# Viscous Coupler - SAE Technical Documentation and Rebuild Info



## rte7x9 (Jun 11, 2008)

*Posting this for reference/discussion purposes. Later posts also document the taredown/rebuild of my own viscous coupler. While the Vanagon VCs are rebuildable, Syncro Passat VCs are not designed to be opened. To my knowledge this thread is the first example of a rebuilt Syncro Passat VC. *

I thought about adding this to the FAQ but with the images and everything it could get to be pretty lengthy. There's really very little information about the Syncro viscous coupler out there, any time it comes up, someone just says something like, "It only locks when the front wheels slip" and dismisses any other information. While, yes, a properly functioning VC will lock when speed differential is different between front and rear wheels, there's really a bit more to it. Pay close to Section 5, it describes torque/power characteristics as functions of other variables such as silicone viscosity, internal pressure, and temperature. Important to note that if your VC seals are bad, the silicone inside (if any still exists) will fail to build pressure as it heats, and will perform poorly or not lock up at all.

*I have also included a couple of links below with information on rebuilding the Viscous Coupler. I haven't had time to rebuild mine yet, but will most likely order a few seal kits and some silicone soon. If anyone here has experience with rebuilds PLEASE feel free to chime in. Thanks!*

http://imageshack.us/a/img802/4387/vc1jpg.jpg

http://imageshack.us/a/img831/2532/vc2jpg.jpg

http://imageshack.us/a/img809/5108/vc3jpg.jpg

http://imageshack.us/a/img17/2705/vc4jpg.jpg

http://imageshack.us/a/img442/1338/vc5jpg.jpg

http://imageshack.us/a/img834/9273/vc6jpg.jpg

http://imageshack.us/a/img600/4917/vc7jpg.jpg

http://imageshack.us/a/img51/4535/vc8jpg.jpg

http://imageshack.us/a/img267/2511/vc9jpg.jpg

http://imageshack.us/a/img542/1816/vc10jpg.jpg

http://imageshack.us/a/img27/5987/vc11jpg.jpg

http://imageshack.us/a/img823/3169/vc12jpg.jpg

http://imageshack.us/a/img203/8748/vc13jpg.jpg

http://imageshack.us/a/img405/1486/vc14jpg.jpg

*UPDATE - Here's the above set of images in a much handier PDF format. Page 8 is in tact as well: http://www.easy2design.de/stuff/visco_sae.pdf*


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## rte7x9 (Jun 11, 2008)

Here are a couple of links to rebuild guides and sources for seals and silicone. Some of the stuff is in German, but if you channel your inner VAG-ness it all starts to make sense. If anyone has any other sources for seal kits in the US, please feel free to post.

*Taredown/plate configuration:* 
http://shufti.wordpress.com/2011/11/21/vanagon-syncro-viscous-coupling-anatomy-part-1/

*German rebuild videos:*
Pay close attention to the amount of silicone weighed out!
http://www.2wd-goes-syncro.de/?p=452
http://www.youtube.com/user/2wdtommy?feature=watch

*Rebuild kits:*
Two kits available, OEM and some higher quality one. This site is a bit sketchy though, since you have to place an order, then actually send them a check or money order before they ship out parts. I'll report back when I (hopefully) receive my kit.
http://www.dieselkontor.de/index.php?cPath=58_59&sort=2a&page=2

*Silicone Oil:* 
The site above wanted around $95 USD for a bottle of silicone oil. I did a little bit of creative research and found their supplier, a soap company in Utah. A 16oz bottle of Dimethicone is $7.20! They also sell it by the gallon. Done and done.
https://www.thesage.com/catalog/Additives.html#Dimethicone

More to come after I rebuild my VC.


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## weejunGL (Feb 2, 2005)

i'm looking forward to see this. please to take some pictures aswell. i've got a 23 year old VC in my car. would be fun to see if you get any gains from this 

but, one question, are you doing this to a VC from a vanagon, or the VC which are in the golfs/rallyes/passats?

i tought the non vanagon vc's was factory sealed?


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## rte7x9 (Jun 11, 2008)

weejunGL said:


> i'm looking forward to see this. please to take some pictures aswell. i've got a 23 year old VC in my car. would be fun to see if you get any gains from this
> 
> but, one question, are you doing this to a VC from a vanagon, or the VC which are in the golfs/rallyes/passats?
> 
> i tought the non vanagon vc's was factory sealed?


I'm using a B3 Passat VC. I haven't torn it apart yet, but it looks just like the one being rebuilt in those German videos. It's got the bolts, snap ring, etc... Unless I was seeing things. More to come!


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## weejunGL (Feb 2, 2005)

i'm using the same VC in my car, from a 1990 G60 Syncro passat 


the VC looks to me like a sealed unit, i know the vanagon VCs are assembled with snaprings etc.


