HD Fan Clutches

Discussion in 'KJ General Discussion' started by JeepJeepster, Jan 23, 2021.

  1. JeepJeepster

    JeepJeepster Full Access Member

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    With all of the threads on HD cooling, I figured I would discuss fan clutches. When I was first looking into adding the HD cooling I remember reading some threads on what clutch to go with but I wasnt able to find them today. Seems I remember people trying to figure out which clutch was best.

    Dont ask why, but many years ago when I added the HD cooling, I couldnt remember what clutch I bought. I always thought I bought the Hayden clutch meant for the KJ and it was just a heavy duty fan clutch... Nope... I evidently bought the severe duty fan clutch that isnt meant for the KJ at all, it fits the 5.2 ZJ.

    Its SUPER tight getting that thing in and out of there. Unfortunately when I removed it today, I shaved the insulation off the wiring for the electric fan... Doesnt appear to have hurt the wiring itself, so I'll patch that up and move on. I was looking at the shaft and I noticed its much longer than the picture I found online. Thats when the little wheel in my head started turning and I found the number on my fan clutch...

    So FYI, the Hayden 2791 is the severe duty clutch with a longer shaft that screws onto the water pump. Im thinking this is why its so tight when trying to fight the electric fan, mechanical fan, and shroud.
    This clutch pretty much roars all of the time and Im thinking this may be why my fuel mileage always seems 2-3mpg low. Even on the 90F+ days and towing, that engine stayed at 200-204F. Electric fan only kicked on when the transmission got hot or the A/C was on.

    I was bored today so I tried messing around with the bimetal spring on the clutch. I took it out of its little home and fully loosened it. Started the Jeep and let it run for ~10min, the fan was still roaring... So trying to manually adjust it was out of the question.

    The Hayden 2736 is the factory replacement and I have one on order. Going to follow up on when it seems to engage and what temp the engine runs at. Probably have to wait till summer to really check it out. I'll get a pic of the two clutches side by side showing the differences when the 2736 clutch arrives.

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  2. LibertyTC

    LibertyTC Well-Known Member Staff Member Moderator

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    You got lucky that the wires did not get sliced into pieces.
    Your HD fan should not be screaming all the time. The idea is that a viscous fan should dis-engage until it gets hot enough to engage.
    I hope you have the correct Hayden # 2736. That should solve the issue. I wonder what the correct Mopar HD fan part # is today?
    Look forward to see the comparison photos...
    Talking about photos..Wow, I thought I had a clean engine bay, yours is absolutely spotless! Nice detailing! ;)
     
  3. JeepJeepster

    JeepJeepster Full Access Member

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    Looks like its 55038106AA and its $160...

    Yeah, I like a clean engine bay. :)
     
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  4. sleazy rider

    sleazy rider Retired moto tech and gearhead KJ Supporting Member

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    No way, no how would mine ever stay that clean. When I leave my street, it's dirt roads for a bit. Mud, snow, dust? Just ain't happening. I've sworn off going to the car wash or detailers. A quick swipe with the pressure washer a couple times a year will suffice.
     
  5. David13

    David13 Full Access Member

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    I am looking at this idea.

    My Liberty came with some parts of the tow package, but not the mechanical clutch and fan. It does have the full spare, hitch and wiring and transmission switch.

    And I intend to tow a small atv trailer. So I may want to add the clutch and fan. In previous reading I saw that the mechanical clutch and fan would come on at about 150 or 160 degrees. Seems a little low, but they have have posted that from experience.

    We get a little summer heat here but not too much. However, we do have some steep trails, and dirt roads (steep) to trails. So I may well need the extra cooling. I do have the larger shroud, so it would be easy to add the clutch and fan.
    dc
     
  6. JeepJeepster

    JeepJeepster Full Access Member

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    I shouldve added that this is only for the KJ, I know nothing about the KK.

    And the clutch driven fan engaging at 150-160 cannot be correct, that just wouldnt work.
     
  7. David13

    David13 Full Access Member

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    I thought that was too low myself.

    As far as I can see the KK works exactly the same with the mechanical fan and clutch. Just screws onto the water pump and uses a larger shroud.
    dc
     
  8. JeepJeepster

    JeepJeepster Full Access Member

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    New clutch arrived today... Big SIGH... Made in Korea... The serve duty clutch was made in USA, the stock electric fan has made in USA on it, and now Ive thrown a korea clutch on it... Bothers me more than it should but at least its not chiner.

    The new clutch is ~3/4" shorter and made the install easier. If youve ever tried to get the big shroud out with the mechanical fan, you know there is nothing easy about it, so I dont have much to say that will help besides it sucks. When putting it on, I put everything down in there together then drop the mechanical fan on down in there below the water pump, that gives you some room to fight the shroud into place. Once its bolted up I pull the fan back up and thread it on. I put a little anti-seize on the water pump threads, orange permatex thread lock on the shroud bolts, and orange thread lock on the clutch to fan blade bolts. The new 2736 did come with new bolts but I just reused the old bolts. I couldnt tell the new bolts were in my hand while the old ones had some heft to them.[​IMG]

    The 2736 does make it a bit harder to get my big adjustable wrench on the nut but it still works. I gave it one smack with the dead blow to set it good. Eventually I'll buy the proper tools for removing the fan clutch.

