Final answer:
The component that ensures both drum assemblies receive the same application force in a park brake system is the hydraulic system based on Pascal's principle.
Step-by-step explanation:
In a park brake system, the component that ensures both drum assemblies receive the same application force is the hydraulic system based on Pascal's principle. Pascal's principle states that pressure changes in an enclosed fluid are transmitted equally in all directions. When the driver pushes the brake pedal, the force is increased by a simple lever and the hydraulic system. As a result, each of the identical wheel cylinders receives the same pressure and creates the same force output.