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Syncro Chat: VC's, solid shafts, decouplers, AWD/4WD, etc.
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raoul mitgong
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PostPosted: Wed Jan 24, 2018 3:08 pm    Post subject: Re: Syncro Chat: VC's, solid shafts, decouplers, AWD/4WD, etc. Reply with quote

Jon_slider wrote:
Facts:
1. The motor of a Syncro w VC or solid shaft, can never power the front diff faster than the rear diff.
2. In a dry curve, front wheels travel a longer distance than rear wheels.
3. To power the front diff faster than the rear diff, requires a center differential.
4. A syncro does not have a center differential.


5. The front wheels don't need to travel faster than the rears to provide forward torque.

Jon's #2 is technically correct but what matters is the RPM difference front vs rear, not how far they are traveling. This is a more complete description:

EDIT: This is at highway speeds, not a parking lot.

Image may have been reduced in size. Click image to view fullscreen.

_________________
84 Westy with a 2.1 (Groover)
86 Tintop Syncro (Crow)
86 Tintop Syncro to Westy project (Tom Servo)
91 Westy (Only the top 12 inches of this van (a burn victim))


Last edited by raoul mitgong on Thu Jan 25, 2018 12:08 pm; edited 1 time in total
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Sodo
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PostPosted: Thu Jan 25, 2018 9:27 am    Post subject: Re: Syncro Chat: VC's, solid shafts, decouplers, AWD/4WD, etc. Reply with quote

Raoul, your diagram is good to describe the relationship when the "geared" drivetrain puts the "rubber to the road". The horizontal line is important to understanding. Syncro fellers have been wanting for this explanation for 10, 20 years.

EDIT I have understood this diagram correctly in the past but today read it wrong.... I'm trying to get Jon to add slip between tire and roadway into his understanding - fwd(drive) & backward (skid). You cannot have the steady state condition of tire speed = roadway speed when there is 80hp being expended.

    Lower speed maneuvering (parking etc) is below the horizontal.
    Highway driving is above the horizontal.


Jon's explanations are all very good for describing the relationships "below the horizontal". Most vans don't get a lot of miles below the horizontal. Most of any vans miles are ticked away above the horizontal, where slippage cancels the binding.


Kinda like where your underwear gets tight sitting in the driver's seat for hours, but feels a lot better after you stop to get out & fix something on the van. Wait a minute....
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'87 Tintop w 47k 53k, '12 SmallCar EJ25, cooled filtered gearbox
....KTMs, GasGas, SPOT mtb


Last edited by Sodo on Thu Jan 25, 2018 1:48 pm; edited 2 times in total
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raoul mitgong
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PostPosted: Thu Jan 25, 2018 12:11 pm    Post subject: Re: Syncro Chat: VC's, solid shafts, decouplers, AWD/4WD, etc. Reply with quote

Sodo,

I'd say that this diagram describes highway speeds.

Parking lot driving would result in a similar graph but the lack of rear wheel slip would just shift the red curve down to where the tip is at x=0 and y=0 (in other words, no forward torque).

(I put an edit above to clarify highway speeds.)

-d
_________________
84 Westy with a 2.1 (Groover)
86 Tintop Syncro (Crow)
86 Tintop Syncro to Westy project (Tom Servo)
91 Westy (Only the top 12 inches of this van (a burn victim))
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WestyBob
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PostPosted: Thu Jan 25, 2018 12:28 pm    Post subject: Re: Syncro Chat: VC's, solid shafts, decouplers, AWD/4WD, etc. Reply with quote

Sodo wrote:
Syncro fellers have been wanting for this explanation for 10, 20 years.


Syncro fellers already had this explanation for 10, 20 years. This thread is mostly a rehash. That is, past heavy discussion on same topic, even back in the 80's -- BTDT Shocked Very Happy
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Sodo
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PostPosted: Thu Jan 25, 2018 1:10 pm    Post subject: Re: Syncro Chat: VC's, solid shafts, decouplers, AWD/4WD, etc. Reply with quote

oops yeah it's curve radius at speed. Sorry for making it MORE confusing.

WestyBob wrote:
Sodo wrote:
Syncro fellers have been wanting for this explanation for 10, 20 years.


