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#1 |
Registered User
Join Date: Jul 2017
Location: Will Co IL
Posts: 30
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Fan clutch install 72 GMC C15 350
In the hopes of just a tad more MPG, I installed a fan clutch to replace the fixed 7 blade fan on our 72 GMC C15 350. Yowza! MPG takes a back seat to quiet. At idle it is world of difference; on the highway I’m no longer hesitant because of the old jet-engine roar at 65mph. It sounded like I was turning 6000 RPM. I was blaming the 3.73 gears. Heck no – it was the fan!
Now I hear a rattle that needs attention, and the exhaust leak that was trivial is now more prominent. I used the following: Fan clutch=AC Delco 15-80245 (Amazon) Fan blade=Dynacorn M1017 7 Blade (Ebay) Water pump studs=Dorman 675-001 (Summit – correct 5/16-24 fine thread on the short end) I had the balance of the hardware in my bins. The fan sits just right, about one inch out of the shroud. I haven’t driven long enough to hear it kick in, but I don’t expect trouble. Thanks to the experts here for all the good info – I got the part numbers from you. I hope this is useful to the next guy. I’m a serious tracker of MPG, more for vehicle condition/efficiency than cost. I’ll see if it really makes a difference. |
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#2 |
Registered User
Join Date: Oct 2015
Location: San Tan Valley, Arizona
Posts: 313
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Re: Fan clutch install 72 GMC C15 350
Thanks for posting this. I have been trying to find a source for those studs for a while. That really helped. Glad the clutch is working out for you.
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#3 |
Who Changed This?
![]() Join Date: Jan 2013
Location: Simi Valley, CA
Posts: 10,439
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Re: Fan clutch install 72 GMC C15 350
You should see an improvement. Please be sure to let us know. I don't think that it will be a lot, though.
__________________
~Steven '70 Chevy 3/4T Longhorn CST 402/400/3.56 Custom Camper Simi Valley, CA |
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#4 |
Registered User
Join Date: Jul 2012
Location: Whitehorse yukon
Posts: 1,218
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Re: Fan clutch install 72 GMC C15 350
Do you have a pic of your setup in the C10 ?
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#5 |
Registered User
Join Date: Jul 2008
Location: Eastern Oregon
Posts: 2,342
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Re: Fan clutch install 72 GMC C15 350
Where they not fitted originally ? My 71 GMC 1500 350 has one installed ?
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71 C-20 07 Magnum RT AWD |
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#6 |
Registered User
Join Date: Jul 2017
Location: Will Co IL
Posts: 30
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Re: Fan clutch install 72 GMC C15 350
Blackhornet,
Better experts than me, but I reckon fan clutch was an option or part of an option. Steveedee - I will. I track tank to tank as well as 10 trailing fill up average. |
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#7 | |
Registered User
Join Date: Jul 2018
Location: Catskill Mountains,NY
Posts: 8,505
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Re: Fan clutch install 72 GMC C15 350
Quote:
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Mark 72 c20 custom camper Husky edition, 66 SS396 Chevelle 1964 Hawk, 63 Avanti,62 lark 1969 AMX , 1968 c20 stepside ,85 K20 1977 Suburban sold 68 anniversary. |
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#8 |
Who Changed This?
![]() Join Date: Jan 2013
Location: Simi Valley, CA
Posts: 10,439
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Re: Fan clutch install 72 GMC C15 350
Generally only came with AC, but if you knew to ask, there was a heavy duty cooling package.
__________________
~Steven '70 Chevy 3/4T Longhorn CST 402/400/3.56 Custom Camper Simi Valley, CA |
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#9 |
Registered User
Join Date: May 2019
Location: Lakewood
Posts: 83
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Re: Fan clutch install 72 GMC C15 350
I just ordered parts to do the same thing. Buying a 50 year old truck sure is an adventure. My C-10 currently has a fixed 4 blade fan that roars. She runs very cool but I suspect the previous owner may have removed the thermostat. He also installed an aluminum 3 pass radiator but the fitment is very poor. There is a large gap between the radiator and the shroud and the radiator is sitting crooked in the mounts. I have to drive out to Brothers Truck this weekend to pickup some back ordered parts so I'll get some replacement rubbers for the mounts and see if I can get it all straightened out.
