Tight viscous coupling

[syncrosimon]

Here speaketh the men without de-couplers.

For me it is about longevity, and on such an old vehicle as these you have to be aware of it. I defy anyone over the speed of twenty miles an hour to be able to tell whether you are in 4 wheel drive or not. (unless you drive like a bell end)

Fit for purpose. 4x4 on a motorway, no-way.

The decoupler with a vc, ideally a new sports one, refines the vehicle to levels that the budget men at VW would not allow on an already expensive vehicle.

Why did VW do a sports VC for the army on the 16, because the normal VC isnt fit for purpose always.

700 notes is a front diff rebuild or a decoupler, spend early and the decoupler should prevent that from ever becoming a necessity.

I went and bought just one tyre day before yesterday for the syncro. 70 quid saved, cheers.

I have been driving syncro's for 20 years, and without doubt it is the best bit of kit you can buy for one.

But then I would say this would'nt I, cause i am considering buying a lambda probe air fuel ratio dash gauge for the dub, so I can tweek the air flow meter for the perfect tune. The vehicle is worth that much to me, and I would not do her the discourtesy of running her around with the front interfering with the back and winding up those precious spinning metal components. I am in 2wd just about all the time. The other bit though with de-coupler engaged is just as important and a solid shaft is plain dumb unless you are off road all the time. VC rules, but the vehicle needs a decoupler.

[toomanytoys]

Er... if its a planetary diff, it wont be viscous surely??????

[desert rat]

Update!

Yeah Simon i definately agree with what you say about saving wear and tear on all those metal bits! but on stripping down the vc i found it was too late for those metal bits now the diff has got to go and have a full rebuild as the pinion bearing is goosed!!
And now its all come off i might as well put a new vc in anyway!! but we have decided it is going to have a decoupler as well to save wear on the front cos like you say there is no point in having 4wd on the motorway really!!
So it looks like i will be writing cheques for a while yet!! but i think it is worth it !!!!!
Hopefully when all this is done we can go away and use it !!!!

[HarryMann]

Here speaketh the men without de-couplers.

I've got one .. probably about the 2nd person here to get one and sourced Russel his too at the same time... haven't fitted it yet but plan to

I just think the historical aspect needs keeping straight, the correct attributions of the VCs origins noted, the business and engineering decisions behind it's adoption on the T3 Syncro too. VW are not idiots, neither did everything come down to 'cost' back in the 80's (the T3 2wd and syncro were some of the most expensive vehicles VW have ever made, as far as profit margin was concerned) This was solid, well-founded engineering development, testing and subsequent decision making.

I also think that far too many blame the VC for normal wear and tear, abusive damage, general load limitations of syncro transmissions and sometimes un-noticed long-term oil leaks. The VC is a maintenance item when it fails, end of! Just a shame they cost £500 instead of £250 which would put a different perspective on things.

VCs should be looked at as a very elegant (read simple and functional) piece of analogue engineering, quite up to the job in hand when specified correctly (and there's nothing wrong with the std VC in 99% of situations when we can climb up the rock at Llanfyllin with consummate ease). More modern systems like the Haldex/4-motion are simply more complex digital equivalents that have usurped the prior technology, though VCs have been used succesfully in many more vehicle applications than some people realise, cross-axle as well inter-axle... and still are in many other non-vehicle power trasmission applications, including some electrically controlled clutch/VC combinations.

Simon: That Scimitar planetary diff is splined on the outside to take the VC plates.. it is/was a combined/ integrated diff/VC unit.

[toomanytoys]

Apparently my scooby has a vc in the middle... and from what I can tell it works fine and no scrubbing after 157500 miles.. and they dont seem to suffer the same symptoms as the Syncro... the outbacks have a vc rear diff....



Mmmm. planetary and VC... now thats odd.. need to understand more of how thats supposed to work...

[syncrosimon]

Here speaketh the men without de-couplers.

I've got one .. probably about the 2nd person here to get one and sourced Russel his too at the same time... haven't fitted it yet but plan to

I just think the historical aspect needs keeping straight, the correct attributions of the VCs origins noted, the business and engineering decisions behind it's adoption on the T3 Syncro too. VW are not idiots, neither did everything come down to 'cost' back in the 80's (the T3 2wd and syncro were some of the most expensive vehicles VW have ever made, as far as profit margin was concerned) This was solid, well-founded engineering development, testing and subsequent decision making.

I also think that far too many blame the VC for normal wear and tear, abusive damage, general load limitations of syncro transmissions and sometimes un-noticed long-term oil leaks. The VC is a maintenance item when it fails, end of! Just a shame they cost £500 instead of £250 which would put a different perspective on things.

