On my old 82 633 (with 3HP22 auto trans), I feel a rumbling vibration when the car is about at the speed of the 1-2 shift. I've pinpointed it enough to say it doesn't occur exactly at shift, but rather around 15 mph, by keeping the car in 1 and accelerating through the vibration range. Sometimes it's a hard rumble, enough to make me worried about the thing falling out or something, and sometimes it's just a little drumroll. Once in a while, it doesn't happen at all, and seems to occur more frequently after the car is warmed up some. I know the drivetrain is such a complex mother when it comes to vibrations, but I'd really like to hear from anyone with any light to shine on the subject. Suggestions, ideas, recommendations, etc are of course very appreciated. Thanks in advance to all, James