Front axle won't engage
 

I have a 2000 F-150 XLT Supercab 5.4 4x4 with the dash knob shifter. My front axle won't engage when shifting into 4x4. A few months ago the vacuum solenoids were replaced and they sound as though they are functioning properly. The diaphragm isn't moving the lever thing and i can't get the lever to move with a screwdriver either.

I know it has worked the past two weekends. Two weeks ago it was in a significant amount of mud and possibly submerged at times. I power washed everything pretty good immediately afterwords though and it has worked in between then and now. What could be going on?

Any ideas at all?

Does the front actuator attempt to move?
You know it has to and the collar engaged to get the front to lock up.
Where does it stop functioning and you have most of your answer.
If your going to off road it expect to have an issue now and then.
Learn how the system works so you can trouble shoot it for repair..
Good luck.

Pull the vacuum hoses off and feel each one as someone shifts into and out of 4 x 4 (motor running).. If you have vacuum on both hoses, then the problem is in the slide mechanism or the vacuum cylinder. Tap on the arm and see if it has rusted or "stuck". Might spray some penetrant on the mechanism. Pry with a screw driver. Watch the cylinder and see if it trys to move (hoses installed) when someone shifts in and out of 4 x 4.... last move is to go internal.

Okay, I'll try and get the vacuum lines off when I get back home next weekend. I probably didn't troubleshoot as well as I could have, but I had engineering homework to do. I hope it ends up being a vacuum issue just so I have an excuse to install a posi-lok on it.

You still need the rest of the system working so the tranfer case engages the front drive shaft.
Good luck.

Sorry for long delay, but it has been thoroughly hectic with mid terms and I just found out my tools have been stolen. I have determined that there is vacuum on both lines.

watch the cylinder and see if it strokes in and out... you may have to spray and tap on it with a bumping hammer or pry bar. might help to have one tire off the ground and have someone rotate it ? Not sure about internal pin alignment.

I know that it doesn't move at all while engaging and disengaging. I tried moving it with a screwdriver prying on it and it didn't move then. I'll go spray some penetrating fluid on it. I am getting new tires, so I'm having the guy look at it while it is on a lift.

I ended up not having the guy look at the 4x4, so I took at it again today. I got it working. It turned out that shaft on the actuation diaphragm was frozen up so bad that simply prying on it didn't move it at all, so after a significant amount of penetrating fluid and banging with some very large wrenches I got it freed up and it is moving properly now.

Amazing things happen when you look into them a bit deeper.
Good luck.

It took a scary amount of force banging on it to get it to work. I thought I was going to break something.