What does the part shown in Figure 3-18 permit the driveshaft to do?

The part depicted in Figure 3-18 allows the driveshaft to change its effective length. This is typically a slip yoke or similar device found in many driveshaft assemblies. Its primary function is to accommodate the movement between the transmission and the rear axle as the vehicle experiences suspension travel.

When the vehicle goes over bumps or during acceleration and deceleration, the rear axle moves relative to the transmission. The capacity to change effective length ensures that the driveshaft maintains a proper connection and alignment, preventing excessive stress or damage. This adjustability is crucial for maintaining proper driveline operation and ensuring smooth power delivery while minimizing vibrations and potential damage to other components.

Other choices, while relevant to vehicle dynamics and component functions, do not accurately describe the primary role of the part in the context of driveshaft operation. Choices relating to wear, fluid flow, or absorbing shock loads pertain to different components or contexts within the vehicle’s drivetrain system.