Out playing in my My 1999 F150 XLT yesterday after the snow storm and got stuck in 2wd, flipped the old switch into 4x. and nothing. back wheels spin, no front engagement. if i switch it to low range 4x. the transfer case goes into low but still no front engagement. how are the 4x4 engaged in this truck? is it in the transfer case and then in the front differential? electric, vacuum? Anybody ever had this problem? What can i check?

 

Check out the vacuum lines for the hubs that's what was wrong on mine

 

I have an '03, not sure if the earlier models are a different setup, but as far as I know these trucks have "live"axles( they turn as the tire turns), it should disconnect in the front diff, if you know for sure the transfer case is engaging, then I agree check the vacuum lines to the actuator, I thought all of these generation trucks had the same setup but I could be wrong

 

Yes, has the vaccum style actuator. looked at it and its moving but (not what looks to me) enough but i oiled it a lot with WD-40 and forgot about it. today we got huge snowstorm and a flash freeze and i was out on the road so i tried it and it works fine now?!? so i odnt know i will try it again and keep seeing if it works...