I have a 2001 f250 superduty that the 4 wheel drive will not engage I have checked all the fuses could it a vacuum line and if so where would i start looking

THE LOCKOUTS ARE BINDING OR STICKING IF YOU ARE MECHANIC SAVY YOU DISSASEMBLE THEM AND CLEAN AND RELUBE THEM AND THEY SHOULD WORK FINE.

Operationally vacuum shifts the front axle between 2WD and 4WD mode. The GEM ( Generic Electronics Module ) applies ground to the solenoid needed for the mode selected on the switch ( for ESOF ) or when the transfer case shift lever is moved ( MSOF ).The contact plates in the transfer case signal the GEM that the transfer case is engaged, and the Vacuum solenoids need to be activated ( either 2WD to 4WD or 4WD to 2WD ).

Lift and support the front of the truck so the front wheels are off the ground ( take safety precautions, chock wheels, jack stands, etc )
Key on, engage 4x4 and try to turn the front drive shaft.
- If it turns it is a problem with the transfer case.
- If it doesn't it is a front axle engagement problem ( this is what you seem to have, the transfer case is engaged and will drive the front shaft mine was a key on engine off test ).

- If the front drive shaft does not turn :
•With the truck running ( with front wheel back on the ground ), switch from 2WD to 4WD and back again, the vacuum shift motor should move the lever on the front axle.

-- If the vacuum shift motor does not move:
1.Check for vacuum on the lines while shifting between modes. Pink vacuum line is 2WD mode, Light Blue vacuum line is 4WD.
2.Check the fuses for the 4WD system and the solenoids.
3.Check the vacuum lines from the vacuum shift motor to the solenoids on the firewall.

4.Check the vacuum lines from the solenoids to the vacuum reservoir box behind the battery.
5.Check the vacuum reservoir box for cracks.
6.Typical solution is the vacuum lines ( to the solenoids or to the vacuum shift motor ) are cracked or the vacuum shift motor has a cracked diaphragm and has water in it.
7.Could be the shift plate contacts in the transfer case are corroded / not making good contact, and not activating the solenoids.


Usually the case is cracked vacuum lines from the solenoids, the next common is a cracked vacuum reservoir box, and 1 time I have seen the mount for the vacuum disconnect motor broken ( motor floating free so it could not push against the axle )

If you can't get 4 high, then you can't get 4 low either. You can get the transfer case to go into 4 low, but unless the front axle is engaged, you will still be in 2 wheel drive. There is a vacuum switch that engages the right front wheel. The left wheel is engaged full time. On earlier models, this vacuum switch is located unerneath the battery tray. It is prone to become disconnected from the vacuum line. Check this and all other vacuum lines that are connected to the 4wd system. The way I test my 4wd Jimmy is to find a dirt or gravel road or parking lot and accelerate hard from a standing start in both 4hi and 4lo. If 4wd is not engaged your back wheels will spin.

The power to the switch seems to be the issue. The vacumm switch is
just a normally closed switch,meaning only when it gets power, will it
send vacumm to the hubs to allow the 4wd to work automatically. You will have to trace the electric back from the switch,to see where it goes,
a relay or fuse. You may just have bad relay contacts. Good luck.
You can always run a toggle switch into the cab,to get the system
working until you figure out what's wrong in the mean time. Just a thought. Good luck.

Check the fuse for the four wheel drive before taking another step,it is electrically engage,hope that help you and clear your mind

I had a problem with vacuum in my F250 diesel. It had a new vacuum pump but would kick out of cruise control every time the vacuum pressure dropped. It turned out to be the vacuum reserve cannister had holes in it.

Seems you reach a tipping point and then all the vacuum systems mess up. You might want to check the reserve cannister and any vacuum servo your 4x4 might have. You can check most of the vacuum stuff with the engine OFF using a vacuum pump. You could have a leaking vacuum pot operating the ductwork. Check your diesel vacuum pump for output and loose belts.

theres a power diseribution box under your hood by the battery its in there

fuses relays in engine compartment or in dash board . look at transfer case look for vacuum lines or electric lines.its probably electric. because most 4 wheel drive uses electric motors.99 up to 2009s model.

I have the same hubs on my truck as what you have. I have been told it can be done you just have to know if you have a dana 50 or 60 front axle. The warn hubs i'm sure are a better quality hub but if your worried about the auto feature of your current hubs. That is vacuum accuated when you 4 wheel drive is engaged. And there fore vacuum engaged. Mine used to work great but after a lot of mudding sand got into seals and vacuum didn't work anymore so i treat them as free/lock hubs.

while in drive, engage the 4wd then shift into neutral for 2 or 3 seconds and shift back into drive. it works for my ram.