An older truck with a two-piece driveshaft shows drivetrain vibration that is noticeable primarily in lower gears. Which explanation is correct?

• A. Technician A: driveshaft worn and U-joints rebuilt.
• B. Technician B: issue is related to suspension design or worn bushings.
• C. Both A and B.
• D. Neither A nor B.

Answer: (B)

When torque is highest (in lower gears), how the drivetrain’s forces are transmitted into the chassis matters most. A two-piece driveshaft can transmit vibrations through its joints and carrier bearing, but those driveline components usually show vibration across a wider range of speeds or with driving conditions, not only in low gears. If the vibration is most noticeable under load in the lower gears, it points to how the suspension and its mounting points handle that torque—worn bushings or a suspension design that doesn’t isolate drivetrain movement well. Those worn or misaligned bushings let the drivetrain’s torque pulses be transferred into the frame more readily, creating the vibration you feel when the engine is delivering more torque. So, the better explanation is that the issue lies with suspension design or worn bushings.