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Syncro Chat: VC's, solid shafts, decouplers, AWD/4WD, etc.
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snowsyncro
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PostPosted: Sat Apr 04, 2015 8:42 am    Post subject: Reply with quote

Waldi wrote:
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.


Agreed. The SAE paper did not say that, and neither am I. It is talking about torque progression, the point at which the torque transfer begins to increase from the 50 N-m static value. I am agreeing with you Waldi; there is around 50 N-m of static friction, when the difference between in and out is less than 5 RPM.

RonC
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Jon_slider
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PostPosted: Sat Apr 04, 2015 12:05 pm    Post subject: Reply with quote

IdahoDoug wrote:
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.


IdahoDoug wrote:
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.


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


snowsyncro wrote:
there is around 50 N-m of static friction, when the difference between in and out is less than 5 RPM.


so, this static friction would Not be happening when the front wheels are turning faster than the rear, correct?

Imo what we feel is the rear wheels braking dragging, not the front wheels pulling. The front wheels cant Make power, they can only receive it from the rear, and only if the Rear turns Faster, which Never happens on dry pavement.

Steering makes the VC plates slip, which creates a braking force afaict, not traction..

I can agree there is 50nM of front wheel Traction when a Syncro firsts starts moving forward from a stop in a straight line on Slippery Surfaces.

However, on dry pavement, with no wheel spin, that 50nM is not traction at the front wheels, because the rear wheels are pushing the van, and the front wheels are being turned by the ground.

So, a VC Syncro STILL does not have front wheel TRACTION, it is NOT All Wheel Drive, on dry pavement, there is no power splitting center differential.. The VC does appear to be very good at Braking the Van.

So, if you want a Braking advantage, couple your VC on dry pavement. But bear in mind that uses geartrain binding for braking. imo it is more economical to decouple, and save the transaxle from any binding, on dry pavement.

A VC does not provide Traction on dry Pavement, Never Ever, it only provides Drag. About 55nM of "residual" or "stiction", Braking Torque for a Sport VC.

moral of the story:
Save Your Tranny! Decouple your VC on Dry Pavement Smile

Happy Passover and Happy Easter!

Update also see http://www.thesamba.com/vw/forum/viewtopic.php?p=7620682#7620682
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Last edited by Jon_slider on Sun Apr 12, 2015 10:26 pm; edited 1 time in total
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IdahoDoug
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PostPosted: Sat Apr 04, 2015 1:28 pm    Post subject: Reply with quote

Jon_slider wrote:
so, this static friction would Not be happening when the front wheels are turning faster than the rear, correct?


>> Incorrect. It is happening, but the static friction is simply operating to slow the front wheels. The VC is bidirectional and generates friction in either direction when one set of plates wants to shear the fluid and move them relative to each other. The situation you describe (fronts moving faster than rears) happens on a curve, corner or anything besides perfectly straight ahead - even wandering within your lane on a straight road. So, the "static friction" a you call it DOES happen when the fronts are turning faster than the rear as in when you drive anything other than perfectly straight.

Quote:
Imo what we feel is the rear wheels braking dragging, not the front wheels pulling.


>> Correct. When driving on a typical curve or road, you are feeling the rear plates in the VC spinning at the slower speed of the rear wheels they are directly connected to. Which means the front plates are spinning at the higher speed required for the front tires to complete the larger diameter circle they describe on a curve. The resultant force is on the contact patches of the front tires, which the ground passing underneath must keep spinning faster despite the resistance of the VC wanting to slow them. Since there is plenty of traction available to accomplish this with the ground, there is no obvious outward sign of it, but the engine must in fact make more power to overcome it. An ordinary differential would not do this binding. It would continue to power both fr/rr axles and all four tire contact patches under driving torque.

Quote:
The front wheels cant Make power, they can only receive it from the rear, and only if the Rear turns Faster, which Never happens on dry pavement.


>>Correct.

Quote:
Steering makes the VC plates slip, which creates a braking force afaict, not traction..


>>Correct.

Quote:
I can agree there is 50nM of front wheel Traction when a Syncro firsts starts moving forward from a stop in a straight line on Slippery Surfaces.


>> No power goes to the front VC plates unless the rears are spinning faster. So if the surface is slippery enough to cause rear wheel spin, There is whatever amount of traction available to the front contact patches the surface will generate. It might be 50nM, it might be 85nM, but with the rear wheels spinning, the fronts will get power immediately. When rear wheelspin stops, the power immediately drops back to zero. It's a great device for quick reactions with no driver input.

