I have a 2001 f150 super crew lariat 4x4, and my grandfather owned it before me and hardly ever used to 4wd. he engaged it a couple times but not more then 1-2 times in 4-5 years. it worked too. He gave it to me and due to custody issues then me leaving for the army the pickup wasnt started/ moved for about 2 years, i went on leave in december 2014-january 2015 and i went out there cleaned her up changed the oil and all that good stuff and cranked her over and everything was running fine, i went over to a buddys house and pulled in the ditch to park and when i went to leave, the *** end sunk lol. so i went to put it in 4H and it would not engage, the light was on . So i put it in N and Put it is 4L . it rolled the gears in the tranny over to low but still no engagment of the front differentials. i was thinking this is either a vacuum leak or a vacuum pump going out. or maybe a fuse

 

If your accurate in what you said, the actuator has failed to engage the front axle.
It may be the hose to the actuator or the actuator .
Good luck.

 

two things happen to get into 4 x 4.. An electric motor on the transfer case moves an arm to engage LO or HI gears, There is a vacuum cylinder on the front axle pumpkin that moves in and out and engages a lever inside the differential to lock in the axle shaft to the drive shaft. Your vacuum cylinder is not engaging. With motor running, pull off one of the two hoses on the cylinder and see if it has vacuum... then change to 4 x 4, pull off the other hose and see if it now has the vacuum....... if the vacuum is changing hoses, then your solenoids and electric all work OK... Normally what happens is the "lever and pin" get corroded and stick and don't change positions. Spray everything with a penetrant and tap on the arm with a 2 pound hammer.. you should be able to move it in and out. You might have to take off a sheetmetal guard... Don't beat it, just make sure it will move. Then connect the hoses and try again... If you have two guys, one can set in truck and put in- out of 4 x 4 and the other can tap on the arm trying to engage.

 

i appreciate it guys! i think its either the vacuum relay fuse, or the vacuum pump. if its never of them then i think its the actuator. i wont be able to know for a couple weeks till i get home lol

 

Only vacuum pump there is is the motor itself.
Good luck.

 

i did some tests and the electric motor engages transter case and the front drive shaft to the front differentials. I checked the vauum lines and the only lines going to the front go to the front gearbox? not to the hubs? and they had no vacuum.... is this the problem?

 

yes this is the problem.. The "gear box" is the front differential that connects the drive shaft to the front axle half shafts. There is a vacuum cylinder mounted in this area and two vacuum hoses, one on each end of the cylinder. the switch on the dash puts vacuum to one hose in 2 x 4 and the other hose in 4 x 4........ under the hood on the drivers side firewall above the steering column you will see two electric solenoids. The dash switch tells these solenoids to open or close.. Note there is a vacuum hose going into the solenoid and two hoses out of the solenoids that goes to the front axle vacuum cylinder.. The hoses run across the back of the motor, down around the right front wheel area on the truck frame, then across the axle to the center differential. Check for vacuum at the solenoids, check that you have power to the solenoids if there is no vacuum out.

 

the wheel hubs are splined to the axle shafts and turn all the time... the vacuum cylinder on the center differential is what engages the drive shaft to the axle shafts.

 

I already check my solenoids, they get vacuum. my question is this though... why in 2H do they both get a live stream of vacuum from the bottom line and then in 4H it is the same??? I didn't understand that..... but there wasn't any vacuum coming from the lines that go on to my actuactor on the gear box, so how can I know if its my actuator if it isn't even getting a chance to work properly even if it is fine?\

 

im having the dealer do a diagnostic check on it Friday, it seems like its a cluster **** lol

 

Besides the fault, you don't understand the operation of the what ,when and why of it.
Here are the basics.
Turn dash switch to 4h powers the case motor to it's first position.
There is a circuit board with the case motor that passes a ground to the firewall solenoid to cause it to operate.
When it operates it passes engine vacuum to the front actuator causing it to pull a linked arm that locks the left front axle together.
When you turn the dash switch off to 2h the case motor returns back to rest, operates a solenoid to return the actuator to non lock condition.
The actuator has two vacuum lines to perform the lock un lock function.
Once you know this you can see what is or is not happening then go looking at the part of the chain that is failing..
Good luck.

 

I Understand this..... what im saying is that there is a stedy Stream of vacuum to BOTH solenoids in 2H, then when you put it into 4H nothing changes it still runs vacuum to both. I know the electric shift motor on the transfer case works . the problem is vacuum related for sure. no vacuum is going to the actuator. the lines have a leak in them I belive. im just baffled that in 2H there is vacuum going to both solenoids.....

 

Not positive but maybe there is vacuum there all the time and when either solenoid is energized or whatever , the respective solenoid allows the vacuum to reach the actuator at the diff.

 

Vacuum has to be there full time or you cannot activate 4wd on demand.
There is no other vacuum line controls.
I told you the case motor has a circuit board that closes ground to these solenoids.
If they don't work, the ground is missing from the Gem module through the case motor board so neither solenoid will pass vacuum when ground signaled if the ground circuits are open...
To prove this put a ground on the ground side of the solenoid at the fire wall and see if the actuator works with the motor running.
The solenoids are fed 12 volts standing on one side of the windings at all times.
If they operate and the actuator pulls in the case motor board contactors are faulty or the harness is open.
Good luck.

 

In your opinion what do you think with the information ive been able to provide you, what would you guess the problem is? and how costly of a fix is this?