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Viscous Coupling: How aggressive is too aggressive?
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candyman
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PostPosted: Wed Apr 08, 2015 9:44 am    Post subject: Viscous Coupling: How aggressive is too aggressive? Reply with quote

Hey all so just completed a 2wd to syncro conversion. The donor syncro had unkown history so its been a real crap shoot. Just had the alignment done and installed the driveshaft to see what condition the vc is in. Drove for a good 30 minutes or so mixed city/highway miles. What i notice is slight scrubbing while tight turns. Not so much that it wants to stop the bus but enough to notice its happening. Even see some outer egde of tire rubber on the pavement on really tight turns. Did the 2X4 trick in low gear but it either would stall completely or want to creep over it. I could not get it to just idle. This vc is in my opinion "slightly aggressive" im hesitant to say that it is fully aggressive. However, I have not had the opportunity to drive it for hours on a hot day and see how it behaves.
My last syncro I was fortunate enough to buy one of Derek Drews last factory VCs. That was a true pleasure to drive and I never had this amount of aggression with that one. In fact that one never felt like it was even working, evem though it was.
That said, does this current vc sound like it is too aggressive? I am at the crossroad of replace the vc or install a decoupler, both of which I will do regardless when funds present themselves. If I were to install a decoupler, would the vc continue to become more aggressive with time even though it is not getting used near as much? Or should I just bite the bullet and purchase a new vc? I can only do one option at this time.
My concern about purchasing a rebuilt vc is that mine may be perfectly fine, say in the neighborhood of a sport vc condition? ( ive never driven a sport bc so have no real experience with that)
Would love to hear your thoughts on this

BTW conversion went smooth, logged about 130 hours total. Now that everything is together time to work out the kinks. Complete front end with whitleine and powerflex bushings from T3Tecniques all around. Super tight front end! Rebuilt driveshaft with new ujoints and so far pretty smooth. Trans is unknown but so far so good. Am budgeting for a rebuild maybe next year. But at the moment it is shifting great so no real concerns there.
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Syncro Jael
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PostPosted: Wed Apr 08, 2015 10:51 am    Post subject: Reply with quote

I would invest in a decoupler then not worry too much about the VC. It will save you in the long run.
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PostPosted: Wed Apr 08, 2015 11:02 am    Post subject: Reply with quote

Decoupler.
Having an aggressive VC is not a bad thing if you plan on using your Syncro off-road. If all you want is the peace of mind of AWD then a milder VC may be in order.
In any case having a decoupler is good, so if you can only afford one I'd invest in the decoupler.
IMHO all Syncros should have come from the factory with decouplers and front and rear lockers, but VW decided that Americans would be too confused by all those knobs. Confused
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candyman
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PostPosted: Wed Apr 08, 2015 11:14 am    Post subject: Reply with quote

Syncro Jael wrote:
I would invest in a decoupler then not worry too much about the VC. It will save you in the long run.


I agree. Just curious, i believe I saw in previous threads that you are running a sport vc. If sp cam you describe how it drives as far as any light scrubbing. And have you done the 2x4 test with it. Im just trying to size up mine
Thanks
Jason
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syncrodoka
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PostPosted: Wed Apr 08, 2015 12:17 pm    Post subject: Reply with quote

My aggressive VC hasn't gotten any more or less aggressive in the last decade, I have a decoupler. Offroad traction is great.
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candyman
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PostPosted: Wed Apr 08, 2015 12:35 pm    Post subject: Reply with quote

syncrodoka wrote:
My aggressive VC hasn't gotten any more or less aggressive in the last decade, I have a decoupler. Offroad traction is great.


That helps. Thank you! Ill decoupler route and deal with vc down the line if I have too
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hans j
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PostPosted: Wed Apr 08, 2015 12:54 pm    Post subject: Reply with quote

If I drive a van and the front tires are skipping/binding in parking lot turns, I then put it on the hoist to confirm. I stick a prybar in the driveline to lock it and turn both front tires by hand at the same time. If I can't spin the tires, it's locked up. If I can spin the tires, I don't fail it as locked up.
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WestyBob
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PostPosted: Wed Apr 08, 2015 1:44 pm    Post subject: Reply with quote

I'll add to the sentiment of getting a decoupler.

Since you had a new VC before you are fortunate to be able to judge the comparison. From your comments you seem to have a middling-aggressive VC now.

I also agree with Mario that with a decoupler your VC shouldn't quickly become even more aggressive. In fact, you should have a really good off-road VC about now.

However, in the unlikely event your VC does become quickly and seriously bad, you then have a choice of a new/rebuilt VC or a solid shaft depending on how you intend to use the syncro.
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gears
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PostPosted: Wed Apr 08, 2015 1:46 pm    Post subject: Reply with quote

I know mine's too aggressive, because over the past couple years, my van has come to feel (and sound) like a pick-up truck stuck in 4WD on pavement (and it fails the 2x4 test @ idle).

