Home » Public Forums » GMCnet » Re: [GMCnet] fan clutch mystery/ theory
| Re: [GMCnet] fan clutch mystery/ theory [message #316440] |
Sat, 22 April 2017 08:26  |
BobDunahugh
Messages: 2465
Registered: October 2010
Location: Cedar Rapids, IA
Karma: 11
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The heat starts building during the climb in the radiator. It takes time to heat up the fan clutch sensor from the radiator's heat. Thus the fan clutch has no idea that you're climbing a hill when your doing it. As to the fan clutch size. The standard duty unit is designed for a smaller fan then we have. Heavy duty unit is designed for our fan's dia, pitch, and number of blades. Sever duty is for a larger dia fan with more pitch, and blades. Thus the SD unit will have a tendency to be engaged for a longer time then it needs too. As our blade can't put enough load on the clutch to disengage the fan. Bob Dunahugh
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| Re: [GMCnet] fan clutch mystery/ theory [message #316447 is a reply to message #316440] |
Sat, 22 April 2017 11:13  |
jhbridges
Messages: 8412
Registered: May 2011
Location: Braselton ga
Karma: -74
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My 23' behaved that way - fan came on on the downhill side except the long hauls. MontEagle a mile before the top, Culowee about a third of the way up. It stayed cool for both with the fan roaring away.
--johnny
Foolish Carriage, 76 26' Eleganza(?) with beaucoup mods and add - ons.
Braselton, Ga.
I forgive them all, save those who hurt the dogs. They must answer to me in hell
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| Re: [GMCnet] fan clutch mystery/ theory [message #316494 is a reply to message #316440] |
Sun, 23 April 2017 13:09 |
jhbridges
Messages: 8412
Registered: May 2011
Location: Braselton ga
Karma: -74
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"They all pull the same amount of air. Bob Dunahugh". Assuming they all have the same fan connected. The several replacements folks have suggested all will move different amounts of air at a given RPM.
--johnny
Foolish Carriage, 76 26' Eleganza(?) with beaucoup mods and add - ons.
Braselton, Ga.
I forgive them all, save those who hurt the dogs. They must answer to me in hell
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| Re: [GMCnet] fan clutch mystery/ theory [message #316495 is a reply to message #316440] |
Sun, 23 April 2017 13:13 |
jhbridges
Messages: 8412
Registered: May 2011
Location: Braselton ga
Karma: -74
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Acturally, what I want is a fan system that bolts on, runs off a temp sensor, tells me when it's engaged, and lets me engage it manually. Which actions the one JimK has will do.
--johnny
Foolish Carriage, 76 26' Eleganza(?) with beaucoup mods and add - ons.
Braselton, Ga.
I forgive them all, save those who hurt the dogs. They must answer to me in hell
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| Re: [GMCnet] fan clutch mystery/ theory [message #316496 is a reply to message #316494] |
Sun, 23 April 2017 13:31 |
Ken Burton
Messages: 10030
Registered: January 2004
Location: Hebron, Indiana
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Johnny Bridges wrote on Sun, 23 April 2017 13:09"They all pull the same amount of air. Bob Dunahugh". Assuming they all have the same fan connected. The several replacements folks have suggested all will move different amounts of air at a given RPM.
--johnny
Actually that is not quite true. The various models of clutch when fully engaged do not produce the same RPM in and out and move the same amount of air flow. I do not remember the numbers exactly but it is something like:
standard duty 60%
heavy duty 75%
severe duty 90%
I'm too lazy to go look up the exact numbers.
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana
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| Re: [GMCnet] fan clutch mystery/ theory [message #316503 is a reply to message #316440] |
Sun, 23 April 2017 15:53 |
jhbridges
Messages: 8412
Registered: May 2011
Location: Braselton ga
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Is it then your contention that f'rinstance the plastic fan shown in Shawnee turning 2000 rpm will move the same amount of air as the 7 blade original metal fan turning at 2000 rpm? Can't agree.
--johnny
Foolish Carriage, 76 26' Eleganza(?) with beaucoup mods and add - ons.
Braselton, Ga.
