Chevrolet Repair Questions? Ask a Mechanic for Answers ASAP
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The water pump pulley is held with a special holder and the wrench is used on the fan nut to remove the clutch.
These usually can be loaned from an auto parts store loan-a-tool program.
Here are GM instructions for fan clutch replacement.
Cooling Fan and Shroud Replacement
Below is a picture of the fan clutch tools