2001 GMC Sierra 1500 Pickup Owner's Manual - Page 372

Hydraulic Clutch The hydraulic clutch linkage in your vehicle is self-adjusting. The clutch master cylinder reservoir is filled with hydraulic clutch fluid. It is not necessary to regularly check clutch fluid unless you suspect there is a leak in the system. Adding fluid won't correct a leak. A fluid loss in this system could indicate a problem. Have the system inspected and repaired. 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. 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 for more information. 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. 6-30