Shiftlinkage for 4X4?

I have a 1998 jeep cherokee that is a mail jeep and the four wheel drive linkage for putting it into 4h keeps coming out and will not stay in the transmission. If you push it back in it will work but after you keep pulling it in and out of 4x4 it will popout and will not work.I have to keep getting under the jeep push it back in it like something is missing that holds the part of the linkage in there.Its a aw4 with 4.0l I6.Thanks for any help.