2000 Ford F-150... 4x4 not engaging
 

Hi. I need some help. My boyrfriend has a Ford F-150 4x4 truck with a long bed, standard cab truck. Up until now he has had no problems with the truck. This past weekend, we were helping family cut and haul wood from a cabin we belong too.
Before we started to load wood into the truck bed, he needed to switch the truck into 4 wheel drive because of the area we were in was covered in snow and mud.
He turned the switch to 4h and nothing happened. He tried 4l and nothing happened. We could hear it click everytime he switched it but it never engaged. After playing with it for a while, driving forward and backward, it finally engaged. Worked all day. Then after coming down off the mountain, he switched it back to 2 wheel drive and it wouldn't come out of 4wd. Again he had to play with it, drive the truck forward and backward and finally, it disengaged.

Q : Has anyone encounted any problems with the 4wd switch not working properly or not engaging? Is there a recall or are they know to fail after some time?

Please advise or give me some links where we could find out more info. Thank You.

Does the truck have the electrical switch or the shifter on the floor? If it's electrical, maybe there's something screwy goin on with the wiring.

There are two vaccum sensors on the passanger side fire wall. Try replacing those they enguadg and disenguadge the 4x4. I had the same problem. How it helps.

The 4x4 switch is a "dial" located on the dash near the steering wheel (beside the radio). I have a 2001 Ford Explorer with the same kind of dash switch.

Yesterday we were unloading the wood (from the trucks from Sunday's wood cutting) and we had to drive up a long driveway to get to the family member's house where the wood was going to be used.
He was able to lock in the 4wd going up but then as he was backing up the truck, it disengaged itself and the wheels just spun and he couldn't get traction. Again, he had to do the 'go-forward-back-up-go-forward' scenario to get it to re-engage but it seems like it's starting to come out of 4wd once it is engaged now. Takes a few attempts to get it into 4wd then, one minute it's working normally, the next it's not.

Sounds like the shift motor on the xfer case.