Locking up a solid shaft Syncro for crosswind stability?

[IdahoDoug]

So, this subject came up recently, and an article on GoWesty's site was cited where the GW writer claimed that locking up a solid shaft Syncro at 75mph on dry pavement was a good idea to enhance stability in crosswinds. Specifically, the article says that in strong crosswinds when the Syncro was presumably not holding its line well, that locking up the solid shaft caused the vehicle to "settle right down."

I read this article many years ago and so I went there to refresh my memory - here's the link: http://www.gowesty.com/tech-article-details.php?id=19 Indeed it suggests locking up a solid shaft Syncro at 75 on dry roads.

I want to help Syncronauts preserve their remarkable vehicles, and also to drive safely on the public roadway, so I thought this worth a post to tell you what is really happening and advise against this practice.

First, its important to know that anytime a vehicle is not going straight ahead, it could be said to be describing a curve, or an arc. On a curve, the front tires are describing a larger diameter arc than the rears - traveling a longer distance. Anyone who's watched a vehicle drive a circle on wet pavement, snow or sand will see that there are 4 tracks in concentric circles. Since they begin the curve at the same moment, and end the curve at the same moment, physics dictates that the front tires turned more revolutions than the rears during the curve.

On a small tight circle such as parking, the relative % difference is large as anyone who's parked a Syncro will tell you - that's when the difference is SO large that the vehicle fights the turn, wanting to straighten itself out on dry pavement and you may even hear rubber chirping from the incredible force.

Using what I call "the law of extremes" to illustrate a point, you won't feel this on a 2 mile long interstate curve, where you will DEFINITELY feel it turning tightly to park. However, it is worth noting that even on the freeway curve, it is still happening - the fronts are turning slightly faster than the rears and there is extreme pressure building up in the contact patches, the axles and the drivetrain components.

So, a fully locked up 4WD vehicle going 75mph is definitely creating binding between the front and rear axles, and it is being released at the contact patches with the road just like when parking. Because you are going 75, the wind is roaring and the engine is singing, you are not going to hear the contact patches complaining. They are also not having to release that pressure with sudden chirps like at parking speeds because the % difference in rotating speed is smaller and released over several revolutions at freeway speeds. Its not nearly as damaging as the low speed parking where you can break pinion gears, strip ring gear teeth and snap CVs.

The writer doesn't explain why locking up the van "settles it right down" but I think I can explain, and I will use my own experience driving a fully locked vehicle at freeway speeds to do so. When I lock my LandCruiser at speed, the steering feels markedly different because the vehicle doesn't want to go round a curve with the center diff locked. We've already covered the difference but the more I try to steer, the more it fights because tighter curves mean a larger % difference. On long interstate curves, this "tension" in the steering wheel makes things feel more stable from the driver's seat. You are pressing the steering wheel against the car's desire to straighten, and crosswinds only lessen that force or make it greater in tiny increments. Without this steering tension, your hand's pressure on the steering wheel sometimes needs to turn left slightly or right slightly in a constant back and forth with gentle sawing that feels less stable when the wind blows and quits, blows and quits.

The reason the vehicle wants to straighten is because the front tire contact patches are under braking tension with the outer front tire being forced to slip the most (its the largest circle) which wants to straighten the vehicle out because its generating the most braking force.

In addition to this "perceived" feeling of stability, there is some true gain in stability because a tire contact patch under torque (either engine torque in the forward direction, or braking force in the rearward direction) actually IS more stable and more difficult to knock off its line. Those who've raced know this as the tendency of a race car getting briefly jukey as you let off the gas for a turn to instantly settle down on the racing line when you brake firmly. So there is something to the stability feeling, its just that I want to clarify you are getting it from an expensive process - binding up your drive train.

So, the writer does not explain why, but I am here to say 'don't ever do that to your beloved Syncro'. That feeling in the steering wheel is causing super high ring and pinion pressure, CV joint pressure and gear pressure in the transaxle. While it may "feel good" on some levels, it absolutely is not good for your Syncro. In the event you need emergency evasive maneuvering (deer, pothole) you will find the vehicle extremely sluggish to respond to steering input. This is the reason every modern 4WD vehicle has a sticker on the driver's visor and the owner's manual warning about engaging 4WD on dry pavement. A flat tire - same thing. The Vanagon is going to exhibit some wild handling at 75mph.
_________________
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

[MsTaboo]

Nice write up.
I remember reading that article a while ago and just shaking my head at that paragraph.
Just another reason to keep the VC vs a solid shaft. The VC gives that extra bit of stability on dry pavement without the worry of transaxle damage.
_________________
Currently:
'90 Syncro Westy 3 knob w/Zetec

The information age has morphed into the age of disinformation and willful ignorance. Agnotology!
Help the fight against Truth Decay.
Defend democracy, support Ukraine.

