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Sun Nov 05, 2017 9:56 pm

MsTaboo wrote: aren't you one of the unfortunate Syncro owners who have had several transaxle failures? Have all those failures been while using a solid shaft instead of a VC?

your question seems to be designed to question the validity of the witness

my personal experience has nothing to do with the descriptions I gave of a syncro, and the painstaking detail in which I explained how a VC can never spin a front diff faster than the rear diff.

I realize not everyone can understand that. Its ok. Read it over and over if it helps, or just keep believing that your syncro is AWD.. I don't mind. Enjoy it, no matter if we understand how a VC works or a Center Diff works.

bottom line, a Center Diff does things a VC cannot do, the reverse is not true, and my tranny history has nothing to do with it.

Sun Nov 05, 2017 11:20 pm

I would think engine power/torque and vehicle weight would effect the tranny the most. And I could have sworn that Jael was recently dealing with tranny issues, and uses a sport VC.
I've driven hundreds of miles on pavement and thousands on dirt all while coupled with a solid shaft. 30k on tranny so far no issues. Except now I probably will since I'm talking about it.
But I've also been pushing my van with a GW 2.3, which forces me to drive conservitavely and slower up hills.

Sun Nov 05, 2017 11:21 pm

Jon_slider wrote: Watch the rear sink more than the front, from the 1 minute 18 second mark. That Doka has an aggressive VC and decoupler:

That is momentum from going WOT in gear, same as it does on hard pavement. Did you catch the speed shift from G to 1 at 1:27? The truck also had a bed full of gear in in so it will squat.

The OP is asking about a syncros AWD ability, a solid shaft doesn't fit that bill so there is no point in bringing it up.
I was mashing through standing water on the freeway in my stock syncro hardtop just the other day without blinking an eye while other cars getting pulled around.

This is a very tired subject. I wish the OP luck

Mon Nov 06, 2017 12:35 am

Agree the topic is getting mission creep, and I suspect most of you know I've been pretty active in the "Syncro/VC" stuff.

So the OP asked if a traditional 4X4's offroad capability is on a par with a locked Syncro? And if an unlocked Syncro would be less capable offroad, but better than a 2WD Vanagon?

I would say to the OP that the comparison of a fully locked Syncro vs a traditional 4X4 vehicle in offroad conditions would be valid. The 4X4 would be superior in some conditions due to likely better ground clearance, likely greater travel, likely ability to have larger tires, and definitely having a low range. Sticking with the same comparo, the Syncro would be superior where fully locked traction is going to pay huge dividends vs the classic 4X4 advantages just covered. So,it would be fair to agree with a rough equality with some wiggles in favor of one or the other based on trail conditions.

But the 2WD Vanagon vs base unlocked Syncro I agree with others that the Syncro is significantly superior offroad due to greater ground clearance, underbody protection, and the powered front axles (when rears are spinning). Modifying a 2WD closes the gap only incrementally and of course if modifications are allowed, the Syncro would benefit from the same modifications.

Doug

Mon Nov 06, 2017 4:24 am

Jon_slider wrote: MsTaboo wrote: aren't you one of the unfortunate Syncro owners who have had several transaxle failures? Have all those failures been while using a solid shaft instead of a VC?

your question seems to be designed to question the validity of the witness

my personal experience has nothing to do with the descriptions I gave of a syncro, and the painstaking detail in which I explained how a VC can never spin a front diff faster than the rear diff.

I realize not everyone can understand that. Its ok. Read it over and over if it helps, or just keep believing that your syncro is AWD.. I don't mind. Enjoy it, no matter if we understand how a VC works or a Center Diff works.

bottom line, a Center Diff does things a VC cannot do, the reverse is not true, and my tranny history has nothing to do with it.

The tiny detail to consider is that the Syncro vct, (for a t3), does not react transfering power just in the case that the rear wheels tend to turn faster, but in any case there is a difference in velocity between the two axles, working as an auto central differential, sending torque at a percentage, and, in the case the difference is within the limits of the operation points of the designed envelope, it locks transferring the 100%. (Yes, as the vw says, it is a central differential).

1)This is the reason why by engaging the handbrake the front wheels are braking, too.

2)This is the reason why you can turn on sharp curves faster than many sport cars, (if you do not afraid to press the gas pedal instead of the brake pedal).

