I have looked at the similar posts on this but want to put up my exact problem. I've got a new to me 01 4x4, automatic with the swithch on the dash.
I've got it running great now. First trip to work today. On the way home I tried the 4x4 on a dirt road. Front wheels didn't seem to spin but the rear did. The front wheels did seem to be locked. The dash 4x4 light came on regular and low 4x4.
Any input would really be great. I'm going to check the fuses mentioned in another post. I am assumming that if the front wheels are locked that the front actuator is working. I am only assumming they were locked as they felt like it but I didn't verify it.
thanks, bullseye670..................

 

When you switched it to 4x4 lo, were you stopped, in neutral, foot on brake when you switched. If not it is not going to do anything.

 

ok heres what I've got. The front wheels are not locking. I've checked the actuator on the front differential. Its got vaccum going to it, switching between the blue and pink hose when the selector is switched. The actuator is moving just the slightest bit. I'm currently letting penetrating oil soak on the area where it attachs to the diff. I've removed the "c" clip but the thing is really corroded on the diff.
I've used a vaccum pump on the actuator but that won't move it either I've got good vaccum comming from the vaccum motors.
Its either the actuator or the shifting fork in the diff. Can anyone tell me how often either of these go bad? I'm praying its the actuator and not the diff.
The previous owner has told me that the 4 wheel drive has almost never been used. Just a few times in the winter.
bullseye670...............

 

So which is it?? Are you sure 4wd isn't working??

Check this switch too:
https://www.f150online.com/forums/sh...d.php?t=192971

 

I switched out the actuator (motor as ford calls it) on the front diff. and it works great now. The old one was definitely froze up.
Not a very hard fix. The actuator was $158 at the dealer. Had to call 3 different dealers to get one. One had just sold the one they had a half hour earlier. Searching this site for similar priblems sure did help me out.
bullseye670...........