The body, instrument panel, and steering wheel vibrate slightly on take-off. This occurs during gradual engagement of the clutch, while the engine is still idling. The shift lever, front seats, body, and steering wheel also vibrate. When you place your feet on the rear floor, you can also feel small vibrations. These vibrations occur at take-off in first gear, at 3/4 to full throttle.
Main causes
Torque fluctuations in the engine
Improper engine mount spring constant
Resonance between the body and the steering wheel
Excessive joint angle on the three-joint propeller shaft
Resonating center bearing of the propeller shaft
Excessive joint angle in the tripod-type constant velocity joint
Mechanism
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.