A while back someone metioned a problem with a vibration in their Oliver and the subject of worn couplers and the possibility of a bad bearing in the tranny input shaft came up. Have had a vibration in my 1955 for some time. No vibration in neutral, no vibration under load but as soon as you got any rpms up when not under load it would vibrate. Since the tractor had recently had the motor out I checked all of the motor mount bolts and they were tight. Changed the coupler and it didn't help. Further examination revealed that the bell housing bolts were not as tight as they should be. One bolt, the one behind the oil filter can, (the one you can't see) had backed out a couple of turns. Am going to take the oil filter can off and retighten all of the bolts and see if the vibration goes away. Hope that's the problem and not a symptom of a deeper problem. I'll keep you posted. At any rate guys if you do have a vibration, you might want to check your bell housing bolts.