2000 GMC Sierra 1500 Pickup Owner's Manual - Page 328

yellowblue 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. Rear 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 See "Owner Checks and Services" and "Recommended Fluids and Lubricants" in the Index. How to Check and Add Fluid 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 reservoir cap. 1500 Series shown, 2500 Series similar 6-25