1999 f150 4x4 reg cab V6 standard , 4x4 shifter on the floor, pull it into high light comes on, front diff actuator goes in , put in 1st only back tires spin, put in reverse front and back spin ( i was on a patch of icy road ) I can hear a slight clicking noise maybe when in forward gear but its very quiet so could be normal ? when i am underneath everything seems to be working and engaged, thanks for any help

 

if it actually is coming OUT of 4 x 4 there are only two options, one is the transfer case motor is not 100% engaged......... or the front differential vacuum cylinder is not 100% engage, or engagement worn out on inside. Look to see if the vacuum cylinder on the axle can be move FARTHER with bumping or prying on the arm when engaged. You can put in 4 x 4 , shut off truck, crawl under and tap in it.. maybe spray with penetrant. ................ if not that, same thing on the transfer case motor linkage end, but I would guess axle first.