1998 GMC Suburban Owner's Manual - Page 316

What to Use Refer to the Maintenance Scheduleto 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. Manual Transfer Case 6-24