Fortunately, I have a decoupler .. but I really need to replace the VC so that the system functions as the factory intended.

If I didn't live in snow country during the winter months, I would be OK with it "as is", and just drive decoupled 99% of the time.
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PostPosted: Wed Apr 08, 2015 2:08 pm    Post subject: Reply with quote

Another vote for the decoupler with your VC.

Excellent post describing how your VC acts. I agree it is mildly aggressive and should not be coupled on dry pavement.

I have also bought a brand new VC from Derek. I found it would bind slightly when parking. I added a Decoupler to that one too. Really happy about that, made tight turns on dry pavement easy.

I would not hesitate to couple your current VC on snow.

you may also find this info about when to couple interesting. I think it applies to both VCs that bind when parking (aggressive to some degree), and Solid Shafts alike

http://www.gowesty.com/library_article.php?id=627
"Basically, it comes down to common sense. I mean, why would anyone want to pull any of the knobs on dry pavement in a situation where you needed to perform tight maneuvers? But, then again, what constitutes a "tight maneuver"? The only thing you HAVE TO remember when driving a Syncro with solid shaft [my edit: or aggressive VC] and decoupler in a high-traction (dry pavement) situation is:

WHEN IN 4WD, NEVER TURN THE STEERING WHEEL MORE THAN 1/4 TURN.

Just stick to that golden rule, and you can't go wrong."

> Viscous Coupling: How aggressive is too aggressive?

Imho, yours is too aggressive to keep coupled on dry pavement when making tight turns.

Too aggressive is any use that causes binding. Aggression is good in slippery situations.

Decouple in binding situations.
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Syncro Jael
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PostPosted: Wed Apr 08, 2015 3:31 pm    Post subject: Reply with quote

candyman wrote:
Syncro Jael wrote:
I would invest in a decoupler then not worry too much about the VC. It will save you in the long run.


I agree. Just curious, i believe I saw in previous threads that you are running a sport vc. If sp cam you describe how it drives as far as any light scrubbing. And have you done the 2x4 test with it. Im just trying to size up mine
Thanks
Jason


Jason, my sport VC will just barely pass the 2x4 test. At a low idle 700rpm and I must let the clutch out very, very, slow and the 2x4 will sometimes hold the van back. At least that was when I installed it over a year ago. I have not tested it since. I always am decoupled when turning sharp on solid surfaces but it will still slip a little, but you can feel it bind up as you turn on slick rock or solid rock.

If it is at all in your budget I would get a decoupler ASAP to save the stress on your drive train and especially the transaxle. They are getting very expensive to rebuild once some of the expensive internal parts (main shaft/ring & pinion) might need replacing.

If a decoupler is not in the budget, just be mindful when you are turning sharp, especially after running down the highway for some time.

Cheers,
Ron
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candyman
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PostPosted: Wed Apr 08, 2015 3:36 pm    Post subject: Reply with quote

Thank you everyone for your input on this. I agree decoupler is the route for now. I would like to point out that snow is my main use for this syncro while offroading is secondary. With that said I am probably on the edge of needed a new vc at some point (not a solid shaft guy) but I will gauge how it goes. I think its slight aggrssive nature is tolerable at this point
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Howesight
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PostPosted: Wed Apr 08, 2015 5:30 pm    Post subject: Reply with quote

My stock VC would chirp the stock tires on pavement or especially concrete in a tight radius turn. That changed when I went to 225/70/16 BFG AT tires due to the larger tires' leverage. I still use that same VC, with 250,000 miles now, only I am SVX powered now, and installed a decoupler. This is the best of both worlds, in my experience. The VC bites when I need it to and is decoupled the rest of the time.

I think the proper VC nomenclature might be:

1. Stock/New
2. Aggressive
3. Vicious Coupling.

Mine is between aggressive and vicious.
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insyncro
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PostPosted: Wed Apr 08, 2015 5:38 pm    Post subject: Reply with quote

Wow, with all of these VC threads, it really sounds like not many have non aggressive units.

Very thankful that I have new and non aggressive VCs that I have collected over the past 15 years.
Just stating the facts, not advertising for sale.

A truely non-binding Syncro is a treat to drive.

From the sounds of it most would be shocked at how smooth my vans are vs what they drive.

I am not a fan of decouplers as I prefer AWD all the time.
That is why I daily drive a $yncro Wink
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Waldi
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PostPosted: Wed Apr 08, 2015 5:52 pm    Post subject: Reply with quote

Decoupler anyway.

