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Discussion Starter #1 (Edited)
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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Discussion Starter #2 (Edited)
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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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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Discussion Starter #4
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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Discussion Starter #6 (Edited)
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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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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Discussion Starter #9
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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Discussion Starter #10
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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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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Discussion Starter #12
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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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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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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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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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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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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