1997 s10 zr2 4wd wasnt shifting back to 2wd completely.Transfer case disengaged but front axle would only partly unlock. So after slowing from highway speed front axle would roar (whine) down to about 30mph then pop hard and free up. This happened several times then it stuck GOOD partly engaged (roaring terrible). I had to return to 4hi to stop the roaring and LIMP home on dry road in 4wd had binding but no roar. NOW FOR THE FIX!! Checked 4wd vacuum actuator and it was full of trans fluid ! It turns out the tranfer case switch had gone bad and pulled trans fluid from automatic trans(4L60E) which in turn over filled transfer case. Then sucked enough fluid via vacuum line to fill actuator ruining it also . I replaced both transfer case switch and vacuum actuator. STILL NO 4WD!! Transfer case was shifting but front axle wasn't locking. It turn out to be the NEW tfc switch was bad ! I replaced tfc switch again and NOW I finally have vaccum to actuator. But axle still won't lock !! Replaced actuator cable. FIXED AT LAST!!! And its SNOWING HARD