Fan Clutch

Ran into a problem today when trying to install a fan clutch on my 73 GMC 1500 350. It currently has two spacers on the 4 blade fan that bolts into the water pump. I was advised to put a fan clutch on it for better performance. If I don't use the larger of the two spacers, the fan will be outside the schroud. If I use the spacer I think it is in perfect position but how in the heck to I bolt it to the water pump. The bolts will be way too long. I don't think this has been standard on 73's. Has anyone else ran into this problem and what was the solution?

Thanks

My ‘75 GMC with A/C has a fan clutch and 7 blade fan, and a stock design water pump, the spacing works out fine. There are no spacers needed. The 4 blade fan was probably the base cooling system, but I think it should have also used a fan clutch.

I don't think there was ever a fan clutch on it but not positive. I've had the truck over thirty years and have never had a cooling issue living in Tucson, AZ. I'm going to put the stock 4 blade fan back on today and not worry with the fan clutch unless there's a real reason why I should?

Thanks

Without a clutch it may take a little longer to warm up on cooler days.
Really they are meant to 'disconnect' the fan from the engine at higher speeds (engine temps) to free up some power and help the engine be more efficient.

Good explainantions here:

Fan blades should be about 1/2 way out of the shroud.

Thanks for the feedback. So I guess my fix would be to get rid of both spacers (would allow fan to be halfway outside the schroud) and find some shorter screws to attach through the fan pulley and into the water pump?

pryden said:

Thanks for the feedback. So I guess my fix would be to get rid of both spacers (would allow fan to be halfway outside the schroud) and find some shorter screws to attach through the fan pulley and into the water pump?

Click to expand...

These may be an option. Several lengths but only 1.5 or larger have dual bolt.

Can't remember any GM fan clutch with a spacer.

pryden said:

Thanks for the feedback. So I guess my fix would be to get rid of both spacers (would allow fan to be halfway outside the schroud) and find some shorter screws to attach through the fan pulley and into the water pump?

Click to expand...

Most originally had studs and nuts. 5/16

The early trucks, 67-72 had a spacer and no fan clutch, probably the earlier squares as well. I think a stock application with a clutch fan has about an inch long maybe an inch and a half, 1/4 inch fine thread studs.

I ended up getting rid of both spacers and used 1" 5/16 fine thread bolts with a lock washer. Everything seems to be good. The fan is halfway in and halfway out of the fan shroud like people on here have said is the correct distance. Thanks for all the help.

pryden said:

Ran into a problem today when trying to install a fan clutch on my 73 GMC 1500 350. It currently has two spacers on the 4 blade fan that bolts into the water pump. I was advised to put a fan clutch on it for better performance. If I don't use the larger of the two spacers, the fan will be outside the schroud. If I use the spacer I think it is in perfect position but how in the heck to I bolt it to the water pump. The bolts will be way too long. I don't think this has been standard on 73's. Has anyone else ran into this problem and what was the solution?

Thanks

Click to expand...

There are many part numbers for fan clutches especially for trucks so if you are looking to get the right combination as it was OEM, some research might benefit you. Just about every GM that had factory A/C came with a fan clutch set up. The fan blade itself is specific to a fan clutch in that it has a large center hole to fit over the clutch shaft and then 4 bolts onto the clutch housing. Then the clutch shaft will fit direct to the pully and water pump however, there are fan clutch fasteners that make this connection. Most auto parts will have "fan clutch bolt/nut kit" in stock that have fine threads on one end and course on the other which fit onto the water pump then attach to the clutch shaft with nuts. Without knowing the OEM set up, its a gamble which part numbers are best with the radiator and shroud that came from the factory. If the radiator has been changed, there's a variable it is the correct one and if the shroud has been replaced, another variable. I'm not sure if the RPO codes on the glove box door have have much other than possibly the fan clutch option. BTW, fan clutch sets ups are the best in my opinion as long as the clutch has the bi-metal spring on the front of it. The fan pretty much freewheels unless the radiator temps get above 200. There's two type of clutches and I'm fairly sure GM used only the bi-metal thermostatic clutches. The other models are NOT recommended as they don't use temperature to engage the fan. Truck fan clutches tend to be much larger than the passenger car models, thicker and a bit larger in diameter. I'd use an OEM GM or Hayden thermostatic fan clutch with the correct fan.