Syncro “AWD” Capabilty

[raoul mitgong]

Jon, you are conveniently ignoring at least 4 posts about tire slip.
-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))

[hellenic vanagon]

[Jon_slider]

[MsTaboo]

So Jon, I never did get an answer to my question; were all your transaxle failures while using a solid shaft?

Another question for anyone who might know; did VW ever outfit any of their Syncro test vehicles with a solid shaft?
We know that the engineers were expecting to equip the Syncro with a decoupler (hence the three knob panel and lines all Syncros came with), but did they ever play with the idea of a solid shaft replacing the VC?
_________________
Currently:
'90 Syncro Westy 3 knob w/Zetec

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[Zeitgeist 13]

The Bay Syncro appears to have a solid input to the front diff

_________________
Casey--

'89 Bluestar ALH w/12mm Waldo pump, PP764 and GT2052
'01 Weekender --> full camper
y u rune klassik?

[IdahoDoug]

I'd like to chime in on the tire slip. 3% is a crazy amount of slip. That means in a mile of driving there is 158 feet of slippage. The study cited states they used only acceleration and braking to achieve the slip. That's not representative of simply driving around as we most often are - merely maintaining a speed mile after mile. They don't identify the vehicle used, but statistically it was FWD - the absolute worst for tire slippage under acceleration because weight transfers off the drive wheels in acceleration.

On the other hand, the Vanagon is perhaps the poster child for absolute minimum slip. Its heavy. Its RWD. The weight of the engine is atop the drive wheels. And it has likely the lowest power to weight ratio of any car I can think of at 95 hp. So we can see the discussion will center around the "fronts pull and are powered all the time" folks like Hellenic saying the rear wheels slip so much even on dry pavement the fronts are powered all the time. And the others positing that there is not enough rear wheel slip to engage the VC on dry pavement.

I doubt even on wet pavement at driving speeds there could even be enough rear wheel slippage on a curve to generate engine torque at the front wheels. At wide open throttle on a wet curve? Hmm. Not sure even that's possible, and I'm not sure how many Syncro drivers would have their foot flat on the floor on a wet curve to achieve this "benefit" that an ordinary real differential provides all day at all throttle settings.

We seem to be leaving the difference between a true center differential and a VC behind as well. A VC is only a clutch (emphatically not a differential), and the output shaft of a clutch (the front drive shaft on a Syncro) cannot be spun faster by engine power than the input shaft (the rear drive shaft on a Syncro). Ever. Not sometimes. Not under certain conditions. Never. Since in a curve this has to happen to power the front tires, it's simply not happening unless the rear wheels are actively spinning. And yes in a curve the instant the rears grip again the fronts just as instantly are not getting power. By contrast a center differential on a curve CAN and DOES power the front wheels while the front drive shaft is rotating faster. That's why a center differential vehicle is more stable on a curve.

The VC is many things, but it is not magic.
_________________
1987 2WD Wolfsburg Vanagon Weekender "Mango", two fully locked 80 Series LandCruisers. 2017 Subaru Outback boxer. 1990 Audi 90 Quattro 20V with rear locking differential, 1990 burgundy parts Vanagon. 1984 Porsche 944, 1988 Toyota Supra 5 speed targa, 2002 BMW 325iX, 1982 Toyota Sunrader

[raoul mitgong]

No Doug, you would not be accelerating the entire time you are driving. No interstellar travel in a Vanagon. Stock WBX might take a whole mile to accelerate to hwy speeds though!
Going to argue the low poster child slip statement. The Vanagon will be using a lot more power to maintain 65mph than a Camry. Most Syncros are not going to be wearing low rolling resistance Michelin’s either. Probably something heavily siped for winter or big lugged for off-roading. These will increase slip.
-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))

[Jon_slider]

[raoul mitgong]

Jon,
I’m just going to quote this guy from two days ago. He seems to know what he is talking about.
-d

[Jon_slider]

[hellenic vanagon]

[Waldi]

If there would not be tire slip, the car would not move at all.
If simple physiks are ignored a discussion is sensless.
All this was clear in earlier posts.
The facts will not change if they are discussed over and over.

