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Syncro Chat: VC's, solid shafts, decouplers, AWD/4WD, etc.
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Syncro Jael
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PostPosted: Fri Apr 03, 2015 10:12 am    Post subject: Reply with quote

I have been researching this to see what VW says. A Video and more reading:


Link


All Syncro Vanagons were originally fitted with a device called a Viscous Coupler (VC) which allows them to be in full-time "kinda" 4WD. The purpose of the Viscous Coupler is to allow slippage between the front and rear axles when the vehicle is driven in high traction situations. For example, when doing tight maneuvering in a dry parking lot. Anyone who has driven a Vanagon Syncro has experienced some level of "binding" when performing such maneuvers. If there were no VC at all, just a solid shaft for example, the binding would be 100 times worse, and in fact after a few maneuvers something would probably break. Part-time 4WD vehicles, like a Toyota truck for example, are 100% fully locked in 4WD when selected, and 2WD otherwise. Vehicles like that are REAL 4WD vehicles. The Syncro Vanagon, like any all-wheel-drive Subaru or Audi Quattro, are considered "all wheel drive" vehicles because they all are full-time "kinda" 4WD, and have some sort of device that allows for slippage. Thus my use of the word "kinda". The problem with a VC system is that, when in an extreme off-road stuck situation like soft sand, if your rear wheels completely lose traction not all of the engine's torque is transmitted to the front wheels. Rather, only the amount of torque the VC is designed to transmit gets there. And in soft sand with the rear wheels completely buried, it ain't enough to get you out. Last time we were in Baja, only one of five pop-top Syncro Vanagons we took got stuck in the sand. All five had a decoupler and solid shaft instead of the VC, except for one. I will let you guess which one of the five got stuck in the sand...

http://www.gowesty.com/library_article.php?id=627

Syncro with its VC only drives the rear wheels when the front wheels are travelling faster, so when the fronts slip, or on tight turns when the front wheels are following a slightly longer path. Haldex can provide a direct mechanical lock between front and rear, but it's not as useful as the True Quattro system which has a Torsen centre diff.

http://forums.vwvortex.com/showthread.php?5555730-syncro-viscous-coupling-delete



I still hear different opinions on this VC issue. Shocked

And here is another article from VW.

The visco coupling is thus of similar construction to a Multi-plate axial clutch. In contrast to such clutches, however, the visco coupling does not have a disengaging device. The plates are free to move in the housing and on the shaft and are slightly Spaced apart; power is transmitted mainly through the silicone oil by its resistance to shear.

http://www.easy2design.de/stuff/visco_sae.pdf
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Last edited by Syncro Jael on Fri Apr 03, 2015 10:34 am; edited 3 times in total
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WestyBob
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PostPosted: Fri Apr 03, 2015 10:14 am    Post subject: Reply with quote

raoul mitgong wrote:
On VC failure:
The SAE paper said the temperature was self limiting because as it locked up, the frictional heating would stop, allowing it to cool. The air space was instrumental in allowing the pressure to stay low enough to not blow the seals.
Not sure how silicone breaks down, but the highest temperature ranges I've seen for any silicone rubber is 400-500F and intermittent at 600F for adhesives.
Towing or radical tire difference would not allow for the self limiting temp control.

-d


Agreed.

As for how viscuous material breaks down, I don't have a direct link handy but I recall (hopefully correctly) Derek Drew did some extensive research into this (and others too although I don't recall names).
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WestyBob
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PostPosted: Fri Apr 03, 2015 10:37 am    Post subject: Reply with quote

Jon_slider wrote:
Bob your questions are invalid because they assume facts that are not in evidence.

Do you Still Beat your Wife? Evil or Very Mad

Is that a No? LOL!


No assumptions here, Jon, and I'll still take that to be a no.

And that highlights some confusion in this debate in that this is not about who 'wins', it's about finding the 'rosetta stone' or 'smoking gun' to derive the facts of the matter, and I consider it all interesting and fun to pursue, not throw furniture around.

For me the heart of it is heat transfer to the VC and how that can happen causing residual torque under real world circumstances when the rear wheels are not slipping. Several ways have been proposed.

But more specifically, for me, it's not about thinking an opposing position is wrong as much as being convinced or unconvinced **for the time being** which is why we'll likely never come to complete concurrence unless we can get some more real world testing done.

