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.

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.

Very helpful information. Thank you.

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

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.

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?

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.

I have a Hayden 2797 and it has a second slot. I was running it with a factory 7 blade AC fan in my ,72 LeMans with a 9:1 455, stock 3 core radiator and a 160 F Tstat. The car would creap up to 200 idling in traffic. I replaced that set-up with a 7 blade flex fan and the car would only get up to 175 on a 90 F day in any driving, highway or traffic. I changed the Tstat to a 180 F and it doesn't get much warmer, up to 180 on a 90 F day after running on the highway.

Just to clarify, you removed the 2797 clutch and went with a direct drive 7-blade fan? Or did you add the flex style fan blade to the clutch? If direct drive, how noisy is the fan at highway speed?

I removed the clutch and factory 7 blade fan and replaced it with a 7 blade direct drive flex fan. Not noisy at all on the highway, or down the track. Put the same set-up in my brothers car with 530 Hp and a 3 core radiator and it runs the same temp.

That's interesting. I may go the flex fan route if this clutch set-up I am trying doesn't pan out. Originally had the 4 blade direct drive OE fan and no shroud. Now have a factory shroud for AC cars and this clutch fan deal I am trying. Mind sharing the brand and diameter of the flex fan?

Did you try adjusting the spring on the clutch?

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Data Point
 

Last winter I had to replace my aluminum radiator. Went
With a ColdCase with two rows of 1.25 tubes. Noticed my
Fan clutch had some wobble and installed original 5 blade
Power flex mechanical fan. Used a 160 superstat I had as
A spare to see how cool she would run. Well she stays at
165 around town and hits 170 on freeway after a few miles.
Once off freeway she goes back to 165! Well I admit the factory
fan has some noise only when getting up to highway speeds but
Quiets down right after. Like the blades flatten once up to speed.
Not planning on reinstalling fanclutch just yet, it’s garage art.
Glad I hung the factory fine on the wall years ago.
I will say the Hayden clutch and 7 blade fan helped immeknsely
When I had original 3 core radiator.
Gerry.

No, I doubt I will ever run it since I have a cold running motor problem using the 7 blade flex fan. I might try it just for a test if I ever get bored.

There was a nice 7 blade 19.5" flex fan offered but the new ones are a little smaller at 19". Maybe I just didn't look hard enough, but think that's the current situation. Both the 19.5" flex fan and the stock 19.5" A/C fan with the 2797 were dead equal in max cooling with my testing, but I found the constant noise of the flex fan a little too much.

While it is a little risky, I bend the end tang of the spring to alter the engagement of the 2797 clutch. I usually see temps higher than what Hayden claims and my new clutches are engaging between 210° and 215°. You go too far on bending the tang and the fan is on all the time, and you make too many adjustments to the tang and the fan will be a paperweight when the end breaks off. It would have saved some time and aggravation if I had been aware of the Chevy magazine article, but I re-invented the wheel on this. The current clutches I've seen have the tang end in an aluminum slot so the magazine way isn't available. I wrote a letter to Hayden years ago suggesting that they could make a fortune by offering a muscle car fan with an earlier engagement temperature, but didn't get any acknowledgement back from them. Here's a copy of my first writeup on PY:

My disclaimer is “results may vary, and try this at your own risk”. I took a new severe duty Hayden clutch fan and re-indexed the valve on the front of the clutch. This fan has the coil thermal spring permanently mounted to the center pin and the outside spring tip dropped into a cast slot where the spring can be lifted out.

The pin controls the fluid coupling. As the pin is rotated counter-clockwise, the fan engages more. Best way to verify this is to take a hair dryer and apply heat to the coil while the clutch is sitting on the workbench and observe the motion of the center pin as the heat is applied. The goal is to have the clutch believe the spring is seeing more heat than it actually is, and the spring needs to be bent to slightly move the center pin in a counter-clockwise direction. Very little adjustment needs to be done and it is easy to over-do the bend. The danger is that the spring could snap off and the fan clutch would be scrap. The actual change needed is to bend the end tang about 5°. Another way to look at it is to make the bend thinking of the minute hand on a clock and move the tip of the tang from 12:00 to about 12:05. It doesn't take much bending, and it's best to start out with very small changes.

Moving the tip of the tang clockwise results in the main spring body moving counter-clockwise which is where it needs to be to engage earlier. While Hayden advertises that the fan engages at 175 air temperature, every fan I've seen waits until about 210° water temp to ramp up. When I got my A/C working the temps wanted to stay right at where the fan clicked in, so I cheated and made the fan come in sooner. My initial attempts were always too much, so try to just barely bend the tang.

