Viscous Coupling Testing Thread

[Cameron Morison]

So ive been testing a few viscous couplings that I have here for condition to see what ones are in good to run in the race car. I need a reasonably tight one to prevent the rear wheels from spinning up with it being a bit lighter at the rear and a decent amount of power.

Anyway, to build your rig you need
~ a vise large enough to hold a viscous coupler
~ test tool, see below
~ centre diff top case
~ a 12.8kg weight (two evo 4 brake discs)
~ a stopwatch
~ a reference marker (magnet and small ruler works)

The test tool bolts onto the top hat of a diff case and allows the weight to hang on a 162mm lever arm.

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The test is to measure the time that it takes to rotate the tool from a starting point of 45 degrees to a finishing point of 135 degrees, so a total of 90 degrees rotation. The top hat has 8 holes so each hole is 45 degrees. I hang the weight off the tool from around the 30 degree point so I have time to start the stopwatch when it passes my starting mark. Stop when it has rotate through to the 135 deg finishing point.

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Start when the mark passes your pointer

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Stop when the second mark passes your pointer

Please if anyone has the tools and time would you please add to the thread. What I would like to get an idea of is what is a rooted VC, what is average and what is good.

Thick VC, Labelled AH, Unknown Origin, 0:30.8
Thick VC, Labelled BN, Unknown Origin, 0:37.2
Thick VC, No Label, Ex Evo1 gearbox (had been opened before), 0:58.8
Thick VC, Labelled BX, Unknown Origin, 1:54.7
Thin VC, Labelled IN, n/a RVR UMXL box, 25:28.3 - this one was mental firm compared to the rest and was only a thin model, Id love to know if this is a common pattern for the thinner VC

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[Canadian_CD9A]

Some more info on testing methods here:

https://www.4gtuner.com/topic/19315-testing-a-viscous-coupling/
https://www.4gtuner.com/topic/11828-viscous-coupling-testing/
https://www.4gtuner.com/topic/14766-evo-i-iii-ralliart-viscous-coupling-unit/

 

[Cameron Morison]

Yeah its interesting, but viscous couplings dont really have a 'breakaway' torque like a normal plate diff does so that technique doesn't work. I'm only applying a maximum of 20nm torque when the tool is at max leverage, but they still move, all of them, even the one which is silly tight. I don't really agree with the practice of using breakaway torque to measure their effectiveness. It's too much of a subjective method, with the subjective part being how fast does it have to turn to take the reading.

The test really should be repeated at say 100 degrees temperature also to see how that effects it. Ill try that by boiling a coupling and retesting, will do it on a weak one and a strong one to see if the relative difference is the same.