Well I have a 98 f150 ext cab 4X4 with 4.6l electronic shift. I am having the problem of the 4X4 not engaging but the light on the dash is coming on. So I've done a bunch of searching and reading on this site. Which is the best resource hands down for anything to do with these truck (maybe the dealerships should start reading this board). So what I've found so far is that the front drive shaft is free to rotate by hand in 2 wheel drive but is not in 4X4 so that seems to be fine. Next I checked the vacuum lines from bellows piston actuator and found no leaks, but with the engine running the piston will not move when switching from 4 wheel to 2 wheel drive. Next I checked the vacuum at the actuator by disconnecting the lines and I found that there was vacuum on one line in 2 wheel and vacuum on both lines in 4 wheel or it could of been the other way around, any ways is this the way it should be? for my next test I gently tapped the actuator piston with a hammer and I could get it to return in 4X4 and then switching back to 2 wheel the piston would extend its self. So I worked it back and forth a bunch of times with some WD40 but it wouldn't free up. I'm wonder if I have a vacuum solinoid problem or an actuator problem? If it is the actuator what is the best fix? Sorry for the long post but I need my 4X4 with all this snow!!

Thanks Mark

 

ANYBODY???

 

Sounds like the actuator on the front axle. Pretty common problem. If you can't turn the front shaft in four wheel drive(with the rear wheels off the ground), the front axle should be locked.

Robbie