WaterPump on '99 4.3

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I tried to change out the waterpump on my '99 Chevy 1/2ton 4x4 with a 4.3 5 speed the other day. It has a regular fan & fan clutch, not electric. I couldn't get the fan clutch off with my crescent wrench while holding the pulley with another wrench on one of the bolts to keep the WP from spinning. I rented the "fan clutch removal" wrenches from AutoZone the other day & will try it again next week. A friend suggested to put the wrench on (thinner fitted wrench) & initially hitting it with a hammer to "impact" it. Does anybody else have any ideas?? The threads on the new WP look like they are regular threads as opposed to reverse threads. Anybody do this before????