Symptom: Annoying vibration and noise at > 60mph Not crazy but not right and driving a lifted Jeep XJ I know driveline vibration symptoms.
Diagnosis: Crash course in Jag propshaft alignment and indexing. By re-indexing the connection between the diff and the jurid coupling and using plumb lines I was able to reduce the vibration significantly but not completely.
Replacement: I decided to pull the propshaft to further investigate and glad I did. U-joints were fine but the center bearing rubber was almost completely separated. It was, as others have mentioned very difficult to see how badly until the rear section of the propshaft is removed.
Notes: Mark ALL your relative positions including the Jurid coupling to the diff and the connection to the transmission. It is possible to remove the propshaft without dropping the exhaust but I needed to separate it at the slip joint at the transmission side of the center bearing to get the clearance Also needed to drop the crossmember that the bearing bolts to (there is a spacer in there). The yoke is secured by a bolt with a tab washer that has to be punched flat to undo. The yoke only fits one way. Pressed the bearing out and pressed a new one on. You will need a sleeve that fits over the splines narrow enough to push on the bearing itself as the collar is pretty soft metal. (ask me how I know :-) It is not that tight I used a HF press. To reinstall I inserted the front section about halfway and bungied so that it was at about a 45 degree angle. Then used a transmission jack angled similarly with the shaft bungied to mate up the rear section. (Trying to re-insert the slip yoke without doing this requires more upper body strength than I have but YMMV). Then it is just a case of bolting everything back just as you took it out. In my case this completely resolved my vibration and noise issue. My initial plan was to have the propshaft balanced but it proved unnecessary. I shot some video of the process and will update the thread when I have edited it. Hope others find this useful.