3)This is the reason why by, just, pressing the gas pedal on a slippery curve, much sooner before the rear inner wheel looses its contact, you have the feeling that, (God's), hand grasps the car and the front wheels are pulling so effectively that the car never looses traction and track.

4)This is the reason why even on straight roads or in windy situations the Syncro is much stabler than the 2wd. (The 2wd with two front passengers is not as stable is the Syncro with only the driver).

5)And, finally, this is the reason that the Eurovan, the Passat, the Golf, the Jetta can be Syncro's, although they have the opposite architecture and their vct has to equate the speed between the two axles in the reverse manner, having as a primary axle the front and as drive wheels, which tend to spin, the fronts and not the rears.

Do not, ever, put a solid axle instead of a vct. This equipment works continuously, stabilizing the car on the road, under any circumstances.

It is a major active safety feature, giving the Syncro the best behavior.

The Syncro, as a 2wd, is worst than a 2wd Vanagon, on the road, because it has different adjustments for the, supposed, off road, suspension.

As a locked 2wd is very capable, (as the military beetles), but much less than a 4wd unlocked, although, in some cases, when the diagonal nightmare is present, it is better.

Mon Nov 06, 2017 9:27 am

Hellenic,

You are drinking WAY too much Syncro Kool-Aid. The VC cannot act as a differential, which has completely different operating characteristics and has 3 shafts (1 input, 2 outputs) to accomplish those different characteristics. The VC is a marvel of technology, but the things you describe it doing are not possible. In addition, other functions and the precision you describe are what a new VC does and we've all discovered they often age poorly - losing a lot of function. Most are driving VCs with 30+ years of age and use.

By contrast, a mechanical center differential does not lose function in normal use - operating the same at 100k miles as it did when new. In the real world that is an important point.

Again, its a great component but you are waaaaay overselling it.

I notice the OP has not even checked back into this thread because I feel we are taking his question in directions that don't mean much to him. If its time to have another argument about VC function, perhaps start another thread?

Doug

Mon Nov 06, 2017 2:18 pm

Jon_slider wrote: MsTaboo wrote: aren't you one of the unfortunate Syncro owners who have had several transaxle failures? Have all those failures been while using a solid shaft instead of a VC?

your question seems to be designed to question the validity of the witness

my personal experience has nothing to do with the descriptions I gave of a syncro, and the painstaking detail in which I explained how a VC can never spin a front diff faster than the rear diff.

I realize not everyone can understand that. Its ok. Read it over and over if it helps, or just keep believing that your syncro is AWD.. I don't mind. Enjoy it, no matter if we understand how a VC works or a Center Diff works.

bottom line, a Center Diff does things a VC cannot do, the reverse is not true, and my tranny history has nothing to do with it.

No, I was asking you if your transaxle troubles were in Syncro with a solid shaft. It had nothing to do with any of the rest. Maybe reread the question.

Mon Nov 06, 2017 2:31 pm

IdahoDoug wrote: Hellenic,

You are drinking WAY too much Syncro Kool-Aid. The VC cannot act as a differential, which has completely different operating characteristics and has 3 shafts (1 input, 2 outputs) to accomplish those different characteristics. The VC is a marvel of technology, but the things you describe it doing are not possible. In addition, other functions and the precision you describe are what a new VC does and we've all discovered they often age poorly - losing a lot of function. Most are driving VCs with 30+ years of age and use.

By contrast, a mechanical center differential does not lose function in normal use - operating the same at 100k miles as it did when new. In the real world that is an important point.

Again, its a great component but you are waaaaay overselling it.

I notice the OP has not even checked back into this thread because I feel we are taking his question in directions that don't mean much to him. If its time to have another argument about VC function, perhaps start another thread?

Doug

1)VW, accurately, names the vct as a "master" or a "speed differential".

2)S.A.E. paper, about the Syncro, calls it an "interaxle differential".

It seems that this, 2 point, differential simulates the operation of a 3 point, auto controlled, central differential, (in a combination with the total architecture).

But is it, really, a central differential?

Of course it is, since separates and connects, operationally, the two axles of the kinematic chain, allowing them to rotate at different speeds, when the torque is transferred, simultaneously, but not freely, as with an open differential, but on demand.

You see, the vct reacts in a closed loop, as a closed cybernetic system, trying to keep the predetermined equilibrium which is the zero difference in velocity between it's plates.

To reveal this better lets take a vct out of the cell.

