Hello all! I'm a long time reader and first time poster
I have a 2004 F-150 XLT affectionately named Curtis Loew that recently had an issue with the 4WD system. I was out wheeling with my buddies and i heard a loud pop from the transfer case area ( somewhere under the cab ) and now when 4WD is engaged in either high or low range the front tires don't spin and there is a grinding noise like the chain slipping, the IWE's seemed fine checked the with truck on and in 2WD and they spin free with no noise and with the truck off and they lock to the diff solidly, the truck shifts into 4Lo and 4Hi but when I apply throttle the front tires dont spin and the grinding noise starts very loud but stops once the truck gets back down to idle, i cant tell if the chain inside the transfer case broke ( which I doubt as the truck only has 31-32" tires and is not off road much ) or if the shift motor isn't engaging properly there is no noise in 2WD but there was previously a ticking sound when slowing down to a stop around 10-15 mph from somewhere under the cab that had been going on for some time
I will look into it more in the morning but any ideas help!

 

Sorry to say but it definitely sounds like something snapped inside the transfer case. It's going to have to come apart for inspection.

 

That is what I thought too at first but after messing with the shift motor today and the MSS on the dash the front wheels started to spin again and the truck seemed to have fixed itself, fortunately the sound came back but with the windows down I could tell it was coming from the front drivers wheel so I jacked it up and left it in 4wd and the wheel spun but the axle and CV joint did not ( this also produced the noise i was hearing) so it turns out to be another IWE that this truck has broken but it seems this time the internal spring wore out and wasn't engaging properly glad its only a $80 fix and not a whole new T-Case

 

Good, you dodged a bullet there, that "loud pop from the transfer case area" seems to have initially led you down the wrong road.