Need a new fan clutch for my 86 K-5 Blazer. Anyone know the rear axle gear ratio?

What?? A clutch fan has to do with the cooling of the engine by pulling air through the radiator by engaging the fan blades in front of the engine. It sits on the water pump just behind the radiator. When the water gets hot enough, the fan engages the blade and it rotates. It has nothing to do with the gear ratio of the drive train. Either you miss-quoted your question or you need to take basic car mechanic classes and don't let some shade tree mechanic take your money to fix what does not exist. This is just like asking: I need to replace my gas cap, what size are the rims on my car?

Ummm, ok. Don't know much about K-5 Blazers I see. There are two different fan cluthces for the K-5. One for 3.42 or lower rear axle gear ratio and one for 3.72 or higher rear axel gear ratio. So, you do need to know the rear axle gear ratio in order to buy the correct fan clutch.

Ok, sorry, I'm a single axle l drive man only.