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:)
As I said Joe, a lower CST fluid will provide less viscous mode torque transfer.

All this non-Newtonian talk really does focus peoples thoughts incorrectly and introduce so many "facts" that are untruths. Viscous mode is not "progressive" - it is "degressive". Once again, see the GKN doc and any other reputable information/science on VCUs. Also see dyno analysis of VCUs - there's graphs on various VCU threads showing reduced transfer as slippage increases until the point of Hump mode when the VCU is, to all intents and purposes, "locked".

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 :)

I have no idea whether a lower viscosity fluid will be able to "hold" hump mode for as long as a higher one, I can not recall reading about this. The fluid in this situation is not dragging the plates (as in viscous mode), it actually pushes them together and it is the mechanical connection between the plates that provides the transfer of torque. So there aren't high levels of force operating on the fluid - so there is no reason to believe that a lower CST will not hold as long. As I say though this is hypothesis.

I agree the requirements on ice are very different to gravel and shale. Jonaf's experiences though show his lower viscosity VCUs work well in snow - I would imaging this is fairly similar to gravel and shale where the wheels sink below the surface and there is a huge amount of drag build up in front of the wheels, as well as low friction. Granted not so much drag as gravel/shale, but similar in concept, the 4WD need is over an "extended" period.

I would think from a "safety" perspective a higher viscosity fluid would be preferable as it will constantly be providing more of a 4WD driving characteristic in normal road going situations. Once off tarmac, my thoughts are that hump mode is more important as the primary requirement is not to get stuck.
 
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 :)

Actually it was this stuff... https://www.bunnings.co.nz/crc-slik-one-drop-bottle-85ml_p00234921

I found it was similar in viscosity (measured dripping through a small hole) as some gearbox silicone lube for RC cars that had the same stated CST as the recommended for our VCU's. I did not smell it, low price and availability was more important for me.
 
Hi GG, the term 'degressive' on the GKN document could mean many things. A more or less flat 'graph' of X prior to hump Y can mean that the amount of wheel slippage remains more or less constant as engine torque increases (as the vcu tightens up) - the relationship of the slippage to increase in torque is therefore degressive in nature - until the hump mode is achieved.
The gravel or shale of which I refer is also not the 'loose kind - it is a virtual solid mass (so perhaps the wrong terms) - perhaps better described as tracks of small rocks and sharp shale pieces embedded in an extremely dry substrate.
 
Good point Joe. It takes a lot more torque to push a car up a rocky slope than along a flat snowy road. I know my last VCU home brew job worked great on rocky conditions cause I tested it in a quarry. That's why I'm not worried about the latest one being as good as i can swap them if needs be.
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':confused: I know how the hump mode works :D:rolleyes::) - 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....:oops:

Joe :)
 
"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 used Xylene on mine. The local hardware chain has it at a reasonable price.
 
All this non-Newtonian talk really does focus peoples thoughts incorrectly and introduce so many "facts" that are untruths. Viscous mode is not "progressive" - it is "degressive". Once again, see the GKN doc and any other reputable information/science on VCUs. Also see dyno analysis of VCUs - there's graphs on various VCU threads showing reduced transfer as slippage increases until the point of Hump mode when the VCU is, to all intents and purposes, "locked".
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 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)
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 used Xylene on mine. The local hardware chain has it at a reasonable price.
Hi Tony,,
Regarding your superb test on the torque characteristics at 75 RPM etc. I would like to offer a second method of checking for alterations in internal makeup of the vcu and hump mode operation - also to address and predict potential issues.

As follows - the Joe_H method of testing modded refillable VCU (with grease nipple etc)
We know that the siloxane oil / fluid internally expands with temperature. We know that the design should have an airgap (Air space) after filling with fluid.
This is quite simply because the 'fluid' (let's use this term for the 'stuff' in the vcu ;)) 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.
More air - more allowable expansion of fluid until air is effectively compressed leaving no space for fluid to expand causing hump in time t. less air means for the same expansion rate the hump mode is entered at less time t.