Quote:
However, on dry pavement, with no wheel spin, that 50nM is not traction at the front wheels, because the rear wheels are pushing the van, and the front wheels are being turned by the ground.


>>Correct.

Quote:
So, a VC Syncro STILL does not have front wheel TRACTION, it is NOT All Wheel Drive, on dry pavement, there is no power splitting center differential.. The VC does appear to be very good at Braking the Van.


>>Correct. And the braking is always done on curves on the fronts only, so it can easily begin cupping the front tires if they are not properly rotated to spread the wear. Good advice on any car, but especially on vehicles with driven front axles.

Quote:
So, if you want a Braking advantage, couple your VC on dry pavement. But bear in mind that uses geartrain binding for braking. imo it is more economical to decouple, and save the transaxle from any binding, on dry pavement.


>>That braking advantage is only under lockup conditions. Negligible on dry pavement, helpful on slippery stuff sometimes. I say sometimes with the following caveat. If you are on slippery stuff on anything but perfectly straight line driving (which as noted is actually rare), the added braking of the fronts may be undesired. On low friction things like ice, the added braking effect of the VC on the fronts only may cause the fronts to break traction before the rears. Its not a panacea but can be helpful. More of a mixed bag. We found when we put a VC on each wheel that it was remarkably helpful on ice to avoid lockup. Then along came ABS.....

Quote:
A VC does not provide Traction on dry Pavement, Never Ever, it only provides Drag. About 55nM of "residual" or "stiction", Braking Torque for a Sport VC.


>>Correct. Never ever (heh).

Quote:
moral of the story:
Save Your Tranny! Decouple your VC on Dry Pavement Smile


>>Agree. It needlessly places pressure on the nondrive side of the gears in the front diff. Possibly the trans as well but I would have to think about that. Nope, thought about it - only the front diff and front CVs.
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hans j
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PostPosted: Sat Apr 04, 2015 2:01 pm    Post subject: Reply with quote

I had asked it before with no response, but how much mpg gain is realized using a decoupler? That should tell you how much the front tires are breaking the van due to the VC.

Happy zombie Jesus day!
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Birdcage
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PostPosted: Sat Apr 04, 2015 2:13 pm    Post subject: Reply with quote

hans j wrote:
I had asked it before with no response, but how much mpg gain is realized using a decoupler? That should tell you how much the front tires are breaking the van due to the VC.

Happy zombie Jesus day!


None seen here, I've kept tabs on mileage in the doka and the van. Comes out about even both cases and several tests done to confirm.

I suppose this is the reason you've gotten no response

I'm sure others will chime in and refute, only because they need to justify spent $$. It helps them sleep at night;)
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Kombi///M3
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PostPosted: Sat Apr 04, 2015 2:56 pm    Post subject: Reply with quote

Wow so much technical knowledge for winter driving question Very Happy
I'm new to Syncro, bought my 2nd vanagon for winter van (syncro).
In replacement of my audi avant, expecting 3rd child need all the space for snowboard trips and such Smile
Picked up 86 syncro with straight shaft and decoupler.. So I should be good then for winter driving..? I know can't make tight turns if engaged but slippery windy roads should be ok when coupled? I'm pretty experienced driver, just want to make sure the van will back me up in keeping the fam safe in case of snow storm and such. Btw I still have the VC, is it worth rebuilding?
Cheers,
Ogi

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IdahoDoug
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PostPosted: Sat Apr 04, 2015 3:57 pm    Post subject: Reply with quote

Negative on slippery roads with curves and solid shaft engaged. That forces two tires to slip at all times when on a curve. Way better off in winter with a VC on roads if that was your goal.

Think about it. Enter a curve with rear axle locked to front axle. Front axle must turn different number of rotations during the curve. A VC would allow for those different rotations albeit with some binding and resultant mild forced tire slippage. A solid shaft will create extreme binding and MUCH forced tire slippage. The tires are already having a hard enough time gripping the road and the shaft makes it worse.

The Quattro Avant is far more adept at winter road conditions.
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snowsyncro
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PostPosted: Sat Apr 04, 2015 4:32 pm    Post subject: Reply with quote

hans j wrote:
I had asked it before with no response, but how much mpg gain is realized using a decoupler? That should tell you how much the front tires are breaking the van due to the VC.

Happy zombie Jesus day!


Hans, there was a fellow in Australia that did a long-term test over several years and a lot if kilometres. There was no significant difference.

RonC
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Jon_slider
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PostPosted: Sat Apr 04, 2015 7:49 pm    Post subject: Reply with quote

Kombi///M3 wrote:
Picked up 86 syncro with straight shaft and decoupler.. ...Btw I still have the VC, is it worth rebuilding


if you mean is it worth putting the VC back in, Not in MY opinion.

