hello this is my first post on this site. I own a 1998 F-150 short-box flare side with just over 207,000 km. Up until now it I have had next to now troubles with it other then a new alternator and battery and tires. My problem is that i have the SOF dash switch and the four wheel drive does not seem to be engaging. The light comes on that usually indicates that its engaged, i hear the click as if it were but nothing, no front wheels locking. I have had no problems with it in the past and I use four wheel drive on a pretty regualr basis. I have no idea what or where the problem would be and worse of all im not really all that machically inclined. I would greatly appreciate any and all advice on what and possibly how $$$ this could be. Once again thank you very much for your help. Love the site

 

Welcome to the site. I would first check the vacuum lines to the solenoids. They are on the firewall near the battery. Also check the line that goes back behind the battery to the vacuum canister, one of them could be broken. You might also check the one on the front differential as well.

 

thank you, I will check that first thing in the morning and post back to see tell if that works, thank you again

 

I managed to get under there and kinda see whats what. I took the guard off of the swtich located on the front axle and pushed and pulled that little rod it seemed to move fine. I tried best i could to trace the lines back and up and onto the firewall, again no problem. Now when i shut the hood and went to fire it up and put it into 4by4 it worked fine. Now just yesterday i washed my truck and next thing i new i when i went to try the 4 wheel drive again the front would not engage. I did the same as above but this time no luck. Could it be the lockout switch? if so where is that? any diagrams or anything would really help alot. I've noticed alot of people have had alot of luck diagnosis their problems on this site and have saved themselves hundreds of $$$ from the dealership. I really appriciate any and all of your help, thank you in advance

 

Did you get your problem fixed? Just wondering because a friend of mine is having the same problem on his 03 F150.

 

if you can move the lever on the frt diff, jack up passenger side and move the lever over to the passenger side, the lever moves a collar to lock the axle shaft to a stub shaft in the diff, rotate the passenger tire with the lever enguaged (to pass side, sometimes you have to move the tire slightly to get to lock in the collar) and the frt d\shaft should turn or the drivers tire will turn, if it does you probably have a vacum problem to the frt diff, check for vacum ( it will suck your finger pretty good if you dont have a vacum guage) on the line closest to the pass side while the engine is running and 4wd selected, if no vacum is there you probably have cracked vacum lines, there is a vacum line connector just below the battery check for vacum there, if there is vacum there your line is cracked from there the the frt vacum motor, if no vacum is there then check for vacum comming out of the solenoid, remember there is a vacum supply to the solenoid that has to stay connected the check vacum. if no vacum comes out of solenoid check for power and gnd at solenoid connector. if you have power and gnd then replace the solnoid. there is 2 solenoids for that control the frt axle, one to enguage 4wd and one to disenguage 4wd, make sure you dont get them mixed up.now back to the frt axle, if the driveshaft or opposite tire did not turn when you enguaged the frt axle shift fork, the shift fork is broke inside the diff case, the passenger side axle tube will have to be removed to replace the shift fork.

most common problems
1, seized frt diff lever
2, broken frt shift fork (mostly on 02-04 heritage models)
3, broken vacum lines
4, solenoid