I forgive them all, save those who hurt the dogs. They must answer to me in hell
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| Re: [GMCnet] fan clutch mystery/ theory [message #316504 is a reply to message #316440] |
Sun, 23 April 2017 16:04 |
jhbridges
Messages: 8412
Registered: May 2011
Location: Braselton ga
Karma: -74
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And, for what it's worth, all the electric clutched fans I've seen have the ability to produce a rotation speed signal - which signal the modern vehicle computers use to modulate the fan clutch and thereby its speed. It's fairly easy to use this to run a cheap tachometer, if you're that into it  They've a Hall effect transducer which produces a pulse train whose rate is directly relative to fan speed. By dividing the pluse train a time or two, you can get a repetition rate which can be read directly by a cheeeep tachometer set to 4, 6, or 8 cylinders depending the number of pulses per revolution. The fan JimK uses produces 6 pulses per revolution. Divide this by two with a simple flip-flop, and a tachometer set for a 6 cylinder engine will read actual fan speed. A 3 pin regulator, 4013 chip, and a capacitor and you can feed a ten dollar chinese tach. And probably be staring at it when you rear-end the slow semi going up the mountain.
--johnny
Foolish Carriage, 76 26' Eleganza(?) with beaucoup mods and add - ons.
Braselton, Ga.
I forgive them all, save those who hurt the dogs. They must answer to me in hell
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| Re: [GMCnet] fan clutch mystery/ theory [message #316512 is a reply to message #316440] |
Sun, 23 April 2017 18:12 |
Ek_Lektro
Messages: 167
Registered: March 2011
Karma: 2
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well, with sunday being a day of rest,
i’m weighing all the appreciated info and trying to figure out what to do down here tomorrow
(before i leave the mechanic’s shop and go to the bodywork shop).
One thing i can see is that its a MUCH bigger job to replace the fan clutch on my ’76 Birchhaven w/455
(which i’ve never had the occasion to do, myself)
than it is to replace the fan clutch on my ’78 Eleganza w/403 (which i’ve done a few times, easily)…
and i suppose that these very different fan shroud set-ups are due to engine size and model year.
Its really tight on this ’76! Looks pretty great for purposes of radiator airflow, but not great for access... for replacing the fan clutch!
So... i don’t think that air flow is my problem. (Comparatively, its seems my ’78 should be having issues,
since its not nearly as closed-in behind the radiator).
The whole cooling system was flushed this past November as regular maintenance,
and i have not seen the temperature creep up anywhere near “hot” (halfway mark) w/original sensor
during either driving or idling, and so i guess its a safe bet that my water pump is OK.
And, hearing from other people experiencing the same “counterintuitive” fan clutch behavior…
I”m guessing that it must be this dang Duralast 222045 that’s the culprit, especially in regard to Ken’s link here:
> Additional information stolen from the Hayden web site:
> http://www.haydenauto.com/featured%20products-fan%20clutches%20and%20fan%20blades/content.aspx
> " Some Chevrolet/GMC truck models are specifically designed to engage at lower temperatures than the original equipment parts that they replace. “
So can i find the proper AC Delco fan clutch down here in Tijuana? i’ll call around tomorrow and see…
If not, should i just have them swap another 22045? (2747)
Standard duty and Severe duty both seem like they have their own drawbacks.
BTW: i can see a very small weep of oil from the sensor coil on the relatively “new” (400 miles) fan clutch. Is a small amount normal?
This is a last chance to get some good affordable labor for a while (with my Mexican insurance policy expiring),
so I’d love to get this sorted out before i need to leave this shop:
monday: mechanic, tues/wed: bodyshop, wed/thurs: reupholstering cockpit seats, thurs dash AC recharge and possibly installing an AC aux kit from Jim Bounds, friday: following up any loose ends (like maybe having had to special order a fan clutch!)
We’ve got our work cut out for us...
Thanks everybody for the support!
Greg / SolarSonic / Los Angeles and technomadic
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| Re: [GMCnet] fan clutch mystery/ theory [message #316513 is a reply to message #316512] |
Sun, 23 April 2017 18:39 |
Ken Burton
Messages: 10030
Registered: January 2004
Location: Hebron, Indiana
Karma: 10
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It is not a difficult job to replace the fan clutch on a 76 GMC. You do not need to touch the shroud.
