1994 GMC Suburban Owner's Manual - Page 279

When to Check and What to Use Refer to the Maintenance Schedule to determine how often you should check the fluid level in your clutch master cylinder reservoir and for the proper fluid. See "Owner Checks and Services" and "Recommended Fluids and Lubricants" in the Index. How to check The proper fluid should be added if the level does not reach the bottom of the diaphragm when it's in place in the reservoir. See the instructions on the reservolr cap. Rear Axle When to Check and Change Lubricant Refer to the Maintenance Schedule to determinehow often to check the lubricant and when to change it. See "Scheduled Maintenance Services" in the Index. How to Check Lubricant 6-33