my front end doesnt engage when i put it in 4. when i put it in 4 low the rear is low but the front doesnt i replacet both axels in the front it doest grind or make any noise could it be the vacuum line that ingages it

 

by the way its a 1992 s10 4.3

 

could be vac related (first thing i would check personally) start with pulling the cable from the actuator to the front axle by hand and clamp a pair of vise grips on to hold it there and test if 4wd is working, if so then you more than likely have vac problems.