VCs should be looked at as a very elegant (read simple and functional) piece of analogue engineering, quite up to the job in hand when specified correctly (and there's nothing wrong with the std VC in 99% of situations when we can climb up the rock at Llanfyllin with consummate ease). More modern systems like the Haldex/4-motion are simply more complex digital equivalents that have usurped the prior technology, though VCs have been used succesfully in many more vehicle applications than some people realise, cross-axle as well inter-axle... and still are in many other non-vehicle power trasmission applications, including some electrically controlled clutch/VC combinations.


Simon.

Simon: That Scimitar planetary diff is splined on the outside to take the VC plates.. it is/was a combined/ integrated diff/VC unit.

Erudite as ever Clive, well said, now we have the facts coming in.

[Aidan]

FYI
SyncroServices currently have stock of the really nice Stefan decoupler as opposed to the buschmeide sourced ones so if you want one now.....

I couldn't make a penny on importing the SA parts and making them up to complete exchange units and haven't found anyone to make the internals in the uk for a sensible price even with the drawings supplied and ime the SA parts aren't anywhere as well made as the german ones.
I'd go along with SyncroSimon with the save the wear and tear argument but I'm happy to stay stock as I started with new VC new tyres and rotate them and am happy with not having to think about wether it's in 2wd or 4wd and being able to hoon it through roundabouts on wet empty roads from time to time, hopefully the VC will last as long as I drive the bus
Sports VC ? Was there really a different VC fitted to military syncros or is this a myth ? I've never seen any proof of it, ie different part numbers or markings on VC - now Dorfbrunner can do them and probably best suited to a decoupled vehicle for sure

I have heard from a customer in Canada that there is a source for Chinese made VCs - but I haven't got any more details, but perhaps worth following up as they may be cheaper (but probably only work once like all the tools they make)

I've just done a gearbox rebuild for a customer who had the weirdest 2wd syncro going
RWD in 1st and 2nd
FWD in 3rd, 4th, reverse and G gears




Pinion shaft had sheared between 2nd and 3rd gears, it still drove, but apparantly was interesting in it's handling characteristics

All sorted now and he's a happy chappy with a proper PT 4wd syncro as per manufacture

[peasant]

Sports VC ? Was there really a different VC fitted to military syncros or is this a myth ?

not to my Syncro, anyway ...14 ex Bundeswehr

[desert rat]

Update!!

Aiden, i have ordered a new vc from syncroservices and it should be with me tomorrow or saturday! As had the courier order number - but yes the decouplers that syncroservices have do look quality!! but for the time being i will be happy once you have rebuilt my front diff and a new vc installed!

[HarryMann]

Sports VC ? Was there really a different VC fitted to military syncros or is this a myth ? I've never seen any proof of it, ie different part numbers or markings on VC - now Dorfbrunner can do them and probably best suited to a decoupled vehicle for sure

Perrrity sure this is a myth, but never say never

When we arranged the first Dorfbrunnen rebuilds through the Calibra 4x4 man in cambs (who lived in Lanzarotte most of the time!), that is AndyMc and myself had one done each, I made enquiries after looking at the calibration curves if I could have one on the 'high' side...

The answer was that 'Yes', we can go up a notch on the Silane viscosity and down a notch on % unfilled-space, but 'at your own risk'...

I may be wrong, but think it was this suggestion that led to what is being called, now, a Sports VC

[HarryMann]

Simon (TMT)

Here is the link with discussion of that prototype Reliant Scimitar GTE 4WD

Oops, forgot it

Hereis: http://www.sporting-reliants.com/Prototypes2.htm

[Syncro G]

Simon (TMT)

Here is the link with discussion of that prototype Reliant Scimitar GTE 4WD

If its the Fergerson Formula system, they use a clutch alongside a plannet centre diff. Idea is if the diff lets too much inbalance the clutch locks up. Presumably its a wet clutch. Ment to work alot faster than a VC and lock up like a solid system without so much slip. Doubtless alot more expencive than a VC hence rare (besides the famous 'FF' car they were fitted to a number of road vehicles as a conversion. Opel Senitors FF, and some exclusive early automatic converted Range Rovers used FF transferbox before automatic was a factory opton (with the standard leyland transferbox!).

I think what VW were perticularly keen on a fully automatic system without driver input over everything else so you can see why they wouldn't have favoured decoupleing. The irony is when you push a syncro off road you'll find yourself reaching for the rear locker which in some ways requires more knolage to use properly than a locking centre diff/coupleing (VW obveously recognised this as they didn't like letting the americans loose with axle lockers!). They must have been on the money though as all the later models are less engineered towards off road work than the T3 so its fair to assume most costomers required the extra traction for poor road conditions and light off road so the HD mud plugging stuff we love was genrally not needed and a waste of money (if you still needed it I guess there was always the VW Taro?).

