#1  
Old 06-27-2020, 09:17 PM
pngoat pngoat is offline
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Default Hayden 2747 & 2797 fan clutches

Does anyone know at what temperature the Hayden 2747 & 2797 fan clutches activate? the 2747 is listed as heavy duty & the 2797 is listed as severe duty. The activation temperature is not listed for either one. Stock cooling system, with shroud, on a 65 GTO 389. Any help appreciated. Thank You.

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Old 06-28-2020, 10:57 AM
mgarblik mgarblik is offline
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I am in the process of heavily researching a fan clutch for a custom application. (62 Catalina) I have found that if you Google Hayden Fan clutch catalog, you can download a 2010 catalog that is easy to print pages and compare specs and dimensions. That's the newest I could find that was easy to work with and print. There is about 15 pages of dimensions and performance info in that catalog. If you don't want to go into that much detail here are some generic specs. The fan clutches you mentioned will begin to clutch at approximately 170 degrees AIR temperature, which would be around 200-205 water temp. The HD 2747 clutch will spin at about 25-35% shaft speed disengaged and 70-90% shaft speed fully engaged. Designed to be used with a fan pitch less than 2". The severe duty 2797 clutch is deeper and heavier. Same engagement temp. 20-30% shaft speed disengaged, 80-90% engaged. Designed for fans with more pitch. Bottom line if you have room for the severe duty clutch without hitting the radiator, it will run a little faster hot and drive a more aggressive fan blade pitch. In either case, the engagement temp is too high for an old muscle car and the thermal spring can be modified to lower the engagement temp 15-20 degrees easily by carefully lifting the spring carefully from it's outer anchor point and twisting it clockwise and letting it rest against the outside of the stop. (not in the slot as OE). This makes them work much better in an old muscle car that you want to run around 180-185 degrees. Hope this helps.

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Old 06-28-2020, 12:02 PM
pngoat pngoat is offline
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Very helpful information. Thank you.

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Old 06-29-2020, 09:57 AM
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Quote:
Originally Posted by mgarblik View Post
I am in the process of heavily researching a fan clutch for a custom application. (62 Catalina) I have found that if you Google Hayden Fan clutch catalog, you can download a 2010 catalog that is easy to print pages and compare specs and dimensions. That's the newest I could find that was easy to work with and print. There is about 15 pages of dimensions and performance info in that catalog. If you don't want to go into that much detail here are some generic specs. The fan clutches you mentioned will begin to clutch at approximately 170 degrees AIR temperature, which would be around 200-205 water temp. The HD 2747 clutch will spin at about 25-35% shaft speed disengaged and 70-90% shaft speed fully engaged. Designed to be used with a fan pitch less than 2". The severe duty 2797 clutch is deeper and heavier. Same engagement temp. 20-30% shaft speed disengaged, 80-90% engaged. Designed for fans with more pitch. Bottom line if you have room for the severe duty clutch without hitting the radiator, it will run a little faster hot and drive a more aggressive fan blade pitch. In either case, the engagement temp is too high for an old muscle car and the thermal spring can be modified to lower the engagement temp 15-20 degrees easily by carefully lifting the spring carefully from it's outer anchor point and twisting it clockwise and letting it rest against the outside of the stop. (not in the slot as OE). This makes them work much better in an old muscle car that you want to run around 180-185 degrees. Hope this helps.
Can you take a picture of that or describe in more detail? It sounds like you are saying you detach the outer anchor point and let it go where it goes?

Thanks, Tony

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1967 Firechicken, 461, Edl heads, 262/266@0.050" duration and 0.627"/0.643 lift SR cam, 3.90 gear, 28" tire, 3520#. 10.01@134.3 mph with a 1.45 60'. Still WAY under the rollbar rule.
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Old 06-29-2020, 09:55 PM
mgarblik mgarblik is offline
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I have an article that describes the process. I don't have a clutch handy to take a pic of. Here is the link. Good information.

http://midamericachevelles.com/tech/...tch_adjust.pdf

Another way of thinking of this is you are pre-loading the bi-metallic spring making it "think" it is hotter than it actually is , engaging the clutch earlier.


Last edited by mgarblik; 06-29-2020 at 10:01 PM.
  #6  
Old Yesterday, 09:24 AM
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I read the article and it looks like you rotate the coil in the direction of tightening it to the next slot, it's that true?

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1967 Firechicken, 461, Edl heads, 262/266@0.050" duration and 0.627"/0.643 lift SR cam, 3.90 gear, 28" tire, 3520#. 10.01@134.3 mph with a 1.45 60'. Still WAY under the rollbar rule.
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Old Yesterday, 09:58 AM
mgarblik mgarblik is offline
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Mostly. You are correct in that you tighten it in the direction that the spring is coiled, pre-loading it. But many of the fan clutches do not have a second slot to put the end into. So you can do one of two things. Carefully cut a new slot near the end of the bracket or just let the spring tang rest against the end of the bracket. It won't go anywhere because you tightened it by rotating it. It will just get tighter as it heats up. I have limited real world experience with this but plan to experiment myself in the near future. It all makes sense. Heavy duty truck clutches are adjustable from the factory.

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