jaluhn83
Full Access Member
Finally got around to putting up a post on my latest project - an electric fan clutch.
Research has shown that the idi fan clutch uses a 1.25-16LH thread. This is finer than a standard UNF, but is still a UN type thread, (dimensions can be found here for reference) which is the same thread used on some DT466 engines. The reference I can find states 1997-2007 but I don't think those are the only years. Notably, the PSD/T444E uses a similar 1.25-18RH thread, but it's clearly not going to be usable on the idi.
There is also a line of electro-magnetic (same type of clutch as the AC compressor) fan clutches speced for medium duty trucks made by Horton Co. The EC450 is the smaller of the 2 they offer and is available to fit the DT466, and hence the idi. These are speced for 850 in-lb (~70 ft-lb) of torque with a rated current draw of 4A. Horton pn# 996127, 996135 & 996128 all seem to have the correct dimensions to work. (mostly, see below) Be careful, 996123 & 996124 are both T444E units that will look identical but have the wrong thread. It looks like there are a couple vendors that have the clutch for ~$700, and there have been a couple on ebay for $300.
Both the DT466 & T444E clutches listed use the same fan bolt pattern as the idi (6 on 6" bolt circle with 5" pilot), however in both cases the fan mounting surface is about 1-1/4" further forward than the idi, which would bring the fan too close to the radiator. The solution I had looked into was buying a Horton plastic fan with the correct dimensions to fit. It looked like they had a couple that would fit and they were in the $1-200 range.
Now, having done all that work to id a Horton clutch, what I wound up with is a different brand - Concepts NREC, which is apparently a German based company that has sense stopped distributing in the US and possibly all fan clutch work. The unit I found was on ebay for $299 and was posted as crossing to the Horton 996127. The pn is 6514-021-1. They also list 6514-021-3 as apparently being the same. These are a different design than the Horton unit, which ultimately turned out to be a blessing. The main design difference is that these are a 2 speed clutch, where the Horton is a on/off. On this design, there is a plate with a number of permanent magnets attached to the fan and parallel to a plate on the input shaft. (the finned casting on the nose of the clutch). This provides a certain amount of drag to make the fan turn and provide some airflow when the electric clutch is off. It appears that this low speed is near the same as you get with an unlocked viscous clutch. While this take a small amount of power, I am happy it has this feature, as it provides enough flow to keep idle temps low and is probably enough for the AC condenser as well.
The main reason the design is a blessing though is it allowed me to use the stock fan. The Horton clutch body appears to be large enough in diameter that you must mount to the front face. his type though, had a flange and small enough body diameter that I was able to mount the fan on the back side of the drive flange in roughly the same position as the stock clutch. It may be that the smaller body means a smaller magnet and thus less torque capacity, but I doubt it's a concern with this small of fan. (relative to a typical 2 ton truck)
As it turned out, the unit I got was actually a PSD/T444E clutch with the RH thread - not sure if the cross reference is wrong or the clutch was misboxed. I suspect the later as the installation instructions reference the part number and specifically state 'left hand thread.' This became simply a good excuse to get a new lathe and practice some creative machine work however. The clutch design was such that it was easy to strip it down to a bare shaft, which I was then able to machine out for a thread insert, weld in an insert (brazed the first one but didn't like the amount of heat/didn't think it penetrated properly) and then machine the required LH thread. Not sure if the Horton design is as easy to take apart - if it is then a T444E EC450 (which is fairly common) clutch would be an option.
Once the machine work was done, installation was fairly straightforward. My eventual plan is to wire the clutch to both a manual switch and a temperature switch in the top radiator tank, but as of now it's just setup on a switch which has worked well. I have only done one heavy (~18k) trip since installing it, and there's only a few miles of steep grade, but it seems to work well. Being able to manually turn the fan on at the start of the hill is nice for piece of mind, and between this and the likely higher flow it seems to run a bit cooler.
When all is said and done it's a nice mod, but also a fair bit of money.
