Which transfer case do you have? Automatic 4wd or electronic shift on the fly

 

I feel like I say this too often -- but I had kind of a hard time following your post.

Failed IWE's will cause your front wheels to rotate when you haven't engaged 4 wheel drive. I probably misunderstood what exactly you meant when you say you checked the vacuum. If you checked the vacuum by pulling the line off the IWE male piece, that wouldn't have shown you if the vacuum problem was in the failed IWE itself.

If you do not have the truck on/running (at least with mine), and you jack the truck up and spin the front tires it will look like you have an IWE/4 wheel drive failure because the trucks maintain 2wd by applying vacuum. Once you shut the vacuum off -- that's when it will engage the front wheels.

Ignore if you've already ruled these things out.

Do your wheels bind up when you take sharp turns at low speeds?

 

I just went out to my 2013 and did a test. Engine not running driveshaft won’t turn with wheels on the ground. Engine running and driveshaft turns freely by hand. When I turned the driveshaft by hand it turned the axel also. Maybe your driveshaft is moving just from friction in the transfer case and not really locked to the power output. If that part made any sense.

 

I’m new here, needing some advice/help. I have a 2013 f150 ecoboost 4x4, my front cv shafts and front drive shaft are turning while vehicle is in motion in 2wd. I came to conclusion to check what’s going on after I’ve been getting a very slight whine from under the vehicle going 65 mph. So some of the tests I have done are...
Testing vacuum on both actuators, turned out great! Checked all mechanisms inside the engine compartment that deals with the 4x4 system, everything seemed to pass perfect. So than I went to the extreme, lifted the rear end off the ground, removed front drive shaft from transfer case and front differential. I had my wife put the truck into drive and noticed my flange on the transfer case is spinning. The front drive shaft should not be spinning in 2wd as that’s the reason for actuators. So I put it into 4hi and 4low. Everything worked great. When switching back into 2wd, my truck shows on my dash that it’s back into 2wd. So is something internally bad inside the transfer case or would possibly be the motor on the transfer case? Thanks, hoping for some informative help!

Did you ever find a solution to this. I have ruled out the IWE actuators by jacking up the truck putting it in gear and the front drive shaft turned. I replaced both IWE's and they are not engaged with vacuum applied.