97 f150,just wondering what make the front wheels engauge in 4wd,the transfer case I can switch manually to 2h,4h and 4l but the front wheels dont engauge.any help??

 

i believe the vacuum locking hubs for 97 and 98 were a common problem. i think the hoses supplying vacuum to the hubs start to crack and leak. i'm not sure exactly where they are, but i'm sure someone else will chime in on where to start checking.