does not shift out of 4 wheel drive. what would cause this. 1999 jeep sport

First of all I'm not a mechanic but I have an 87 Cherokee Pioneer and had this problem which a mechanic caused. Had to go to another mechanic to figure it out. First he told me to drive it in reverse a little ways and it should come out of 4 wheel drive but it did not. Upon further inspection he noticed the vacuum line was broken. Apparently the 4 wheel drive engages and disengages by vacuum pressure lines on my rig. Hope this helps but you probably already got it fixed by now anyway.