I would argue the decoupled setup was far more old fashioned than the VC. Before the 80's most vehicles were RWD when not locked up (though in the early 80's there was a 4x4 conversion of the 'blue oval' tran-sit with perminant 4WD as an option. The maker was 'NAM' though besides an early sales broture (which also includes the far more common and heavyer duty County4x4 model) I've never heard of or seen one, do you know different? Besides the obveous inclusion of CV joints and a 4 speed manual in the front axle I have no idea what style transfer box it was running; probubly all desolved by now!). The biggest development from the syncro setup to today is favouring the front axle rather than the rear (in cars, workhorses are still near 50/50!). This works better with modern FWD cars from which a 4WD model usally shares parts. As most of these vehicles are designed for softroader markets they also have alot less agressive transmissions so are basicly FWD cars that have enough power to the back to stop it bogging down, but still handle mainly like a FWD - its all most users ask so why do more? (think Honda CR-V, Land-Rover Freelander, Golf syncro...). The other predicatable change is the adition of electronic control over mecanical ones, which sometimes can mislead into what its actully doing. VWs electronic diff lock is an open diff it just makes it act like its locked with the brakes/tranction control! Not sure why some soft roaders are now offering 4x2 running modes (presumably decoupled? maybe they just turn the rear drive right down) when they send so little power to the back anyway, guess it must be eather so the driver thinks they are not driving around in a fuel sapping 4x4 all the time which will help them sleep though media harrasment or the vehicle manufacturer doesn't expect the rear to do much so hasn't engineered it to be able to cope with much? (why overengineer).

One of the more interesting decoupleing 4x4 systems I've come across was used on the 'Lancia Y10 4WD'. Its basicly a Fiat Panda4x4 (Steyr Puch of course) as they are the same car underneath, but instead of a mecanical decoupler on the rear PTO, its vacuum operated. It has extra vacuum decouplers on the rear axle, so it truely would be able to offer 4x2 running from the push of a button. None of those cumbersome manual locking 'free wheeling hubs' (which do make a slight difference) or the automatic version (which is rubbish!). Aparently it was prone to faults as it aged, doubtless through lack of use, but I don't know of a simular design despite the fact it seems plausable.

I have needed 4WD on the motorway and was very glad of it, though the snow was comming down quite harshly . I don't have powersteering and I can feel the extra grip comming in in normal driving when I'm not driving like knob, though obveously if I didn't have it at that moment I wouldn't crash eather. There have been the odd ocassion though when things have cought me out and I'm convinced 4WD helped out - its always ready! I also remember a scarry corner in the wet soon after I disconected the front drive, I'd got used to it being there (again I didn't crash but I noticed its absence). I'm sure I will get a decoupler one day, as they are a useful lazy thing to have without removing the prop all the time and increase versatility slightly when something could cause damage or those long sun drenched motorways where you probubly won't meet a patch of diesel. The VC is an important asset to the way the syncro drives though in my opinion. Without it it'd be just another part time 4x4, and I've already got one of them! No on road 4WD to play with there!

[HarryMann]

Enjoyed reading that Glen !

Must disagree the VC is rare, unless you mean on the original Jensen FF system... But VC versions were subsequently offered with full mfr. approval and warranty to Opels Senator, Monza and Biiter during the 1980's...

Their (FFD) next milestone was the revolutionary viscous control unit which allowed a much better central differential slip control with the benefit of being much more compact than its predecessor. It required less maintenance and much lower production costs yet still utilised their Maxaret anti-lock braking system.

Both the aforementioned systems were marketed as 'all wheel control'.

Conversions of Senators, Monzas and Bitters by Ferguson Formula of Coventry were first offered to the general public in 1980 employing their novel & revolutionary viscous control unit. All the conversions were approved by their respective vehicle manufacturers and therefore did not affect the warranty. As the cost of conversion was roughly 50% of the cost of the car, (Senator, Monza), new; relatively few were produced despite excellent road test report & results.

To some Granadas and Tranists also hand-in-hand with Ford. FF Developments subsequently offered it on almost any vehicle, incl. ambulances and police Granadas...
Also for Dodge Challengers..
In the early 60's, the succesful front-engined P99 F1 car won at Oulton Park (Stirling Moss) in the rain, and even in dry practice was 2nd on the grid by just 2/10ths of a second and became the last front-engined car to win an F1 race, before mid/rear engined designs balanced axle loading more sensibly and then wings solved the grip problems many had experienced in 1968's wet, wet, wet season... Cosworth developed their own ssytem at some point I believe, whereas several others used systems based on the FF e.g. Lotus.

