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Jon_slider
Samba Member
Joined: April 11, 2007
Posts: 5091
Location: Santa Cruz, Crowdifornia
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 Posted: Thu Nov 27, 2014 7:30 pm Post subject: |
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| Phishman068 wrote: |
| My VC test, which is pretty simple and foolproof proves the point of just how efficient the VC can be. On my first syncro, I first tried to move the vehicle after I fixed the engine but had left out the rear axles. Sure enough, it moved fine |
I agree a VC is a great match for a Snow Syncro. That test will cause VC lockup, even if you only remove one rear axle, because the rear trasaxle output flange will be spinning.
Does your VC cause any tire binding when parking? iow, is it easier to park without the Propshaft installed?
| gears wrote: |
| Any binding between front & rear translates to additional Extreme Pressure on gear faces, especially R&P. Accelerated R&P wear is something I noticed straight away with the first Syncro transaxles I worked on. |
Does a coupled aggressive VC cause more Accelerated R&P wear, compared to decoupled?
Do all VCs cause some degree of tire binding when parking?
If binding IS happening, then isnt the VC transmitting power even before wheelspin causes VC lockup?
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IdahoDoug
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Joined: June 12, 2010
Posts: 10248
Location: N. Idaho
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| Posted: Thu Nov 27, 2014 9:06 pm Post subject: |
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Jon, not familiar w varying lbs.? Just fluid viscosity changes?
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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 |
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IdahoDoug
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Joined: June 12, 2010
Posts: 10248
Location: N. Idaho
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| Posted: Thu Nov 27, 2014 9:16 pm Post subject: |
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Parking binding comes from diff f/r axle speeds causing the coupling to lock up but tires need diff rotational speed. W pavement under them nothing slips so axles literally twist. Front tires r trying to slow/drag rears are pushing. Very bad cause ring gear getting pressure on the back side in front diff. Not where you want stress on pricy front Syncro bits...
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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 |
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alaskadan
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Joined: January 09, 2013
Posts: 1857
Location: anchor pt. alaska
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| Posted: Fri Nov 28, 2014 9:02 am Post subject: |
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| So now im wondering how stiff of a vc ive got. Havent done the 2x4 trick. About a month ago i did whole front end bushing job. While front end was up on jack stands i noticed that if i turned one of the front wheels the other turned backwards as one would expect from an open diff. But really felt no drag from vc and no movement at driveline. Would that indicate a non agressive vc? I know there is awd happening when i spin the rear. Or was last time i was in a situation when pushed. No snow here yet to go and try to break the ass end loose. |
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IdahoDoug
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Joined: June 12, 2010
Posts: 10248
Location: N. Idaho
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| Posted: Fri Nov 28, 2014 10:48 am Post subject: |
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Normal to feel no VC w both in the air. You r only actuating the front diff. Drop one front down and now if you try to spin one front in air you will feel your vc power! At that point, you'd be trying to spin the rear wheels with your front tire in the air. Since they're not moving, you would be feeling the stiffness of the VC and you'd be astonished at how hard it is to move that baby. The VC is non directional AFAIK, so it would attempt to transfer torque to the rear with the exact same qualities as when it is in normal use transfering torque to the front.
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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 |
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WLD*WSTY
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Joined: November 04, 2009
Posts: 438
Location: Arizona
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| Posted: Fri Nov 28, 2014 8:38 pm Post subject: |
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| Jon_slider wrote: |
| The VC generally does not transfer much power to the front diff unless the rear wheels spin, so a VC equipped Syncro is most of the time acting like a decoupled solid shaft equipped Syncro. |
After having driven my Syncro for twelve years in the Wasatch, I can tell you that that statement was not true for my van. That's why I always preferred driving the Syncro in winter rather than my company Ford fwd truck with weight in the box. The Syncro was sure-footed on the same snowy streets that the 2wd Ford was nearly uncontrollable at any but the slowest speeds. Put the Ford in 4wd and the next curve on bare pavement required going back to 2wd! The Syncro just drove on, totally unfazed.
| Quote: |
imo a solid shaft can work in snow, IF the operator is selective and actively participates in decoupling on solid pavement, and in hairpin turns and driveways…
Basically the operator has to act like the VC, and only engage front diff in anticipation of when rear wheels would be spinning.
I would not couple a solid shaft at freeway speeds unless the snow was very soft and fresh. Otherwise if the snow is firm, the van will skate more when coupled. |
And there it is... 
