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Syncro Chat: VC's, solid shafts, decouplers, AWD/4WD, etc.
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soap0007
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PostPosted: Tue Nov 25, 2014 10:10 pm    Post subject: Syncro Chat: VC's, solid shafts, decouplers, AWD/4WD, etc. Reply with quote

looking for someone that has a solid shaft syncro with a decoupler that drives it on the highway in winter driving conditions wondering how well it works or doesnt thx



Moderator edits:
1) Title changed to reflect the course of discussion since it is no longer winter driving-specific.

2) Additional discussion about VC's, 4WD/AWD can be found here:
http://www.thesamba.com/vw/forum/viewtopic.php?t=624135 .

3) Winter driving tips & tricks posts have been split off into their own thread: http://www.thesamba.com/vw/forum/viewtopic.php?t=624647 .
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PostPosted: Tue Nov 25, 2014 10:20 pm    Post subject: Re: syncro winter highway driving Reply with quote

soap0007 wrote:
looking for someone that has a solid shaft syncro with a decoupler that drives it on the highway in winter driving conditions wondering how well it works or doesnt thx


I do, and I've run it with Nokian Hakkapeliita CS, BFG AT/TA and Nokian WRC Van tires. No complaints. I've never been stuck in the snow anywhere with any of those combinations.

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PostPosted: Tue Nov 25, 2014 10:29 pm    Post subject: Re: syncro winter highway driving Reply with quote

I do by default. My VC locked solid years ago. I mean really solid.
The Syncro ends up having the exact feel as a old 4x4 truck, or old jeep. Kind of slows down around bends, becasue of front to back axles binding.
Not complains.


soap0007 wrote:
looking for someone that has a solid shaft syncro with a decoupler that drives it on the highway in winter driving conditions wondering how well it works or doesnt thx
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soap0007
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PostPosted: Tue Nov 25, 2014 10:42 pm    Post subject: syncro solid shaft Reply with quote

sweet thanks for the info wanted to know before i install the solid shaft ive read that there not good on the road but most of the people saying that live where they dont drive in snow conditions
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PostPosted: Wed Nov 26, 2014 12:59 am    Post subject: Reply with quote

Soap,

Your question is not unique to Vanagons, and I'm surprised by the comments that the vehicle runs fine on snowy roads with essentially a locked center differential (locked VC or solid shaft with decoupler coupled).

I have two vehicles with locking center diffs that when engaged allow me to compare how they behave on snowy conditions versus unlocked. No way would I say they are fine on snowy roads. On a snowy curve, they are completely unstable and I have to drive SLOWER than if unlocked. At any kind of speed, you are definitely running wide and the vehicle changes attitude constantly as you run on and off road surfaces with more traction, less traction and bare spots. By contrast, when unlocked these same curves at the same speeds are uneventful.

This is simply because the front axles on a curve are describing longer arcs on average than the rears, so there MUST be a speed differential between the front and rear differentials. Lock them, and you have two tires always slipping as one end or the other loses the battle vs the other axle. This is simple geometry.

When you are turning sharper slow speed corners such as when entering a parking lot, or turning at an intersection the slippage is far worse, simply because the % of slippage is much higher the sharper the turn. Under come conditions, you will be turning a corner and suddenly find your turning circle is MUCH larger and you may slide into traffic in the other lane. I don't recommend a solid shaft for operating a Syncro in 4WD on snowy roads. Trails, sure. But there are huge compromises on the road to your safety.

That is my experience using Michelin Arctic Alpin 4X4s, siped Dunlop Radial Rover RVs with studs, siped Safari DTRs with studs, and Michelin X-Ice tires. There is no way to avoid or counter that slippage - it is due to geometry of the various tires paths on a curve.

When someone simply says "It's fine" I have to wonder what their personal definition is.
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PostPosted: Wed Nov 26, 2014 1:45 am    Post subject: Reply with quote

IdahoDoug wrote:
I have two vehicles with locking center diffs that when engaged allow me to compare how they behave on snowy conditions versus unlocked. No way would I say they are fine on snowy roads. On a snowy curve, they are completely unstable and I have to drive SLOWER than if unlocked. At any kind of speed, you are definitely running wide and the vehicle changes attitude constantly as you run on and off road surfaces with more traction, less traction and bare spots. By contrast, when unlocked these same curves at the same speeds are uneventful.


