1999 Chevrolet Silverado 1500 Pickup Owner's Manual - Page 325

yellowblue Front Axle When to Check Lubricant Refer to the Maintenance Schedule to determine how often to check the lubricant. See "Scheduled Maintenance Services" in the Index. How to Check Lubricant If the level is below the bottom of the filler plug hole, you may need to add some lubricant. When the differential is cold, add enough lubricant to raise the level to 1/2 inch (12 mm) below the filler plug hole. When the differential is at operating temperature (warm), add enough lubricant to raise the level to the bottom of the filler plug hole. What to Use Refer to the Maintenance Schedule to determine what kind of lubricant to use. See "Recommended Fluids and Lubricants" in the Index. 6-27