1.Engine torque fluctuations
On take-off, the engine rpm drops when the clutch is engaged. At this time the engine torque fluctuations increase, causing the engine to vibrate on its roll axis.
The “roll axis” of an engine is the centerline based on the center of gravity around which the engine attempts to roll.
These vibrations are transmitted to the body via the engine mounts, resulting in instrument panel or steering wheel vibrations.
2.Joint angle of three-joint propeller shaft
The angle of the propeller shaft (created by the universal joints) causes torsional force to be applied to the universal joints, causing vibrations.
The drive torque at sudden take-off increases this torsional force.
The center bearing resonates with this force. The vibration that has thus been amplified is transmitted to the body.