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## rte7x9 (Jun 11, 2008)

So I've been doing some calling around and have some interesting findings. First, this exists: http://www.van-cafe.com/home/van/page_109_1248/rebuilt_viscous_coupler_coupling.html

Van-cafe is some sort of authorized reseller of refurbished VC units. These units are rebuilt by German Transaxles out of Bend, OR (http://www.germantransaxle.com) and have a 6 month guarantee. Old posts on Vanagon forums I've scraped off of Google don't seem to have good things to say about their work though. Specifically, GTA has a habit of COMPLETELY filling units with silicone fluid, this is just plain wrong. The VC is a closed system, so the silicone must have room to expand when the unit heats up. Lockup is a function of heat and pressure, so if you don't have just the right amount of air, then the pressure is wrong. If you have no air, the silicone can actually heat up enough to blow the seals and ruin your VC! 

But don't take my word for it... http://www.vanagon.com/syncros/technica/vc-expert-interview/index.htm

I will report back after I talk to someone of knowledge at GTA and find out what their process is. If I go to the shop tonight and discover that I have a non-rebuildable VC unit, I'll have no choice but to find a vanagon one, or just buy one through them! At that point I may as well foot the bill for a Haldex conversion!

EDIT: I spoke with a tech at GTA to confirm their methods. They do leave the required amount of air in the VC. They use the same silicone across all three performance levels they offer. As expected, the difference is the size of the shims between each fin. *Stock Vanagon VC rebuilds are $495.* You have to send them your unit, they do not have any extra cores if your unit is internally damaged.

When asked about seals, they were not interested in selling me their seal kits, and only told me that the seals are completely custom! If I wasn't confident in my ability to rebuild my own unit, I am confident that they are the only knowledgeable VC rebuilders in the US. If you're interested in having your unit rebuilt by them, you can contact them here: http://www.germantransaxle.com/contact-us/ (I just called them.)


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## weejunGL (Feb 2, 2005)

i tought this wasn't going to be easy  however, i'm super interested. seeing that a new VC is crap-o-lainen expensive


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## scott66 (Jul 5, 2003)

Original poster, thank you for the research and posting of the results as you go. I too have a synchro setup that has yet to see the underneath of my Golf...but, one soon, it may just happen and this is the type of information I need to do just that.


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## rte7x9 (Jun 11, 2008)

weejunGL said:


> i tought this wasn't going to be easy  however, i'm super interested. seeing that a new VC is crap-o-lainen expensive


Oh, it won't be easy, but it will be worth doing. Took a closer look at my factory unit last night and discovered that while there isn't a snap ring to remove the cover, there is a slot in the case that allows you to pry off the cover. Heating the case (aluminum) enough should make cover (steel) removal much easier. It's a bit delicate, since the silicone is really only rated up to 350F or so.

In regards to modifying lockup characteristics, the tech I spoke with at GTA let me know that the only modification they do is to use different thickness shims. Stock shims are .065", McMaster Carr sells .060" shim washers that just might make the VC perform a bit better. GTA didn't want to reveal shim sizes, as that would be proprietary. I'm really not sure how much smaller you could go, since the fins are .040" thick.









_From http://shufti.wordpress.com/2011/11/21/vanagon-syncro-viscous-coupling-anatomy-part-1/_

Should have more time to break down the VC next week and start measuring. Will need to source new lip ring seals for the inner shaft. It looks like the way that the steel end cap is pressed into the case, there isn't an outer o-ring like the Vanagon units use.


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## rte7x9 (Jun 11, 2008)

scott66 said:


> Original poster, thank you for the research and posting of the results as you go. I too have a synchro setup that has yet to see the underneath of my Golf...but, one soon, it may just happen and this is the type of information I need to do just that.


Thanks! I'm glad someone is reading this! Dust off that drivetrain and get to work! I want to make sure all of the decent knowledge on these units gets consolidated into one location so it's not lost. Most of my sources are around 10 years old, so it was time to freshen all of this stuff up!

I hope that more folks realize how critical the VC is to a proper Syncro swap. I'd be willing to bet there are plenty of folks out there that bolted up 200lbs of unused drivetrain to the back of their golf because they didn't take the time to freshen up the VC!

If anyone has any questions about the units, don't hesitate to ask! I've spent way too much time researching this crap.


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## weejunGL (Feb 2, 2005)

for my part, i've got traction to the rear wheels. but the vc has done over 350 000kms so i guess it can only be better if "overhauled" or even made to engange better. the silicone should be worn out by now. and the plates could be worn out aswell.

i've got one VC lying in the garage, which is the "smaller" golf/jetta one. (same size on the outside, but the recessed edge on the 3 mounting holes are smaller then on the passat one)

i could easily sacrifice this just to have a look


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## rte7x9 (Jun 11, 2008)

weejunGL said:


> for my part, i've got traction to the rear wheels. but the vc has done over 350 000kms so i guess it can only be better if "overhauled" or even made to engange better. the silicone should be worn out by now. and the plates could be worn out aswell.
> 
> i've got one VC lying in the garage, which is the "smaller" golf/jetta one. (same size on the outside, but the recessed edge on the 3 mounting holes are smaller then on the passat one)
> 
> i could easily sacrifice this just to have a look


Not a bad idea. If you can heat the case to separate it without damaging anything, go for it! I would be interested to see what the thickness of the shims and plates are. 