[Sodo]

[mrshrimp]

[IdahoDoug]

Mr Shrimp,

I'll take that bet. Snowy roads around town. We'll make a a race around the 4 roads around the square of any ski town in winter. You locked up will oversteer into every single snowbank on every turn. Taboo will drop you like a hot potato.
_________________
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

[MsTaboo]

_________________
Currently:
'90 Syncro Westy 3 knob w/Zetec

The information age has morphed into the age of disinformation and willful ignorance. Agnotology!
Help the fight against Truth Decay.
Defend democracy, support Ukraine.

[Sodo]

Wait a minute Doug, what happened to drivetrain loading and Syncro solid-shaft peril?
_________________


'90 Westy EJ25, 2Peloquins, 3knobs, pressure-oiled GT mainshaft, filtered, cooled gearbox
'87 Tintop w 47k 53k, '12 SmallCar EJ25, cooled filtered gearbox
....KTMs, GasGas, SPOT mtb

[IdahoDoug]

Sodo,

Heh, I'm pretty sure (like 99.99%) that you're engaging in chain yanking, but I'll bite.

With slick roads, there's hardly any stress on the locked up solid shaft Syncro, which I'll pull out of the snowbank on Turn 1 when I complete my lap and come back around. The drivetrain loading will be minimal because the dry road loading at the contact patches I caution against won't happen here. The tires will release it easily in the snow race because of the low coefficient of friction on snow. And because the front tire patches are resisting rolling through the curves with the braking effect of axle binding, they will be using a lot of the available traction in the contact patch already. When you then ask them to steer the car, there will not be much left for that function and it will wildly understeer right into the snowbank.

I'm sure there are a few ex-rally pilots who'll claim they would nail every turn in a 4 wheel drift at full opposite lock and leave the VC Syncro behind.

In a dry road race with otherwise identical Syncros, the locked up solid shaft Syncro would again lose because it is eating up valuable horsepower in drivetrain binding. To see that in effect, try parking a locked up solid shaft Syncro on dry pavement. Halfway into the parking spot let off the gas and feel the Syncro lurch to a stop from the friction.

The VC has many "issues" but on all road conditions in a speed/handling contest, it will drop a locked up solid shaft Syncro.
_________________
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

[Wildthings]

So you are driving down the road and the van gets a bit squirrelly feeling in the wind so at this critical instant your take one of your hands off the wheel and engage the front axle, only to discover that the steering wheel is being ripped out of your hand because part of the squirrelliness was being caused by one of your tires having low air pressure or because your tires are otherwise mismatched.

FWIW running a 4wd locked in on the highway resembles the setup that engineers use to test gear sets. They take a relatively smallish motor say 20HP and power a gearset that ultimately feeds the power back to itself through a friction devise thus putting a 200HP load on the gears.

[WestyBob]

Doug --

One of the most experienced, skilled and knowledgable drivers of vanagon syncros I know is Tom Lengyel in Aurora, Oregon, which is about 25 miles south of Portland off I-5.

If you have the time and inclination I invite you to talk with him about solid shafts, cross-winds, and related component destruction while traveling at high speeds on expedition road trips coupled with the solid shaft.

What he tells me doesn't completely aligned with your treatise.

Tom does engine rebuilds, conversions, tranny rebuilds, just about anything vanagon. He owns about 7 or 8 syncros now and has owned syncros since '86.

I believe he was the first **in the US** to manufacture and sell solid shafts, later as a supplier to several of our well known Vw parts shops.

His place is called "Syncro Shop" and his public business number is 503-228-1102.

I'd be curious as to your feedback after talking with him. You both may agree or not but it would be interesting to hear how that goes.

Also, whenever you lecture on how you feel the VC system is working I'd strongly recommend, as a service to your viewing audience, especially newbies, that you also mention as an aside and courtesy that not all experienced vanagon syncro drivers completely agree with you. This will allow them to not only consider your theories in full but also help them to do more self-research and then derive their own conclusions.

[Sodo]

WestyBob thanks for the background. Doug likes campfire talk, this I know for a fact but he's ignoring me for the moment. We're like "two clowns, each wielding a pie" but he can see that my pie is bigger than his and he's afeard.

[IdahoDoug]

Bob,

I've met Tom and he's a brilliant guy - shared time around the campfire with him more than once. We've never discussed this topic but I think it would be a fruitful conversation based on logic, physics, and the seeking of truth.

