How do I:Vacumn disconnect sys. check

OK..I seem to be having a binding sound. Sounds is heard a slow speeds when turning, and sounds to me what I would think you would hear if you had part time 4wheel drive engaged on pavement. sorts of creaking, snapping sound. This has become an issue since I have just completed a fairly major front end job detailed in my previous message:What the?!..etc...
It was suggested that i make sure the vacumn disconnect is working properly.
Can anyone suggest a procedure to check this?
OR can anyone suggest what the heck the sounds are...I don't want to have to fix anything i've just replaced.
It seems to go in and out of 4wd fine.
Any help is greatly appreciated...
Thanks to asatxj for all his help so far!

OH details...89 xj, 3" budget lift, 4.0L, manual trans., pretty stock everywhere else...new u-joint, ball-joint, sway bar links, and hub$! Thanks.

Put it in 2WD, and jack up the right front wheel. Turn it. If it turns the front driveshaft it's staying engaged. If it doesn't it isn't.

While you're at it, turn the steering to full lock, and rotate the wheel on each side, to check if one of your new u-joints might be binding.