But a broken vc is not a "sport" vc.
You should try to move the kardan with 2 13mm keys on the screws. Rear wheels up.
Why 2 ? Because it is realy hard to move it even when the vc is ok.
If you cannot move at all, so the vc is broken the other way. Means it is loked. The plates inside are bent. This happens when it becomes too hot and/or it was loose (silicon out, oil in) before and was slipping fast and a lot offroad.
When you cant move the kardan at all, use the syncro coppled only on loose ground.
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PostPosted: Wed Apr 08, 2015 8:31 pm    Post subject: Reply with quote

insyncro wrote:
I am not a fan of decouplers as I prefer AWD all the time.
That is why I daily drive a $yncro Wink


I agree with Dylan! (OMG, did I really write that? Must be off my meds.)
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PostPosted: Wed Apr 08, 2015 8:49 pm    Post subject: Reply with quote

In my research on the European forums it seemed like someone had a pretty good handle on the failure modes for the VC. They'd get more aggressive, then fail and become very loose. I seem to recall the leading theory was once they got aggressive the VC was then routinely dealing with much more heat than it was designed to on a constant basis in road driving (something the fresh stock ones will not do - they'll slip more easily and thus have lower peak temps/pressures) That in turn led to higher pressures inside the VC, the VC would blow a seal and lose some silicone fluid. Now the car is parked and the VC cools and the pressure is reversed (vacuum in the VC) and it sucks in some gear oil from the differential via the same compromised seal.

If that's accurate, then you are kind of in the "Oh cool, I have a nicely aggressive VC" mode that precedes the seal issue. So now would be a perfect time to put in a decoupler to avoid that heat from road driving and it may then remain the ideal VC when you want it coupled for a really long time. The super high heat/high pressure mode seems to actually cause the steel plates to warp and hit each other.

So, another vote for decoupler. Gives you the option of having a sport version if/when you eventually need it rebuilt.
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insyncro
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PostPosted: Wed Apr 08, 2015 9:46 pm    Post subject: Reply with quote

Heat, that is the part of the equation that most don't grasp.
Watch Seth Drew's video.

Syncro transmission cooling is all the rage now, next will be front differential heat management.
I am already there with a working model, plus started my datalogging with a brand new VC, not too many of those floating around.

Y'all need to get with the times and ditch this decoupler crap and than realize how limiting a solid shaft is as well.

Remember, most of you purchased a Syncro with over 100,000 miles on it and have never felt what a brand new VC feels like.
The VC was designed for roughly 100,000-150,000 miles, so most Syncro vans on the road today have a VC that is considered used up by the designers and producers of the part and driveline.
By the sounds of most descriptions I read of how the van is to park, how it performs after long hiway drives and just overall comments about VC, this explains why decouplers are so popular.
There is no need for a decoupler with a properly functioning VC and let's also remember that USDM Syncro did not come with decouplers, even as an option...because with a well maintained driveline, they serve no purpose and offer no efficiency gains whatsoever.
Taken even further, I feel that a decoupler, mounted to a fully loaded Syncro Westy, at speeds above 40mph, in variable conditions is actually dangerous.
You have to be coupled for any benefit of torque transfer to the front wheels and in a split second, conditions may change and if uncoupled, you could find yourself in a very sticky situation and not be able to remove your hands from the wheel or your eyes from the road.

This is why I run a VC and only have decouplers on a few of my vans, just to be a member of the 3 knob club....it really helps on the resale Laughing
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insyncro
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PostPosted: Wed Apr 08, 2015 10:00 pm    Post subject: Reply with quote

I would also like to add that in my shop experience of the past 10 years, many Syncros have come to me with owners crying about how the VC is binding in turns and when parking.

More often than not, a proper alignment, taking into account suspension upgrades, tire width and diameter cured many of these vans perceived VC ills.
Derek Drew's calculator turned me on to the changes that need to be made for a buttery feeling front end, experimentation and datalogging has taken it far beyond that.

Give it a shot.
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Waldi
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PostPosted: Thu Apr 09, 2015 1:44 am    Post subject: Reply with quote

insyncro wrote:

...
There is no need for a decoupler with a properly functioning VC and let's also remember that USDM Syncro did not come with decouplers, even as an option...because with a well maintained driveline, they serve no purpose and offer no efficiency gains whatsoever.
Taken even further, I feel that a decoupler, mounted to a fully loaded Syncro Westy, at speeds above 40mph, in variable conditions is actually dangerous.
You have to be coupled for any benefit of torque transfer to the front wheels and in a split second, conditions may change and if uncoupled, you could find yourself in a very sticky situation and not be able to remove your hands from the wheel or your eyes from the road.

This is why I run a VC and only have decouplers on a few of my vans, just to be a member of the 3 knob club....it really helps on the resale Laughing


This all was already sayed, but once more.
The decoupler saves the vc and drivetrain.
The vc stands easy double(or more) time/km with decoupler than without.

And please stop to tell nonsence, that driving a loaded 2wd van is dangerous.
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