a buddy of mine has a 1992 s-series blazer with the 4.3, auto, 4wd. he bought a posi-lock cable and installed it the other day. the 4wd still wont engage with the cable. i couldnt turn the front driveshaft by hand when the t-case was engaged in 4wd. wondered if there was a way to tell if the shift fork or something is broken inside the differential and if there is an easy way to fix it without tearing the entire differential out.