I have a problem with my front hubs won't lock in. The problem started getting worse gradually. I have changed the vacuum actuator on the axle. I have also changed both vacuum solinoids on the fire wall. I have checked all vacuum connections and hoses. I'm stumped Need help!

 

Look for a crack on the vacuum lines. That is all it takes to stop the front diff from locking in.

 

I had the same problem, Pulled axel apart found fork plastic gone! You will need Kit # F75Z3N139KG. This was not to hard to repair.

https://www.f150online.com/forums/ot...t-working.html

Mark

 

It's usually as kingfish posted - Most common problems and they crack between the battery box and firewall.

You can stick a vac pump on the actuator to test it, go from there if the lines are good.



Also - DO NOT connect Blue and Pink lines to actuator as Ford Service directs. They have it backwards for the 97 lol. - Not kidding.