First off, shout out to TehRaydarlover for paving the way with a how-to on viscous couplers https://www.r3vlimited.com/board/forum/e30-technical-forums/325ix-technical-and-discussion/367707-325ix-rebuild-able-viscous-coupling.
Secondly, if anyone has a previously brand new unused viscous coupler on the shelf and is willing to rent it for me to test, please DM me! I would like to have data from the epitome of a factory OE coupler. This will help define what a good coupler should look like.
I ran across Ray's post when I first bought my car and thought one day I'd like to try this. I figured maybe I could rebuild some for other people along the way and help save some cars from scrap. I rallycross my iX regularly and feared that I might one day need to replace mine...plus it gave me an excuse to play with my machinery
I decided I wanted the ability to prove that the rebuilt couplers had the performance desired. I ended up building myself a test stand for the lathe that would allow me to measure the output torque at various speeds using my lathe. I calculated the HP needed based on a Subaru center diff (4 kgf-m @ 100 RPM) and figured I should get the lathe up to speed and quickly stop the coupler. The setup below is what I came up with. It uses an Arduino Uno to monitor the speed of the lathe, the viscous coupler and measure the torque output of the viscous coupler. #Nerd
Keep in mind my reference to 'good' coupler is one I got that did not have a proven jack test or anything else (I hope to get a second test sample to weigh this against). The bad coupler was very clearly bad. The silicone fluid was on the outside and the case looked like it had been heated cherry red then cooled down.
Next I ran a 'good' coupler through a bunch of speeds to see what it did (Each color is a different speed). I ran the lathe up to each speed and applied the brake for about 3 seconds. This showed the peak torque as well as the dynamic torque. Unfortunately, the peak torques are hard to capture consistently on a viscous coupler. In order to really capture and characterize each speed, I would need to let the coupler completely cool and settle before rerunning. I figured this is a good starting point and I will improve my data collection techniques as time progresses.
Here is an example of how to read one of the curves above (140 RPM in this case). The peak torque occurs about 0.373 seconds after a speed differential occurs from front/rear axle. If that 140 RPM speed differential continues the torque will plateau at around 93 ft-lbs at 2.6 seconds.
Next I took the peak torques of the 'good' coupler and a very bad coupler. I'm not sure how Subaru measures their center diff viscous couplers; It might be at peak torque or dynamic torque. If they use peak torque the 'good' coupler I have is around 16.9 kgf-m @ 100 RPM. If they use dynamic torque it is closer to 10 kgf-m @ 100 RPM. Either way that is quite a bit stiffer than a stock Subaru which is 4 kgf-m @ 100 RPM.
Secondly, if anyone has a previously brand new unused viscous coupler on the shelf and is willing to rent it for me to test, please DM me! I would like to have data from the epitome of a factory OE coupler. This will help define what a good coupler should look like.
I ran across Ray's post when I first bought my car and thought one day I'd like to try this. I figured maybe I could rebuild some for other people along the way and help save some cars from scrap. I rallycross my iX regularly and feared that I might one day need to replace mine...plus it gave me an excuse to play with my machinery
I decided I wanted the ability to prove that the rebuilt couplers had the performance desired. I ended up building myself a test stand for the lathe that would allow me to measure the output torque at various speeds using my lathe. I calculated the HP needed based on a Subaru center diff (4 kgf-m @ 100 RPM) and figured I should get the lathe up to speed and quickly stop the coupler. The setup below is what I came up with. It uses an Arduino Uno to monitor the speed of the lathe, the viscous coupler and measure the torque output of the viscous coupler. #Nerd
Keep in mind my reference to 'good' coupler is one I got that did not have a proven jack test or anything else (I hope to get a second test sample to weigh this against). The bad coupler was very clearly bad. The silicone fluid was on the outside and the case looked like it had been heated cherry red then cooled down.
Next I ran a 'good' coupler through a bunch of speeds to see what it did (Each color is a different speed). I ran the lathe up to each speed and applied the brake for about 3 seconds. This showed the peak torque as well as the dynamic torque. Unfortunately, the peak torques are hard to capture consistently on a viscous coupler. In order to really capture and characterize each speed, I would need to let the coupler completely cool and settle before rerunning. I figured this is a good starting point and I will improve my data collection techniques as time progresses.
Here is an example of how to read one of the curves above (140 RPM in this case). The peak torque occurs about 0.373 seconds after a speed differential occurs from front/rear axle. If that 140 RPM speed differential continues the torque will plateau at around 93 ft-lbs at 2.6 seconds.
Next I took the peak torques of the 'good' coupler and a very bad coupler. I'm not sure how Subaru measures their center diff viscous couplers; It might be at peak torque or dynamic torque. If they use peak torque the 'good' coupler I have is around 16.9 kgf-m @ 100 RPM. If they use dynamic torque it is closer to 10 kgf-m @ 100 RPM. Either way that is quite a bit stiffer than a stock Subaru which is 4 kgf-m @ 100 RPM.
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