I got an f-150, 1999, 4x4 Lariat and the 4x4 is not working!!!

When I switch to the 4x4, the transfer engaged but the hub-lock is not working. I can feel the low gear and the transfer engage, but the front wheels are not locking, I think that the problem is on the free/lock hub?

How does it work?

How do the 4x4 connect?

any hints?

 

A 99 does not have front hubs. It has CV joints. If the front driveshaft is turning, but not the front wheels, the problem will be with the front diff. Either you don't have vacuum to the vacuum motor or the vacuum motor itself is broke. Check for vacuum leaks going from the solenoids on the firewall. Passenger side high up towards hood. There are 2 of them. One engages the front diff, the other disengages them. They could be bad or the vacuum lines to the front diff could have a leak. Other than that it could be the vacuum motor on the diff that locks or unlocks the front diff.