You're overseas, right? Are VC's easier to come by there? They're nearly impossible in the US!


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## weejunGL (Feb 2, 2005)

yes, i'm from overseas  norway. and yes, they are a lot easier to come by here. there has been chopped a crapload of passats with syncro etc in norway


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## weejunGL (Feb 2, 2005)

did a quick clean of the VC unit that i had lying around. and took some photos of it

VC partnumber and "code"









Overlook from the propshaft side (front)









Overlook from the diff side (rear)









Filler cap and a bolt that goes through the lid









guess this has something with locking the lid somehow









the 15mm bolt undone. yu can see the fluid here. or rather, half solid. its like semicold honey. you can also see that this bolt somehow looks to be a part of securing the lid to the rest of the VC unit









this wasn't the best pic, but there is a oneway valve down here, a steel ball. probably where they fill the fluid from









that was all i felt like doing today, didnt try to take the lid off 


Dan


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## DigiMatrix (Apr 16, 2010)

I was reading this post and the documents, and was wondering the following:

-if the plates in the VC pair up as described in the SAE document, could you swap the plates around when reassembling to get the plate couples to pair on the unworn side of the plates?

this way, on rebuild, the plates would essentially be as new even though the opposite side was worn.

Any comments?


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## weejunGL (Feb 2, 2005)

just thinking..

the end plate or lid. perhaps that it is screwed into place? seeing that there is this giant 12point around the centre?

there are two drilled out holes in the casing opposite to eachother. maybe they are supposed to be set in somekind of fixture? then use a bigg-ass 12point socket and unscrew it?


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## DigiMatrix (Apr 16, 2010)

That would seem to make sense, however, the locking square pin seems to be odd. Is that only showing on the inside piece, or is it protruding through to the outside? Might be difficult to remove, and it may have messed up the threads if there is any. I agree though, why the large 12 point nut if it isn't used for something.

I have to pull my spare and have a closer look as well.


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## weejunGL (Feb 2, 2005)

the square pin isn't going trough the outside. i'll try to use a wisegrip on it the next time i'm in the garage


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## veedublub (Aug 20, 2004)

In for more info. A "performance" oriented rebuild for my syncro swapped golf would be awesome! Keep it up guys.


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## boner (May 19, 2002)

HUGE BUMP!!!

thank you so much for the investigation folks! i am in the final stages of building my syncro equipped race car and have discovered that somewhere along the way someone put in a proshaft bolt that was too long and i suspect i have a small leak in my VC. it would not surprise me if i will be forse to run in fwd mode by some point this season! 

i have been looking off an on for resources on repairing these units with zero luck so far untill this afternoon. 

thanks so much for this and i eagerly await updates!!!

and FWIW, i wouldn't think the slot is for prying it open. i woulda thought if it were simply a press fit, they surely would have found a way to come apart unintentionally on the road for SOMEONE by now. espesially in around these parts with guys stuffing a few hundred horsepower thru them.... as well, why the 12pt on the end? i tend to think it unscrews somehow and the removal of that bolt may have provided the clue required.

i may have found a bum rear end on ebay.de for a reasonable price that has a VC... might get that over here and experiment with my current VC along with you guys...


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## weejunGL (Feb 2, 2005)

any takers on how much torque the VC can handle? they weak point to the "syncro/VC" drivetrain is really the angledrive. i've never actually heard of a failed VC unit anywhere. but would be great to encounter one that has failed to have a look at it.


i'm going to the garage tomorrow. so i'll have a go at opening the VC then. how this is going to happen i can't tell you, but i'll get that little ****er opened somehow. i don't plan on using this VC. so this will die in the name of science


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## boner (May 19, 2002)

weejunGL said:


> . how this is going to happen i can't tell you, but i'll get that little ****er opened somehow. i don't plan on using this VC. so this will die in the name of science


Well, if you don't care what happens to it and time is short, i hear big hammers make short work of cast aluminum!!!!!


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## weejunGL (Feb 2, 2005)

we'll so how it works out  pics will follow tomorrow evening (its 9:07pm here now)


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## weejunGL (Feb 2, 2005)

tried getting the lid of today. unfortunatly no pictures, as my gold cam decided to go out of power 

however. i think ive figured it out. and i will try to explain this as good as i can. altho explaining this will be kinda hard in english :/

anyhow. it appears that the lid is only mounted with a long square metal thingy.

the exact same one that is coming out of the lid. there is grooves in the lid and the casing and this metal thingy lies between the two.

it looks like its stuck into the lid trough a cutout on the casing and then the lid is turned about 90 degrees making the metal strip gointo the grooves. 

