When to check and what to use, How to check and add fluid, Rear axle – GMC 2000 Sierra User Manual
Page 328: When to check lubricant, How to check lubricant

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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 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. See “Scheduled
Maintenance Services” in the Index.
How to Check Lubricant
1500 Series shown, 2500 Series similar