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'82 SyncroWesty, the first ever conversion.'06 Subaru 2.5L |
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IdahoDoug
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Joined: June 12, 2010
Posts: 10248
Location: N. Idaho
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| Posted: Fri Nov 28, 2014 11:33 pm Post subject: |
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WldWsty,
I don't know what would be different about your VC in your Syncro, but that statement is true. To wit: There is no torque transfer to the front wheels without rear wheel spin. Yes, compared to your company truck the curves on bare pavement are handled just fine - a huge advantage to the Syncro. But that does not make the statement untrue.
FYI - a part time 4WD truck as you describe is exactly like a Syncro with a solid shaft. Engage the truck's 4WD system and now the front and rear axles are locked together and create fighting of the axles on curves. Engage the Syncro's solid shaft (no VC) and its front and rear axles are locked together and fighting on curves.
I agree the Syncro factory system is superior to a part time 4wd system due to that issue alone. It was a great call by VW engineers.
_________________
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 |
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WestyBob
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Joined: June 11, 2004
Posts: 2346
Location: Portland, Oregon
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| Posted: Sat Nov 29, 2014 1:24 am Post subject: |
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| IdahoDoug wrote: |
| To wit: There is no torque transfer to the front wheels without rear wheel spin |
Sorry Doug but we'll have to agree to disagree on this one.
Nearly twenty years ago I sat in an evening cafe with a bunch of other syncro owners talking about this point over too many beers and one produced a document from VW of Germany stating about 3% of torque was always transferred to the front (when coupled) even traveling at higher speeds in a straight line on dry pavement. The 'about' part, according to the document, allows for the variance between VC's.
Since then I've had innumerable similar discussions with other syncro owners, especially the more experienced, with opinioned numbers ranging from that 3% up to the highest heard, 10%.
I don't have the scientific documents to prove anything (yet) but I personally know that three of my syncros with decouplers and perfectly working VC's definitely have a slight but noticable pulling front end 'feel' when coupled as opposed to uncoupled (straight line, dry pavement) along with my earlier statement about crosswind stability assistance. I really don't think it's a placebo effect at all.
I think there are other dynamics at work. I suspect you're thinking in more clinical, lab test type terms as to how can the VC be in operation if the rear wheels aren't spinning (say, in place) and I get that -- it's somewhat mysterious.
But another way to say it is I suspect there are missing details in that lab formula that are allowing some torque transfer to the front at all times when coupled, varying between syncros and dry road circumstance. I've always considered it a minor 'residual' torque transfer related to the properties of the viscuous material itself which can vary from VC to VC and with age and usage as well.
Just my opinion ... |
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4x4BNB
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Joined: January 08, 2012
Posts: 274
Location: PNW
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| Posted: Sat Nov 29, 2014 7:34 am Post subject: |
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| IdahoDoug wrote: |
FYI - a part time 4WD truck as you describe is exactly like a Syncro with a solid shaft. Engage the truck's 4WD system and now the front and rear axles are locked together and create fighting of the axles on curves. Engage the Syncro's solid shaft (no VC) and its front and rear axles are locked together and fighting on curves. |
Maybe I'm missing something here...I have a three knobs with a solid shaft. If I engage the 4wd and DO NOT lock either the rear or the front...are you saying that I am now completely locked, front to back, and have so slippage? |
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T3 Pilot
Samba Member
Joined: January 10, 2011
Posts: 1507
Location: Deep South of the Great White North
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| Posted: Sat Nov 29, 2014 8:06 am Post subject: |
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That is correct. Solid is solid.
Here is a detailed SAE research paper on the relative merits of the viscous coupling. If Sheldon cooper of "Big Bang Theory" could drive and owned a syncro he could probably find fault in the research, but for me it is my go to reference document for all VC discussions.
Read this and may the force be with you..........
https://shufti.files.wordpress.com/2009/12/vc.pdf
(Hat tip to Syncro owner Alistair for keeping this bookmarked....)
Have fun.
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1988 Vanagon
The most important part in every vehicle is the nut behind the wheel...... |
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4x4BNB
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Joined: January 08, 2012
Posts: 274
Location: PNW
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| Posted: Sat Nov 29, 2014 8:26 am Post subject: |
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So why have the front and rear locker knobs if they are all locked (engaged) simply by engaging 4wd???
