As I said Joe, a lower CST fluid will provide less viscous mode torque transfer.Hi GG, I think there are two things very wrong with your hypothesis that throw virtually everything else in your comments here into deep question.
First is viscosity - as in the viscous mode of operation of the VCU. the operation of the viscous mode - which is designed to be progressive ! - is directly related to the 'weight' of the fluid given a set amount of plates. You even have a test to confirm that as Tony demonstrated and also a figure to test on based on Landrover spec (the rotating test measuring static load.)
The hump mode of operation you also appear to be presuming is a constant applied 'locking force' - as in - when in effect the coupling is effectively locked - I disagree. With higher viscosity fluids the hump mode when activated will have a far higher eventual shear limit than the 'hump mode' with very low viscosity fluid. In other words, the hump mode of a low viscosity fluid will have a form of hump activation but a far lower break away force - it will not cause a 'lock up action' of = force to the higher weight fluid, it will cause an increase in tightening only that more than likely WILL be overcome by the torque of the engine / drive. Hence what appears to work on snow and ice and soft mud will not work effectively on shale / rock.
Viscous modes and Hump modes are not all equal across differing fluids and will not be overcome and made equal by altering quantity
There are also other factors at play in areas such as rate of hump activation and perhaps more importantly de-activation.
It is therefore not "easily quantifiable to say whether it works or not"
A veritable minefield.
Joe
A
As you say, Tony has replicated the LR Service recommendations for testing his VCU. Do you know what fluid he has in his VCU? I believe it was sold as some form of toiletry supplies or something!!! Definitely not a tub sold as a "VCU Silicone Fluid" or sold as "Silicone Fluid ZZ9.999 CST" - it just happens to be the right sort of substance! Probably similar to GKN's fluid - just smells nicer
Hi Alibro mate.
I know how the hump mode works - and also a possible way of testing a vcu in the future AFTER it has been modified with the two hole rinse - repeat and fill method. (a brain wave) - or possibly - a brain fart....
"Silicone oils generally have very low surface tension and even an aqueous cleaner with a very good surfactant mixture will likely not be very effective at removal.
You will want to dissolve the oil with a solvent to remove as much as possible. Most aromatic (ring structure) solvents are effective at dissolving silicone oil. These include toluene, xylene and naphtha.
I am still not convinced of the non Newtonian aspects. the 'degressive' as I mentioned - can be interpreted in differing ways. Shear thickening or shear thinning are both examples non Newtonian effects.
) - I do think that - a yes it is definitely an NN fluid, but that could also equate to commonly available 'siloxanes depending on formulation. Yes, 'weight' will effect viscous mode which is a very important function of the VCU. and YES, fluid expansion space (air!) in the VCU will definitely alter the Hump characteristics (and yes - I believe the peak torque transfer due to original viscosity)
Hi Tony,,
) expands with heat - heat is generated by the slippage, the expansion is related to the heat AND the original 'weight' / Viscosity. The air space effectively controls the point at which hump mode will be activated as once the airspace is used up due to expansion of the fluid and hence reduction (compression) of the airspace. the fluid expansion between the plates compresses the plate assembly effectively causing a lock up (HUMP mode (within given parameters). The airspace is ONLY there to control the time to hump mode based on temp / viscosity hence rate of expansion of fluid.
All documentation I've seen on viscous couplings indicates that the fluid is Polydimethylsiloxane (PDMS). As Tony says, the "CRC Slik One Drop" is PDMS (CAS Number 63148-62-9). As Tony probably found, they don't document its viscosity, but they do say it is Odourless!I am still not convinced of the non Newtonian aspects. the 'degressive' as I mentioned - can be interpreted in differing ways. Shear thickening or shear thinning are both examples non Newtonian effects.
However, does a generally available 'silicone' 'oil' (usually a siloxane that can have multiple polymer structures and designs and additives) follow or not the ''near enough' product ? - where we do agree (I think?) is that the definitive answer is that we don't know really - but we can make relatively informed and educated assumptions. What we do know (I hope) is that there is absolutely no such thing as a 'one product' 'silicone oil' - even with 'weight' quoted.
I must confess - after more reflection on previous research (from another thread that I am sure you will remember lol
I also believe that the home brew solutions offer a tremendous opportunity for experimentation provided they are refillable and not a closed unit.
Joe
I'm just using white spirit to flush the VCU. Partly because it leaves no oily or sticky residue, but mostly cause I have some handy. Having flushed it several times the VCU is turning much more freely but I have to say this is no easy way to sort a VCU. The gunge is still coming out black and yucky so many more flushes required.Hi Alibro mate.
When you clean out your VCU, it might be worth looking at this I came across. I dunno what you used in the past (as a solvent) .. but this might help.
I AM tempted to try the drill and fill method just for Sh!ts n Giggles.. It could be quite interesting. I would imagine that the cleaning out of the old cr&p would be the hardest part.
"Silicone oils generally have very low surface tension and even an aqueous cleaner with a very good surfactant mixture will likely not be very effective at removal.
You will want to dissolve the oil with a solvent to remove as much as possible. Most aromatic (ring structure) solvents are effective at dissolving silicone oil. These include toluene, xylene and naphtha. Additionally, silicone oils are reported to be soluble in chlorinated solvents such as trichloroethylene, perchloroethylene and methylene chloride. Polar solvents such as alcohols and acetone will not be effective at dissolving silicone oils. "
Check this also for household products that may contain the chemical you want -
http://allerair.blogspot.pt/2012/07/demystifying-household-chemicals-toluene.html (hopefully it is possible to navigate to other chemicals)
Would also like to have some piccies of your next drill session if possible mate ? - also, if possible - a peek down the drilled hole to see if the plates were indeed touched - not that I actually think it would make too much difference.
I finally decided that I am 100% convinced that I 'think'
Joe
What a brilliant article, good find
Hi GrumpyWhat a brilliant article, good find
Confirms (again!) that the silicon fluid is not dilatant and the rate of torque transfer in viscous mode diminishes as shear increases.
The comments about Hump mode wear are alarming - ie after 240 600nm hump mode episodes the plates would no longer sustain hump mode and lead to continued temp rise and catastrophic failure! That's not to long off the tarmac. Presumably this means that its best not to give it too much of the loud peddle off-road so the events are more like the 300nm tests giving 3,700 cycles.
So it was interesting that they recommended using as lower viscosity fluid as possible so that wear to the fluid would not increase viscosity over limits (eg 1WUT timings!). That would presumably result in more hump mode events and the dangers of wear to the metal bits.
The concepts discussed would be absolutely relevant to Freelander, but the numbers would presumably be different.
- I am quite surprised that you think the article is 'brilliant' and a 'good find' as you have quoted the misleading graphs and info from there before 
