After overhaul of the front differential carrier assembly on a tandem axle, which action should NOT be performed?

• A. Check for leaks
• B. Add oil to the inter-axle differential
• C. Check the differential lockout operation
• D. Check the differential housing angle

Answer: (B)

The main idea here is to verify mechanical integrity and proper function before introducing lubrication. After overhaul, you want to confirm there are no leaks, the differential lockout operates correctly, and the housing is mounted at the correct angle. These checks ensure the seals seating, actuator/linkage, and alignment are all correct, so the assembly won’t fail once it’s in service.

Adding oil to the inter-axle differential at this stage is not advised because filling a partially assembled or unverified unit can obscure leaks, introduce contaminants, or cause an incorrect oil level if the seals or mounting haven’t been proven to be holding properly. Once you’ve confirmed there are no leaks, the lockout engages smoothly, and the housing angle is correct, you then proceed with the proper oil fill to the specified capacity.