hopefully you understand what i mean? i don't know how long this metal strip is. but you need a big ass 12point socket to turn it and take the metal strip out

i think its about 52mm. i shall measure this better tomorrow. and try to source a socket suited for the job


and just to have said it. the fluid smells so fekking bad you won't believe it

Dan


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## boner (May 19, 2002)

so there's a bar or sumthin silly like that that gets extracted thru the slot in the side of the aluminum case??? wow, that's pretty difficult i imagine. looking forward to the pics


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## weejunGL (Feb 2, 2005)

not difficult nor high tech or anything. but i suck at explaining **** in english


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## DigiMatrix (Apr 16, 2010)

I can't quite figure out what you are trying to describe.
So, do you just leave the little square pin installed as it is and then just turn the big nut counterclockwise 90 degrees and then the end cover is released from the slot in the outer case?


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## weejunGL (Feb 2, 2005)

i believe the metal strip acts kinda like a snap ring. only internal. i don't know of any ways to explain this. but i will get this bugger open somehow  just going slow


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## wantacad (Apr 4, 2003)

in for results since the thread starter is putting this in my old car. :thumbup:


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## rte7x9 (Jun 11, 2008)

weejunGL said:


> i believe the metal strip acts kinda like a snap ring. only internal. i don't know of any ways to explain this. but i will get this bugger open somehow  just going slow


I TOTALLY understand what you're talking about and it makes sense to me! Seems like the factory indexed that square hole on the inside to line up with the hole in the aluminum case, inserted a soft square pin of some unknown length, then turned the center to bend the pin and pull it around the square slots on the edges of the case/cap. 

I checked at the shop last night and didn't have a 12-point socket even close to the size on that thing. If you know for sure it's a 52mm, that would be awesome. They're $42 on eBay, but it's kinda worth it if you ask me.

Thanks so much for taking the time to tare yours apart! I look forward to doing the same soon. Looking forward to the photos!



wantacad said:


> in for results since the thread starter is putting this in my old car. :thumbup:


Thanks, Trent! You're always welcome to stop by and poke fun at my mediocre lathe skills...


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## boner (May 19, 2002)

rte7x9 said:


> Seems like the factory indexed that square hole on the inside to line up with the hole in the aluminum case, inserted a soft square pin of some unknown length, then turned the center to bend the pin and pull it around the square slots on the edges of the case/cap.


so if i get this right, get the right sized 12-pt socket, turb the cap so the nub of the wire is lined up with the slot on the side, poke the wire out, and then turn the cap in such a way that the wire then "unwinds" out of the slot and then you'll be able to pop the cover off?

yikes, that seems like one hell of a PITA procedure!!! what happens if the wire breaks? i tend to think you up sh!tcreek then. replacement would be a hooor to i think!

why couldn't they have just used a normal snap ring like they do EVERYWHERE else on the system?!?!?! oh ya, that woulda been too easy


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## rte7x9 (Jun 11, 2008)

boner said:


> so if i get this right, get the right sized 12-pt socket, turb the cap so the nub of the wire is lined up with the slot on the side, poke the wire out, and then turn the cap in such a way that the wire then "unwinds" out of the slot and then you'll be able to pop the cover off?
> 
> yikes, that seems like one hell of a PITA procedure!!! what happens if the wire breaks? i tend to think you up sh!tcreek then. replacement would be a hooor to i think!
> 
> why couldn't they have just used a normal snap ring like they do EVERYWHERE else on the system?!?!?! oh ya, that woulda been too easy


You got it. I'm not really worried about disassembly now that we've got a good idea of how it's done. I'm moreso worried about finding the right keyway to use. McMaster Carr sells brass stock. That could work.

weejunGL; What's the size on the keyway you pulled out?


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## boner (May 19, 2002)

i'm gonna go with that piece being steel tho. i looks rusted in the pic and i don't think brass would do that??? (trying to think back now!!!). plus, i don't think brass would be as strong. my guess is that as long as the grooves are clean, you have proper lubrication and a method of feeding the wire as you turn the cap so as to reduce the stress on the wire as the cap is turned, all will be well. 

weejun, the ball is in your court. that said, i will make a call to a locak shop i know that does syncro work. they didn't have a functional VC for me but they may have a pooped one....


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## weejunGL (Feb 2, 2005)

i havn't taken it completly appart yet 


but, regarding how to put it all to gether again, i was thinking that it might be possible to place the lid on a lathe, then take some material away. so you can install a snapring instead of that metal strip


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## rte7x9 (Jun 11, 2008)

boner said:


> i'm gonna go with that piece being steel tho. i looks rusted in the pic and i don't think brass would do that??? (trying to think back now!!!). plus, i don't think brass would be as strong. my guess is that as long as the grooves are clean, you have proper lubrication and a method of feeding the wire as you turn the cap so as to reduce the stress on the wire as the cap is turned, all will be well.
> 
> weejun, the ball is in your court. that said, i will make a call to a locak shop i know that does syncro work. they didn't have a functional VC for me but they may have a pooped one....