1. Place a piece of cardboard between the fan and the radiator to protect the radiator from the fan blades.
2. Reach inside the shroud and remove the bolts holding the fan to the clutch.
3. Remove the 4 bolts holding the clutch to the water pump.
4. DO NOT REMOVE THE PULLEY or the BELTS.
5. Remove the clutch and leave the fan inside the shroud.
6. Reinstall in reverse order.
Note: I do not loosen the belts while replacing the fan clutch.
I have a 1976 GMC with a 455 engine and can do this in about 20 minutes.
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana
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| Re: [GMCnet] fan clutch mystery/ theory [message #316515 is a reply to message #316503] |
Sun, 23 April 2017 18:55 |
Ken Burton
Messages: 10030
Registered: January 2004
Location: Hebron, Indiana
Karma: 10
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When I worked Delco Engineering, the number of blades on the fan was of no concern to them. It was diameter and pitch that they wanted. Keep in mind that the difference between standard, heavy, and severe duty clutches is the speed that they drive the fan. So changing from one to the other changes how fast the fan will turn reference the input speed (the water pump). The fan shuts off at higher input RPM. The assumption in this design was the radiator already has more than enough ram air at higher RPM because the vehicle is going faster. The clutch was designed to provide additional air when the vehicle is hot and idling or going slow. A flex fan operates under the same design assumption.
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana
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| Re: [GMCnet] fan clutch mystery/ theory [message #316516 is a reply to message #316440] |
Sun, 23 April 2017 20:08 |
jhbridges
Messages: 8412
Registered: May 2011
Location: Braselton ga
Karma: -74
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Thanks, that clarifies your rpm comment. I was misinterpreting it.... nothing new thee:)
--johnny
Foolish Carriage, 76 26' Eleganza(?) with beaucoup mods and add - ons.
Braselton, Ga.
I forgive them all, save those who hurt the dogs. They must answer to me in hell
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| Re: [GMCnet] fan clutch mystery/ theory [message #316518 is a reply to message #316503] |
Sun, 23 April 2017 23:13 |
Ken Burton
Messages: 10030
Registered: January 2004
Location: Hebron, Indiana
Karma: 10
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Johnny Bridges wrote on Sun, 23 April 2017 15:53Is it then your contention that f'rinstance the plastic fan shown in Shawnee turning 2000 rpm will move the same amount of air as the 7 blade original metal fan turning at 2000 rpm? Can't agree.
--johnny
Johnny,
Having only once seen and never used that 10 blade plastic fan setup, I can not comment on it's ability to move air. I would assume the rotational energy consumed for the amount of air moved would be similar, but I can not comment on the difference between the two on the total amount of air moved at any RPM. I also know of no easy way to measure the difference if there is any.
Finally, the existing fan and clutch has worked well for many, many years. So I see no reason to try to improve it's operation. I feel that people are replacing clutches, and now fans, in an attempt to cover up for other cooling system problems.
I have no complaints with passive improvements to the cooling system like baffling and fender vents etc. GM did some of that on later coaches. In fact I added a piece foam on the inside of the fan shroud in an attempt to reduce the amount of air that could leak by the end of the fan. Did it help? I have no idea because I did not have a problem to start with but it was an easy and cheap addition.
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana
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| Re: [GMCnet] fan clutch mystery/ theory [message #316519 is a reply to message #316496] |
Sun, 23 April 2017 23:21 |
Ken Burton
Messages: 10030
Registered: January 2004
Location: Hebron, Indiana
Karma: 10
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Senior Member |
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Ken Burton wrote on Sun, 23 April 2017 13:31Johnny Bridges wrote on Sun, 23 April 2017 13:09"They all pull the same amount of air. Bob Dunahugh". Assuming they all have the same fan connected. The several replacements folks have suggested all will move different amounts of air at a given RPM.
--johnny
Actually that is not quite true. The various models of clutch when fully engaged do not produce the same RPM in and out and move the same amount of air flow. I do not remember the numbers exactly but it is something like:
standard duty 60%
heavy duty 75%
severe duty 90%
I'm too lazy to go look up the exact numbers.
I received the following information by email from another GMCer reference clutch output speeds. He said that it came from the Hayden web site.
