Curious...explain fan clutch operation

[SIXt7]

Replaced my water pump so I decided to replace the fan clutch as well. The clutch that came with the car has a flat face toward the radiator with no coiled spring visible. It was almost frozen solid...couldn't turn the shaft once off the car and it was extremenly hard to manually turn when it was on the car with either a cold or hor engine. So I get a new cluth from GM Parts Direct. Shaft turns easily off the car...coiled spring facing radiator...turns about one and one-half turns on the car with hot or cold engine. The car had no overheat problem with the old clutch except in crawling traffic. Was the old clutch really bad? Can someone explain how the fan clutch operates? 67 327/350 no air.

[JohnZ]

The old clutch was apparently locked up almost solid. The inside of the clutch is like a torque converter in principle. The bi-metallic coil element on the front reacts to the temperature of the air coming through the radiator, and operates an internal valve that controls the flow of a viscous fluid between two reservoirs and and a clutch element; cool air, little resistance - hot air, more resistance. It's also rpm-sensitive, so it essentially disengages over 3500 rpm.

There were two suppliers for the original clutch - Eaton (coil spring element) and Schwitzer (flat plate element); both had the same specs, just had different methods of operating the internal valving. The bi-metallic flat plate on the Schwitzer clutch operates a pin connected to the internal valve.

[SIXt7]

Originally Posted by JohnZ

The old clutch was apparently locked up almost solid. The inside of the clutch is like a torque converter in principle. The bi-metallic coil element on the front reacts to the temperature of the air coming through the radiator, and operates an internal valve that controls the flow of a viscous fluid between two reservoirs and and a clutch element; cool air, little resistance - hot air, more resistance. It's also rpm-sensitive, so it essentially disengages over 3500 rpm.

There were two suppliers for the original clutch - Eaton (coil spring element) and Schwitzer (flat plate element); both had the same specs, just had different methods of operating the internal valving. The bi-metallic flat plate on the Schwitzer clutch operates a pin connected to the internal valve.

John Z...Thanks so much for your input, again. Getting a braver wrench this year so I'll likely be posting a lot here from SE Michigan. Have done a lot of British car wrenching but these Vettes....

If you don't mind, see my new post on valve cover gaskets. Thanks.