There's got to be some some slippage or protection from binding? |
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syncrodoka
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Joined: December 27, 2005
Posts: 12005
Location: Santa Cruz, CA
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| Posted: Sat Nov 29, 2014 8:59 am Post subject: |
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| 4x4BNB wrote: |
So why have the front and rear locker knobs if they are all locked (engaged) simply by engaging 4wd???
There's got to be some some slippage or protection from binding? |
The front and rear locker knobs only lock those axles differential unit from functioning and they act more like a posi axle. When there is a turn in the road and the differential is locked there is no speed difference in the inner or outer tire and there is binding or slippage depending on the driving surface.
The center knob only engages/disengages the driveshaft connecting the rear to the front diff that can have either have a VC or solid shaft as a replacement. When the diffs aren't locked there can be a speed difference of the inner and outer tire but power is transferred through the driveshaft. If there is a VC in place then drive on without issues, if there is a solid shaft in place then driver beware.
Solid shafts shine offroad and nowhere else. |
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WestyBob
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Joined: June 11, 2004
Posts: 2346
Location: Portland, Oregon
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| Posted: Sat Nov 29, 2014 9:23 am Post subject: |
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| syncrodoka wrote: |
| Solid shafts shine offroad and nowhere else. |
X2 |
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4x4BNB
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Joined: January 08, 2012
Posts: 274
Location: PNW
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| Posted: Sat Nov 29, 2014 9:27 am Post subject: |
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| syncrodoka wrote: |
| 4x4BNB wrote: |
So why have the front and rear locker knobs if they are all locked (engaged) simply by engaging 4wd???
There's got to be some some slippage or protection from binding? |
The front and rear locker knobs only lock those axles differential unit from functioning and they act more like a posi axle. When there is a turn in the road and the differential is locked there is no speed difference in the inner or outer tire and there is binding or slippage depending on the driving surface.
The center knob only engages/disengages the driveshaft connecting the rear to the front diff that can have either have a VC or solid shaft as a replacement. When the diffs aren't locked there can be a speed difference of the inner and outer tire but power is transferred through the driveshaft. If there is a VC in place then drive on without issues, if there is a solid shaft in place then driver beware.
Solid shafts shine offroad and nowhere else. |
Ok. I think I'm getting it... There's still some slippage (play) even with the solid shaft engaged? |
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IdahoDoug
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Joined: June 12, 2010
Posts: 10248
Location: N. Idaho
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| Posted: Sat Nov 29, 2014 10:40 am Post subject: |
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4x4,
Nope, no slippage through a locked center axle shaft with a solid coupling that has no VC. I will call your decoupled shaft from front to rear the center axle on your Syncro because that is what it is - an axle transmitting power from rear to front.
So here's a quick education what happens on curves to all axle shafts. Imagine you pull up to a large parking lot with a fresh inch of snow. Now you drive in a counterclockwise circle until your tracks meet again and stop. You will actually see 4 circles. Each of these circles has a different diameter, which also means each tire actually traveled a different distance (or circumference). That's the root of the whole discussion.
So when you are driving on that circle, the inner (left side) tires don't travel as far as the outer ones. Unlocked differentials handle that beautifully - allowing the left and right tires to travel at different speeds on curves.
Back to our snowy parking lot. You will also notice that the front tires circles are larger than the rear tires circles. So, the front axle will have turned more times than the rear axle will. If you are in 2WD, that's fine because there is no solid connection from front to rear. But if you pull your center knob and lock the front and rear axles together with a locked center axle, those tracks in the snow will have a jagged component as the tires alternately roll, and slip in little jagged movements.
Translated to driving on the road, if you lock your center decoupler and there is now a solid shaft between the front and rear axles, there is no ability for the front and rear axles to turn different distances on a curve. So something must slip, and that something is the tires which slip constantly as you drive through a curve. Try sharp turns such as turning into a parking spot and you will feel the powerful binding and slipping of the front and rear tires fighting. You are forcing the front tires describing a large circle to turn the same number of times as the tires on the rear axle which are describing a smaller circle.
If you then lock the front and rear axles, you are adding even more stress to the equation as now even individual tires on each axle are fighting each other in addition to the front and rear fight.
So, no - with the center knob engaging only 4WD on your particular Syncro, you have not locked up anything in the front or rear axles, but have locked up what would be considered a center axle and will get binding.