You're absolutely correct; the stock keyway appears to be mild steel. I'm just not comfortable installing a new one with something hard enough to damage the case. I'd think brass would be a safer option, and would make for a better interface between the case and cap.


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## weejunGL (Feb 2, 2005)

i'm going to try hard this weekend 

just have to wait until payday on friday to buy som tools

the VC is slowly draining itself. makes it a bit less messy to work with


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## wantacad (Apr 4, 2003)

rte7x9 said:


> I checked at the shop last night and didn't have a 12-point socket even close to the size on that thing. If you know for sure it's a 52mm, that would be awesome. They're $42 on eBay, but it's kinda worth it if you ask me.


FWIW a 2 1/16th socket is about half the price and only .015 bigger. and they are half the price of a 52mm

sorry, just the cheapness in me coming out.

and your lathe skills can't be any worse than mine. I push a green button 99% of the time, not turn cranks.


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## Mr. Tickles (Jul 25, 1999)

wantacad said:


> FWIW a 2 1/16th socket is about half the price and only .015 bigger. and they are half the price of a 52mm
> 
> sorry, just the cheapness in me coming out.
> 
> and your lathe skills can't be any worse than mine. I push a green button 99% of the time, not turn cranks.


I cut it apart and it looks good. Didn't want Ron to hurt his self. He'll post pictures later.


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## rte7x9 (Jun 11, 2008)

Managed to get the VC open last night with Kendall's help (above poster) without the use of any massive sockets, torches, or really any brute force methods that could mangle/ruin the unit. Here's how we did it!

As discovered earlier by weejunGL, the cap is held on by a captured section of mild steel keyway. Rather than attempting to remove the keyway the reverse of how it was installed, we will turn down the cap to expose the keyway and remove it.

*Step 1:* Find a lathe big enough to chuck the VC up in and set it (and the tooling) up like this. 









*Step 2:* Turn down the cap without cutting the aluminum case until you have cut all the way through the section of keyway that extends through the cap. Now that the once-captured section of keyway is exposed, pry it out. BE VERY CAREFUL! Mine sprung out and nearly hit me in the face. That would hurt. I did this while the VC was still in the lathe to make things easier.









*Step 3:* Remove the cap by hammering the driveshaft centering pin on the opposite side. This shouldn't take too much force, so don't get too crazy with it. 









Obviously Kendall is awesome and just happened to have a lathe in his shop. You'll need to find a machine shop to do this work for you. If you can't find anywhere, we've entertained the idea of doing the cutting for anyone who was willing to throw a couple bucks our way. No rebuild, just the cutting required to open the case.

From here it's pretty straightforward, so I'll just post what photos I have and annotate them as needed. I don't have any good measurements yet, so I'll be sure to detail those in a coming post. Overall we were surprised at how well the VC survived the test of time. Compared to VW automatic transmissions, this thing is wayyy overbuilt. It's also nothing like the Vanagon unit so the German rebuild videos will no longer be of any help.









Here's the cap, you can see we turned down material until just before the bottom of the keyway's hole was reached. When the unit is reassembled, it's really as simple as sourcing a large snap ring to fit the case just like the Vanagon unit. This will make rebuilds MUCH EASIER.









The outer cap seal is a standard o-ring, these will be easy to source a replacement for.









The inner cap seal isn't so standard. Mine looks decent so I'm probably not even going to remove it. 









The case has two seals, one just like the cap, and another more standard lip ring seal (Part #009 525 583) available in stock form HERE for $28. Chances are another VW seal can be substituted. More to come on this.









Here's the inside of the case, mostly cleaned out. 









An exploded view of all parts involved, without the stack of discs. There are two plates that sandwich the discs, these are substantially thicker than the discs themselves.









All of the discs, still coated in silicone! This stuff is really sticky. Be careful when separating them, as prying them apart could bend one. It's better to slide each disc off the top of the stack.









Two cleaned discs. NOTICE THERE ARE NO SPACERS! This astonished me, really. This is the main difference between the Vanagon and Passat/Golf VCs. This tells me already that Passat VCs should lock up much better!

Right now my only worry is that I can no longer count on the German rebuild videos to tell me how much silicone to add when the unit is rebuilt. I was very surprised to see that the unit was nearly full of silicone. This is not what I expected, but we really didn't get an accurate measurement since silicone went everywhere as soon as the case separated.

The plan is to reassemble the unit dry and fill it with mineral spirits to get an accurate measurement of volume. Once we know how much the unit will hold, simply calculate 86% of that volume and only add that much silicone. That's the magic amount of air that must be in the case to allow room for the silicone to expand into when heated. (Documented HERE) I have a feeling the unit was much more than 86% full though, so I'm still pretty torn on this.

More to come soon as I take measurements and source replacement seals/rings. Enjoy!