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#10 | |
Senior Member
![]() Join Date: Mar 2011
Location: Hanover NJ
Posts: 4,167
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Re: Fan clutch install 72 GMC C15 350
Quote:
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Doc & Kim build http://67-72chevytrucks.com/vboard/s...d.php?t=722288 I am from the desert http://67-72chevytrucks.com/vboard/s...d.php?t=650332 basket case build SOLD http://67-72chevytrucks.com/vboard/s...d.php?t=648557 |
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#11 |
Registered User
Join Date: May 2019
Location: Lakewood
Posts: 83
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Re: Fan clutch install 72 GMC C15 350
Glad I read this thread again. Did not realize I needed the studs for my fan install. On the way from Summit! Thanks!
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#12 |
20' Daredevil (Ret)
![]() Join Date: May 2003
Location: Jefferson State
Posts: 13,647
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Re: Fan clutch install 72 GMC C15 350
..... And I have not seen studs used in that application. My K20's fan clutch is attached with 4 bolts, which is how it left the factory.
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- Mike - 1972 K20 LWB 350/350/205 RIP El Jay |
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#13 | |
Registered User
Join Date: Jun 2016
Location: West Palm Beach, Florida
Posts: 295
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Re: Fan clutch install 72 GMC C15 350
Quote:
Mine has 3.73 and turns about 2900 at 60mph, with the Flowmasters it is very difficult to hear anything. |
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#14 |
Registered User
Join Date: Apr 2018
Location: Riverdale, NJ
Posts: 85
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Re: Fan clutch install 72 GMC C15 350
Before my 283 blew up, I swapped the existing direct drive fan for a seven- blade clutch fan. What a treat it was to not sound like a jet dryer truck past 3k rpm! Thinking about it now, my new- found inclination to go a little higher in the revs may have been the silver bullet for that tired old engine...
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#15 |
Registered User
Join Date: Jun 2010
Location: San Diego Co.
Posts: 1,167
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Re: Fan clutch install 72 GMC C15 350
Sub'd!
Thanks for posting this up. The testimonials on noise reduction alone make this upgrade very appealing to me. Won't be right away, but this is definitely on the list!
__________________
1972 Chevy C-10, SWB, Fleet, 350/350, PS, PB, HEI, mostly stock, Survivor. ![]() |
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#16 |
Registered User
Join Date: Jan 2011
Location: Chattanooga, TN
Posts: 2,151
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Re: Fan clutch install 72 GMC C15 350
I have not looked lately, but used to be those studs with the different threads were available in a kit of 4 in the HELP section of the parts stores.
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'83 K20-TPI '73 C10 '79 C10-ex-diesel(SOLD) '07 Tahoe(Son driving) '14 Suburban-DD '71 C10-current project |
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#17 |
Registered User
Join Date: Jul 2017
Location: Will Co IL
Posts: 30
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Re: Fan clutch install 72 GMC C15 350
Another post about fan clutches prompted this replay. 2-1/2 months, 1250 miles, 7 fill ups. Old truck mods don’t occur in vacuum, however. I did play with the timing curve, and replaced a bad plug with a full new set. I installed a cheap manual choke conversion. The divorced choke was perfect all winter, but for the life of me I couldn’t get it to perform well in summer. After 2 weeks, I trashed it, bought a good cable, made solid brackets & linkage and it works perfectly.