Informationally, generally the front will fail because during a turn the front CVs are "bent" and experiencing more stress than the rears.
DougM
_________________
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 |
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gears
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Joined: October 28, 2002
Posts: 4391
Location: Tamarack, Bend, Kailua
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| Posted: Sat Nov 29, 2014 10:56 am Post subject: |
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The center knob locks front to rear. With straight shaft, this would be the same as with any 4WD vehicle. At this point, you are "in 4WD without diff locks engaged". True 4WD? .. no, not quite, because there is still the possibility of wheel slippage side-to-side (differential action).
The other knobs lock side-to-side by locking each diff fully. This eliminates any possibility of independent tire slippage .. the reason why usage is for special circumstances only (to avoid breaking an axle).
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9.36 @ 146 in '86 Hot & Sticky
'90 Syncro Westy SVX
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4x4BNB
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Joined: January 08, 2012
Posts: 274
Location: PNW
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| Posted: Sat Nov 29, 2014 11:01 am Post subject: |
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| Thank you for that explanation |
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IdahoDoug
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Joined: June 12, 2010
Posts: 10248
Location: N. Idaho
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| Posted: Sat Nov 29, 2014 11:36 am Post subject: |
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4X4,
Congrats on your 200th post!!
_________________
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 |
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Jon_slider
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Joined: April 11, 2007
Posts: 5091
Location: Santa Cruz, Crowdifornia
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| Posted: Sat Nov 29, 2014 1:19 pm Post subject: |
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| WLD*WSTY wrote: |
| Jon_slider wrote: |
| The VC generally does not transfer much power to the front diff unless the rear wheels spin |
After having driven my Syncro for twelve years in the Wasatch, I can tell you that that statement was not true for my van. That's why I always preferred driving the Syncro in winter rather than my company Ford fwd truck with weight in the box. The Syncro was sure-footed on the same snowy streets that the 2wd Ford was nearly uncontrollable |
I have changed my opinion. I no longer believe a VC is disengaged before wheelspin.
I agree there is power to the front wheels before wheel spin. You are not the only person to experience the shure footedness of a syncro compared to 2wd. Even in straight line travel with no wheel spin.
At this point my opinion is a VC is always transmitting power, even without wheel spin. IMO, if steering produces enough tire binding to defeat the torque preload of a VC, then a VC decouples in turns on pavement.
Here is my opinion of the VC operation.
1. A VC has air in it, plus fluid.
2. When front and rear plates rotate out of sync, the fluid churns the air into a silicone milkshake that heats up.
3. The hot air expands, raising internal pressure. this is incorrect, but illustrates the concept of pressure increase that actually comes from the silicone expanding. see
for a more accurate explanation of silicone expansion, humping, and plate pairing due to sausages of dense silicone forcing alternating plate pairs together)
4. Increasing pressure acts like a viscosity modifyer to the silicone fluid, which then resists allowing the front and rear plates in the VC from slipping past each other, and promotes them syncronizing, and transferring power like a solid shaft, when there is rear wheel spin. (again oversimplified but illustrative)
5. When there is no wheel spin there is still some preload pressure inside the VC, that transfers power unless resistance at the wheels overcomes the viscosity of that pressure.
This model explains why VCs seems to transfer power without wheelspin, it explains why VCs are set up to varying torque preloads, and covers the wheel spin activation of additional hardening.
Just my opinions. And yes, I agree a VC is highly recommended for a snow based syncro. Solid shaft is better for sand and offroad, due to consistent 50/50 front rear power distribution. But a solid shaft has none of the automatic features of a VC.
Here is a post that makes a very strong argument in favor of non aggressive VCs, with NO decoupler.
http://forum.club8090.co.uk/viewtopic.php?f=4&t=118775
Since I currently have no plans to go up Truck Hill again, I think its time to remove my Syncro's solid shaft and put the VC back in, and prepare to go skiing!
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My Soapboxes: Inflation; Handling; Gearing; Decoupling; Swepco
Last edited by Jon_slider on Sat Nov 29, 2014 3:19 pm; edited 4 times in total |
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insyncro
Banned
Joined: March 07, 2002
Posts: 15086
Location: New York
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| Posted: Sat Nov 29, 2014 1:30 pm Post subject: |
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| Jon_slider wrote: |
I have changed my opinion. I no longer believe a VC is disengaged before wheelspin.
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Welcome to reality  |
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