[RocktimusPryme]

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.

[mgarblik]

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.

[gto19]

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 ?

[mgarblik]

Originally Posted by gto19

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 ?

Ha, now I don't know. I may have moved it the wrong way but it seemed to work better? I have to remove the fan, clutch and shroud tomorrow to send it out for powdercoat. I will play with the spring with a hair dryer on the bench and see what the heck I actually did. Sorry for the confusion.

[RocktimusPryme]

Originally Posted by gto19

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 ?

That was kinda my question too. The videos I posted both moved it to the left (CC) as well. But they may have been reverse spinning water pumps?

Im still slightly confused. I might take a picture later and draw on it just to clear up the confusion.

I think I might be afflicted by exactly what you guys are talking about. The fan coming fully on too late. My car sits dead on the 180 thermostat when moving, but climbs some when idling. So I would like to give this mod a shot, but Im still not sure where I should put the outter tang of the spring.

Im a visual person lol. Trying to visualize it in my head Im struggling with.

[RocktimusPryme]

Okay lets look at an illustration to try and clear this up.

So Mick this is how you are saying it should go right? Move the spring to tighten it? And let the outer tang just rest against the side like that.

[gto19]

Originally Posted by RocktimusPryme

Okay lets look at an illustration to try and clear this up.

So Mick this is how you are saying it should go right? Move the spring to tighten it? And let the outer tang just rest against the side like that.

No
Go the other way . You wanna loosen the spring . What he was saying is bend the outer tang clockwise and that will force the coil and center pin counterclockwise. On your fan clutch picture bending the tang really won’t do anything since you don’t have a slot that it rests in .

I provided a picture of my original fan clutch without the modification and a pic of a fan clutch with the modification

[gto19]

Actually looking at yours more close up you probably could bend the tang clockwise and leave it in the hole and it would force the coil counterclockwise

[michaelfind]

Originally Posted by RocktimusPryme

Okay lets look at an illustration to try and clear this up.

So Mick this is how you are saying it should go right? Move the spring to tighten it? And let the outer tang just rest against the side like that.

I realize this is an old question from an old thread and y'all already figured out that the adjustment needs to go counter clockwise. I have been experimenting with my clutch and I think I found what works best for my set up.

I tried moving the tang to the left of the circle but that resulted in the clutch not resetting when cool and basically staying engaged all the time.
I tried to bend a slight tip of the end to stay in the slot but there is not enough material there to make that work.
Also, Super glue did not hold.

I ultimately straightened the end of the spring so that it is held (barely but enough) in the bottom of the original slot but also pushes the coil spring CCW to give me a much cooler temp at idle. I hope this is helpful for others.

[grivera]

Originally Posted by mgarblik

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.

How does one measure fan pitch in inches?

[mgarblik]

I measured the pitch of my blade by laying it flat on a table and using a carpenter square to measure the distance from the table to the trailing edge of the blade. (greatest distance from table to blade)

[lust4speed]

Originally Posted by RocktimusPryme

...Mick, you are saying moving the tip of the tank clockwise makes the fan engage at a lower temp. Both videos show moving the outer 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 agument...

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.

[jschaible]

Mike, thank you so much for this careful research. This is incredibly useful for my situation, and also caused me to join the forum. I feel like I found a gold mine.

I installed a Hayden 2747 clutch in my 69 Catalina 400 yesterday. But after reading your post last night, I took it back out this morning and cut a new slot for the spring tang, as you showed in those pictures. I do not have a temp gauge on this car, but I can confirm that the fan is clutching up at lower temperatures and consistently declutching when it should. It's running noticably cooler across the board (by sound). Today was 85F and sunny, AC on and car loaded with 800lb of passengers and cargo. Kept the heat under control at traffic creep and 75 mph cruise. Thank you again.

[mgarblik]

There are many very smart people on this forum. Carburetors, tuning, engine building, body and paint, you name it. I have over 40 years of experience and learn new things nearly every day on here. This is THE place for Pontiac people.