I agree that a solid shaft should only be coupled when the pavement is completely covered in snow and direction of travel is mostly straight.

Solid shaft imo should be decoupled on bare pavement unless going straight.

Generally speaking, on snow covered pavement, I decouple my solid shaft in turns, and especially when making tighter than say 45 degree turns. So I decouple pulling into a driveway or parking spot, even if the pavement is fully snow covered.

In patchy snow, I do not engage the front.

IdahoDoug wrote:
When you are turning sharper slow speed corners such as when entering a parking lot, or turning at an intersection the slippage is far worse, simply because the % of slippage is much higher the sharper the turn.


agreed.

A solid shaft requires an intelligent operator, that actively engages the front diff only in conditions where wheel slippage is possible, and disengages in conditions that cause the drivetrain to bind because the wheels cannot slip.

A VC is able to slip in a turn, and a VC can also slip when tires are on solid traction surface. 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.

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.
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PostPosted: Wed Nov 26, 2014 5:46 am    Post subject: Reply with quote

i drive engaged solid shaft 90 percent once snow falls. if the highways been plowed real good with no black ice or wind kickup ill turn it off.
its supposed to be seamless so i cant tell the difference on or off on the highway= because it is seamless Very Happy . but i am glad i have it on black ice patches and wind blowing with 20 temps going 55...so give it a pull.
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PostPosted: Wed Nov 26, 2014 7:29 am    Post subject: Reply with quote

If you live in an area that has winter condition driving a lot an agressive VC or sport VC would be more desire able.
Off road in sand is where a solid shaft shines.
A VC is still nice to have because it keeps a little "give" in the drivetrain and less stress on the tranny.

If you off-road a lot the solid shaft might be your ticket. If you are on pavement most of the time then stay with a VC. Pulling the center knob in crosswinds on slick surfaces makes you feel all giddy inside. All wheel drive for winter driving. 4 wheel drive for off road. Wink
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PostPosted: Wed Nov 26, 2014 7:33 am    Post subject: Reply with quote

Dont let responses compare a locking front diff with being able to decouple an open diff from the rear. A locking diff is no good on snow or ice when locked. An open front diff with a solid shaft is the same a regular 4x4. As jon slider stated you have to be an aware driver and know when to use 4 wheel drive. I have a chevy k5 with detroit lockers front and back. When i have to drive it in snow im very carefull. Touch the gas and they lock.
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PostPosted: Wed Nov 26, 2014 8:59 am    Post subject: Reply with quote

I've driven old-school (read: locked center) 4wd a lot on mixed snowy highways that patchwork from snow to pavement. The biggest difference in handling is that a locked center will understeer a bit more than a VC center because of the slipping issue (which shouldn't be as big on the short wheel base van as the long wheel base trucks I'm thinking of).

If you hit backwoods snowy roads where you're really fighting for traction, solid shaft is the way to go. If your cruising highways where seamless operation and dynamic stability are key, VC. If you want the best of everything for winter, aggressive VC with decoupler.
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PostPosted: Wed Nov 26, 2014 9:37 am    Post subject: Reply with quote

I drove a 2nd in Fairbanks, Alaska for three years.

Rule #1: Ice is ice and 4 wheel drive won't make a difference.
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PostPosted: Wed Nov 26, 2014 10:30 am    Post subject: Reply with quote

Corwyn wrote:
I drove a 2nd in Fairbanks, Alaska for three years.

Rule #1: Ice is ice and 4 wheel drive won't make a difference.


Corwyn, I assume you mean 2WD ..

Driving in Alaska for 3 years definitely makes you more experienced than I, however .. last snow season when I got stuck down a small rise with a balky decoupler on a black ice day, coaxing the system into AWD was the ONLY way I got out of a tight situation. The difference was immediate, and it was night & day.
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PostPosted: Wed Nov 26, 2014 12:02 pm    Post subject: Reply with quote

Jon Slider sez:

"Basically the operator has to act like the VC, and only engage front diff in anticipation of when rear wheels would be spinning. "

This is perhaps the most accurate way to frame the issue of using a locked center device (either a decoupler or a locked center diff) on public roads. When traction is extremely poor, and your 4 tire contact patches are barely able to generate enough friction with the ground to accelerate or brake your Vanagon, the last thing they need is to be fighting each other. And yet when you lock them to each other, that is what happens unless you are driving perfectly straight ahead. Perfectly straight. Any deviation from perfectly straight and you are causing tension between the front and rear contact patches that ranges from mere mild pressure on a very gentle interstate curve, to easily felt slippage on a country lane curve.

