When inspected, the differential or PTO oil is dark or black

Bulletin number

SA-056-25

Component

Power train

Summary

When inspected, the differential or PTO oil is dark or black. This is considered normal and NO repair should be performed. During production, differential ring and pinion gears receive a manganese phosphate coating (commonly referred to as black oxide). This coating forms a porous, oil-retentive surface that improves boundary lubrication and reduces adhesive wear during initial contact cycles. Designed as a sacrificial layer, it is gradually removed under load throughout the break-in process. As a result, after the first few hundred miles, or at the initial gear oil service interval, the lubricant may appear darkened by the worn-off coating. It will contain trace ferrous particles from the normal run-in of the gear teeth and bearing surfaces. This condition is expected and does not, by itself, indicate an issue with the differential or PTO gears.

Owners of these vehicles have filed 313 complaints in the transmission category.