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## boner (May 19, 2002)

to you sir, i present the internet.

great thinking on how to get it apart :beer::beer::beer::beer::thumbup::thumbup::thumbup:

and a question:

the aluminum part, can you take a better pic of the holes where the propshaft mounts? the problem i have is that i am 99% certain someone along the line put too long a bolt in there and peirced into the fluid cavity. from the pic you show, it's almost like they threaded all the way thru and just put a cap on the inside???


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## rte7x9 (Jun 11, 2008)

boner said:


> to you sir, i present the internet.
> 
> great thinking on how to get it apart :beer::beer::beer::beer::thumbup::thumbup::thumbup:
> 
> ...


Haha thanks! I know we had a few beers last night.

This is a slightly different (albeit crappier) photo that might help. The prop shaft mounting holes are splined/threaded/hardened inserts. Mine were definitely still sealed. You'd have to put some serious force on a bolt to get it to punch through! The only way I even see that happening is if the open pocket in the end disc (pictured in my exploded view nearest to the case) was positioned over the back of the insert, allowing some space for the blown out insert to occupy. Even this would be improbable. That disc is only 1/8" or so thick. You're probably fine!










I'll get a couple more detailed ones soon. Keep the questions coming!


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## wantacad (Apr 4, 2003)

Mr. Tickles said:


> I cut it apart and it looks good.* Didn't want Ron to hurt his self.* He'll post pictures later.


 :laugh:



Love the out of box thinking. :thumbup:


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## boner (May 19, 2002)

thanks for the detailed pic man. it's odd then, cuz i DEFINITLY had some very goopy heavy crap come outta that hole.... 

DISCLAIMER: i didn't get to look at it very had because i didn't inspect it when it was on my bench and i only had problems when I was trying to get the propshaft on.... on my back, in the winter, on a cold ass concrete floor, when i had promised my wife i was only gonna be about an hour then we could do some stuff outta the house but i'd already burned thru 2 hours and she was starting to get pissed at me for spending too much time in the garage!!!!! 

the VC is the only thing i haven't really serviced when i put my system in the car but given the info you're providing, maybe i don't have a problem and it's just that the hole was just full of crap.... 

EDIT: reread the link you sent with the inerview with the VC designer... interesting. never thought they were service items.... i can see me doing this within a year now....


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## rte7x9 (Jun 11, 2008)

boner said:


> thanks for the detailed pic man. it's odd then, cuz i DEFINITLY had some very goopy heavy crap come outta that hole....
> 
> DISCLAIMER: i didn't get to look at it very had because i didn't inspect it when it was on my bench and i only had problems when I was trying to get the propshaft on.... on my back, in the winter, on a cold ass concrete floor, when i had promised my wife i was only gonna be about an hour then we could do some stuff outta the house but i'd already burned thru 2 hours and she was starting to get pissed at me for spending too much time in the garage!!!!!
> 
> ...


 Understood, you may be right then! 

FYI, I cross-posted this on Facebook and one of my friends was able to dig up an unmolested version of the SAE paper in the first post, in PDF form no less! http://www.easy2design.de/stuff/visco_sae.pdf 

I'll update the first post here in a bit.


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## weejunGL (Feb 2, 2005)

nice  you beat me to it. 

i too was thinking that using a lathe to grind down the lid enough could be a good idea.. 


and this also makes it easier to open on a later time. if thats ever needed


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## rte7x9 (Jun 11, 2008)

weejunGL said:


> nice  you beat me to it.
> 
> i too was thinking that using a lathe to grind down the lid enough could be a good idea..
> 
> ...


 Heck yes! Please post your own pics if you can, always good to have multiple sources! 

Finished cleaning the discs last night and stacked them up in the case to see what kind of space the silicone realistically occupied in the case. I wanted to make sure the 86% air rule made sense. Note the healthy distance between where the case splines start and the top disc. Still need to fill the unit with mineral spirits to get a better volume measurement, but this is a good visual representation: 










Also here's the requested photo of the bottom of the case, hope this helps: 









My next post will cover all of the case/cap measurements and (ideally) part numbers for new seals and a snap ring. I also found out that my 1gal container of silicone shipped, so once the new seals arrive we'll be ready to reassemble!


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## weejunGL (Feb 2, 2005)

i tried this weekend to do it the "right" way.. didn't work as good. the backplate won't budge. i need to make some kind of fixture to hold the vc. just putting it in the wise didn't quite work out 


oh, and the 12point "nut" on the backplate is 55mm, not 52 as i frist said  

i bought the tool, here it is. along with a common 13mm one  









could not make it move even a millimeter  so its no easy way of doing it. thinking that the metalstrip probably has rusted stuck there. 

i didn't think the strip was as long as it was. (as seen on the pics eariler in this thread).. 

ohwell. i won't give up this easy


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## polov8 (Apr 14, 2004)

Found this 2 page pic in a golf syncro brochure I found in my "drawer of many things" and thought of you:


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## rte7x9 (Jun 11, 2008)

polov8 said:


> Found this 2 page pic in a golf syncro brochure I found in my "drawer of many things" and thought of you:


Good find! Thanks for thinking of us.