You seem to be willing to make decisions about when to pull the knob and when not to. A VC does nothing until the rear wheels spin.

you can use a solid shaft to advantage when there is snow covered ground, which is the only time a VC is going to spin anyway

otoh, if the Van is to be driven by someone that does not understand 4wd, then a VC is better, since its automatic..

read this and know that I have a solid shaft, and like you I have a VC I could put back in. So far I prefer to decide myself when I want to pull the knob, I dont currently desire an automatic coupler that works only when the wheels are spinning.

I like to couple solid on snow covered pavement, I also sometimes couple in wind driven rain (not on dry pavement), following this GW Golden Rule:

http://www.gowesty.com/library_article.php?id=627
"Even on totally dry days I use mine. When driving my '87 Wolfsburg Syncro Westy weekender on the highway at 75 mph, and I hit a stiff cross wind, I just reach down and pull the middle knob, and viola! It settles the van right down. It is simply the best of both worlds. But, just like with the use of the factor rear locker (when so equipped), caution must be exercised when negotiating tight maneuvers on dry pavement to keep from breaking an axle, CV joint, or drive shaft U-joint since there is no longer a device (viscous coupler) that allows for slippage.

Basically, it comes down to common sense. I mean, why would anyone want to pull any of the knobs on dry pavement in a situation where you needed to perform tight maneuvers? But, then again, what constitutes a "tight maneuver"? The only thing you HAVE TO remember when driving a Syncro with solid shaft and decoupler in a high-traction (dry pavement) situation is:

WHEN IN 4WD, NEVER TURN THE STEERING WHEEL MORE THAN 1/4 TURN.

Just stick to that golden rule, and you can't go wrong.

GoWesty is so convinced that the decoupler is the ONLY way to go that we will not warranty our rebuilt Syncro transaxles UNLESS the customer has a decoupler, or agrees to add a decoupler at the time of install. We and many other shops learned this lesson the hard way: Warranty repairs over and over and over and over again on Syncro transaxles until, finally, the VC was replaced. And since a new VC costs about the same as our decoupler/solid shaft combo (which never wear out)... well, you get the picture—everyone goes with the solid shaft and decoupler. Furthermore, we will not sell a Syncro Vanagon without the decoupler. Period."
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Bassyaks
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PostPosted: Sat Apr 04, 2015 8:02 pm    Post subject: Reply with quote

If the rear axles are removed will the VC drive the front wheels, I'm trying to see if mine is working.
I'm leaning toward a de-coupler and a straight shaft.
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PostPosted: Sat Apr 04, 2015 8:17 pm    Post subject: Reply with quote

Thanks for the input Doug and Jon, Ya.. I've read the gowesty syncro article, no more than 1/4 turn sounds good. Just thinking of local ski road trip roads like Mt baker, whistler. I like the idea on pulling the knob when I have to and no interest on putting the VC back in service. Can't wait to unleash the "Goat"
Laughing
Cheers Very Happy
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PostPosted: Sat Apr 04, 2015 8:29 pm    Post subject: Reply with quote

Bassyaks wrote:
I'm trying to see if mine is working.


I sent you a private message yesterday about that.
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hans j
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PostPosted: Sat Apr 04, 2015 8:47 pm    Post subject: Reply with quote

Bassyaks wrote:
If the rear axles are removed will the VC drive the front wheels, I'm trying to see if mine is working.
I'm leaning toward a de-coupler and a straight shaft.


Yes. I had mine out recently and no discernible difference while driving around the shop parking lot.
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PostPosted: Sat Apr 04, 2015 9:37 pm    Post subject: Reply with quote

hans j wrote:
Yes. I had mine out recently and no discernible difference while driving around the shop parking lot.


It is important to do the complete 2x4 test to determine whether a decoupler should be used if the VC is too aggressive.

the test is described in the links Ive given Bassyaks privately, but here they are for anyone else trying to figure out how to test their VC

http://users.rcn.com/derekdrew/vanagon/viscous_couplings_vanagon_syncro.htm

http://syncro.org/?page_id=2133

if after reading this material someone is still not sure how to proceed, seek professional help, do not endanger yourself trying things that are not in the instructions.
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PostPosted: Sun Apr 05, 2015 1:00 am    Post subject: Reply with quote

hans j wrote:
I had asked it before with no response, but how much mpg gain is realized using a decoupler? That should tell you how much the front tires are breaking the van due to the VC.

Happy zombie Jesus day!