And, oh yes, I'm currently no longer married, just occasionally partnered Wink -- my true love and intended died a long time ago.
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Syncro Jael
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PostPosted: Fri Apr 03, 2015 10:41 am    Post subject: Reply with quote

WestyBob wrote:
Sure wish someone had some torque measurement hubs ! Cool


Read page (8)eight. Measurements in the Vehicle:



http://www.easy2design.de/stuff/visco_sae.pdf

Most of this is way above my simple thinking! Shocked

I found this on the internet so it must all be true! right? Wink
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WestyBob
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PostPosted: Fri Apr 03, 2015 11:02 am    Post subject: Reply with quote

Syncro Jael wrote:
Read page (8)eight. Measurements in the Vehicle:



http://www.easy2design.de/stuff/visco_sae.pdf

Most of this is way above my simple thinking! Shocked


Thanks for the link but unfortunately my ancient PC couldn't pull it up.

But I suspect it's Vw's initial testing report ?

If so, I think it was discussed a while back it wasn't clear what the conditions surrounding the testing were (lab/real world/etc.). Hence the ideal to have some new real world driving testing done. That would be of great interest to me no matter the results.
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Jake de Villiers
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PostPosted: Fri Apr 03, 2015 11:26 am    Post subject: Reply with quote

WestyBob wrote:
Syncro Jael wrote:
Read page (8)eight. Measurements in the Vehicle:



http://www.easy2design.de/stuff/visco_sae.pdf

Most of this is way above my simple thinking! Shocked


Thanks for the link but unfortunately my ancient PC couldn't pull it up.

But I suspect it's Vw's initial testing report ?

If so, I think it was discussed a while back it wasn't clear what the conditions surrounding the testing were (lab/real world/etc.). Hence the ideal to have some new real world driving testing done. That would be of great interest to me no matter the results.


Hey Bob, if you send me your email to subyjake AT gmail.com I'll send you the PDF.
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WestyBob
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PostPosted: Fri Apr 03, 2015 11:35 am    Post subject: Reply with quote

Jake de Villiers wrote:
Hey Bob, if you send me your email to subyjake AT gmail.com I'll send you the PDF.


Many thanks for the offer, Jake.

First I think I'll haul myself up to a nearby cafe for some lunch and free wifi and see if I can pull it up there.

I'm embarrassed Embarassed to say I'm still on cheapo dial-up and need to fix that one of these days although high speed is very expensive around here.

Anyway, I'll take you up on it if wifi fails.
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raoul mitgong
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PostPosted: Fri Apr 03, 2015 11:49 am    Post subject: Reply with quote

Syncro Jael wrote:
WestyBob wrote:
Sure wish someone had some torque measurement hubs ! Cool


Read page (8)eight. Measurements in the Vehicle:



http://www.easy2design.de/stuff/visco_sae.pdf

Most of this is way above my simple thinking! Shocked

I found this on the internet so it must all be true! right? Wink


Hey Jael, you've come full circle. That is the same article where I originally talked about the torque measuring hubs that Westy Bob then referred to. That article doesn't answer the questions but I'd bet the raw data has the answer we are trying to find.

-d
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raoul mitgong
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PostPosted: Fri Apr 03, 2015 12:02 pm    Post subject: Reply with quote

Since iDoug seems to be the most entrenched here on the NO torque without wheel slippage, this hypothetical is for him but others are welcome to join of course.

Two wheels driven by a differential on a steel roller. Now add two more wheels onto that same roller on the same axis (concentric) as the first two wheels. Those two new outer wheels are linked to the inner two wheels with a clutch that slips at 30Nm. All 4 tires are the same diameter.

You accelerate the inner tires through the diff. Any torque transfer to the outer wheels however negligible?
Now hard mount the outer wheels (like a dually) any torque transfer to the outer wheels?

-d
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Syncro Jael
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PostPosted: Fri Apr 03, 2015 12:14 pm    Post subject: Reply with quote

Yup sorry. This is a long thread with a big circle. Embarassed
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PostPosted: Fri Apr 03, 2015 1:02 pm    Post subject: Reply with quote

Jake de Villiers wrote:


http://www.easy2design.de/stuff/visco_sae.pdf



I'm at the cafe now and ah, yes, I remember this document before way back in the thread. I read it thoroughly and commented they were just as obtuse as Vw when describing things using the terms "almost all" the power in the rear wheels.