*Update regarding silicone fluids:*

I ordered and received the silicone fluid that I noted earlier in the thread. Even though this is the fluid sold/used by Vanagon VC rebuilders overseas, I am extremely disappointed with its low viscosity. After quite a bit more research I've located a few more sources of silicone fluid and learned a bit more about viscosities. The SAE document tested various viscosities of silicone fluid all the way up to 100,000 mm^2/s. I think what they meant was millipascal seconds, which are equal to centistrokes, the cSt unit used more commonly now. 

Fluid anywhere between 30,000 and 100,000 cSt will work in a VC unit, but I'm obviously going to favor the highest viscosity I can get away with, to get the best lockup characteristics. 

*Dow Corning* 3-9160 - 10,000 cSt

*Dow Corning* 3-9161 - 60,000 cSt

*Dow Corning* 3-9162 - 88,000 cSt

Dow Corning's fluids are designed specifically with this purpose in mind, and have been used in other aftermarket VC rebuild situations (this thread on e30tech.com specifically.)

88,000 cSt was good, but I haven't actually found a way to buy the stuff and have yet to get a response from Dow. I kept looking.

*Clearco *- High Viscosity Silicone Fluids

Much better! Clearco offers a 100,000 cSt silicone fluid that should do nicely. They responded quickly, $110 a gallon (that's the minimum order) but I had to fudge a bit and say I'm with a university to get any info. Chances are you could just call and say you were with some company and order it anyhow. Hopefully I should have a gallon of this magical liquid on the way soon.

There were a few more sources, but they had either discontinued products or didn't sell them in quantities over a couple ounces.

*Update regarding rebuild hardware:*

I placed an order with McMaster Carr for o-rings and snap rings. None of them were exactly the right size, but are within 5mm or so. Got a few different sizes so there are plenty of options to try.

More to come once all of this stuff arrives!


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## weejunGL (Feb 2, 2005)

i could be interested in buying the right amount of fluid if you can only get it by the gallon, ofcourse if you don't need all of it for experimental purpouses that is


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## boner (May 19, 2002)

i could kiss you guys for your efforts (no ****  ). racing starts in 3 weeks so my system's days are probably numbered 

and given the unsuccessful effort to turn the top plate, i'm gonna guess the lathe solution is best. i can just see the case cracking in the wost case scenario... that would be balls for sure.


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## rte7x9 (Jun 11, 2008)

weejunGL said:


> i could be interested in buying the right amount of fluid if you can only get it by the gallon, ofcourse if you don't need all of it for experimental purpouses that is


We'll see how much is left once I fill mine, I would like to keep enough extra around for myself, but I'm not opposed to sending some overseas! :beer:



boner said:


> i could kiss you guys for your efforts (no ****  ). racing starts in 3 weeks so my system's days are probably numbered
> 
> and given the unsuccessful effort to turn the top plate, i'm gonna guess the lathe solution is best. i can just see the case cracking in the wost case scenario... that would be balls for sure.


I'm flattered, but you can buy me a beer instead! 

*----------
UPDATE:
----------*

I've been swamped over the past few weeks (out of the country, etc) so progress has been slow, but I finally made a few breakthroughs. I have received all of the necessary rebuild items (silicone, o-ring, and snap ring) so I successfully cut a groove into the case to capture the ring. a 1/4" section of tool steel was the perfect size to cut the groove and I had no problem re-seating the lid with a new o-ring and installing the snap ring, it was a perfect fit!

*O-RING:* Metric Buna-N O-Ring, 3 mm Width, 124 mm ID (McMaster Carr P# 9262K333)

*SNAP RING:* DHO DIN 472 135mm Carbon Steel w/Oil Finish Internal Retaining Ring (Fastenall P# 4115865)

*SILICONE:* I recieved 1gal of the 100,000cSt Silicone from Clearco, it's thicker than honey!

Groove in the case:









Cap installed:









Close up of the groove/snap ring:









*CAUTION!* Be very careful when installing a snap ring this big! It took some serious effort to install, and could easily injure someone if it comes flying out.

*NEXT STEPS:*

Time to fill the unit! This is clearly the hardest and most tedious part, my next post will explain the process in detail, but there are two steps I need to take to fill the unit and ensure that only 8% of air remains, this is the amount noted by the author of the original SAE paper I posted (see below.) First, I will close the unit and fill it with mineral spirits using a finely graduated syringe to determine the full volume, then subtract the 8% to find my fill volume. This volume will then be converted to weight using the density of the silicone (different per compound, noted on the datasheet) and filled using a digital scale. The silicone is so thick it's not realistic to try and measure it volumetrically.


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## boner (May 19, 2002)

so you had to cut the groove in the case a bit thicker to get the ring to fit? but ya man, that looks great. thanks for all the research you've put into this!!!


