Truck Repair: Ford f150 ext cab --4WD doesnt work, rear wheels, steering knuckle

Question
I was plowing and heard a loud bang like hitting a rock with the plow then could not back up. NO MORE 4WD.. Front driveshaft still turns from transfer case. Hubs are manual and were locked.Shifter is on floor and was in 4wd low. Runs ok in 2wd ,no noise from any parts. Do I maybe have broken hub or worse something in the front differential?Have worked on F150 but not 4wd so need help. Thanks for the help.

Answer
Get it on a pile of snow or something so the rear wheels are spinning, and while they are spinning, look under the front and see if the U joints inside the steering knuckle are turning.
If one of them is turning, that hub is not engaged, or is broke.

You could also jack the front up when 4X4 is engaged, and see if you can rotate the wheel. If the hub is locked, that same u joint should turn.

Van