I want to address this comment you made:

"Also, whenever you lecture on how you feel the VC system is working I'd strongly recommend, as a service to your viewing audience, especially newbies, that you also mention as an aside and courtesy that not all experienced vanagon syncro drivers completely agree with you. This will allow them to not only consider your theories in full but also help them to do more self-research and then derive their own conclusions."

You used the phrase "how I feel the VC system is working". In the world of engineering, there is little room for "feeling". Either a set of front tires describes a larger pair of arcs in a curve than the rears, or it does not. In my discussions, I try to explain things from a factual basis and I try to make them approachable for every level of knowledge. Undoubtedly I fail. Sometimes because I stay away from esoteric engineering terms and try to find everyday phrases. Sometimes because I try to include too much at one time. And sometimes because of my own inability to communicate the concept correctly.

But at the end of the day, my posts are based on sound and correct engineering principles from my own education, my life experiences, my physical observations as a vehicle developer, and my knowledge of the Syncro and other vehicles.

Driving a center locked 4wd vehicle on the road is a bad idea for a lot of reasons. Each tire in a curve must roll a different distance and open diffs/VCs allow for that. Lock them together and you are asking for trouble. That's not my "feeling". It is provable, demonstrable fact and I welcome anyone to engage me in it - not to be a jerk, but to discuss it in a way that mutually seeks the truth. If there is actual interest in challenging my assertion on what locked axles on the road does, please state the position and I will be respectful, attentive and truth-focused in explaining it.

Our society in general has lost the art of conversation and I'm determined to regain it. It's winter and we can't have this conversation around a campfire, so lets have it here on Samba.

Doug
_________________
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

[Sodo]

GoWesty has a point. If gusty-road stability is a benefit you want out of your 4WD contraption, then do it - judiciuously of course. Whats the use of paying the Syncro tax and not taking the benefits?

[Merian]

Let's consider the initial perturbation for both wind pressure ahead of and behind the center of pressure, as well as the later phase during the driver recovery time period. Plots for steering angle will be helpful...
_________________
....

[WestyBob]

[IdahoDoug]

Bob,

I appreciate the discussion tone of your post, and the willingness to listen, weigh and consider.

Sodo,

Yes, I think you are 100% correct. Lock up a decoupler on a solid shaft Syncro for everyday driving on dry pavement and the resulting additional friction will increase fuel burn, gear pressure, and tire wear. A transaxle temp sensor should pick up the temp change.

To properly measure it, best way would be to get everything up to temp on a day with stable temps and drive the same 10 mile stretch of road back to back, taking the same period of time to do it. I picked 10 miles as probably long enough to gain a difference and the temp point should be near or at the end. The heat will be most pronounced at the gear contact faces, and less pronounced in the oil at large. In other words, if there is a 1 degree F difference in the gear oil on a sensor in an open area inside the assembly, it should not be inferred that the heat difference at the gear faces where it really matters was only that single degree.

Either way, I think the temp check is a great idea. A precise fuel burn would also reveal the added tire contact patch friction because you have to slightly give engine power to maintain speed against the friction. The curvier the course, the greater the expected data difference.

There is another way that many Syncronauts could do with zero prep and not needing an internal temp sender in their transaxle. Find a gentle hill with a gentle curve you could coast the Syncro down and mark the stopping point. Let it roll from a dead stop at a marked spot at the top and mark where it comes to a rest at the bottom. Do it a couple times unlocked in neutral. Do it a couple times locked in neutral (I'm not clear on what keeps it locked as to vacuum so I don't know if the engine needs to be running for that or not). This would similarly provide data that the forward movement of the locked condition creates additional tire contact patch friction. It would then be an easy conclusion to see that locked makes the axles/tires fight and creates added friction.

Sodo - next time we get together, I'll have you drive the Cruiser I slept in last summer and you can lock the center diff while driving it around and feel the added friction. Since its stock tires are huge (275/70-16!) you will have no doubt that the drivetrain is generating huge binding and friction on the tires. It's also a burly beast with factory 1-ton full floater axles that won't suffer harm from some experimentation like that.

Doug
_________________
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

[Sodo]

[djkeev]

My F150 4x4 I would NEVER drive on dry pavement in 4wd.

It creates so much tension and tire chirping that I fear for the driveline components!

When plowing snow I dread any bare pavement intervals!

Dave
_________________
Stop Dead Photo Links how to post photos

Ghia
http://www.thesamba.com/vw/forum/viewtopic.php?t=392473

Vanagon
http://www.thesamba.com/vw/forum/viewtopic.php?p=6315537#6315537

Beetle
https://www.thesamba.com/vw/forum/viewtopic.php?t=482968&highlight=74+super+vert

[jackbombay]

[vanagonjr]