Syncro fellers already had this explanation for 10, 20 years. This thread is mostly a rehash. That is, past heavy discussion on same topic, even back in the 80's -- BTDT Shocked Very Happy


Syncro fellers have been wanting for this diagram for 10, 20 years.
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'87 Tintop w 47k 53k, '12 SmallCar EJ25, cooled filtered gearbox
....KTMs, GasGas, SPOT mtb
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WestyBob
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PostPosted: Thu Jan 25, 2018 1:35 pm    Post subject: Re: Syncro Chat: VC's, solid shafts, decouplers, AWD/4WD, etc. Reply with quote

Sodo wrote:
Syncro fellers have been wanting for this diagram for 10, 20 years.


I'll have to hunt around for some of the diagrams I and others used to compile going back to about '88 but in the 90's in earnest, and see if there are any similarities.

The whole Vw vanagon VC system and how it works in the real world has always been a curiosity virtually from the day they were sold. After reading too many Vw promo lit. and technical testing pamphlets I had the impression even VoG was surprised at what it was or wasn't doing under different circumstances.

But the diagram above is a nice general one.
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Waldi
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PostPosted: Fri Jan 26, 2018 1:35 am    Post subject: Re: Syncro Chat: VC's, solid shafts, decouplers, AWD/4WD, etc. Reply with quote

I see the VC made the way over the Atlantic and is used in some Jeeps.
They call it "full time AWD"
The problem is, Jeep installed the VC into the main gearbox and the VC suffers from the heat.
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Jon_slider
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PostPosted: Sat Jan 27, 2018 12:00 pm    Post subject: Re: Syncro Chat: VC's, solid shafts, decouplers, AWD/4WD, etc. Reply with quote

A VC is just an automated decoupler, that never completely decouples. It also acts as a coupler, that never completely couples. It is not magic, and does not generate torque on dry pavement, it actually creates drag.

Here is a retrospective, of where we have been, I searched keyword "magic".

WestyBob wrote:
The ... VC system and how it works
...
even VoG was surprised...


Sodo wrote:
Lets proclaim it magic.


Syncro Jael wrote:
... it seems like even the engineers who designed this "magical" viscous coupler are not really sure what it can do.
...
It is just really difficult to hold a prop-shaft in your hand, linked to a working VC, and say it does not transmit torque all the time. It is very simple, yet complex with all the variables. For me the only way to turn it off is to de-couple it.

It is like a solid shaft at the beginning, then releases under certain conditions, and then locks up like a solid shaft again.
...
I still have this gut feeling my VC is always transferring torque unless the vehicle is just coasting straight down the road.


IdahoDoug wrote:
a center differential is always applying torque to both f/r axles. This is simply because the input shaft from the engine applies torque to both output shafts at all times because it is designed to do that.

A VC is designed only to apply torque to the output shaft when a condition applies. That condition is that the input shaft speed is faster than the output shaft. When you are driving straight along a road in a VC Syncro, the front shaft is spinning at the same speed as the rear, with the power to spin the shaft coming from the road passing under the front tires. If you magically removed the VC for an instant, the front shaft would merrily continue to spin along at the exact same speed. It is NOT being driven by the rear input shaft. Zero torque being applied.

Back to the center differential. Straight ahead - it is applying torque to the front shaft as well as the rear shaft. It has TWO output shafts and two sets of spider gears and ring gears designed for this.

These are two completely different designs and people seem to easily interpret the VC as the same mechanical function.

So, as I have mentioned previously, a Syncro driving straight along dry pavement is getting driving torque to its rear tire contact patches. And it is getting mild braking torque to the front contact patches. The behavior of the vehicle starts from there and is not the same as 4 driven contact patches like a Quattro, etc. But the important part is for people to absorb and grasp this state of affairs as the starting point of the Syncro's behavior.

The VC is not transferring any torque under the above conditions, and IT IS NOT DESIGNED TO.


IdahoDoug wrote:
If the front output shaft is already powered and spinning at the same speed while you drive down the road because of the road under the front wheels passing, and you are on dry pavement, there is no torque being transferred from the rear. The VC is spinning along with zero relative movement inside between the plates and transferring zero torque. Go in to a curve, and the front wheels are spinning slightly faster, meaning inside the VC, the front plates are actually PULLING the rear plates slightly and generating torque to the rear! Heh. And of course that means the front tire contact patches are experiencing slight braking torque in the process to push against the rear contact patches in their unsuccessful attempt to pull them faster.
...

a few seem delighted to obfuscate that in order to make it seem like the thing is magic.

