D2 viscous fan clutch “upgrade”

Maximumwarp

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Callsign: KN4PCA
Mar 22, 2015
788
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Fairburn GA
Fan clutch on my 99 D2 crapped out, so I figured I’d try one of the slightly beefier Hayden units, a 2781. It is too large in diameter to fit the fan properly, but I’ve seen numerous threads that describe the 2781 being a drop-in replacement (same for the 2991, which has the same diameter as the 2781). What am I missing here? I swear I did this swap on my other D2 years ago, and I don’t remember any challenge to it aside from getting the correct bolts.

Pics with measurements attached, but I’m not sure why they uploaded sideways
 

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best4x4

Well-known member
Mar 1, 2015
423
5
Beaumont, TX
Like I said the 2991 is guaranteed to fit. Hayden list it for 94-04 basically (03-04 will require an 18inch fan blade). I'm running the Hayden 2991 in a 95 D1, 97 D1, 99 D2, 02 D2, and an 04 D2. Zero fitment issues.
 

Maximumwarp

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Callsign: KN4PCA
Mar 22, 2015
788
10
Fairburn GA
I mean, I read what you wrote, but you also see the pictures, right? The outer diameter of a 2991 is over 7 inches, and the diameter of the center section of my fan is like 6 and 1/2”, so that won’t fit. Is it possible I have a different fan blade than what works with the bigger Haydens? It’s the original LR part, #ERR4960
 

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Maximumwarp

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Callsign: KN4PCA
Mar 22, 2015
788
10
Fairburn GA
Could the part have been packaged wrong?
The fan clutch? It’s definitely a 2781, has it printed on the back. And its dimensions match what I’m seeing advertised online. I didn’t pay much attention to the measurements when I ordered it at first. I’m beginning to suspect that my fan blade just isn’t the right one.
 

Maximumwarp

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Callsign: KN4PCA
Mar 22, 2015
788
10
Fairburn GA
After checking in other places, it appears that the 2991 “Extreme Duty” is actually 6.5” in diameter, while the 2781 “Heavy Duty” is 7.2”. Interesting that the stronger clutch is actually a little smaller, and that some places have the dimensions listed wrong. Going to order the 2991 now.
 

CORover

Well-known member
Jun 11, 2007
672
41
Colorado, USA
Also if your OEM fan blade ever shows signs of cracking you can use the Dorman 620-112 as a direct replacement. They normally sell for around 25.00
My current DD fan whines like a jet during take off. I wonder if this one would make a better sound or the earlier Discovery equivalent?
 
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JUKE179r

Well-known member
Sep 14, 2016
394
26
Suffolk, UK
Hayden Heavy Duty #2781 fan clutch and Dorman #620-112 fan user here on my V8 with a soft spring 180 degree t-stat. No problems here and temps stay around 183.
 

mlnnc

Well-known member
Mar 23, 2008
199
5
Charlotte
Different bolts? I don't understand.

I installed a 2991 three months ago and reused the original bolts. What is there about the original bolts that prevents you from using them?
 

Maximumwarp

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Callsign: KN4PCA
Mar 22, 2015
788
10
Fairburn GA
Different bolts? I don't understand.

I installed a 2991 three months ago and reused the original bolts. What is there about the original bolts that prevents you from using them?
The old clutch was not an OEM clutch. It was a Hayden 2626. So three different Hayden clutches, three different types of bolt.
 

CORover

Well-known member
Jun 11, 2007
672
41
Colorado, USA
Threadjack... I was going to start a new thread but thought it fit here and would keep it all in one place. This exercise got me wondering why my 99 sounded like a jet taking off. Last night I swapped in a spare stock coupler and fan assembly I had laying around and the sound was much better right away. I am guessing my original had failed. So the questions are;
How to tell if it has gone bad? Can I use a heat gun, should the coupler nut be easy to turn or hard to turn?
Do they fail the same way all the time, as in coupled or uncoupled?
So if mine failed in the coupled action, it would just be cooling all the time and might affect warm up and interior heat at startup?
 

Maximumwarp

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Callsign: KN4PCA
Mar 22, 2015
788
10
Fairburn GA
I think when they fail, they get looser, so less effective cooling. On the 2626 that was on there before, I could literally see oil coming out of the fan clutch itself. You can kinda see it on the blades of the fan in my pics.