So anyway, my tank-to-tank mileage has increased consistently, up 10%. Ten trailing is up 5%. My truck does like summer, but it has never shown such a regular increase. How much is the fan clutch responsible for? Some, but exactly I can’t say. It is irrelevant. The free and easy acceleration and cruising more than compensate. At first, I was really enjoying the throttle, but as mileage increased every fill from 12.5mpg to 13.8 mpg, I’m sure some psychological factor came into play. My commute is consistent, averaging 45mph, anticipating lights for fewest stops possible. The truck is so much more enjoyable, I’d highly recommend the fan clutch conversion. Stocker – the studs make aligning WP, pulley, and clutch a breeze. We sold them all the time back in the ‘real’ auto parts store. Many pumps even included them. Bolts are a pain in the dupa with limited clearance and a pump & pulley that want to rotate freely. Minkota – TH350, 3.73 rear, 235/75R/15 Michelin Defender LTX, no tach but by the calculator about 2700 at 60 mph. Without that fan noise, we enjoy the revs coming so easy. |
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#18 |
Senior Member
![]() Join Date: Feb 2010
Location: Falls City, Nebraska "100 Miles From Nowhere"
Posts: 2,219
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Re: Fan clutch install 72 GMC C15 350
Good info! Thank you for sharing!
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Michael of the clan Hill, "Two Seventy Two's" 71 1-ton Dually 350 4-Speed 71 C/50 Grain Truck, 350 Split-Axle 4-Speed 02 3/4 ton Express 14 Indian Chief Vintage 1952 Ford 8N, "Only Ford Allowed On The Property" ![]() "Be American, Buy American" ![]() |
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#19 | |
20' Daredevil (Ret)
![]() Join Date: May 2003
Location: Jefferson State
Posts: 13,647
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Re: Fan clutch install 72 GMC C15 350
Quote:
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- Mike - 1972 K20 LWB 350/350/205 RIP El Jay |
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#20 |
Senior Member
![]() Join Date: Dec 2013
Location: Gods country East,Tn
Posts: 8,545
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Re: Fan clutch install 72 GMC C15 350
O'rielly's has the studs for .79 each
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![]() 1967 Factory short bed - Old school '71 - 350 / 4bolt / 487 heads / Edelbrock C3BX Muncie M-22 4 speed / Hurst Comp plus Factory 12 bolt posi 3.73 / 255-70-15 Smoothed firewall / Factory cowl induction Power disc brakes / power steering / 3.5-5" drop |
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#21 |
Proprietor of Dale's Corner
![]() Join Date: Nov 2012
Location: Vacaville , CA
Posts: 16,130
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Re: Fan clutch install 72 GMC C15 350
I've been wanting to do this. Now I know where to find th fan. Thanks for posting part# and the brand names.
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"Some Days Chickens And Some Days Feathers" Dale XNGH ECV Sam Brannan 1004 R.I.P. 67ChevyRedneck R.I.P. Grumpy Old Man |
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#22 | ||
"I ain't nobody, dork."
Join Date: Sep 2007
Location: Whidbey Island, Washington
Posts: 8,940
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Re: Fan clutch install 72 GMC C15 350
I did this swap in my 1972 GMC C1500 as well. My truck came stock with a 7 blade 1:1 fixed fan. I swapped it out for a Hayden fan clutch and a Derale 6 blade clutch fan. My rig runs more in the heat zone it should and no more belt squeal when I wind up the RPM's.
Best 70 bucks I've spent on my truck yet. Gary
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'cuz chicks dig scars... My 1972 GMC 1500 Super Custom (Creeping Death) "long term" build thread. The Rebuild of Creeping Death after the wreck Quote:
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#23 |
Senior Member
![]() Join Date: Dec 2013
Location: Gods country East,Tn
Posts: 8,545
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Re: Fan clutch install 72 GMC C15 350
__________________
![]() 1967 Factory short bed - Old school '71 - 350 / 4bolt / 487 heads / Edelbrock C3BX Muncie M-22 4 speed / Hurst Comp plus Factory 12 bolt posi 3.73 / 255-70-15 Smoothed firewall / Factory cowl induction Power disc brakes / power steering / 3.5-5" drop |
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