hey everyone, about 8 months ago we did ball joints, seals hubs rotors etc on my dads 03 f350 v10. I was trying so see why his 4wd wasn’t engaging while we had it apart, figured the hub knuckle seals were bad so while we were doing the front end we replaced them, after we got everything back together I manually pulled a vacuum on the hose on both sides and the hubs engaged. Release the vacuum and the disengage, apply the vacuum manually and they engage again, however when the vacuum hoses are pluged back in to the vacuum lines on the frame and the selector is moved to either 4w hi or 4w lo the hubs just spin and do not engage, hard to tell when its running but so far cant hear a vacuum leak, since it was spring we weren’t too concerned about it as his hubs lock manually as well. With winter approaching i figured we might as well get it fixed. I know to start with tracing the lines to check for a vacuum leak, from what we can tell the lines look good, any guidance or other prone issues with this system to start with? Thanks guys.

 

There's a 4x4 solenoid right next to the vacuum that you may want to try. Seen them for $26 on Amazon. I've been researching the same stuff as you, so I'm interested to see what you find. I had the issue with no 4x4 even though I get the high and low lights to come on. Plus my vent were defaulted to defrost no matter what position I put them in. found a mouse had chewed through the bottom on a 90 degree elbow coming right off vacuum. All my vents work right now but still no luck with 4x4.