Home » Public Forums » GMCnet » Fan Clutches ((original))
| Fan Clutches [message #63214] |
Thu, 05 November 2009 10:38  |
bryant374
Messages: 563
Registered: May 2004
Location: Pleasant Valley, NY 12569
Karma: 1
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Senior Member |
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In case anyone thinks the "radiator air flow" subject hasn't been duscussed sufficiently, allow me to throw in a related item:
For many years I had been under the impression that GMC Motorhomes (GMC interiors) were equipped with the "standard" OEM fan clutch (p/n 550528) and the Transmode was equipped with a "heavy duty" OEM fan clutch (p/n 724457).
I thought I would check the parts manual to verify this and if I am reading this correctly, I found the following:
GMC Motorhomes-
p/n 550528 1973 thru 1977 all with 455 engines.
p/n 724457 1977 thru 1978 all with 403 engines.
The above seems straight forward and makes sense to me.
Transmodes-
p/n 724457 1975 to <6V100878.
p/n 550528 6V100878 thru 1978.
Now I'm confused. The Transmode starts with the newer fan clutch p/n (heavy duty?) and then reverts to the older p/n, just the opposite of what the Motorhome did.
Anyone care to make sense of this?
Notes:
- 6V100878 was the changeover to the 1976 design when many new changes were implemented (NOT 455->403). 1976 models before this were really the same as 1975 models.
The 455->403 changeover caused changes with radiator air baffles & fan clutch in the Motorhome, but not with the Transmode.
Bill Bryant
PO 1976~PB (owned 34 years)
1914 Ford (owned 70 years)
1965 Corvette (owned 39 years)
GMC Motorhome History
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| Re: [GMCnet] Fan Clutches [message #63223 is a reply to message #63214] |
Thu, 05 November 2009 11:58  |
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Human error?
No matter how automated things may have been, if a human makes a mistake the
computer can't overcome it because it only knows what it is told. Somewhere
along the line, a human touches the data. Therein lies a problem.
Byron Songer
1978 Royale by Coachmen
Louisville, KY
Personal - http://web.me.com/bnsonger
Eastern States - http://www.gmceast.com
Bill Bryant wrote:
>
>
> In case anyone thinks the "radiator air flow" subject hasn't been duscussed
> sufficiently, allow me to throw in a related item:
>
> For many years I had been under the impression that GMC Motorhomes (GMC
> interiors) were equipped with the "standard" OEM fan clutch (p/n 550528) and
> the Transmode was equipped with a "heavy duty" OEM fan clutch (p/n 724457).
>
> I thought I would check the parts manual to verify this and if I am reading
> this correctly, I found the following:
>
> GMC Motorhomes-
> p/n 550528 1973 thru 1977 all with 455 engines.
> p/n 724457 1977 thru 1978 all with 403 engines.
> The above seems straight forward and makes sense to me.
>
>
> Transmodes-
> p/n 724457 1975 to <6V100878.
> p/n 550528 6V100878 thru 1978.
> Now I'm confused. The Transmode starts with the newer fan clutch p/n (heavy
> duty?) and then reverts to the older p/n, just the opposite of what the
> Motorhome did.
>
> Anyone care to make sense of this?
>
> Notes:
> - 6V100878 was the changeover to the 1976 design when many new changes were
> implemented (NOT 455->403). 1976 models before this were really the same as
> 1975 models.
>
> The 455->403 changeover caused changes with radiator air baffles & fan clutch
> in the Motorhome, but not with the Transmode.
>
>
>
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--
Byron Songer
Full-timing to enjoy the USA
Former owner but still an admirer
GMC paint schemes at -
http://www.songerconsulting.net
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| Re: [GMCnet] Fan Clutches [message #63273 is a reply to message #63223] |
Fri, 06 November 2009 08:55 |
bryant374
Messages: 563
Registered: May 2004
Location: Pleasant Valley, NY 12569
Karma: 1
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Senior Member |
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> GMC Motorhomes-
> p/n 550528 1973 thru 1977 all with 455 engines.
> p/n 724457 1977 thru 1978 all with 403 engines.
> The above seems straight forward and makes sense to me.