Ok, how can we use this to our advantage. ?

Well, on refilling the vcu and leaving an appropriate air gap / space.- then connecting an hydraulic pressure gauge to the vcu 'access port' (I say access port as I am uncertain as to the best 'access port arrangement)
On first filling - and appropriate air gap - and with a cold vcu - the pressure should be zero. on a VCU that has suffered from fluid expansion due to degradation (the most common (by far) failure - leading to too early a hump mode! - then the air space will be highly compressed - or well compressed above zero (depending on ambient temps and pressure). So, if a reasonable /considerable increase in pressure is noted on a cold unit then the vcu is suffering from a static fluid expansion. (which it should not)
Releasing a small amount of pressure (air or fluid) may help in the short term, reverting back to zero - however there is no way to really judge the air content and could be quite dangerous to the transmission.

Any signs of degradation and with a suitable solvent the unit could be cleansed and refilled.

It would be 'challenging' to arrange a pressure tap on the VCU but would if accomplished be most informative.

The thermal expansion of the fluid in a failing VCU would also explain the continued issuing of fluid over a considerable time observed by members when drilling a hole in the suspect / failed VCU. - In the event of issues the contained pressure in the VCU could be surprisingly high. This fits with all data I have seen and all observations made by members.

Just a mid day ponder :) :)

Joe
 
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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 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)
I also believe that the home brew solutions offer a tremendous opportunity for experimentation provided they are refillable and not a closed unit.
Joe :)
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've just spent ages Googling Silicone Lubricants because it appears illogical that something used in the VCU to inhibit metal plates slipping, should be used as a lubricant! It has been an epic waste of time, as trying to understand anything related to the VCU invariably is. In all this Googling, I have learnt only 2 things...

1) Silicone-based lubricants have not been shown to increase the risk of HIV transmission during anal intercourse, as some water-based lubes have
2) Silicone-based lubricants are not usually recommended for use with sex toys or other products that are made from silicone because the formula may dissolve the surface making it sticky to the touch.

So, driving Freelander should stop us catching AIDS, but if you're out dogging, leave the sex toys at home.
 
Where is your source for this information?
I'm happy to be disproved, but I believe that once again this is another "fact" about the VCU that's actually totally untrue.
My source for stating this, other than every other reputable documentation about Viscous Couplings, is the GKN document relating to their Viscous Couplings. It clearly states "Silicone fluid is optimised with specific additives for lifetime performance" - so it IS using a Silicone fluid as the primary/sole operating material and the diagram clearly highlights the fluid as "Silicone Fluid".

I've read on this very forum, that 100K silicone oil makes a stiff VCU pass the OWUT. However standard silicone oil, like that used in shock absorbers isn't that same stuff.
VCU fluid has unique properties that, as we know change viscosity when agitated.
 
I don't suppose anyone knows what the stuff is that VW use to recon their VCU's? I believe they have a similar system but of course VW had the sense to make them repairable and never considered them (and the drive train) consumable.

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':confused: I know how the hump mode works :D:rolleyes::) - 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....:oops:

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. :(
Petrol, diesel and pariffin are also good at softening the fluid which as I've said before can become more like glue than the gloopy fluid it was.
 
Now me and Joe_H don't quite see eye to eye this but here's my thoughts.
I actually believe that the OWUT is a worthwhile and valid test for an un bodged VCU.
The OWUT is actually no different to the test that Bell use. The only difference is, they test it in a vise and turn it directly with a weighted lever, which obviously requires the VCU to be off the vehicle. I don't know why Austin (from Bell)dismisses our test, when it's effectively the same as there own.
The OWUT doesn't test the VCU forfunction, nor does the Bell test. What it does do is give an indication that the fluid has begun to thicken. Now themechanisms of VCU are far too longwinded for this thread and are always upfor considerable debate anyway. But whatwe do know is:
A working VCU has two states. The free turning state, (there is some minimal drag). This is where it will just slowly turn while fitted in the drive train. In this state, it is passing little torque and because of the drive train design, shouldn't pass much torque.