We put it on the bench and we rotate the one half, (a). The other one half, (b), needs to accelerate, following the rotation in order to equalize it's velocity to the (a).

But what will happen if you rotate at a constant speed the (a), and the (b) is rotated at a higher speed?

The vct again reacts transferring torque within it's plates, but, now, is trying to decelerate the (b).

This operation is not on/off but at a smooth and continuous varied speed, according to the resistance it senses.

And this result is obvious for the driver of a Vanagon Syncro, where the vct tends to pull the front of the car into the curve, as well as, for the driver of a Passat Syncro, where the vct tends to push the rear of the car out of the curve, (and the 4ws corrects).

At this point let the S.A.E. to explain it better:

Now trying a comparison to a car with a center differential with a locking capability, we can see that on the contrary to the Syncro, usually, it has to stop to engage the locker when the Syncro does it continuously, variably and at any speed, automatically.

And if the "competitor" has an auto controlled central differential, in many cases, does not have the capability to transmit 100% of the power to the rear axle, (as it is needed for climbing), where the t3 has a solid connection.

So it is better to say that the vct simulates the operation of a 3 point central differential, but it makes it better, especially if the primary axle is the rear, as per t3, (and some Porsches).

Mon Nov 06, 2017 2:34 pm

Like mrshrimp, Tom Lengyel has put thousands of miles on a Syncro with solid shaft continuously coupled. He claims that there's been no obvious wear associated with this practice. This is contrary to what I had always assumed, but there you have it. We learn something new every day.

The OP had his question answered pages ago, so there's nothing wrong with the direction the thread has headed. Who cares if there's disagreement? We're all big boys, able to sort through the differing facts/opinions.

I can tell you one thing with certainty, and that's that putting a TBD up front is a waste of money.

Mon Nov 06, 2017 6:13 pm

hellenic vanagon wrote: It seems that this, 2 point, differential simulates the operation of a 3 point, auto controlled, central differential

in its ability to lockup yes, a VC simulates an auto Locking Center Diff (4WD mode)
but not in the ability to send forward traction to the front wheels in a turn, when not locked. (AWD mode)

look at these pictures
try to understand that there is a separate power shaft to the front diff, that rotates independent of the speed of the rear diff

a VC can NEVER rotate the front diff faster than the rear

a Center Diff can spin the front diff faster than the rear diff.. Try to understand that..

look closely at the photos:

visuals:

Viscous Coupling: one input, one output at the same speed, or slower than the input. Not possible for front diff to spin faster than rear diff.
https://shufti.blog/2010/04/02/viscous-coupling-hump-condition/

Center Diff: one input, TWO outputs capable of different speeds from each other, and front diff can spin faster than rear diff.
http://www.awdwiki.com/en/subaru/

A syncro is not Full Time AWD, it is Part Time 4WD.

learn why the front diff needs to spin faster on non slippery surfaces:(starting at the 36 second mark)

while looking for videos I see hellenic vanagon posted a really rough Offroad section.. thanks for the show!:-)

Mon Nov 06, 2017 7:19 pm

Jon:
Quote: a VC can NEVER rotate the front diff faster than the rear

Yes, but the fronts can spin faster than the rears because of the VC. Is there really any argument about this?

-d

Mon Nov 06, 2017 7:47 pm

Jon_slider wrote:

while looking for videos I see hellenic vanagon posted a really rough Offroad section.. thanks for the show!:-)

Holy wow! I would love to put my syncro westy thru that but with two propane tanks, im pretty sure id lose atleast one ;)

Mon Nov 06, 2017 7:59 pm

Offroad driving:
candyman wrote: Holy wow!
my reaction as well

If that white Syncro had used a Solid shaft, it would have been smoother going, less bucking..

Im not sure they locked the rear diff either, I think it would have helped also..