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Last edited by Jon_slider on Sat Jan 27, 2018 8:30 pm; edited 3 times in total
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IdahoDoug
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PostPosted: Sat Jan 27, 2018 4:42 pm    Post subject: Re: Syncro Chat: VC's, solid shafts, decouplers, AWD/4WD, etc. Reply with quote

Waldi,

The Jeep VC is used in a completely different fashion from the Syncro. Where the Syncro's default position is uncoupled, NOT transferring torque (only couples with differences in shaft speed), the Jeep's is always transferring torque and its purpose is to reduce binding by allowing small shaft speed differences in a full time 4WD/AWD system.

The Jeep VC is also housed in a transfer case, and it has 1 input shaft and 2 output shafts. The Syncro VC only has a single input shaft and a single output shaft which limits its functions. Completely different application.

My LandCruisers also have this feature. Great setup.
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Last edited by IdahoDoug on Sat Jan 27, 2018 4:48 pm; edited 2 times in total
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raoul mitgong
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PostPosted: Sat Jan 27, 2018 10:31 pm    Post subject: Re: Syncro Chat: VC's, solid shafts, decouplers, AWD/4WD, etc. Reply with quote

Jon_slider wrote:
A VC is just an automated decoupler, that never completely decouples. It also acts as a coupler, that never completely couples. It is not magic, and does not generate torque on dry pavement, it actually creates drag.


This statement is in direct conflict with the simple diagram above. We still haven’t read where this diagram is in error. Simply saying what you think it does with nothing to back it up is not an argument. Describing other transmissions is irrelevant.
The “forward torque” side has presented SAE papers, published studies, wear on actual parts, math, diagrams, and descriptions that conform to the laws of physics.
The “no-forward torque” side has presented transmissions not installed in a Syncro, examples that omit real world conditions (tire slip), and a “feel” of the fronts braking. Somehow the forward torque side is accused of non-scientific, religious, magical, or biased thought.
To some it must matter more to win a discussion than to get to the truth.
-d
_________________
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86 Tintop Syncro (Crow)
86 Tintop Syncro to Westy project (Tom Servo)
91 Westy (Only the top 12 inches of this van (a burn victim))
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WestyBob
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PostPosted: Sat Jan 27, 2018 11:25 pm    Post subject: Re: Syncro Chat: VC's, solid shafts, decouplers, AWD/4WD, etc. Reply with quote

Raoul -- perfect and X2.
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Sodo
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PostPosted: Sat Jan 27, 2018 11:51 pm    Post subject: Re: Syncro Chat: VC's, solid shafts, decouplers, AWD/4WD, etc. Reply with quote

Agreed Raoul, Thanks for your patience and the reverse engineering. I don't understand why anyone would avoid the full understanding.. They are omitting the reality of tire slip, and it seems "intentional" at this point (pages and pages in) to NOT understand it.

IdahoDoug wrote:
a few seem delighted to obfuscate that in order to make it seem like the thing is magic.


Sodo is delighted to obfuscate a flawed premise however. The coast side ball tracks (on the front CVs) remain pristine, showing that the Syncro fronts are NOT "braking" a lot. And Sodo is delighted to opine that the drive-side wear on all used Syncro front CVs is PROOF that the Syncro front wheels PULL hard.

Do we really have to discuss whether or not Syncro front wheels PULL? Of course they do! And that's why it's a pleasure to drive. It's sure-footed on gravel. Its a Syncro.

Syncro fronts pull because of the rear wheel slip.
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'87 Tintop w 47k 53k, '12 SmallCar EJ25, cooled filtered gearbox
....KTMs, GasGas, SPOT mtb
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Honuak
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PostPosted: Sat Feb 09, 2019 6:18 pm    Post subject: Re: Syncro Chat: VC's, solid shafts, decouplers, AWD/4WD, etc. Reply with quote

https://en.wikipedia.org/wiki/Tesla_turbine

Is the viscous coupling a kind of tesla turbine?
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