There is no gain with or without decoupler.
Decoupled, the rear wheels spin nearly all time which causes a bit of more consume.
Coupled the rear wheels spin less, but there is torque between front and rear.
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PostPosted: Sun Apr 05, 2015 1:18 am    Post subject: Reply with quote

Quote:


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..


In a turn both systems VC and solid shaft (it is the same) dont transafer torque form engine to front wheels as long as the front turn fanster than the rear. And because the front and rear is always coupled with min 50nm driving on snow curv road makes the tires loose traction.

Thats why i drive also at snow decoupled as long i dont realy need it.

A syncro with VC is more usable at maybe 99% of conditions than one with solid shaft.
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PostPosted: Sun Apr 05, 2015 9:04 am    Post subject: Reply with quote

Waldi wrote:
A syncro with VC is more usable at maybe 99% of conditions than one with solid shaft.


That's correct. The solid shaft was developed primarily for off-roading, especially the more extreme, where drivers wanted more instantaneous pull from the front wheels instead of the slight delay the VC offered. Beyond that the VC is more versatile.

The solid shaft is a less expensive option when the VC dies, and can be even preferable for those who rarely use their VC to begin with as in say 98% hard surface driving. But it requires some know-how when using it on hard surfaces for safety reasons and also to avoid shearing the rubber off the tire(s).

It goes without saying, as in clearly obvious, that a decoupler is preferable with both the VC and obviously the solid shaft, and I don't see any argument there. I have three that have decouplers and in fact most of the time I couple on occasion only to keep the decoupler operational rather than seizing from lack of use. Of course when off-roading or inclement conditions they see use.

As for stock syncros without a decoupler and all the 'scary' things that can purportedly happen as a result, I have a completely stock garage queen doka that I just took for a run up the mountains and through the dales a few days ago to eventually test whether or not the VC was still working (it is). It has nearly 50k original miles, all driven without a decoupler. The VC is still average (not particularly aggressive), the tranny still shifts like it is brand new, the CV's are all original, the drive shaft is still stock original (I have the slip-yoke type on the others), in essence the entire drive train is still tight as a drum and working like new. In fact it still has some now-scary (agewise) awesome looking NLA Dunlop tires with plenty of chunky tread that must be at least twenty years or older so I guess all that driving hasn't caused much rubber shearing from excessive drag or other forces. The point is no one needs to get too paranoid if they don't have a decoupler yet unless there are some obvious VC issues, but a decoupler is still preferable.

About 15 to 20 years ago there was something like a all Euro 4x4 challenge involving the usual suspects like Land Rover, Volvo, Mercedes, etc. and of course Vw with the syncro where they caravanned across the Sahara testing out the various four wheeling systems. The one vehicle that tended to get stuck the most was the Vw syncro. The assessment at that time was mostly (IIRC) the stock tires were too narrow for the dry loose and deep sands. To a lesser extent the slight delay of the VC torque transfer was also mentioned.

Both the VC and solid shaft systems can get stuck in mud and sand but it's a matter of degrees and circumstance. The biggest complaint about the VC is the rear wheels will dig in and sink before the front wheels can engage and kick in as opposed to the instantaneous response from a solid shaft (if the driver is on the ball). If a driver of a solid shaft rig is driving decoupled and allows the rear wheels to sink in deep before engaging the decoupler then they'll likely get as stuck as a rig with a VC.

Class is dismissed Wink
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Waldi
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PostPosted: Sun Apr 05, 2015 9:57 am    Post subject: Reply with quote

Jon_slider wrote:
Waldi wrote:
In a turn both systems VC and solid shaft (it is the same) dont transafer torque form engine to front wheels as long as the front turn fanster than the rear.

with solid, there can be NO faster front, only slip

the reason the VC does not transfer torque in a turn is that the VC slips, instead of the wheels with a solid.



And because the front and rear is always coupled with min 50nm driving on snow curv road makes the tires loose traction.

not coupled with a VC, the plates are slipping in a turn, with 50nM of DRAG

Thats why i drive also at snow decoupled as long i dont realy need it.

total agreement that ANY VC benefits from the option to reduce DRAG, by decoupling.

A syncro with VC is more usable at maybe 99% of conditions than one with solid shaft.

no agreement, imo the Solid is 100% more useful in ALL situations where coupling is actually needed.

the only thing a VC does better is that it decouples itself, although with drag, 99% of the time automatically. With a solid shaft, decoupling requires an intelligent operator.


The vc slips only over 50nm in the beginning and than it becomes with time always siffer if there is wheel slipping. So once more, the vc transfers always torque.
With solid shaft you have always slip in front and rear when the engine is not pushing. If engine pushing you have mostly slip on front.