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## rte7x9 (Jun 11, 2008)

boner said:


> so you had to cut the groove in the case a bit thicker to get the ring to fit? but ya man, that looks great. thanks for all the research you've put into this!!!


Yeah, if I remember correctly it was about 4mm. Snap rings get prety thick when they're 125mm!

Don't thank me yet, still plenty of work to be done.


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## rte7x9 (Jun 11, 2008)

And now the moment we've all been waiting for; filling the coupler! I used mineral spirits to determine the *full volume of the VC was 330cc*, so that would mean that we need 306.9ml of Silicone fluid for a fill with 7% air present. Since volumetrically measuring something with such a high viscosity is really impractical and inaccurate, *we calculated the mass of silicone needed given the density (listed on the MSDS) was 300g.* Remember that density is just mass per unit volume. 

I started by carefully cleaning each plate off using lint free painters wipes. They're basically pre-washed cotton rags and are super cheap. This insures each plate is perfectly clean. I separated them with pieces of cut newsprint to keep dust off and make assembly easier. 

I cleaned the case and assembled the two halves to make final assembly easier. The case is supported by a metal ring since the center shaft protrudes below by an inch or so. Install the small steel ring and then the splined shaft. Remember to lubricate all seals with a small amount of grease. I used CV moly grease. 

I also pre-attached the top splined plate with the cap bolts to ensure the holes are lined up when capped. Do not tighten them all the way down, since the plate will need to move a bit when the cap is installed. 










I then tared a scale with an empty pint glass and two spoons. I filled the pint glass with around 400g of silicone. Note the full weight and carefully add silicone to the unit, reweighing the glass, spoons, and silicone until only the difference in weight remains. *300g on the nose.* 










Start dropping plates in, pushing them down into the silicone every 5th plate or so. Nothing crazy, just enough to make sure they're displacing fluid. Push carefully and evenly. Once all plates are in, install the small top snap ring on the center shaft and small end ring. 










Cap the unit with both fill bolts still loose. Make sure the o-ring is greased as well. Leave the unit sit for a while (overnight) before tightening the fill bolts. After tightening, lay the unit on its side and rotate it a couple degrees every few hours to ensure silicone is evenly distributed. 

*Here is the first fully user serviceable Passat Syncro Viscous Coupler:* 










I would suggest taking it easy on the unit for the first couple miles. This is just a suggestion. My car is still in the build phase so I won't be able to test the unit for quite a while. 

*If the price is right I would consider rebuilding units for others, but I'm not really interested in the liability at this time. *If you're really interested, PM me and we can work something out. My friend and I have entertained the idea of doing the lathe work and mailing the unit back with a rebuild kit (o-ring, snap ring, silicone) for a fee. It's really too early (no testing has been done on my own system) to have 100% faith in the process. I mean, I'm just a guy who cut something open, cleaned it, and put it back together with some new goop inside. 

*As always, I welcome your questions and comments. *


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## Seano (Jan 2, 2003)

You may have made yourself rather popular with more than just the Passat community as this appears to be the same VC that is found under many T4 (Eurovan) Syncro's in Europe and Australia. And they (me included) also have this problem of unobtainium rebuild VC's.

Big ups to you for sure...


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## Alchemist17 (May 25, 2013)

*T4 VC*



Seano said:


> You may have made yourself rather popular with more than just the Passat community as this appears to be the same VC that is found under many T4 (Eurovan) Syncro's in Europe and Australia. And they (me included) also have this problem of unobtainium rebuild VC's.


I am not 100% sure that the T4 VC is the same as the Passat, I have been scrabbling around on the floor under mine today and it appears to be different at the end that comes apart. Mine seems to have an extra steel bit? Does anyone know if this end piece comes off leaving the same plate that can be machined out like above?


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## rte7x9 (Jun 11, 2008)

Oh dear! I thought all vans had rebuildable units with factory snap rings. I just figured you guys would send your VCs to the shop out west I had mentioned previously. They are rather expensive but have been rebuilding units for years. Keep in mind that unless you have the exact same part number VC, none of my calculations or replacement parts will work. 

You can, however, use the same silicone that I used. In fact, I'm pretty sure the original SAE paper used a Vanagon unit for testing!

Feel free to link this thread over on the vanagon forums. Hopefully I can be of some help.


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## rte7x9 (Jun 11, 2008)

http://www.vwt4forum.co.uk/showthread.php?t=289806

Another rebuild thread to follow for the Transporter/Vanagon folks! Thanks for the credit, Alex!


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## lowburb (May 14, 2005)

So, were you ever able to test the rebuilt VC? Did you come up with a price for doing it for customers?


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## vwabbitman (Mar 12, 2006)

polov8 said:


> Found this 2 page pic in a golf syncro brochure I found in my "drawer of many things" and thought of you:


that actually answered my question on what these things do.


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## jettasmooth (Aug 7, 2002)

Any of you guys have one of these visco cases that they are not using? 
I am just looking for an empty case (with front and back for mounting) so that I can mock up a bracket for my haldex conversion.


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