| [GMCnet] RE. Old Subject AGAIN......Fan Clutchs [message #303197] |
Wed, 06 July 2016 22:17  |
BobDunahugh
Messages: 2465
Registered: October 2010
Location: Cedar Rapids, IA
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Don't get confused by the duty terms. Fan clutch duty is determined by the dia, blade pitch, and number of blades. Those terms have nothing to do with how long the clutch will last. Or how much air it can pull in. The ones listed as sever duty are for fans larger then we can install in our GMC's with stock shrouds. Don't install one. The one in my 403, 3.70 GMC comes on very seldom on the highway. Just long hills. And that's with a GVW of 17 to 21,000 lbs. The Hyden website will give you the correct unit to get by the info above.
Bob Dunahugh
78 Royale 403.
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| Re: [GMCnet] RE. Old Subject AGAIN......Fan Clutchs [message #303209 is a reply to message #303197] |
Thu, 07 July 2016 08:59  |
lw8000
Messages: 201
Registered: July 2012
Location: S.E. Michigan
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BobDunahugh wrote on Wed, 06 July 2016 22:17Don't get confused by the duty terms. Fan clutch duty is determined by the dia, blade pitch, and number of blades. Those terms have nothing to do with how long the clutch will last. Or how much air it can pull in. The ones listed as sever duty are for fans larger then we can install in our GMC's with stock shrouds. Don't install one. The one in my 403, 3.70 GMC comes on very seldom on the highway. Just long hills. And that's with a GVW of 17 to 21,000 lbs. The Hyden website will give you the correct unit to get by the info above.
Bob Dunahugh
78 Royale 403.
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Hopefully I wasn't the one that started all of this on the clutch discussion again  Bob, I see you also have the 403 & 3.70 FD, do you know which clutch you have installed? Just wondering as we've got the same combination here. Thanks.
Chris S. -
77 Kingsley, 3.70 FD, mostly OEM -
S.E. Michigan
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| Re: [GMCnet] RE. Old Subject AGAIN......Fan Clutchs [message #303241 is a reply to message #303209] |
Thu, 07 July 2016 17:53 |
Ray Erspamer
Messages: 1707
Registered: May 2007
Location: Milwaukee Wisconsin
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I know this is a frustrating topic. You hear use the 15-4644 which is actually a severe duty clutch, and they don't get any 747 roar, the next guy that uses the same clutch does get the roar and cycling....I know I do. One person says DON'T BUY HAYDEN. Next person says use the STANDARD DUTY and not the medium duty. All I want is something that works, is quiet and lasts. Does such a thing exist???
Ray Erspamer
78 GMC Royale Center Kitchen
403, 3.70 Final Drive
Holley Sniper Quadrajet EFI System,
Holley Hyperspark Ignition System
414-484-9431
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| Re: [GMCnet] RE. Old Subject AGAIN......Fan Clutchs [message #303248 is a reply to message #303197] |
Thu, 07 July 2016 19:48 |
JohnL455
Messages: 4447
Registered: October 2006
Location: Woodstock, IL
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I think once this is sorted we should list the "prefered" numbers in the interchange. The others should be listed as "use in emergency only" where you have a failure and need to get home from a smaller town.
John Lebetski
Woodstock, IL
77 Eleganza II
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| Re: [GMCnet] RE. Old Subject AGAIN......Fan Clutchs [message #303259 is a reply to message #303241] |
Fri, 08 July 2016 08:38 |
jknezek
Messages: 1057
Registered: December 2007
Karma: 5
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Ray Erspamer wrote on Thu, 07 July 2016 18:53I know this is a frustrating topic. You hear use the 15-4644 which is actually a severe duty clutch, and they don't get any 747 roar, the next guy that uses the same clutch does get the roar and cycling....I know I do. One person says DON'T BUY HAYDEN. Next person says use the STANDARD DUTY and not the medium duty. All I want is something that works, is quiet and lasts. Does such a thing exist???
No. As often as this topic has come up there has never been a consistent solution. In 9 years I think I'm on my 3rd fan clutch. When I bought the coach it had regular duty. When that died the most recent wisdom was to go to severe duty. That didn't work for crud for me, so I shifted down to heavy duty a few years ago. I'm not unhappy with it, don't ask the part number I can't remember, it's the Hayden. It roars like a jet when I turn the coach on, when I get off the interstate or slow on a rural road on a hot day, and very occasionally if I lay off the gas while on the interstate. It's doing it's job, but I have no love for it.
Thanks,
Jeremy Knezek
1976 Glenbrook
Birmingham, AL
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| Re: [GMCnet] RE. Old Subject AGAIN......Fan Clutchs [message #303265 is a reply to message #303197] |
Fri, 08 July 2016 11:07 |
Ken Burton
Messages: 10030
Registered: January 2004
Location: Hebron, Indiana
Karma: 10
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BobDunahugh wrote on Wed, 06 July 2016 22:17Don't get confused by the duty terms. Fan clutch duty is determined by the dia, blade pitch, and number of blades. Those terms have nothing to do with how long the clutch will last. Or how much air it can pull in. The ones listed as sever duty are for fans larger then we can install in our GMC's with stock shrouds. Don't install one. The one in my 403, 3.70 GMC comes on very seldom on the highway. Just long hills. And that's with a GVW of 17 to 21,000 lbs. The Hyden website will give you the correct unit to get by the info above.
Bob Dunahugh
78 Royale 403.
I agree with your comment except for the use of a Hayden clutches. Rather then post actual part numbers which change over the years, I use the categories of clutches Standard duty, Heavy Duty, and Severe Duty. The three categories are defined by the size of the the clutch and it's output RPM. I forget percentage coupling numbers at the moment, but as you go up in duty rating the amount of coupling between input and output speeds increase. The OEM clutch used on the GMC was of the heavy duty category.
The clutch and fan should not normally be needed to cool the coach. They are only there for the exception situation. If you are relying on the clutch to cool the vehicle, then you have other cooling system problems that you are masking over by using the fan and clutch to force additional air through the radiator and across the engine.
So if your clutch is engaging in other than abnormal cooling situations like extended idling or pulling long grades while towing, then you need to figure out why the existing cooling system is not adequate for your coach.
Using severe duty (designed to larger fans) or early turn on Hayden clutches are just band aids for other cooling system problems.
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana
[Updated on: Fri, 08 July 2016 11:17] Report message to a moderator |
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| Re: [GMCnet] RE. Old Subject AGAIN......Fan Clutchs [message #303286 is a reply to message #303197] |
Fri, 08 July 2016 14:00 |
JohnL455
Messages: 4447
Registered: October 2006
Location: Woodstock, IL
Karma: 12
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Except it is not a simple on /off situation. When cold once the fluid is redistributed it will largely free wheel at a lower speed. On an 80 deg day you will see at idle it moves more air, essential for good AC. However if you rev to a higher speed it will speed limit at fairly low RPM. Then at high temp it will fully engage, though still speed limited according to the GM FSM.
John Lebetski
Woodstock, IL
77 Eleganza II
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