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Fan Clutch question

Discussion in 'The Garage' started by opfor2, Jul 17, 2005.

  1. opfor2

    opfor2 1/2 ton status

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    Hi all,

    I need to replace the fan clutch on my 90 K-5, I want to use a Hayden # 2734 Heavy duty clutch from Kragen Autoparts but when I looked it up on the net it said the following: "Heavy Duty Thermal Fan Clutch: C.C.W.; w/A.C.; w/3.42 or 3.08 or 2.73 or Lower Rr. Axle Ratio" What the hell does axle ratio have to do with a fan clutch?

    Dan..
     
  2. tRustyK5

    tRustyK5 Big meanie Staff Member Super Moderator GMOTM Winner Author

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    I'd guess the gear ratio tells them approx what rpm the fan will be turning...:dunno:


    Rene
     
  3. unclematty

    unclematty 1/2 ton status

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    Not sure what to make of that :confused: but my guess is that since the gear ratio is higher the engine won't be spinning as fast and hence the fan would essentially have to lock up to cool the engine enough, just my thoughts, try it out and see how it affects engine operating temp. Good luck
     
  4. Mad-Dog

    Mad-Dog 1/2 ton status

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    At highway speeds the fan is useless so i don't have a clue other than maybe with taller gearing like 3.42's and down then the motor turns less rpm at a given speed so more blades are needed on the fan and and and and and.....
    what the heck does this have to do with a fan-clutch...... :confused:
     
  5. dyeager535

    dyeager535 1 ton status Premium Member

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    May be way off base, but I would almost guarantee that GM used those specs to determine which vehicles got which fan clutch. There are at least two, maybe three+ fan clutches for Chev motors.
     
  6. nvrenuf

    nvrenuf NONE shall pass! Premium Member

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    You have to remember that a truck with an OE lower gear will turn faster rpm's even while cruising in traffic (like a 3/4 ton w/ 4.10's compared to a 1/2 ton w/ 3.08's). For instance, if you used the fan clutch for the 1/2 ton on the 3/4 it might freewheel too early causing the truck to overheat since there would not be enough air flow thru the rad.

    Both my crew cab and K5 use a fan clutch for a truck with 4sd & 4.56 gears, TARussell showed me this application. It stays engaged all the time while driving in town, it puts a load on the motor but things stay nice and cool. :wink1:
     
  7. dyeager535

    dyeager535 1 ton status Premium Member

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    Fan operation should have nothing to do with engine operation, rear gearing, etc. Fan clutch *lockup* is controlled thermostatically. Any changes between the clutches would be based on the temp that they locked up.

    Obviously a heavy duty truck is much more likely to need maximum cooling than the most basic C10.

    Even the cars (say an 80's Caprice wagon with tow package) utilized a larger clutch, more fan blades, etc. compared to stripped down of the same make/model. I doubt the lockup temp for the fan clutch is known, I'm sure that is also a variable based on application, or there wouldn't BE different clutch numbers, since almost all GM stuff for our time frame ran 195* thermostats.

    I'd suspect engine bay temps were also a factor, a smaller engine bay with less airflow (camaro) would heat a fan clutch up to a higher temp, faster, then say, a truck.
     
  8. tarussell

    tarussell 1/2 ton status

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    The spring does control the point at which a fan will start to lock up or un lock but the fan clutches ability to maintain a certain percentage of lock up is of it design and bulk of the clutch with in and the fluid coupling capacity.
    The fan clutch for a higher geared vehicle ( like the 4.56 application ) is much stouter and has a higher rate of lock up when needed and will be more inclined to free wheel at higher RPM's.
    This application of a fan clutch has been proven for the past twenty five years with flawless results on many different engine combos - it really works !

    Tom
     
  9. ryoken

    ryoken Puppy Fabricator Premium Member GMOTM Winner

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    had to buy one for my 87 last week... 2 available, 3.73 and up and one for the lower gears...

    was a little annoyed cuz i've been contemplating going electric only, but i don't quite have what i need to do it right now... guess i can take my time going that route now... eh, i want a new huge aluminum rad in first to do the shroud anyway...
     

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