Most 240sx have the center driveshaft carrier bearing shot and will move under load.
This will cause vibration and knocking noise.
Aluminum 1-piece driveshaft eliminates the need for a bearing completely, and also reduce overall mass on the drivetrain resulting in more power to the wheels.
*This driveshaft is made in USA and high-speed balanced. Comes with 1310 U-joints for a direct drop-in replacement. Zero modifications needed.