Ford Super Duty (1999-2016) :: Strong Vibration Like Shuddering / Growling And Rumbling In 2WD Intermittently

My 2000 f250 4x4 V10 5spd manual with LSD and 63k mi gets an intermittent but very strong vibration like a shuddering, growling, rumbling in 2WD. The 1st time it only lasted about 1 second. It had been making a swooshing noise that sounded like front left wheel bearing for several thousand miles before this, so i replaced bearing assembly even though it turned smoothly.

After that, It still made the exact same swooshing noise and after a couple miles at 45mph, it had the strong vibration/shudder that lasted about 3 seconds. I stopped and locked the hubs manually. The vibration happened again in a couple miles, so seems like it's not the needle bearings in front stub shafts or locking hubs. On that last occurrence, the vibe went on for 5 seconds, felt the same with clutch in, and went away only after truck slowed down to nearly a stop. I've driven it about 6 mi total since the 1st occurrence.

Front right Wheel bearings feel smooth. I unbolted the driveshaft support bearing and it spins smoothly. The front u-joint maybe had a tiny bit of play, all bolts tight. I didn't check the nuts for yokes, but it didn't look like yokes had any play. Drive shaft slip joint moves smoothly. No up-down play at pinion shaft input into rear diff and output from transfer case. Rear diff oil was full with a little bit of silvery sludge on the magnetic filler plug, maybe 1/10 of a cc, no metals slivers or chunks. I raised the rear wheels and ran 5th gear 2WD at idle (~30mph) and touched a 4' listening stick to the drivetrain components.

The only odd sounds were from the rear differential. It sounded like a bad bearing with random crunches and thuds mixed in with the normal whirring. Crunches and thuds were loudest at front of diff housing. I blocked one wheel and repeated in 3rd gear. You could hear noise like gears meshing (noisy spider gears? maybe was LSD clutches?). The differential was warm after 5-10 minutes, with the hottest area being about 3" from the front of diff, just before the housing widens.

So, I'm guessing the pinion bearing is bad and the intermittent shudder is the bearing race spinning in the case when bearing seizes.