Yep, lent my 3500 4x4 Ram and 20 foot 5th wheel trailer to my brother to haul a vehicle to his house. It just has the dial with little LEDs. Apparently it was a bit muddy in the back area and he engaged the transfer case 4x4.
He unloaded the vehicle, but forgot to put my truck back in two wheel drive.
He then drove it 12 miles on dry pavement (still with the 10k rated fifth wheel rated trailer attached) , Turns and all.
Leaves the truck and trailer and gets a ride home.
Go to move the trailer to disconnect it, immediately notice the front wheels trying to hop while turning.
Disengage the 4x4 and disconnect the trailer.
Moving the truck back to park it and still hopping when in a turn.
Put the truck up on the lift and discovered Both front outer u joints ruined and binding with missing needle bearings and broken cap. That was a bit of labor to fix.
Brother " I am sure i took it out of 4 x 4...." plus your truck already has close to 100k on it. Those u joints must have been worn out.
ps. The main outer unit bearings were both fine no damage at all.
On a tractor front axle, those outer bearings are usually ball bearings and my bet would be that the failures start in most cases with the bearing cage "failing" since they are just a sheet metal piece.
If the cage fails, the balls are free of being held in correct equidistant load supporting location, and they can Migrate out of the race, unfortunately usually into the ring and pinion teeth which results in carnage because the ball bearing Chrome steel is much harder than the pinion or ring gear metal.