Which element pivots when moved by the input rod in a hydraulic assist?

In a hydraulic assist system, the element that pivots when moved by the input rod is the lever. The lever serves as a mechanical advantage, translating the input movement into a more forceful motion due to the hydraulic pressure applied. When the input rod moves, it activates the lever which then operates the hydraulic system, helping to amplify the driver's input for easier steering or braking. This mechanism is crucial in hydraulic systems as it enhances the effectiveness of the original input, allowing for smoother and more efficient operation.

The diaphragm, return spring, and power booster also serve important functions in hydraulic assist systems, but they do not pivot in the same way the lever does when force is applied by the input rod. The diaphragm typically serves to separate different fluids or provide a flexible barrier within a system, while the return spring aids in returning the lever to its original position after being activated. The power booster is a term that can refer to the whole hydraulic mechanism rather than a specific pivoting part. Thus, the lever is the correct choice as it directly responds to the movement of the input rod.