Noticed today while I had the truck jacked up that only one tire made a full rotation and the other did not. It seemed one side was acting as is if it was in 4wd and the other in 2wd. Cv axle was only locked in on driver side. The other spun freely. Dash says it's in 2wd. I'm assuming its differential related? Cv axle was just replaced literally 4 days ago. Wasn't sure what would cause this. Thanks for any help

 

How 'bout IWE related?

 

You have a PRE 2004 truck. It has no IWE. The transfer case motor pulls in and connects to drive the front drive shaft... see if it will turn by hand... After the shaft locks in, there is a vacuum cylinder on the front differential that locks the driveshaft to the front axle half shafts... the vacuum cylinder can be STUCK and case the front end to be connected... When you turn the tire , does the driveshaft turn ? The CV joints are for flex/ movement when turning, not 4 x 4 operation.

 

If I am understanding correctly it sounds as if the front differential is operating correctly. In 2wd both the vacuum actuator and transfer case should be in the disengaged position. This means the front passenger wheel is fully disconnected from differential and you should be able turn the front driveshaft by hand. The the front wheels have no direct connection in 2wd. When 4wd engages, the vacuum actuator connects the front passenger wheel to the differential and engages the transfer case. If in park while in 4wd everything should be locked up and not move.

When 4wd is engaged, if the wheel lock together but the front driveshaft is still free, then the transfer case didn't engage.

If the front driveshaft no longer turns freely, but the front wheels aren't connected together then the vacuum actuator has failed or the front diff didn't engage for a less likely reason.

If you have anymore questions on the 4wd systems of the 10th gen F-150s I will be glad to answer them. I have become much more intimately involved in the disassembly and reassembly of their 4wd systems than I ever wanted to be. I have replaced the transfer case shift motor, both cv shafts, the vacuum solenoids and diaphragm, and had to replace an internal pin on the shift linkage in the differential. It is actually a very good system of disengaging the front differential if only it wasn't vacuum operated.

If you rely on your 4wd a lot, I highly recommend the 4x4Posi-Lok system (http://4x4posi-lok.com/). It gives you full control of your 4x4 system and gives more functionality by allowing 2wd low lock operation which is perfect for backing heavy trailers up steep hills.