Ok truck was dead for a few months.... replaced multiple cables and some eletrical equipment......truck is running again...... but for some reason the 4x4 won't enegage...... the hubs turn to free and lock position........the shifter goes into 4 hi 4 lo N and 2 wd.......But the front tires are not engageing...... I found a pinched vac line that I cut away and put back on connector but don't know if that was to 4x4 system or not.........What vac lines go to that system on a 1978 F1150 4X4? there is a metal line with 3 outlets that thick vac lines are coming off of...... it is right behind the carb........have to take off air cleaner to get to......the line that was pinched is a old line.....possible dry rot so will be replacing that tube......it come towards the firewall and connects to a small bowl looking object that has 2 other vac lines coming from it....... Is this part of the 4X4 system? If so where do these lines go so I can try and track them down to check for more leaks/breaks etc.... And Thanks for all the help......

 

The hubs when going from free to the lock position only lock the hub/wheel to the axle. When you engage 4x4 the transfer case then provides power to the front diff via a driveshaft. The front diff is connected to the front axles and the hubs are then locked to the axles. If you use the process of elimination you should be able to figure out what is causing the issue. Maybe the belt/chain in the transfer case has broke. Maybe its not engaged completely.

 

Everything on your truck for 4x4 is mechanical. Either the hubs arn't locking, the front diff is toast, or the transfercase isn't sending power up front.

Adrianspeeder

 

im bettin its not the front diff. or hubs. id look in to the t-case.