The vc never decouples under 50 nm.
Just try to move the kardan when the back whells are up.

Edit:
Seems you are going always uphill with your solid shaft and stay up. Or can you explain what is better on it going down ? So you can say, if you get stucked in sand/mud (which is mostly drivers foult), in 99% the solid is better than a stiffer vc.
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PostPosted: Sun Apr 05, 2015 1:27 pm    Post subject: Reply with quote

Just a question for the solid shaft fellows...

I know a bunch of you have been to Moab on the slick rock which to me is almost like being on a paved surface. What do you do in these conditions? I am sure you are coupled and possibly locked up to climb some of the obstacles? My decoupler sometimes needs a blip on the throttle to disengage if there is torque or drag transfer happening between the front and rear. How do you deal with this? I am guessing you guys have learned to push and pull knobs pretty quickly or there would be CV's and axles popping and breaking Shocked

I am also guessing you only couple up when going in a straight line but how do you handle turns in rock when you need to stay coupled up? When I was in Colorado on some of the rock passes I was thankful that I had a little give with a VC when I just stayed coupled up. Switchback turns on rock ledges happened frequently. I am sure I still put a lot of stress on my drivetrain anyway.

I usually always couple up before I start locking front or rear. Usually that is all I need to do to continue in most conditions. In sand I always couple and lock the rear end before I need to and after previously airing down. Except last week Rolling Eyes

It is good to learn about this stuff and help prevent stresses to our expensive transaxles. Back when I was having vibration issues and removed the propshaft to help locate my problem, I noticed how easily the Syncro would turn sharp. That was my first clue I had a VC issue being to aggressive. Now that I run a decoupler, I will always have one installed on my van and suggest that as one of the first modifications anyone make to theirs. As stated earlier it is a "Day and Night" difference that you can feel instantly.

I don't have a preference to a VC or Solid Shaft. I believe that they each have their place depending on conditions and the operator. I am looking forward "seeing" the difference at one of these events we all go to.

It was also good to understand about the drag and I will be more apt to not couple up just driving on snow/ice conditions. And I felt safe when in turns coupled up with my Sport VC Shocked
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PostPosted: Sun Apr 05, 2015 8:34 pm    Post subject: Reply with quote

Hopefully, my Cruisers qualify me as a "solid shaft fellow" - heh!

I've done many trails in Moab and agree locked shafts can be a tough call with such grippy rock. The LandCruiser has the same issue you mention when trying to unlock things with axle windup going on. We are often sawing at the wheel trying to find a position that makes the shafts briefly equal and letting the splined sections release.

If I'm approaching an obstacle difficult enough I worry about body damage if I slip, I will use a locker and also modify my approach so I can go over the obstacle in a straight line. In other words, a series of ledges with a turn at the last one, I will accept the slight danger or discomfort of going diagonally up the ledges locked if it makes the turn at the top less tight. We Cruiser Wagon drivers also tend to do this because we have the turning radius of the Queen Mary and many of those trails were cut by Jeeps with wheelbases nearly two feet shorter.

One tip to unlocking I will pass along is that in addition to some steering input to help disengage your decoupler, you can also blip and release the throttle and be rewarded with the click and dash light going off.

I also never turn the steering wheel when at a dead stop if I'm locked - enormous stresses. Even if it is the tiniest incremental movement, I will initiate a bit while turning to help the contact patch squirm away some pressure from lockers.

Having said that, if the obstacle is gnarly enough to require lockers, it is likely the tires will be able to release the binding themselves because that terrain means one tire is briefly out of contact with the ground, or barely touching. The barely touching tire will easily release the pressure. Or one or more tires are only touching rock with a single edge, or traversing a pointy rock where the whole contact patch is not touching - just a little of it, etc. The binding will release on this type of terrain.

The worst, and I suspect you are referring to this, is when you are on grippy, steep Moab slick rock where the terrain is relatively even but the angle freaks you out. I'm OK with letting my drivetrain take some abuse under these conditions, so I don't scream like a little girl every time the truck lurches!! Heh..
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1987 2WD Wolfsburg Vanagon Weekender "Mango", two fully locked 80 Series LandCruisers. 2016 Subaru Outback boxer. 1990 Audi 90 Quattro 20V with rear locking differential. 1988 Mitsubishi Van w/ dual spinny seats, mid engine and solid axle.1990 burgundy parts Vanagon. 1984 Porsche 944, 1992 Lexus LS400, 2002 BMW 325Xi 5 speed.
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