Also a free picture of the alternator belt idler I made up out of a pipe coupler - creativity!
Research has shown that the idi fan clutch uses a 1.25-16LH thread. This is finer than a standard UNF, but is still a UN type thread, (dimensions can be found here for reference) which is the same thread used on some DT466 engines. The reference I can find states 1997-2007 but I don't think those are the only years. Notably, the PSD/T444E uses a similar 1.25-18RH thread, but it's clearly not going to be usable on the idi.
There is also a line of electro-magnetic (same type of clutch as the AC compressor) fan clutches speced for medium duty trucks made by Horton Co. The EC450 is the smaller of the 2 they offer and is available to fit the DT466, and hence the idi. These are speced for 850 in-lb (~70 ft-lb) of torque with a rated current draw of 4A. Horton pn# 996127, 996135 & 996128 all seem to have the correct dimensions to work. (mostly, see below) Be careful, 996123 & 996124 are both T444E units that will look identical but have the wrong thread. It looks like there are a couple vendors that have the clutch for ~$700, and there have been a couple on ebay for $300.
Both the DT466 & T444E clutches listed use the same fan bolt pattern as the idi (6 on 6" bolt circle with 5" pilot), however in both cases the fan mounting surface is about 1-1/4" further forward than the idi, which would bring the fan too close to the radiator. The solution I had looked into was buying a Horton plastic fan with the correct dimensions to fit. It looked like they had a couple that would fit and they were in the $1-200 range.
Now, having done all that work to id a Horton clutch, what I wound up with is a different brand - Concepts NREC, which is apparently a German based company that has sense stopped distributing in the US and possibly all fan clutch work. The unit I found was on ebay for $299 and was posted as crossing to the Horton 996127. The pn is 6514-021-1. They also list 6514-021-3 as apparently being the same. These are a different design than the Horton unit, which ultimately turned out to be a blessing. The main design difference is that these are a 2 speed clutch, where the Horton is a on/off. On this design, there is a plate with a number of permanent magnets attached to the fan and parallel to a plate on the input shaft. (the finned casting on the nose of the clutch). This provides a certain amount of drag to make the fan turn and provide some airflow when the electric clutch is off. It appears that this low speed is near the same as you get with an unlocked viscous clutch. While this take a small amount of power, I am happy it has this feature, as it provides enough flow to keep idle temps low and is probably enough for the AC condenser as well.
The main reason the design is a blessing though is it allowed me to use the stock fan. The Horton clutch body appears to be large enough in diameter that you must mount to the front face. his type though, had a flange and small enough body diameter that I was able to mount the fan on the back side of the drive flange in roughly the same position as the stock clutch. It may be that the smaller body means a smaller magnet and thus less torque capacity, but I doubt it's a concern with this small of fan. (relative to a typical 2 ton truck)
As it turned out, the unit I got was actually a PSD/T444E clutch with the RH thread - not sure if the cross reference is wrong or the clutch was misboxed. I suspect the later as the installation instructions reference the part number and specifically state 'left hand thread.' This became simply a good excuse to get a new lathe and practice some creative machine work however. The clutch design was such that it was easy to strip it down to a bare shaft, which I was then able to machine out for a thread insert, weld in an insert (brazed the first one but didn't like the amount of heat/didn't think it penetrated properly) and then machine the required LH thread. Not sure if the Horton design is as easy to take apart - if it is then a T444E EC450 (which is fairly common) clutch would be an option.
Once the machine work was done, installation was fairly straightforward. My eventual plan is to wire the clutch to both a manual switch and a temperature switch in the top radiator tank, but as of now it's just setup on a switch which has worked well. I have only done one heavy (~18k) trip since installing it, and there's only a few miles of steep grade, but it seems to work well. Being able to manually turn the fan on at the start of the hill is nice for piece of mind, and between this and the likely higher flow it seems to run a bit cooler.
When all is said and done it's a nice mod, but also a fair bit of money.
Also a free picture of the alternator belt idler I made up out of a pipe coupler - creativity!
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