2001 GMC Yukon Owner's Manual - Page 328

Rear Axle When to Check Lubricant Refer to the Maintenance Schedule to determine how often to check the lubricant. Additional rear axle scheduled maintenance is required when trailer towing. See "Scheduled Maintenance Services" in the Index. The proper level for the 1500 Series is from 5/8 inch to 1 5/8 inch (15 mm to 40 mm) below the filler plug. The proper level for the 2500 Series is from 0 to 3/8 inch (0 to 10 mm) below the filler plug. Add only enough fluid to reach the proper level. What to Use Refer to the Maintenance Schedule to determine what kind of lubricant to use. See "Recommended Fluids and Lubricants" in the Index. How to Check Lubricant Four-Wheel Drive Most lubricant checks in this section also apply to four-wheel-drive vehicles. However, they have two additional systems that need lubrication. Transfer Case When to Check Lubricant Refer to the Maintenance Schedule to determine how often to check the lubricant. See "Periodic Maintenance Inspections" in the Index. 1500 Series shown, 2500 and 3500 Series similar 6-25