Hey auto guys or gals. I have taken the 61 tbird to the shop because it has a whole car shaking vibration at 60 mph. It also had a shuttering vibration at take off but went away at about 25 mph. I am told the alignment is good in the front end even after I replaced majority of the components. Mechanics feel the shutter vibration at start up is in the differential. The drive shaft is balanced and U joints I believe are ok. They did find a rear wheel bearing bad and replaced it but can not get the start up shutter to go away. They are thinking about trying a diff from a 63 Galaxy if the splines in the axle are the same. I am not sure this is the direction I should take. What are your thoughts or suggeston?