hell i got a 2006 f150 4x4 and the other day i went off road put it in 4x4 went to go up hill and it made a loud pop sound and no 4x4 went back home on the way i left it in 4x4 gave it som gas and starts poping all on driver side new hub and cv axle and accuator iwe all new still same problem

 

Problem with front differential or transfer case motor? (probably not though) Sounds awful. The only reason why I say the diff or tran case is maybe they are putting too much torque into the hubs for some strange reason though that doesn't sound right now that I have it written out. Maybe the hubs aren't engaging fully and cannot overcome the amount of torque given to them by the driveline (even though you just had them replaced, maybe the shop did a poor job).

 

Well Ill throw my 2 cents in since you havent got any other responses although the search feature is very helpful especially in 4x4 issues, but maybe its one of your vacuum lines that may have a crack or leak and not allowing the hub to fully engage...

 

Yeah check out the post Good old IWE humming...cv's locked in as I talked about the hubs in that one and a test you can do on them to see if the vacuum is not working.

 

well from what i under stand when the 4x4 is engaged the vaccum is cut from the hubs so if it was a vacuum leak it would be in 4x4 all the time. the other day i went in a empty gravel and dirt lot i put it in 4x4 and just give it hell everything was good get on the road or in the snow it pops out dont work checked the hubs cv again everything looks perfect

 

now i only did the driver side bc thats where the pop ic at by some odd chance if the pass side is shot whould it make that sound still on the driver side

 

So I did some searching to try and settle down the mass amount of 4x4 issues and I think this will help 90% of questions and issues!!! ENJOY

The neutral/foot on brake or park is only if you are shifting into 4L. If you are shifting into 4H, applying light throttle up to 55 mph shift on the fly is fine ( per owners manual ).

Operationally vacuum holds the IWE ( Integrated Wheel Ends ) out, and once vac is removed the spring engages the IWE.

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.

- If the front drive shaft does not turn :
Shut of the truck ( still jacked up, and supported ) remove the vac lines from the IWE. The spring should push the gears in, without the vac line on.
Check the vent line ( tube that is routed into the engine compartment with nothing attached to it ), for blockages.
If the vent line is clear, and with the vac lines off the IWE should be engaged ( both front wheels locked ).
If they lock, the problem is with the IWE solenoid not shutting off vacuum to the IWEs. There is a TSB on the 2004-2006 IWE solenoids, a newer revision has been made, and used from 2007 and newer MYs.

Here is a block diagram of the IWE system

If the front drive shaft turns, I have seen some lightly hit the back of the transfer case, to free up the shift motor, with mixed results.
If you had a vacuum leak, the front wheels would be locked in, or poping in and out of locked in, causing a grinding noise ( IWE gears not engaging fully, grinding the teeth off ).

If you find a problem with the vacuum lines or the IWE solenoids, you can pull the vacuum lines and plug them, this would leave the front wheels locked in all the time. Fine for short use, don't try racing like this ( pushing a dead axle is a lot of HP