Final answer:
A leaking air spring, a torque rod that is out of adjustment, and worn equalizer bushings could affect ride height in a tandem axle air suspension system. The most direct cause would be a leaking air spring, as it affects the air pressure maintaining the vehicle's ride height.
Step-by-step explanation:
The condition that could affect ride height when inspecting spring equalizers on a tandem axle air suspension system could be a leaking air spring, a torque rod that is out of adjustment, or worn equalizer bushings. A tie rod that is out of adjustment generally does not directly affect ride height but could cause steering and handling issues.
In such a suspension system, if there is a leaking air spring, the suspension may not maintain the correct ride height, resulting in more extension in the spring that is not leaking. If a torque rod is out of adjustment, this could potentially change the geometry of the suspension components, thus affecting the ride height indirectly. Worn equalizer bushings could cause a shift in the load distribution between the springs, which might affect the ride height as well.
If this question is part of a test or an assessment, option (a) A leaking air spring is typically the correct answer as it directly affects the air volume and pressure supporting the vehicle's ride height, while choices (b), (c), and (d) involve other components that might contribute to suspension issues, but not explicitly ride height of air suspension systems.