1993 GMC Suburban Owner's Manual - Page 290

When to Cheek and Change Lubricant.. Refer to theMaintenanceSchedule to determine how often to checkthe lubricantandwhentochange it. See"ScheduledMaintenanceServices" in theIndex. PO231 If thelevel is belowthebottom of the filler plug hole,you'll need to add somelubricant. If thedifferential is atoperatingtemperature(warm), add enoughlubricanttoraisethe level to thebottom of thefiller plug hole. If thedifferential is cold, add enoughlubricant to raisethe level to 112 inch (12 rnm) belowthefiller plug hole. What to use: Refer to theMaintenanceScheduletodeterminewhat use.See"RecommendedFluidsandLubricants"intheIndex. kind of lubricant to When to Check and Change Lubricant: Refer to theMaintenanceSchedule to determinehowoften to checkthe lubricantandwhen to changeit.See"RecommendedFluidsandLubricants" in theIndex. 6-24