Ok, I got one for ya...This one is killing me!
1999 Ford F350 4 door dually, 7.3 Diesel.
I live in Upper Michigan and bought this truck in Texas and drove it home. On the way every so often I would hit a rough spot in the road which would set off a slight grinding noise from the front end, like splines trying to engage. Took lockouts apart and found them to be questionable. Took splined engaging nut out since I didn't need to use 4wd. Left locking hub center in to balance axle shaft. This was last year, have put about 10000 miles on it now. Had no problems till recently. Now noise is more of a spinning rumble. Noise goes away when put in 4wd. Rules out wheel bearing, axle joint, and caliper slop. Noise does not go away when brakes applied. Tore down to unit bearing, unit bearing is tight like it should be, spindle bearings seem good, axle shaft seems good, installed new MM hubs, (yes they fit on a dually), test drive ended with same symptoms. I am thinking that the spindle bearings are causing the axle to cavitate while not in 4wd due to wheel spinning around axle shaft when not in 4wd. This would explain why the shudder goes away when put in 4wd. I am puzzled though because the spindle bearing looked good. Any suggestions? I think I will have to replace the unit bearing and take a chance that the spindle bearings are actually bad....If you have any suggestions please help with them...