>
>
> Transmodes-
> p/n 724457 1975 to <6V100878.
> p/n 550528 6V100878 thru 1978.
> Now I'm confused. The Transmode starts with the newer fan clutch p/n (heavy
> duty?) and then reverts to the older p/n, just the opposite of what the
> Motorhome did.
>
> Anyone care to make sense of this?
>
> Notes:
> - 6V100878 was the changeover to the 1976 design when many new changes were
> implemented (NOT 455->403). 1976 models before this were really the same as
> 1975 models.
>
> The 455->403 changeover caused changes with radiator air baffles & fan clutch
> in the Motorhome, but not with the Transmode.
>
>
Human error?
No matter how automated things may have been, if a human makes a mistake the
computer can't overcome it because it only knows what it is told. Somewhere
along the line, a human touches the data. Therein lies a problem.
Byron Songer
1978 Royale by Coachmen
Louisville, KY
Byron,
There are certainally mistakes in our GMC manuals and that might explain part of this, the differences between the Motorhome & Transmode seem to me to go beyond this. The Transmode not only changes part numbers, but makes the change at 6V100878 when no changes to the engine or cooling system were made. To make the change when a new engine was used, as was done by the Motorhome change, makes a great deal of sense to me.
Just another mystery to add to the list of GMC questions 
Bill Bryant
PO 1976~PB (owned 34 years)
1914 Ford (owned 70 years)
1965 Corvette (owned 39 years)
GMC Motorhome History
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| Re: [GMCnet] Fan Clutches [message #63275 is a reply to message #63273] |
Fri, 06 November 2009 09:15 |
Rick Denney
Messages: 430
Registered: January 2004
Karma: 0
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Senior Member |
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Bill Bryant writes...
> There are certainally mistakes in our GMC manuals and that might
> explain part of this, the differences between the Motorhome &
> Transmode seem to me to go beyond this. The Transmode not only
> changes part numbers, but makes the change at 6V100878 when no
> changes to the engine or cooling system were made. To make the
> change when a new engine was used, as was done by the Motorhome
> change, makes a great deal of sense to me.
Is possible that they did it to respond to working up an order for the
sale of Transmodes to, say, the government, or the postal service.
Those would likely have involved some set of specifications that would
not always trace to any definable need, and it may have been easier
just to spec the part than to justify not doing so. And it might have
had so little cost impact that they just did it for all Transmodes,
with the idea that they were accommodating a wider range of future
applications.
And it isn't necessarily just an arbitrary standard--Transmodes in
normal service as, say, a mobile post office might be expected to sit
and idle for extended periods in ways outside the design operation of
a motorhome.
Rick "speculating" Denney
'73 230 Ex-Glacier "Jaws"
Northern Virginia
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'73 Glacier 230 "Jaws"
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| Re: [GMCnet] Fan Clutches [message #63280 is a reply to message #63275] |
Fri, 06 November 2009 10:13 |
bryant374
Messages: 563
Registered: May 2004
Location: Pleasant Valley, NY 12569
Karma: 1
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Senior Member |
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Bill Bryant writes...
> There are certainally mistakes in our GMC manuals and that might
> explain part of this, the differences between the Motorhome &
> Transmode seem to me to go beyond this. The Transmode not only
> changes part numbers, but makes the change at 6V100878 when no
> changes to the engine or cooling system were made. To make the
> change when a new engine was used, as was done by the Motorhome
> change, makes a great deal of sense to me.
Is possible that they did it to respond to working up an order for the
sale of Transmodes to, say, the government, or the postal service.
Those would likely have involved some set of specifications that would
not always trace to any definable need, and it may have been easier
just to spec the part than to justify not doing so. And it might have
had so little cost impact that they just did it for all Transmodes,
with the idea that they were accommodating a wider range of future
applications.
And it isn't necessarily just an arbitrary standard--Transmodes in
normal service as, say, a mobile post office might be expected to sit
and idle for extended periods in ways outside the design operation of
a motorhome.