Standard 60% to 70% engaged; 20% to 30% disengaged
Heavy Duty 70% to 80% engaged; 25% to 35% disengaged
Severe Duty 80% to 90% engaged; 20% to 30% disengaged
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana
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| Re: [GMCnet] fan clutch mystery/ theory [message #316522 is a reply to message #316519] |
Mon, 24 April 2017 02:48 |
Ken Burton
Messages: 10030
Registered: January 2004
Location: Hebron, Indiana
Karma: 10
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Senior Member |
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Ken Burton wrote on Sun, 23 April 2017 23:21
I received the following information by email from another GMCer reference clutch output speeds. He said that it came from the Hayden web site.
Standard 60% to 70% engaged; 20% to 30% disengaged
Heavy Duty 70% to 80% engaged; 25% to 35% disengaged
Severe Duty 80% to 90% engaged; 20% to 30% disengaged
I found this additional information on the the Internet. While the numbers are slightly different they do follow the same trend. This does include pitch information and square inch information. I do not know what "Land and groove design" is.
Standard Duty Thermal
Turns the fan 50-60% of shaft speed when engaged. Used with fans with lighter pitch. (1-1/2" of pitch) Flat plate impeller design with 30 Sq. In. of working surface.
Heavy-Duty Thermal
Turns the fan 65-75% of the shaft speed when engaged for increased cooling. Used with deeper pitch fans. (2" of pitch). Land and groove design with 47 Sq. In. of working area allows higher operating RPM's.
Severe Duty Thermal
Turns the fan 80-90% of the shaft speed when engaged. Used with deeper pitch fans. (2-1/2" of pitch). Land and groove design with 65 Sq. In. of working area.
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana
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| Re: [GMCnet] fan clutch mystery/ theory [message #316524 is a reply to message #316522] |
Mon, 24 April 2017 07:16 |
 |
USAussie
Messages: 15912
Registered: July 2007
Location: Sydney, Australia
Karma: 6
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Ken,
Here's a link to a presentation made by Steve Ferguson on the cooling system
that provides a LOT of good info:
http://gmcws.org/Tech/Engine_Cooling_System_Basics_-_Steve_Ferguson.pdf
Here's a link to a presentation Billy Massey put together on modifying the
existing fan shroud:
http://gmcws.org/Tech/fan_shroud/fanshroud.htm
Regards,
Rob M.
The Pedantic Mechanic
USAussie - Downunder
AUS '75 Avion - The Blue Streak TZE365V100428
USA '75 Avion - Double Trouble TZE365V100426
USA '77 Kingsley - TZE 267V100808
-----Original Message-----
From: Gmclist [mailto:gmclist-bounces@list.gmcnet.org] On Behalf Of Ken
Burton
Sent: Monday, April 24, 2017 2:49 AM
To: gmclist@list.gmcnet.org
Subject: Re: [GMCnet] fan clutch mystery/ theory
Ken Burton wrote on Sun, 23 April 2017 23:21
> I received the following information by email from another GMCer reference
clutch output speeds. He said that it came from the Hayden web site.
>
>
> Standard 60% to 70% engaged; 20% to 30% disengaged
>
> Heavy Duty 70% to 80% engaged; 25% to 35% disengaged
>
> Severe Duty 80% to 90% engaged; 20% to 30% disengaged
I found this additional information on the the Internet. While the numbers
are slightly different they do follow the same trend. This does include
pitch information and square inch information. I do not know what "Land
and groove design" is.
Standard Duty Thermal
Turns the fan 50-60% of shaft speed when engaged. Used with fans with
lighter pitch. (1-1/2" of pitch) Flat plate impeller design with 30 Sq. In.
of working surface.
Heavy-Duty Thermal
Turns the fan 65-75% of the shaft speed when engaged for increased cooling.
Used with deeper pitch fans. (2" of pitch). Land and groove design with 47
Sq. In. of working area allows higher operating RPM's.
Severe Duty Thermal
Turns the fan 80-90% of the shaft speed when engaged. Used with deeper pitch
fans. (2-1/2" of pitch). Land and groove design with 65 Sq. In. of
working area.
--
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana
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Regards,
Rob M. (USAussie)
The Pedantic Mechanic
Sydney, Australia
'75 Avion - AUS - The Blue Streak TZE365V100428
'75 Avion - USA - Double Trouble TZE365V100426
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