The rear tires spin always faster than the fronts on the syncro even on low curves, as long the engine is pushing the van. The VC gets harder, the tires spin more equal, the VC gets looser, the rear tires spin again more.
Thats VC action is continual, it is not like it takes seconds for the change.
There is no need for hump mode to transfer torque to the front.
The VC transfers always a amount of torque.

On a car with center diff, the tires on the axle with less weight will spin/slip more than the others. Even driving straight on pavement.
In a turn the inner tires slip more than the outer tires.
In a fast driven sharp turn the inner rear tire would loose significant weight and slip more than all other tires. The front axle would not pull the car.

Nobody wants a system where the front tires spin faster on accelaration, on a car with a rear engine. Even if the weight is nearly 50/50 on a syncro. The car moves up in the front and would cause more tire slip on front wheels.
Thats why a Porsche is accelarating better than a front driven car with front engine.
And this is the reason why modern electronic controled AWD/4WD cars have a 60/40 power transfer rear/front.

[Jon_slider]

[raoul mitgong]

[gears]

If your meaning is exactly as it's written, this is WAY off. The front and rear diffs have the same R&P ratio. This says that one set of tires is rotating 4.86 times faster than the other ..

[raoul mitgong]

If the rear wheels are spinning at 60 rpms and the fronts are spinning at 59.5 rpms. The difference is 0.5 rpm between the wheels.
The front of the VC will be spinning at 289.17 rpms while the back of the VC will be spinning at 291.6 rpms. This difference is 2.43 rpms.

[gears]

Ah, got your meaning now, thanks ..
_________________
aka Pablo, Geary
9.36 @ 146 in '86 Hot & Sticky
'90 Syncro Westy SVX
'87 Syncro GL 2.5
https://guardtransaxle.com

[flomulgator]

what does the release time look like for the VC? I assume it has to undergo some cooling for the silicone to lose viscosity, after the front and rears regain rolling equilibrium.

Ideally this would be answered by a 2 variable graph showing heat and viscosity on the y-axis and time on the x-axis.

Edit: I'm going to kind of answer my own question. I really wish I could copy/paste this, but I simply can't and the preview is missing pages and I'm not paying $340 for a (albiet cool) textbook on the topic. Seriously though, all syncro owners should read this, it even mentions the T3 specifically. Sometimes it will show pg. 249, which is interesting in that it explains that silicone viscosity decreases with heat, and it's the design of the plates that actually make it all work.

https://books.google.com/books?id=vJJwAgAAQBAJ&...mp;f=false

Also, now I want a magnetorheological coupling
_________________
She's built like a steakhouse, but she handles like a bistro!

[raoul mitgong]

I'll need to double check my Excel spreadsheet but I'm getting the following rough numbers:
3% tire slip = 119 rpm difference in VC
1% tire slip = 39.9 rpm difference in VC
0.1% tire slip = 3.99 rpm difference in VC

EDIT: THIS IS WITH STOCK TIRES OF 820 REVS/MILE AT 60 MPH.

A 0.1% tire slip is only .012" of slip per revolution. A box knife razor blade is twice that thick. Going to assume we are getting more tire slip than that.

Obviously a working VC is not letting 119 or even 39.9 rpm difference occur. This has me thinking deeper about what is going on and perhaps more power is going forward than I thought.

I think the VC engages around a 5 rpm difference.
Going to think/write outloud... rear slip transfers power forward, results in less slip in rear, fronts have slip as well to prevent a 119 rpm difference...

I hope these calculations start some real well thought out discussions and not more round and round about the VC can't pull in a straight line. If you are are about to write that, reread this post please.

-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))

[Syncro Jael]