Most vibration problems are caused by an unbalanced
torque converter assembly, a poorly mounted torque
converter, or a faulty output shaft. The key to determining
the cause of the vibration is to pay particular attention
to the vibration in relationship to engine and vehicle
speed. If the vibration changes with a change in engine
speed, the cause of the problem is most probably the
torque converter. If the vibration changes with vehicle
speed, the cause is probably the output shaft or the
driveline connected to it. The latter type of problem can be a
bad extension housing bushing or U-joint, which would
become worse at higher speeds.