Ferguson Research went on in racing, supplying the Novi-powered P104 to the STP team for Indianapolis.
Ferguson later supplied 4WD transmissions to various Indy and F1 teams. BRM used the Ferguson 4WD system on the P67 in 1964.

Ferguson Formula Developments

The story behind Ferguson Formula Systems is an amazing one. It starts 30 years before the first production Jensen FF was born. Brooklands Riley racer Freddie Dixon (who worked with fellow Irishman Harry Ferguson) worked on a 4x4 for racing. Being out and out racers, their only motive was to win races. They eventually met up with another driver, Tony Rolt, a born innovator, PoW escapee and 24 Hour Le Mans winner. It was shortly after his Le Mans win that he and Ferguson started development on what was to become the FF's predecessor, the P99. Building a simple 4 wheel drive system is one thing, but to build a 4 wheel drive system with unequal front/rear torque splitting, self locking centre differential and to incorporate a Maxaret anti-lock brake system is an amazing achievement.

Rolt didn't consider his multiple escapes were 'fun' nor his lead-role in the Colditz '"cock"' Glider episode, but that escaping was simply a duty. He was in fact awarded a bar to his Military Cross for what was an incredible record of POW camp escapes, being lucky not to be summarily shot I should think!

He & his wife witnessed the tragic Le Mans accident where 80 people were killed, at which point he decided that working in vehicle development was a better contribution to society.

He subsequently built Indianapolis 500 track-racing 4WD cars for the American STP Corporation, and Ferguson transmissions appeared in the Lotus, Novi, STP and Shelby Indy cars of 1964 to 1969. With the technical director Claude Hill and the project engineer Derek Gardner, Rolt was among the unsung backroom heroes of British racing development.

Ferguson Developments was closed when, after Harry's death and with the Ferguson family's blessing, Rolt founded his own FF Developments company in 1971, converting cars, vans and ambulances to 4WD. FFD became an important partner of Ford, Chrysler, Audi, Fiat/Lancia and General Motors. In 1994 the business was sold to Ricardo.

==
Reading this following may imply that Derek Gardner first had the idea that a Viscous clutch could be developed into a self-locking coupling... or that Gardner proposed it be wrapped a round a planetary diff.

Tony Rolt MD of Harry Ferguson Research patented Derek Gardener's idea using Potty Putty as viscous coupling for slip control as part of differential between front & rear drive. Rolt sold 4wd patents to GKN to finance his new company Ferguson Formula Developments FFD. The new Wolston factory provided capacity to meet the new Chrysler project. Os Webb went as part of the package to GKN.

Os developed the idea into a working coupling using internally splined plates over centre epicyclic diff with slots & gaps in multiplates running in viscous fluid. Rolt's FFD retained the right to produce low volume 4wd & continue development "

The planetary centre-diff which locked a wrap-around VC when its shafts differed considerably in speed, was built and proposed for the production Scimitar GTE 4WD... but not fitted to the single prototype, allegedly now somewhere in Cheshire - Aidan!

Ricardo Group bought FF Developments in 1994. FFD were then based in Coventry and Livonia nr Detroit, employing 80 and 140 respectively

1969 has been given as date Rolt and/or Dixon and/or Gardner developed the VC.

It is thought that GKN hold the VC patents and much further development ensued with many production licenses sold. It's even been used cross-axle on a Japanese car I believe...

[HarryMann]

As we've gone well off topic
Have started to archive this discussion in the Wiki, as it seems to come up annually when we all get a bit proprietorial

As Russel said a page or so back, it really is a personal choice... and for many the straight VC (but a good one) is just fine & of course if you want guaranteed 100% drive to the front when off-road via a solid shaft, then a de-coupler is needed. The difference is most noticeable when rock climbing it is said, and also when driving across deserts or beaches with loose slippery sand where the rear can dig in if momentum is lost.

Then for others it makes sense to keep a VC that hasn't failed open (rather than a tight one) yet still fit a decoupler...

[HarryMann]

A nice GKN pdf that describes the modern Viscous Coupling (GKN Visco Drive), with some illustrations

Actually differentiates between initial viscous and (frictional) hump-mode operation... outing the lie that it's silicon fluid's (weird) viscous behaviour that creates the lock.

http://www.gkndriveline.com/drivelinecm ... s-engl.pdf