If drive pinion preload is not sufficient, what action should be taken?

In the context of adjusting drive pinion preload, increasing the shims is the correct action to take when there is insufficient preload. Preload is critical in ensuring the proper functioning of the rear axle assembly, as it affects the bearing performance and gear alignment.

When the preload is inadequate, it can lead to excessive gear noise, increased wear, and potential failure of the differential components. By increasing the shims, additional spacing is created, which tightens the assembly and applies the necessary preload on the pinion bearings. This adjustment helps ensure that the pinion gear maintains optimal contact with the ring gear, promoting efficient operation and longevity of the drivetrain components.

The other choices suggest actions that would not properly address the issue of insufficient preload. For example, decreasing the shims or removing them entirely would only exacerbate the lack of preload and lead to further complications. Installing an oversized spacer may not provide a precise adjustment and could introduce new problems. Lastly, merely installing a thicker adjusting washer might not correlate effectively with the intended preload correction without a careful assessment of existing shim measurements.

Therefore, increasing the shims is the most reliable method to achieve appropriate drive pinion preload.