1998 F150 4x4
Last winter driveing on snowy roads in 4 hi It felt like it was engaging and disengaging as i ws driving. Eventually during the year it got to where i had to turn the **** a number of times before it would engage. Finally I couldn't get it to engage in either 4hi or 4lo. Thought it had something to do with the vacuum! This eve. I was messing with it and tried to get it to engage by tyruning the **** and it sounded like it was engaging (the telltale clunking ), but when I drove it it was only in rear wheel drive. Any ideas?

 

The vacuum operated solenoid on the front diff is bad, you have a vacuum leak, or the electric solenoid located behind the Battery has gone. Check those.

 

How do I diagnose which of these things is faulty? Is there a selenoid behind the Case that holds the battery? Theres two vac. selenoids on the firewall that the vac. lines go to, Is that the one youre talking about? How do I test those to see if there woking?