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    Last edited: Jan 27, 2021
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  9. JeepJeepster

    JeepJeepster Full Access Member

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    You'll have to let me know if this video works. This is after letting the Jeep run for a few minutes, its still cold. The 2791 never spun like this. It always stopped immediately and had a lot of resistance. Wild thing is, I would've said this clutch was bad if I saw it spinning like that. I've never seen a clutch let a fan spin that much no matter what the temp. Its snowing so the ol liberty is staying in the garage for now... But I'm interested to see if it still roars after stopping. The only time the 2791 didn't roar was after driving 3-4 minutes. Anytime I stopped it would start roaring again till I was driving for a bit. Even with the fan roaring like that the trans still got too warm IMHO.... Which tells me that little factory cooler is way too small.

    https://imgur.com/Ysq0QFl
     
    Last edited: Jan 27, 2021
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  10. LibertyTC

    LibertyTC Well-Known Member Staff Member Moderator

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    No go on the Imgur video. It's too bad imgur does not allow videos. Youtube only, unless someone has some other video upload suggestions.
     
  11. uss2defiant

    uss2defiant Full Access Member

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  12. jeeptorino68

    jeeptorino68 Full Access Member

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    Here is how to mod the fan shroud to get it out easier

    https://www.jeepkj.com/threads/hd-fan-shroud-mod-for-quick-removal.59988/
     
  13. JeepJeepster

    JeepJeepster Full Access Member

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    Maybe Im misleading people, the 2791 severe duty works fine, its just that it stays engaged almost all the time and its very close to the electric fan. When you unthread the fan its tight against the electric fan. Which is the reason why I ground the insulation off my electric fan wiring since I didnt know it was rubbing on the wiring when I was unthreading it.

    The main reason I put the 2736 in is b/c Ive decided I dont need or want the 2791 and completely forgot that I bought the severe duty clutch. I had it in my mind that I had the factory clutch replacement and just discovered that I didnt while removing the shroud for something else.

    You'll notice someone in that thread USS posted said to use a 2905 clutch, so theres another model that someone says to use.
     
    Last edited: Jan 28, 2021
  14. mercdudecbr600

    mercdudecbr600 Full Access Member

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    Here's something interesting... my KJ came with the towing package and what I assumed was the HD fan/shroud (definitely HD shroud). When I replaced the serpentine belt, I thought that I should change the fan clutch as well (hey it was OEM and 19 years old and it was already off). The OEM fan clutch behaved exactly like the new one you show on the video... which led me to believe it was too loose/needed replacement. I went to napa auto and got the HD fan clutch replacement and installed it. Now it is ALWAYS engaged at least 25-30% and roars on startup until I get about 500' down the road. I lost at least 1-2mpg unless on the highway for long periods. This has always bothered me, and I'd be interested in replacing.

    What's the correct part# again?
     
  15. JeepJeepster

    JeepJeepster Full Access Member

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    I've not driven it yet so I cant confirm that it doesnt roar like the severe duty, but the 2736 is suppose to be the factory replacement and just from starting it in my garage and then spinning it by hand, it has much less resistance than the 2791 I took out.

    Hayden 2736=stock replacement
    Hayden 2791=Severe duty not shown to work on the KJ but will, its just a little longer thus harder to install.

    The factory 2 speed fan is more than capable of keeping the 3.7 cool, I just want the extra capacity in case it fails.
     
  16. mercdudecbr600

    mercdudecbr600 Full Access Member

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    shoot a short video of it on startup and idling?
     
  17. JeepJeepster

    JeepJeepster Full Access Member

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    Finally drove the liberty today after waiting for the salt to wash off the roads. This fan clutch is much MUCH quieter than the 2791 clutch. When cold, it will roar for just a few seconds and it never roars again. Its only 40F today but the engine didnt get over 204F after idling for ~10min.

    I did something that YOU SHOULD NOT TRY but I am able to stop the fan when the engine is running. I'm curious to see if the fan engages this summer when the temps are higher.

     
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  18. mercdudecbr600

    mercdudecbr600 Full Access Member

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    Ok now I’m convinced that my fan is also the severe duty one. No way can you touch the fan clutch even at idle. Thanks for posting this video!
     
  19. mercdudecbr600

    mercdudecbr600 Full Access Member

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    Installed the 2746 clutch. Physically identical to the one from napa but a different part number and slight difference in spring. But, turned off much faster than the other one and I'm noting about 2-3mpg better on my instant readout. Power seems better too.

    Though mine (at about 60deg outside) still runs pretty hard for a while during cold idle but at warm idle it's moving much less than the previous. It seems about 20-30% better than the other one which was about 1 year old.
     
  20. JeepJeepster

    JeepJeepster Full Access Member

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    What led you to this clutch? When I google hayden 2746 it doesnt even show up.
     
    Last edited: Feb 13, 2021