Originally Posted by tnjeeprider
Leave jeep in gear and jack up front end, see if you can spin both front wheels. If wheels spin you are in 2wd, if wheels do not spin you are in 4wd.
If you are in 2wd, check the front axle u-joints. I friend of mine has u-joints going bad in his jeep and there is vibration and light clunking coming from them.
That's a horrible way to test. The open differential will allow both wheels to spin when engaged into 4wd. If the vacuum actuator is working properly, then it will disengage the passenger side wheel, so if you spin one wheel, the other will not spin.
Easy test to see if the front axle is still locked: Try to spin the front driveshaft. If it's still engaged up front, then it will cause all of these bad vibrations, since the front shafts aren't balanced.