The other state is known as hump mode. This is where the fluid transfers much more torque by thickening with agitation. Now the actual mechanism to start hump mode is still a cause for debate. Butwhatever the mechanism, it still thickens. However hump mode is where the Freelander's drive train damagepotentially occurs. What triggers humpmode is known, but only in a new unit. Hump mode will happen at 75 Rpm with ~400Nm of torque passing through it.
It appears however that as the fluid degrades with age, hump mode becomes easier to achieve. This is bad as the torque transfer can become considerable. This isobviously undesirable, when driving down the street.
So what the OWUT does is test for fluiddegradation (thickening) without putting the VCU into hump mode.
The problem with early hump mode onset is this. It basically reduces the safetymargin built into the VCU to compensate for cornering and slight tyre mismatch.Once this reduced safety margin has beenexceeded, the VCU starts transferring torque all the time.
So for example, the VCU is old with littlemargin until it achieves hump mode. Now you get a slow puncture in a rear tyrewhile you are on a 100 mile drive on the M1 at 70. The front and rear propshaft willrotate at different rates because the rolling radius of the tyres has changed.This difference is enough to cause early onset hump mode (torque transfer) tostart. Now the IRD and rear diff are taking high torque as the VCU is trying to equalise the rotational difference, but the tyres won't slip to lessen the load. Thismassively overloads both the IRD and rear diff one of which will fail.

This is my analysis of the failure mode ofthe VCU. It may not 100% correct, but I believe it's accurate enough for our needs.

So by checking the time on the OWUT, we get a guide as to the state of the fluid. The thicker the fluid, the earlier hump mode occurs. The earlier hump mode occurs,the less tolerance there is for tyre mismatch.
 
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Now you get a slow puncture in a rear tyrewhile you are on a 100 mile drive on the M1 at 70. The front and rear propshaft willrotate at different rates because the rolling radius of the tyres has changed.This difference is enough to cause early onset hump mode (torque transfer) tostart. Now the IRD and rear diff are taking high torque as the VCU is trying to equalise the rotational difference, but the tyres won't slip to lessen the load. Thismassively overloads both the IRD and rear diff one of which will fail.

Why do I not like the FL 4WD system - ARGHHHHHH
 
Useful description of Hump Mode and how it happens here (English is a second language of the writer)... http://vw-kern.at/visco_en.php
What 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.
 
It's interesting that pressure rise is the main hump mode agent. And that the fluid gets more viscose as it ages, which we already know happens.
 
What 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.
Hi Grumpy :) - 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 :p

That site - firstly - is a re conditioner of vcu units. (note the PUCH service sticker he stuck on the home built vcu turning unit - purely for effect - nothing to do with PUCH!):rolleyes:
Also, most of the stuff he writes is 'selectively' plagiarised from the original (and early) work of Wolfgang Peschke, (ie - made to fit his beliefs and sell his products)

If you want to refer to the article that he plagiarised then look at the link to Peschke's original papers referred to on the linked site - which also includes a graph and data by VW. showing the generalised torque transfer characteristics.(note - not the minute drop in torque transfer as shear load increases - which does NOT mean that the torque to the rear DECREASES with increases slippage - the effect of the torque increase from the delta of the shear balances the slight viscosity drop of the fluid (which is non Newtonian). The rate of torque transfer - in actual use remains more or less linear until hump mode is achieved.
The technical publication by Peschke and the data from VW are far more reliable than a guy who wants to make his re-con units fit 'his' model. :)

http://syncro.org/the-viscous-coupler/

Peschke's original work

http://www.syncro.org/sitephotos/Galleries/peschke_viscous_coupling_article/pages/VC1_jpg.htm

:)
 
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