Well, it's a good refresher Wink
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raoul mitgong
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PostPosted: Fri Apr 03, 2015 1:53 pm    Post subject: Reply with quote

Syncro Jael wrote:
Yup sorry. This is a long thread with a big circle. Embarassed


I think it might turn into an 8 on its side. Wink

-d
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Bassyaks
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PostPosted: Fri Apr 03, 2015 3:44 pm    Post subject: Reply with quote

So would a Locking rear diff and a front de coupler with a solid shaft (no VC)be most like a true 4WD. And if there is a front differential, wouldn't this be the best way to go?

Another question: isn't the VC working in reverse when the de-coupler is engaged? it's still spinning from the front tire rotation, thus is the VC is being driven off the front wheels.

Does the VC work like a torque converter

I picked up a syncro with what I surmise as having a bad VC ( free wheeling all the time, no pull at all) and a stuck diff lock shaft

I'm totally confused on which way to go, I want to drive it on the highway for trips but than also off road occasionally in soft sand behind the dunes at the shore.
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IdahoDoug
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PostPosted: Fri Apr 03, 2015 9:32 pm    Post subject: Reply with quote

Finding VW marketing materials where they will admit that it is a 2WD vehicle that engages 4WD only with rear wheel slippage would be tough. VW seemed guilty of over selling the system to me, which I wouldn't hold against them since we all did it with various systems from ABS, to independent suspension. So, you won't likely find it just like you won't find manufacturers mentioning that the ABS systems lengthen stopping distances, and the airbags cause thousands of injuries. VW marketing wanted it to have 4WD credentials so bad, they even sprung for the "4WD" stickers on the door.

Bob, as for the comment above wondering if this idea of the residual torque powers the front wheels all the time. Unequivocally no. A center differential quite literally was "invented" to accomplish this in a vehicle with two powered axles. It does it because each axle (front/rear) can be powered by the differential even when their speeds are different. One input shaft from the engine is split into two independent powered shafts powered by a differential which can let one shaft accelerate. The Syncro uses a single powered shaft, which can power another shaft only if that shaft is spinning slower. It is physically impossible to power that (front) shaft if it is spinning either the same speed, or faster. Physically impossible.

That isn't theory on my part. It isn't personal bias on my part. It is quite basic powertrain engineering.

Doug
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PostPosted: Sat Apr 04, 2015 3:37 am    Post subject: Reply with quote

I completely understand what you're saying, Doug, and respect that.

However, for some dang reason the syncros I('ve) own(ed) are misbehaving differently leading me to the current conclusion that something else is going on which in turn has led to various plausible theories falling into the general category of why does the impossible seem to be possible ? Wink

Trivia: Many if not most of the syncros shipped to NA did not have the 4WD stickers although most had the 'syncro' sticker on the nose. Dealers often added the 4WD but some were still sold without -- I have or have had several that were sold that way.

But that's typical Vw where there was nearly an exception to everything they did like why sell some syncros without rear dif.locks ?

Anyway, shouldn't that 4WD really be a 3WD ? Or maybe a 2+WD or 2WD+ ? Then are we absolutely sure a 2WD vanagon is really a 2WD instead of a 1WD, or what (?) when people add limited slips (Peloquins or TBD's) and rear dif locks .... Laughing
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PostPosted: Sat Apr 04, 2015 5:35 am    Post subject: Reply with quote

In that SAE paper, Figure 7.1 shows torque transfer as a function of slip speed. When slip = 0, torque transfer = 0. SAE technical papers are a pretty credible source of information, I think. As for the practical side, the paper notes that about a 5 RPM difference (output to input) is required for the VC to go into torque progression. Meaning, that below that 5 RPM difference, the available torque transfer is the static friction value that Waldi mentioned early on. However, as Doug keeps pointing out, just because that value is available doesn't mean it is realized. A straight shaft will have orders of magnitude more torque transfer capability, but the actual torque transfer while driving down a straight road will be very small, and variable depending on conditions.

RonC
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PostPosted: Sat Apr 04, 2015 6:41 am    Post subject: Reply with quote

snowsyncro wrote:
In that SAE paper, Figure 7.1 shows torque transfer as a function of slip speed. When slip = 0, torque transfer = 0. SAE technical papers are a pretty credible source of information, I think. As for the practical side, the paper notes that about a 5 RPM difference (output to input) is required for the VC to go into torque progression. Meaning, that below that 5 RPM difference, the available torque transfer is the static friction value that Waldi mentioned early on. However, as Doug keeps pointing out, just because that value is available doesn't mean it is realized. A straight shaft will have orders of magnitude more torque transfer capability, but the actual torque transfer while driving down a straight road will be very small, and variable depending on conditions.

