In the pinion bearing preload setup, what is being measured?

The correct answer focuses on what is specifically being measured in the context of pinion bearing preload setup. In this scenario, the primary measurement of interest is indeed the pinion bearing preload, which relates to the amount of force applied to the bearings that supports the pinion gear in the differential assembly.

Pinion bearing preload is vital because it affects gear mesh, noise, and overall performance. Proper preload ensures that there is enough tension in the bearings to maintain correct alignment while also allowing for sufficient lubrication and flexibility for the gears under load.

While seal drag can be a contributing factor to resistance in the system, it is not the primary parameter being measured when setting up pinion bearing preload. The setup process usually involves measuring the rotational resistance that directly correlates with the preload on the bearings themselves, rather than the drag caused by the pinion seal. Hence, the measurement is specifically about quantifying the preload on the pinion bearings.