Rick "speculating" Denney
'73 230 Ex-Glacier "Jaws"
Northern Virginia
Rick,
Your response pretty much matches my original (long ago) reasoning that the Transmode used the "heavy duty" fan clutch for the reasons you mentioned. That could explain the implementation at 6V100878 if they just needed a point in time to hook this change to. It still leaves the question of changing from a heavy duty to a standard duty clutch at that time. Maybe Byron's reason fits that.
Maybe, there is no rational answer 
Maybe, I shouldn't speculate on your speculation.............
Bill Bryant
PO 1976~PB (owned 34 years)
1914 Ford (owned 70 years)
1965 Corvette (owned 39 years)
GMC Motorhome History
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| Re: [GMCnet] Fan Clutches [message #63295 is a reply to message #63280] |
Fri, 06 November 2009 13:41 |
Bob de Kruyff
Messages: 4260
Registered: January 2004
Location: Chandler, AZ
Karma: 1
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Senior Member |
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Bill--were there any other changes in the cooling/ AC system around that time? The fan clutch was considered more or less as a tuning item based on overall system performance. Another possibility is that later cooling tests showed a different combination was appropriate. I know that till this day, many systems are looked at after a couple of years (wind tunnel or Death Valley) and subsequently re-calibrated.
I guess another question I may have is our nomenclature or interpretation of "standard or heavy duty" may not really tell the whole story about the clutch characteristics. Other considerations such as fan noise, engagement point, ultimate engagement level may be tuned for typical usage of a transmode vs motorhome.
Bob de Kruyff
78 Eleganza
Chandler, AZ
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| Re: [GMCnet] Fan Clutches [message #63311 is a reply to message #63295] |
Fri, 06 November 2009 16:39 |
bryant374
Messages: 563
Registered: May 2004
Location: Pleasant Valley, NY 12569
Karma: 1
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Senior Member |
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Bill--were there any other changes in the cooling/ AC system around that time? The fan clutch was considered more or less as a tuning item based on overall system performance. Another possibility is that later cooling tests showed a different combination was appropriate. I know that till this day, many systems are looked at after a couple of years (wind tunnel or Death Valley) and subsequently re-calibrated.
I guess another question I may have is our nomenclature or interpretation of "standard or heavy duty" may not really tell the whole story about the clutch characteristics. Other considerations such as fan noise, engagement point, ultimate engagement level may be tuned for typical usage of a transmode vs motorhome.
Bob de Kruyff
Bob, thanks for your input. I don't know the specs for the original fan clutches, but the 2 part numbers in question were used on thousands of GMCs throughout their production period, I therefore think it reasonable to assume they preformed satisfactorily. (it wasn't until at least 25 years later that we got into questioning which replacement fan clutch was the right one)
My original comments were intended to point out 2 things that seemed inconsistent to me:
1- the two fan clutch part numbers were implemented in the reverse to each other (Motorhome vs Transmode).
2- the timing of each implementation (Motorhome vs Transmode)were different (questionable but less important).
Old news to be sure, but that doesn't stop me from wondering.
Bill Bryant
PO 1976~PB (owned 34 years)
1914 Ford (owned 70 years)
1965 Corvette (owned 39 years)
GMC Motorhome History
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| Re: [GMCnet] Fan Clutches [message #63360 is a reply to message #63311] |
Sat, 07 November 2009 10:48 |
Bob de Kruyff
Messages: 4260
Registered: January 2004
Location: Chandler, AZ
Karma: 1
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Senior Member |
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""My original comments were intended to point out 2 things that seemed inconsistent to me:
1- the two fan clutch part numbers were implemented in the reverse to each other (Motorhome vs Transmode).
2- the timing of each implementation (Motorhome vs Transmode)were different (questionable but less important).
Old news to be sure, but that doesn't stop me from wondering.""
Bill, I didn't explain my thinking very well (if that's possible). When I was still with the truck group, we had a library of fan clutches that had been validated for performance,noise, durability, etc. Once we were familiar with the various characteristics, we would stay with that library and continue to refine the correct applications on various truck models. It was not unusual to switch usage between or across models once we became more familiar with how things were working in the field. After two or so years of on-the-road experience, we would re-assess whether we had the correct clutches on the correct applications. Additionally, when an engineering change is made, implementation on the line gets more complicated. Once manifests are created for ordered vehicles (sometimes months in advance), material is ordered and scheduled accordingly. The material planning group would then figure out how and when the change would occur on the line. The end result many times appears to defy normal logic when looking back.