And you are doing this when the contact patches are already having trouble doing their job of providing traction for steering, braking and accelerating.

So, understand that you are not helping the Van get around safely. The proper time on the road to use a locking feature (or decoupler) is when conditions are so bad you need the feature to accelerate from rest in deep snow or on slick ice or polished snow. But understand you are now generating speed that may be inappropriate to the available traction for braking, or steering. I get it that we are all engaged and sporty involved owners of unique vehicles and its fun to tromp on the gas and fishtail, etc. And I accept that.

And if you posit that on a snowy curvy lane where applying the gas in 2WD causes the rear tires to slip out, so you're going to engage the decoupler, then I say you are now possibly making a bad judgement call. You are adding to your acceleration abilities, while reducing your cornering abilities (because while locked the contact patches are now fighting on curves).

I get it that there are few things more fun that having the vehicle at the limit of adhesion and horsing around. But consider that for safe travel on the slippery road with a decoupler you may be better off in an overall sense to be unlocked.

It is also worth noting that if you are locked on a curve and lose control only slightly with the rear coming around, now you are definitely worse off than if you were in 2WD. Because you are essentially suddenly turning sharply like you would be in a snowy lot trying to park (which everyone acknowledges is the worst), but you have perhaps 35mph of vehicle momentum to deal with while fighting for control.

I'm sure that many will disagree, but if you do then you need to explain how you are on a curve and your contact patches are not fighting each other.

I have owned a few Audis over the years. My current one has a locking rear differential. The feature automatically unlocks at about 12mph in recognition of exactly the issues I am raising. A locked diff is at its best getting you going in deep snow or on ice. But it is at its worst when you are moving well down the road and now need to deal with curves. I'm sure that VW engineers went through exactly this reasoning when they opted for the viscous coupling. I personally went through this same reasoning at GM while working on the AWD VC system that eventually was used on the Pontiac 6000 STE AWD model. We did exhaustive research on artificial ice, took high speed photos of tire contact patches from under the road, etc.

So, don't be uninformed about the downside of locked devices on the road. On the trail - absolutely the best. And for fun on the road - the best. I am one of those who also finds an empty snowy road, locks up and does my best rally driver imitation with a huge grin on my face (and often a sprained thumb from frantically whirling the steering wheel from lock to lock). But know the limitations of these devices well for actual travel on public roads where the goal is safe travel.
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PostPosted: Wed Nov 26, 2014 12:06 pm    Post subject: Reply with quote

We had a little snow in Denver the other day. I had some fun sliding the Reimo around in two wheel drive. Little 1600jx putting the van sideways was ridiculous fun but also concerning. It went sidways easily. It is a handful drifting a diesel hightop with manual steering. The steering wheel is huge. I do not want to be driving mountain passes and slide unsuspectingly. I like fulltime 4wd with a VC. I have no desire to be clicking in and out of 4wd. The Reimo Syncro has front and rear lockers and the decoupler. I hope I have the VC and not a straight shaft? I need to lock in 4wd and test it. I don't think it is a straight shaft. I have not felt it binding, but I have not tested it either. I've only engaged 4wd in the dirt. If anybody is going straight shaft and dumping the VC, I would like to check out the rebuild process of a VC. Please PM me I would like the core VC. As far as front Diff lock, look out. No power steering and a locked front diff is a workout. I could never imagine locking in on the road, snowy or not.
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PostPosted: Wed Nov 26, 2014 1:14 pm    Post subject: Reply with quote

In snow,
Controlled progressive locking of a TBD (like Peloquin) is desirable.
Aggressive locking of LSD is borderline controllable.
Fully locked diff is suicidal .. only good for getting unstuck (very temporary, slow speed use).

(Straying a bit from the VC / decoupler discussion)
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PostPosted: Wed Nov 26, 2014 1:30 pm    Post subject: Reply with quote

Makes me glad I don't have a Syncro. If the roads are bad I either drive the Jetta with studded Hancooks or let my friends drive me around in their pickups or Subarus. Laughing
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PostPosted: Wed Nov 26, 2014 1:35 pm    Post subject: Reply with quote

I drive 50 miles to NYC daily. I have a 4wd Nissan p/u with manual hubs & open diffs. I usually keep it in 2wd most of the time as I get more road feedback (IE tire spinning). Most people drive way too fast in their AWD SUV's & end up in the ditch. My biggest concern is stopping, not going. 4wd does help with that with downshifting if you keep power inputs smooth, but the extra drag on the front can make the back loose on icy corners & going down icy hills.

