PO put block lifts on and no shims, ran it for who knows how long that way.
• Vibrations only when the rear shaft is on
• Clunky, cyclical sound when slowing to a stop; disappeared when the shaft was off (i thought it was brakes)

Makes me think the output shaft bearing or something at the output of the xfer case is at fault.

 

what is the angle of your Transfer case output shaft?

also it could help to make sure the slip yoke is well greased, not that its contributing, but its worth checking while your under there.