Pavement driving:
raoul mitgong wrote: the fronts can spin faster than the rears
yes, when decoupled, or when a VC is slipping (no traction in front, so RWD configuration)

you keep changing back and forth, every time I discuss the locked mode, you bring up the unlocked mode.. yes, both exist

there is a difference though
an unlocked VC can not drive the front wheels around a curve (so not True Full Time AWD)

an unlocked Center Diff can drive the front wheels around a curve (True Full Time AWD)

now back to the locked mode
yes a VC can spin the front diff slower (partial slip), or equal to (full hump mode), the speed of the rear diff

a locked center diff (or coupled solid shaft), will spin the front diff at equal speed as the rear

review, driving a curve on dry pavement
1. VC coupled =some drag, no forward traction at front wheels in a curve
2. Solid Shaft coupled =some drag, no forward traction at front wheels in a curve
3. VC w No Decoupler = some drag, no forward traction at front wheels in a curve
4. VC Decoupled = no drag, and no front wheel traction
5. Solid shaft decoupled = no drag, no front wheel traction
6. Planetary Center Diff open (not locked) = no drag, yes forward traction at both front and rear diffs

Mon Nov 06, 2017 10:24 pm

Jon,
I believe you are reading my posts but not thinking about what I’ve written.

I’m not going back and forth on coupled/uncoupled. Only talking stock coupled VC on snowy highways here.

Again, in another way:
Driving straight in snow, packed snow, or ice, the inevitable rear wheel slip causes an rpm difference in the vc. This sends power forward. Don’t forget that the drive shaft is spinning 4.86x (most cases) faster than the wheels so the 5% rpm difference in the VC can be reached easily on snow/ice.
Entering a curve, power decreases to the front. Once you pass the point of “VC rpm equilibrium” where rear wheel slip matches the faster fronts due to the larger curve radius, the VC will start to slip (in the opposite direction now) instead of your tire/tires (hopefully). This is desirable vs a ss with decoupler for me and a lot of Syncro owners who do more snow that rock crawling.

That video was insane. I won’t be taking any of my vans up that rock garden! Ouch.

-d

Mon Nov 06, 2017 10:25 pm

That's a nice piece of driving by the white Syncro. I've been a part of actual offroad testing at one of the world's largest automakers and that driver did a great job reflecting talent. No idea what's going on with the Rover, which is a much more competent vehicle on that terrain. I noted it is a RHD vehicle and that makes it much MUCH more difficult to drive on a trail if the driver is not quite accomplished with it and/or a native RHD driver. I personally have driven a RHD LandCruiser on a trail and found it almost like starting over (embarrassingly, I damaged it as a result). Either way, great driving on the Syncro, sharing the trail with a true purpose built offroad capable vehicle.

I agree with John Slider on the limitations of the VC. It's cheap and essentially zero maintenance component that provides power to the front axle only when the rear axle is spinning faster. But it's not pulling through corners as described by Hellenic. If you want that type of benefit, you need a true center differential that can provide full time power to the front wheels whether they are rotating faster, slower or the same speed. A car like an Audi Quattro would be a perfect example, and even though its not a sports car it will drive circles around a Syncro in any road competition you could devise. I happen to have one and would be glad to race anyone for pink slips. I've always wanted another Syncro. :lol:

Mon Nov 06, 2017 11:45 pm

raoul mitgong wrote: the inevitable rear wheel slip causes an rpm difference in the vc. This sends power forward.
...
Entering a curve, power decreases to the front. Once you pass the point of “VC rpm equilibrium” where rear wheel slip matches the faster fronts due to the larger curve radius, the VC will start to slip (in the opposite direction now) instead of your tire/tires (hopefully).

maybe I don't understand your thinking, and Im open to you helping me

this is my starting point
in response to your "sends power forward" comment:
The front diff will NOT spin faster than the Rear Diff, EVER

therefore at no time will the front wheel pull the vehicle forward unless there is wheel slip to compensate for the equal speed differentials, during lockup

IF the VC slips, that is a NO Lockup condition, the vehicle returns to its RWD configuration

therefore, again the front diff cannot provide forward traction through a curve

from where I am so far in my understanding, it appears your basic premise assumes that the front diff can pull the van through a turn while the rear wheels spin.. well yes, IF the rear wheels are spinning, then the VC will lockup.. thats why I consider the syncro a part time 4wd system..

the white syncro did well with a VC.. you can see the rear wheels spin faster than the front in the video

imagine if he had a solid shaft ;-)

as to a VC being better in snow, well, I disagree. A VC turns itself on later, a solid shaft turns on when you tell it to.. better.. depends on who is at the knob..

otoh if its driven by a person that is not interested in pulling knobs, a VC does an excellent job of activating automatically, without any thought from the driver.. but the VC drags the rest of the time, when the rear wheels are not spinning, so I still think a decoupler is beneficial

An obvious example of syncro drag is noticeable on dry pavement when parking, but that drag is happening all the time to a lesser degree.. because a syncro has no Center Differential to spin the front diff faster than the rear. Do you "get" that?