RonC


To read a SAE Paper and to understand it are 2 ways.
When there is no diference between in and out of VC, there is no torque transmitted.
But as i sayed, practicaly there is nearly never same revos between rear and front. There is always (99,99%) difference reat to front while driving.
And there is no need of 5 revos to transfere torque. If you try the VC outside the gearbox, you will see it transferes around 50nm from begining of turning.
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PostPosted: Sat Apr 04, 2015 8:05 am    Post subject: Reply with quote

Waldi wrote:
When there is no diference between in and out of VC, there is no torque transmitted.
But as i sayed, practicaly there is nearly never same revos between rear and front. There is always (99,99%) difference reat to front while driving.


All correct. However, there is a key point within your comment that the rear and front drive shafts almost never spin the same. On dry, wet or windy roads WHENEVER there is a difference between the rear and front drive shafts, it is ALWAYS the front drive shaft spinning faster than the rear. ALWAYS. Always. Always. Always.

If anyone can give me a single example where that is not true, please give it. I don't mean that defiantly, but simply to make the point for all time. It has become like a mantra to me and if you are having trouble either understanding it, or accepting it - watch some of the videos linked several pages ago for a pretty simple visual explanation many will have that "aha!" moment with.

Since the front is always spinning faster (or the same) than the rear on the road, there is zero engine torque transfer to the fronts driving a Syncro on the road.

As I mentioned a bit ago, some are quite sure they feel "something" in curves on dry roads. Yes, you are feeling the front tires braking slightly which I would expect to make the Syncro "feel" more stable. Whenever you put a tire patch in a bit of tension, it will feel different. The braking forces on the front tire patches come from the fronts spinning faster on a curve but being fought from doing so by needing to spin the plates in the VC to do so. The rears are trying to slow the fronts and slippage in the VC is how that happens, causing some braking force at the front wheels. Now that I'm thinking of it, a driver who maintains the same speed in this vehicle will be applying more driving torque to the rear wheels, which also stabilizes the rear contact patches. So I want those who feel the "stablizing" feeling in a Syncro to know I now realize that is mechanically true. Very interesting.
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raoul mitgong
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PostPosted: Sat Apr 04, 2015 8:19 am    Post subject: Reply with quote

Idoug, any response to my question on page 33?
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PostPosted: Sat Apr 04, 2015 8:24 am    Post subject: Reply with quote

IdahoDoug wrote:
I want those who feel the "stablizing" feeling in a Syncro to know I now realize that is mechanically true. Very interesting.


stabilization from Drag, yup, I get a lot of that from my solid shaft too. Drivetrain binding is stabilizing, true, like brakes are stabilizing.

In fact, coupled on dry pavement and attempting to make a U turn, I get about 1/2 way into the first 90 degrees, and my van becomes so stable it wont move at all.

like you said, the front is trying to go faster, and the rear is holding it back.

Kind of like a martial artist in Horse stance, adductors increase friction on the floor. But each foot is moving in opposite directions, so its mostly good for staying still.

In a syncro, the DRAG is stabilizing, if you want to call it that, but I would not call the DRAG Traction.

So, yes, in a turn a VC syncro is more "stable", but it is not pulling with the front wheels, and is not sending traction to the front wheels from the motor.. The Syncro is NOT operating in All Wheel Drive, its operating in All Wheel Braking. Its still just the road turning the front wheels faster than the front, and the slower back wheels are essentially turning backwards, relative to the front. This is also why a coupled VC Syncro requires more throttle pedal to hold speed in a turn, the VC is providing BRAKING action, not ... what was that T word? yea, T Raction..

iDoug
could you please add the word VC when you are talking about a VC Syncro.. otherwise us Solid Shaft guys get confused if youre talking about BOTH VC and Solid Shaft syncros. (And maybe you are, but I would appreciate you saying so specifically)

I do think Both a VC and a Solid shaft can be very "Stabilizing" on dry pavement..

Ive learned a great deal in this thread, about why I would not want a VC without a decoupler, and why I would want an aggressive VC instead of a normal one.. So I can decouple on dry pavement, and get less delay for front wheel engagement on slippery terrain.

Thank you all for your contributions.
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