Anyway, I find my FWD Jetta TDI to be much more predictable & forgiving in most snow & any type of ice. I do have very good tires tho - Blizzack's. I usually only drive my truck if the roads are not plowed. Note, my truck also has good tires: BFG T/A KO. 30x9.5x15

I've yet to drive my Syncro, but I plan on keeping the VC for a while instead of a solid shaft + decoupler for the smooth transitions mentioned above

I will keep my Syncro 3-knob plan for later when I end up in Mexico Cool
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PostPosted: Wed Nov 26, 2014 2:44 pm    Post subject: Reply with quote

Exploring the Mystery of VC engagement
Im no expert, just a driver. Some variables to explore
1. in straight line travel on pavement a coupled solid shaft sends equal power to the front and rear differentials.
2. In straight line travel on pavement a coupled Viscous Coupling sends less power to the front diff than the rear diff, because the VC does not lock up unless rear wheel spins.
3. A VC is always partially engaged, sending for sake of example, about 10% power to the front diff, but in a turn, the VC can slip if there is resistance, such as when making tight turns.
4. Aggressive VCs send a higher percentage of power to the front diff in normal operation on pavement, without rear wheel spin. This means in a turn there is more pressure built up in the drivetrain with a coupled VC, than decoupled
5. A VC will lock up when the rear wheels start to spin. Spin normally does not happen on dry pavement.
6. In snow, if the rear wheels spin, the VC engages solidly, only while rear spin continues. When spin stops, the VC cools and disengages. That is why in sand, the rear of the van runs lower than the front, with a VC. Whereas in sand, a solid shaft allows the front and rear wheels to run at the same depth. I agree a solid shaft has an advantage in Sand. Imo a solid shaft also has an advantage over a VC in Snow, because a solid shaft is fully engaging the front diff when coupled, whereas a VC is intermittent, and rarely actually locks up.

Syncro Jael wrote:
A VC is still nice to have because it keeps a little "give" in the drivetrain and less stress on the tranny.

agreed, but mainly because the VC is mostly operating disengaged (almost equivalent to decoupled)

Syncro Jael wrote:
Pulling the center knob in crosswinds on slick surfaces

Coupling a VC in crosswind on slick surfaces, how much power is being transferred to the front diff? I would say maybe 10%. Im suggesting coupling a VC has placebo effect Smile, its not really acting like a coupled solid shaft.

Syncro Jael wrote:
All wheel drive for winter driving. 4 wheel drive for off road. 

All wheel drive is not actually what a Syncro with VC has. imo, its actually rear wheel drive with a slipping VC, that only engages the front if the rear spins. With the added variable that a VC is always semi solid, to say 5-10%. This can be verified by turning into a parking space with coupled VC. The front wheels of a VC equipped syncro will bind slightly, slowing the van down, unless the VC is decoupled.

4 Wheel drive, technically, only happens when all 3 knobs are pulled on a syncro with solid shaft. If the front and rear lockers are open, disengaged, a Solid shaft equipped syncro, when coupled, will send power to one rear and one front wheel. Whereas a VC equipped syncro will mostly only send power to one rear wheel, until it spins, at which point power will temporarily be increased to the front diff.

flomulgator wrote:
a locked [Coupled actually] center [with Solid Shaft in the front diff] will understeer a bit more than a (coupled) VC

agreed (but I use the term coupled instead of Locked, when speaking of engaging the center traction control knob on a syncro.

this difference could be caused by a solid shaft that is fully engaged compared to a VC that is not locking up, except for that marginal 5-10%

alaskadan wrote:
A locking diff is no good on snow or ice when locked

I agree, except when starting from a full stop on slippery surface. Locking differentials at front and rear is reserved for crossing holes offroad. In sand, I find open diffs dig me down less, especially when turning. In Snow, locking the differentials, except when starting from a full stop on slick surface, is not a good idea

In fact, I prefer how a Syncro handles decoupled, over coupled to a VC, when driving curves on dry pavement. I find rear wheel drive is more consistent at holding a line with fewer steering and throttle adjustments, than when coupled to a VC. So overall, I do not consider a Syncro an All Wheel drive vehicle. My Subaru, yes, is All Wheel drive, but not a Syncro, even with a VC coupled.

