My viscous coupler rebuild

[syncrodoka]

Supposedly they get more aggressive as they get hotter.

Thank you for sharing.

[tim_ha]

From the following forum:
http://forum.club8090.co.uk/viewtopic.php?f=4&...;start=165

[syncrodoka]

http://sethdrew.com/Uganda/technology.html
Several threads with information about VCs here have gone over the theory and include videos and tech specs if you haven't seen them.

[photogdave]

I have to agree that the VC gets more aggressive in warmer temperatures. In the mild climate of the BC west coast my VC almost never engages during normal driving. But on a road trip to California in the spring, or on summer road trips when it's much hotter the VC kicks in after a few hours of continuous driving and I have a tough time parking!
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[ragnarhairybreeks]

Heat is a result of viscous shearing of the silicone fluid. The fluid was chosen as it does not exhibit a viscosity drop due to heating as severe as other fluids, say mineral oil. But the viscosity does decrease with increased temperature.

The heat produced by the viscous shearing of the fluid results in a pressure increase within the vc unit. The fluid expands as you would expect, with heating.

Then the magic happens. One would think that in an enclosed space all areas would experience the same pressure. But there are localized pressure differences that force the plates together and thus transfer the power from the input shaft to the output shaft. This condition is commonly called the "hump condition".

It is this that gets the power to the front wheels. When you jack up one side of the front of the van and try turning the wheel you feel the viscous drag for the plate moving through the silicone fluid. You do not feel the hump condition unless you turn the wheel fast enough.

Measuring the viscous drag does give an indication of the viscosity of the fluid. But you need a specialized test set up to determine the hump condition parameters.

What confuses a lot of us is the published data showing the test results, temperature versus power transfer. Temperature is used a a metric, an indirect if you will, measure of the internal pressure of the vc.

Of course if you increase the temperature of the vc the internal pressure will increase. But it is the internal pressure that is important for vc function, not temperature. If one could pressurize the vc from some external source ( and that was postulated by that VW engineer who's name escapes me right now), then you could adjust the agressiveness of the vc. But it is hard to do that, it is easier to heat or cool the vc (as Derek Drew's son did).

It might seem like semantics, and I agree that temperature affects vc function. But it is not temperature that is the direct cause of the plates coming together, it is inter-plate pressure differences.

Alistair
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[T3 Pilot]

Found it....

http://shufti.files.wordpress.com/2009/12/vc.pdf


"Hump Condition" - I think I had that back in high school......
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[beelzibus]

It's been a while since I did any thinking or reading about VC rebuilding, this is a great thread. So is anyone able to offer a kit of the fluid and seals now then?

[rubbachicken]

[SyncroChrick]

Would the fluid be the same as other Syncro application, such as the Golf/Passat, etc?

That should be available somewhere.

[SyncroChrick]

Looks like a possibility here:

http://www.silikon-profis.de/index.php?f=sysnr&c=0003_10011&t=artikel&sid=bdlyharfaxme


the bottle on that site seems similar to the one in these videos:

http://www.2wd-goes-syncro.de/

From google translate:

Here, the utensils used again in writing. Also, the prices paid by me.
requires your:

- 2x quad ring (X-Ring) 40.64 x 5.33 in FKM (Viton) (~ 10 € / unit)
- 1x O-ring 124 x 2.5 mm made ​​of FKM, go here also similar dimensions (eg 126 x 2.2 mm) (~ € 5 / pcs)
bring about 300g silicone oil with a viscosity of 100,000 mm ² / s (~ 70 € / 1kg), here we just want the original viscosity over a rheometer in experience -

[tim_ha]

Perhaps IdahoDoug can post where he sourced the fluid from. He was able to help me as well as another member out with enough for a rebuild. In our communications, he said he got it from an east coast company.
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[MarkWard]

Using the Google. I found this.

http://www.globaloring.com/Item/326-quad-ring-x-ri...0-40-64mm/

I have not had mine apart, but am interested in attempting this myself. It seems fairly straight forward.


This looks like the second O ring.

http://www.aceseal.com/124.00-x-2.5-p-2661-l-en.html

All that is left then is the secret sauce. This must be a very guarded secret supply. How about a group buy on a case?
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[IdahoDoug]

Hey guys, thanks Tim for letting me know of the thread. I researched the silicone fluid, corresponded with some of the European folks (my multilingual wifey!), and called several prospective vendors. I settled on a lab in Bensalem, PA called Clearco Products, and their 30,000 CST fluid as best match for stock performance as new from VW. I wanted functioning as VW intended for good road behavior and to avoid stressing the pricey front drive system with aggressive fluid.

I have been selling bottles with enough to refill your VC, plus some to play with or spill for $45 to your door and have a few remaining. It's in the Samba classifieds if you are interested.

Rgds,
DougM[/i]
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[rubbachicken]

i think your ad must have expired, you only have a sliding door interior panel in the classifieds

[IdahoDoug]

Ooh thanks! Yeah hoping to find a home for that sweet panel. Will up the ad immediately..
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1987 2WD Wolfsburg Vanagon Weekender "Mango", two fully locked 80 Series LandCruisers. 2017 Subaru Outback boxer. 1990 Audi 90 Quattro 20V with rear locking differential, 1990 burgundy parts Vanagon. 1984 Porsche 944, 1988 Toyota Supra 5 speed targa, 2002 BMW 325iX, 1982 Toyota Sunrader

[danfromsyr]

here's a Samba thread on Viscous couple rebuilding with pics and some details on fluid and Oring sizing.

http://www.thesamba.com/vw/forum/viewtopic.php?t=443009


and another 8090 club post on rebuilds
http://forum.club8090.co.uk/viewtopic.php?f=4&...;start=135
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[MarkWard]

Tim, I was wondering if you could update on how your serviced VC is performing. Anything you would have done differently? Any advice or suggestions? Thank you.
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[randedge]

Hi!

THis is my First post. I actually made an account just to make an inquiry!

But before that, I must say, good job on this writeup and I thank you for the info.

Anywho, I came across this so called "ultra thick silicone oil" as used by RC people.

http://www.redrc.net/2012/12/hudy-ultra-thick-silicone-oils/

Compared to the 80,000 cSt you used, these are 500,000 and 1,000,000 centi Stokes! Perhaps you could say these oils are so awesome that they are just so stoked to lock up, yo.

Sorry, couldn't help it. Perhaps such thickness is not needed since you find what you use to be aggressive enough. Nonetheless, I wonder: Is this the right kind of oil?

[MarkWard]

Welcome to the samba. Good first post. The fluid we have used is 30,000 and my understanding is that the guys in Europe are using a secret blend of fluids even less cst.

I completed my refill and finally drove the van. I had zero sense that the VC was working even nailing it on dirt. Drove back home, in the garage, jacked the rear with two floor jacks, placed 2x4's in front of the front tires. The van climbed over them like they were not even there. Very satisfied with my initial results.

Let us know how that thick stuff works for you. Doug, if you still have one left, I may get it from you. mark
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[86 for nix]

The video states they used oil with a viscosity of 100,000 square mm/second. Which I gather is the same as 100,000 cST. They sourced all their supplies including the oil from German companies (I speak german, so let me know if you'd like a translation of any particular parts of the video )

I found a guy on e-bay selling the oil out of the UK and says he can supply other viscosities as well.
http://www.ebay.com/itm/Silicone-Oil-25-000-25000C...35e7c47c14

I already have the seals and am going to take the plunge on this before too long. I'd be interested in what viscosity the OP used, since he had such good results. 30,000cSt seems to be working out for rsxsr, but how many grams did you use? IdahoDoug, what viscosity was the batches you were selling?