Wonder if one could make a spacer or bracket or doo hickey that would perform the same function as bending the tang but without danger of breaking it

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After reading this I did a little indepentant research and have a question.

https://www.youtube.com/watch?v=QVMN7LmKLYA

This video shows a heavy duty clutch with an adjustment in it, which would be awesome, but Im guessing its only available in busses etc.

https://www.youtube.com/watch?v=UHWxqRWt9Kw

Another one with what looks like a later LS style truck fan.

Mick, you are saying moving the tip of the tank clockwise makes the fan engage at a lower temp. Both videos show moving the outter tang counter clockwise to lower the engagement temp of the fan.

Am I misunderstanding what you are saying?

A little wisdom of my own on the subject. Many have said that the SD Harden clutch is a bad option. That it will just never disengage on normal car duties. Its a big ongoing arument. I have a severe duty clutch. Originally I used a 6 blade 18" Hayden aftermarket fan.

I got lucky one day at a swap and got a couple 19.5" 7 blade GM fans out of a $5 pile. So I switched to that. While my overall sustained temps are probably lower with the bigger 7 blade, I did notice that it got warmer faster with the bigger fan.

My theory is that with the 6 blade, the SD clutch was indeed never disengaging. It was always on, so it took my car longer to get to the thermostat. So I think there is something to the SD clutch maybe being the wrong choice unless you have a big honker of a fan.

The parts I had been waiting for finally came today. Spent a couple hours fitting and testing. I have the heavy duty 2747 clutch not the severe duty 2797. Couple of reasons for the choice. The Hayden tech info recommends the severe duty clutch with fan blades of 2.5" pitch or more. That may be why some people are unhappy with this clutch if they are using a 2" pitch or less fan blade. My 6 blade fan has a 2" pitch. The severe duty clutch has so much viscous clutch surface area compared to the heavy duty one, those blades may not offer enough resistance to declutch them. The clutch valve may be functioning but not enough driving force to clear the channels out. Also I bought the heavy duty clutch so less weight would be hanging out front, especially with the 1" spacer I thought I would be using. Turns out, not using the spacer because the factory shroud is made at an angle when installed. About 75% of the blade is in the shroud from the center to the bottom, and about 30% or so is in the shroud at the top half. That's just the way it's made. Fits the radiator and core support prefect. Now I know why the finger guard for the shroud equip[ped cars is 2" longer. It makes sense now. Anyway I ran the clutch everything stock and it stayed de-clutched too long for my taste. Water temp was 200-205 before it really clutched up tight and moved maximum air. When it's clutched, the 19.5" 6 blade fan really moves tons of air and drops the temperature right back to 180. I took the tang out of the fixed slot and rotated it about 5 minutes of clock position as mentioned in an above post and just let the tang rest against the stop outside of the slot clockwise. Put it back together and ran it some more. Now the clutch begins to clutch at 175-180 water temp and I was never able to really get it to clutch all the way up. These were static tests in the driveway. It's in the mid 90's here every day though and I could not get it to run over 180. That was letting it run at a steady 2500 RPM's for about 1/2 hour. I will do some more testing over the next couple weeks with an infra-red heat gun and get some air temps. Happy so far.

Mgarblik

Good info !

If I read your posts correctly you say to move the spring clockwise which would tighten the coil up but when I look at this picture provided in the chevelle link you can see they actually loosened the coil counterclockwise. So what’s the correct way to move it ?

Confusion might come in because I was trying to describe the actual bending of the tang. To simplify things the center pin has to move counter-clockwise to have the clutch engage earlier. So if bending the tang sticking out of the coil it is bent a little clockwise which forces the coil and center pin counter-clockwise. Somewhat confusing.

We have about 10 members in our GTO club that I have talked into the severe duty fan, and one of those complained and removed it. I have the SD clutch on 4 Pontiacs and they cycle properly with the stock fans. My blue GTO has the SD fan on it with the original H.O. 18" fan and it cycles fine. That club member donated the removed clutch fan to me but it's sitting on the shelf and I haven't tested it to see if it might be defective. It is as sold and he didn't play with the spring so I'm really thinking that it might be locked up out of the box.

Hayden changed the specs of the heavy duty fan clutch and brought the specs up so close to the SD clutch that it should work very similar now. Old HD clutches were way low on their lock up percentage but new ones are pretty high.