Four-Wheel Drive - GMC 2007 Sierra 1500 Pickup Owner's Manual

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The proper level for the 2500HD with the
6.6L diesel engine (RPO LLY) or 8.1L V8
engine (RPO L18), and 3500 Series is from
0.6 to 0.8 inch (17 mm to 21 mm) below the
bottom of the filler plug hole.
Add only enough fluid to reach the proper level.
What to Use
To determine what kind of lubricant to use see
Recommended Fluids and Lubricants on page 629.

Four-Wheel Drive

Lubricant checks in this section also apply to
these vehicles. There are two additional systems
that need lubrication.
528
Transfer Case
When to Check Lubricant
It is not necessary to regularly check transfer case
fluid unless you suspect there is a leak or you
hear an unusual noise. A fluid loss could indicate
a problem. Have it inspected and repaired.
How to Check Lubricant
Manual Transfer Case