Tue Nov 07, 2017 2:34 am

Jon_slider wrote: raoul mitgong wrote: the inevitable rear wheel slip causes an rpm difference in the vc. This sends power forward.
...
Entering a curve, power decreases to the front. Once you pass the point of “VC rpm equilibrium” where rear wheel slip matches the faster fronts due to the larger curve radius, the VC will start to slip (in the opposite direction now) instead of your tire/tires (hopefully).

maybe I don't understand your thinking, and Im open to you helping me

this is my starting point
in response to your "sends power forward" comment:
The front diff will NOT spin faster than the Rear Diff, EVER

therefore at no time will the front wheel pull the vehicle forward unless there is wheel slip to compensate for the equal speed differentials, during lockup

IF the VC slips, that is a NO Lockup condition, the vehicle returns to its RWD configuration

therefore, again the front diff cannot provide forward traction through a curve

from where I am so far in my understanding, it appears your basic premise assumes that the front diff can pull the van through a turn while the rear wheels spin.. well yes, IF the rear wheels are spinning, then the VC will lockup.. thats why I consider the syncro a part time 4wd system..

the white syncro did well with a VC.. you can see the rear wheels spin faster than the front in the video

imagine if he had a solid shaft ;-)

as to a VC being better in snow, well, I disagree. A VC turns itself on later, a solid shaft turns on when you tell it to.. better.. depends on who is at the knob..

otoh if its driven by a person that is not interested in pulling knobs, a VC does an excellent job of activating automatically, without any thought from the driver.. but the VC drags the rest of the time, when the rear wheels are not spinning, so I still think a decoupler is beneficial

An obvious example of syncro drag is noticeable on dry pavement when parking, but that drag is happening all the time to a lesser degree.. because a syncro has no Planetary Center Differential to spin the front diff faster than the rear. Do you "get" that?

The man in the video equates the vct to the epicyclical differential saying that it is a "simplistic" epicyclical differential.

So here we are:

(Or how the front differential is spinning with more rpms in a curve).

Tue Nov 07, 2017 3:19 am

IdahoDoug wrote: That's a nice piece of driving by the white Syncro. I've been a part of actual offroad testing at one of the world's largest automakers and that driver did a great job reflecting talent. No idea what's going on with the Rover, which is a much more competent vehicle on that terrain. I noted it is a RHD vehicle and that makes it much MUCH more difficult to drive on a trail if the driver is not quite accomplished with it and/or a native RHD driver. I personally have driven a RHD LandCruiser on a trail and found it almost like starting over (embarrassingly, I damaged it as a result). Either way, great driving on the Syncro, sharing the trail with a true purpose built offroad capable vehicle.

I agree with John Slider on the limitations of the VC. It's cheap and essentially zero maintenance component that provides power to the front axle only when the rear axle is spinning faster. But it's not pulling through corners as described by Hellenic. If you want that type of benefit, you need a true center differential that can provide full time power to the front wheels whether they are rotating faster, slower or the same speed. A car like an Audi Quattro would be a perfect example, and even though its not a sports car it will drive circles around a Syncro in any road competition you could devise. I happen to have one and would be glad to race anyone for pink slips. I've always wanted another Syncro. :lol:

The Syncro is better than the Quattro:

http://www.vwsyncro.eu/p/blog-page_91.html

The "pulling effect" is described by S.A.E., too, here:

Driving both configurations for years, (rear engine Syncro, primary axle the rear, secondary the front, and front engine Syncro, primary axle the front, secondary the rear), I can confirm that, what S.A.E. paper says, is absolutely accurate.

Tue Nov 07, 2017 4:23 am

A car with a center diff without loks is just a 1wd.
A car with VC without diff locks is a 2wd.

Helenic, you will give up soon (as me) to explain that a VC is better than a center diff ;)

Gears, if a box lasts longer driven with decoupler, how it can last as long driven with a solid shaft ?
You will need more fuel, means you need more force to drive the rear wheels against the front wheels, means more heat and load on both boxes.
Means more load on the CVs.

This is like driving a locked center diff all the time.

Tue Nov 07, 2017 4:27 am

>>>”The front diff will never spin faster than the rear diff, ever”

... but the front wheels can spin faster than the vehicle speed, in which case they are “pulling”.