Bob de Kruyff
78 Eleganza
Chandler, AZ
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| Re: [GMCnet] Fan Clutches [message #63387 is a reply to message #63360] |
Sat, 07 November 2009 16:14 |
bryant374
Messages: 563
Registered: May 2004
Location: Pleasant Valley, NY 12569
Karma: 1
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Senior Member |
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""My original comments were intended to point out 2 things that seemed inconsistent to me:
1- the two fan clutch part numbers were implemented in the reverse to each other (Motorhome vs Transmode).
2- the timing of each implementation (Motorhome vs Transmode)were different (questionable but less important).
Old news to be sure, but that doesn't stop me from wondering.""
Bill, I didn't explain my thinking very well (if that's possible). When I was still with the truck group, we had a library of fan clutches that had been validated for performance,noise, durability, etc. Once we were familiar with the various characteristics, we would stay with that library and continue to refine the correct applications on various truck models. It was not unusual to switch usage between or across models once we became more familiar with how things were working in the field. After two or so years of on-the-road experience, we would re-assess whether we had the correct clutches on the correct applications. Additionally, when an engineering change is made, implementation on the line gets more complicated. Once manifests are created for ordered vehicles (sometimes months in advance), material is ordered and scheduled accordingly. The material planning group would then figure out how and when the change would occur on the line. The end result many times appears to defy normal logic when looking back.
>
Makes great sense, thanks.
Bill Bryant
PO 1976~PB (owned 34 years)
1914 Ford (owned 70 years)
1965 Corvette (owned 39 years)
GMC Motorhome History
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| Re: [GMCnet] Fan Clutches [message #63391 is a reply to message #63360] |
Sat, 07 November 2009 17:47 |
Steven Ferguson
Messages: 3447
Registered: May 2006
Karma: 0
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Senior Member |
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I sure wish you could do a complete data dump Bob.
You have so much inside knowledge and too often it takes a jab to get
it to come to print. Your inputs are invaluable.
Mebbe see you at Quartszite?
On Sat, Nov 7, 2009 at 9:48 AM, Bob de Kruyff <NEXT2POOL@aol.com> wrote:
>
>
> ""My original comments were intended to point out 2 things that seemed inconsistent to me:
> 1- the two fan clutch part numbers were implemented in the reverse to each other (Motorhome vs Transmode).
>
> 2- the timing of each implementation (Motorhome vs Transmode)were different (questionable but less important).
>
> Old news to be sure, but that doesn't stop me from wondering.""
>
> Bill, I didn't explain my thinking very well (if that's possible). When I was still with the truck group, we had a library of fan clutches that had been validated for performance,noise, durability, etc. Once we were familiar with the various characteristics, we would stay with that library and continue to refine the correct applications on various truck models. It was not unusual to switch usage between or across models once we became more familiar with how things were working in the field. After two or so years of on-the-road experience, we would re-assess whether we had the correct clutches on the correct applications. Additionally, when an engineering change is made, implementation on the line gets more complicated. Once manifests are created for ordered vehicles (sometimes months in advance), material is ordered and scheduled accordingly. The material planning group would then figure out how and when the change would occur on the line. The end result many times appears to
> defy normal logic when looking back.
>
> --
> Bob de Kruyff
> 78 Eleganza
> Chandler, AZ
> _______________________________________________
> GMCnet mailing list
> List Information and Subscription Options:
> http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
>
--
Steve Ferguson
'76 EII
Sierra Vista, AZ
Urethane bushing source
www.bdub.net/ferguson/
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| Re: [GMCnet] Fan Clutches [message #63439 is a reply to message #63391] |
Sun, 08 November 2009 09:37 |
Bob de Kruyff
Messages: 4260
Registered: January 2004
Location: Chandler, AZ
Karma: 1
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Senior Member |
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Let me know when a few of you are there (like last year) and we can tip a few beers. I'd definitely like to swing by!!
Bob de Kruyff
78 Eleganza
Chandler, AZ
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