Won't Shift Into 4 Wheel Drive
 

I bought a used 1998 Ford F-150 4X4. I tried to switch it to 4x4 and it would not switch.

Anyone have any idea what it might be?

Thanks

What type of 4x4,,Shifter on the floor,,,,or Knob on the dash ?

IT's the one with a switch on the dash

Do the Dash "4x4" lights come on when you turn the knob?
If they do,,,
There is a vacum operated lever on the front diff,,,some of your favorite penetrating oil sprayed on it may help(may have to remove plastic cover),,check the vacum line for cracks,,or broken,, missing,,etc
also on the fire wall, behind the battery(pass side) there are 2 vacum solenoids for the 4x4 system check them out for cracked vacum lines etc,,

If no dash lights,,check fuses,, any clicks when knob is turned from under dash ?,,I have read about what they call the GEM module,,I have no experience with it,,someone should chime in with a bit more knowledge,,Good luck.

Thanks for all the info i'll slide under the truck to have a look thanks again

that there vacuum in your dang ol' 4 wheel drive aint working cause your old lady is usin it to clean the trailer