IdahoDoug wrote:
But consider that for safe travel on the slippery road with a decoupler you may be better off in an overall sense to be unlocked [decoupled]… if you are locked [coupled] on a curve and lose control only slightly with the rear coming around, now you are definitely worse off than if you were in 2WD.

I agree, though I prefer the term decoupled to unlocked, when speaking of a center diff on a syncro.

IdahoDoug wrote:
A locked [front or rear] diff is at its best getting you going in deep snow or on ice. But it is at its worst when you are moving well down the road and now need to deal with curves.

completely agree

IdahoDoug wrote:
I'm sure that VW engineers went through exactly this reasoning when they opted for the viscous coupling.

caution combining comments about locking front or rear diff, not to be confused with coupling the VC

IdahoDoug wrote:
know the limitations of these devices well for actual travel on public roads where the goal is safe travel.

agree completely
locking diffs when underway on road, is not helpful or safer. Open diff is safer. Coupled solid shaft when underway on road is helpful IF the road surface allows one of the front wheels to slip, for reasons iDoug explained so clearly, relating to differences in front wheel rotation speeds in a turn.

BavarianWrench wrote:
The Reimo Syncro has front and rear lockers and the decoupler. I hope I have the VC and not a straight shaft?

I suspect you have a solid shaft, because Ive seen a number of European vans with front and rear locker, and NO center knob. IF someone went to the trouble to add a decoupler, it seems highly likely that the front diff does not have a normal VC. It either has an aggressive VC, or a solid shaft.

You can probably determine which configuration is in your front diff, by doing the 2x4 test. Set a 2x4 in front of the front tires. Jack up one rear wheel on a rolling floor jack. Make sure the rear diff is NOT locked. A Normal VC will not pull you over the 2x4 until you give throttle, and generate rear wheel spin. Whereas a solid shaft should crawl over the 2x4 at idle, since power is already being delivered to the front diff, even without rear wheel spin. An aggressive VC will likely act more like the solid shaft, it should transfer power to the front at lower rpm, and with less wheel spin, than a Normal VC.

You can also get a sense of how much a VC is engaged under normal dry pavement operation, by observing how tight a circle you can make, without the Van drivetrain binding. A Solid Shaft will bind at a lesser amount of turning than a VC. For sake of illustration, lets say I can make a 90 degree turn into a parking space with a VC, with slight binding. With a coupled Solid Shaft, the van will probably stop due to drivetrain binding, before achieving a 90 degree change in direction, possibly closer to 45 degrees.. An aggressive VC will bind more than a normal VC, but maybe less than a solid shaft.

Regarding the VC, aggressive or normal, the lockup of the VC is based on a silicone fluid. IF a sudden shock load is applied to a VC, it can be forced to slip. This is protective of the drivetrain, moreso with a normal VC, than with an aggressive VC. A Solid Shaft otoh, has zero ability to slip, and is therefore the most likely to create binding in the drivetrain. That is why I am very quick to deco;e my solid shaft, even offroad, if the dirt is hardpack, when making tight turns.

I have witnessed CV Bill break a front outer CV, when making a tight turn on dirt, coupled solid shaft. He did the same thing in Moab, trying to turn around on slick rock with the front locked.

disclaimer, these are just my current thoughts, open to reconsider based on more info.

Great thread!
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PostPosted: Wed Nov 26, 2014 2:53 pm    Post subject: Reply with quote

Jon_slider wrote:


You can probably determine which configuration is in your front diff, by doing the 2x4 test. Set a 2x4 in front of the front tires. Jack up one rear wheel on a rolling floor jack. Make sure the rear diff is NOT locked. A Normal VC will not pull you over the 2x4 until you give throttle, and generate rear wheel spin. Whereas a solid shaft should crawl over the 2x4 at idle....



Thanks for the tip. I'm going to try that when I get it running
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PostPosted: Wed Nov 26, 2014 3:25 pm    Post subject: Reply with quote

I think my VC, which has become more aggressive in it's old age, will idle right over the 2x4. I prefer the stiffer VC. During summer months, I drive decoupled. In snow or rain, I'm coupled until pulling into a parking lot.
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