Tight viscous coupling

[peasant]

If your VC heats up on the road and wheels start rubbing excessively your VC is simply old and needs to be refurbed/replaced.

To get a VC refurbed cost me 400 something Euro ...cheaper than a decoupler and lots cheaper than most "new technology" on modern cars and 4x4's.

So after 18 years my 4WD needed 400 Euro spent on it and now it works perfectly again ...in all weathers, on all surfaces without me having to do anything. (...and without the possibility of me doing something WRONG )

Sorry, what was the issue again?


Ah yes ...unless you want to use your Syncro as a mudplugger, boulder hopper or dune climber (which it wasn't designed for in the first place) with a solid shaft or a buggered, rock hard VC, a decoupler is an expensive downgrade.

[v-lux]

Uh oh.....here we go again.....

[syncrosimon]

Oh boy!
Cant I have something because I want it?
Decoupler racism

[syncrosimon]

to go back to the first question why use a decoupler if a working vc doesnt start to put power to the front till the rear slips if theres no slip on the motor way theres no drive to the front. Also how does a decoupler save wear to the front, the drive shafts and diff etc are still turned by the front wheels are they not.

Or have i missed to point?

You are correct in what you say and no you havent missed the point. People who have bought de couplers will always tell you how great they are because they have just spent a load of money on a 'gadget' so they dont want to look like a numpty and tell you it makes no difference. People will tell you things like "I use my syncro 95% on the road, and just don't use the 4x4. The front driveshafts on mine have done 45,000 miles and I have never removed them, partly due to the fact that there is no strain going through them" when they have a de coupler - well I dont have a de coupler and I can say that I use my syncro 95% on the road, and just don't use the 4x4 either cuz I have a VC. The front driveshafts on mine have done 285,000kms and I have never removed them, partly due to the fact that there is no strain going through them because I have a VC that works! The VC is a wear item like most stuff on cars and thats how manufacturers make money by selling new ones!

I am personally sure that VW left the wiring in place in the syncro on all models up to 1992 as an insurance against having to retro fit it in case the VC had unexpected long term issues.

WHAT???? Why would they have to retro fit two bits of wire? Its cheaper to leave two bits of wire on the loom than take it out - any production engineer will tell you that. Modifications on parts that are homologated cost too much money

Well if I am a numpty, you sir are a buffoon

[peasant]

Oh boy!
Cant I have something because I want it?
Decoupler racism

Course you can have it ...it's just that wanting it makes about as much sense as wanting a set of fake boobs (for yourself) ...nice idea in principle ...but kinda pointless in the end and not neccessarily an improvement

[HarryMann]

As far as that 1 or 2% slip at the rear wheels goes... perhaps I should also have reminded that the prop and VC run at road-wheel speed x diff-ratio.

So if we say we need a 40 to 80 rpm difference to start generating significant torque transfer that might be 10 to 20 rpm wheel speed.

Coming at it from another angle, engine speed (assume top-gear is 1:1 for simplicity) = prop speed, then cruising in top at say 4000 rpm, 1.5% of that is 60 rpm, right bang in the middle of that active range

This may mean that the slightest further slip and torque will be progressively transferred forward - but immediately.

I have never been of the persuasion that a VC is such a crude device that you can feel torque transfer shuttling around, or that you have to 'wait' for lock-up/STA/hump before the device is worth having - far from it, I've always found it does its job fairly transparently and progressively. Because a tyre can be felt to slip slightly here & there or the vehicle appears to scrabble for grip at times, doesn't to me imply that the VC has just started to do its job, it simply implies that grip is becoming marginal (full stop).

I also have to say I have never driven a solid shaft (billet or otherwise, hahaha ) equipped Syncro, but will jump at the first chance to do so, offroad.

[MoonlightCustoms]

so in the end there is no need for a decoupler unless your vc is tight, evan then the front end and prop is still turned by the wheels so is still wearing. A decoupler wont save you fuel or wear unless you could also fit free wheeling hubs to the front and as such leave the front drive shafts, diff, vc and prop stod still your not going to gain anything. If some one designs free wheel hubs for a syncro then i MIGHT concider a decoupler but till then i would rather put my hard earned into a new vc when the time comes. mine is a little tight but i dont do a lot of motorway miles so for now its good enough

Not trying to upset any one, more thinking alowed

[HarryMann]

Another factlet, from one of the Mohan SAE papers, is that....

'Rotary viscous couplings have been used since the 1920s for torque transmission or as torsional dampers.... '

No history or attribution is made in any of the SAE papers, but then it's also not suggested that earlier (than 1969) viscous couplings exhibited anything other than viscous shear dependent torque i.e. resistive torque that would drop steadily as the whole device heats up.

We are dealing here with a device with another operational mechanism that steps in as heat builds up - and rather rapidly too.

[syncropaddy]

I don't think the diff oil is necessarily overheating the VC itself, but maybe there is a problem with the radiator airflow and overall diff temperature. It wouldn't be too hard to fit some sort of oil circulation and cooling device, or modify the airflow somewhat.
Don't forget that diff oil (at the right nominal temperature) is also a cooling and equilibrating medium, bringing the VC case back down to oil temp more rapidly than air itself would.

Dont you think that Steyr/VW would have thought of this already and the fact that we dont have an oil cooling circuit on the front diff would mean that it is not necessary. Aidan speaks regularly about a 100,000 mile life expectancy and it is apparent that many components are outlasting this figure under 'normal' usage. The cost to VW at the time to fit a front diff cooling system to an already expensive vehicle was probably deemed excessive on more than a cost front. VW responded to their customers requests and made the necessary modifications to the Syncro throughout its production life - the 16" for example. Diff cooling didnt happen because its not necessary. I have a 6mm aluminium skid plate fitted to protect my diff and it hasnt had any effect on the VC which works fine and doesn't bind up after long trips. That VC has a lot of Kms on it!

The modifications we all talk about here on this and other forums are things that VW discounted as not being necessary to their T3 Syncro customer demographic and the design scope for product liability. Were any of us part of that group? One or two of us might have bought a brand new Syncro, otherwise no. We talk of 15" wheels, De couplers, Lift kits, Big brake kits, Rear discs, Big CV joints, modified this and modified that, none of which were necessary to be fitted to the T3 Syncro sold by VW to their customers at the time of its production and sale. We talk of all this stuff because we need to modify and make more user friendly almost 20 years on in a similar way to any other group of car enthusiasts will, to their older vehicles. Its what we do because we are enthusiasts. However, if you modify something dont say its brilliant unless you have proven documented evidence that says it is.

I remember reading an article on 'the Samba' about suspension mods and was quite amused at the lengths people have gone to, to achieve something better. Thousands of dollars spent on trying to achieve the ultimate in Syncro suspension with twin shock, hydraulic systems that look brilliant and took massive amounts of skill and workmanship to achieve and Im sure the sense of achievement by the people who did them was immense. In actuality they achieved nothing as a standard Syncro beat them all in a trial but it looked great!

[syncropaddy]

Oh boy!
Cant I have something because I want it?
Decoupler racism

Of course you can but dont give us 'fact' based on opinion. Fact: de couplers do sometimes fail to function ( when you need them most)

Course you can have it ...it's just that wanting it makes about as much sense as wanting a set of fake boobs (for yourself) ...nice idea in principle ...but kinda pointless in the end and not neccessarily an improvement

I am not a lone voice in the wilderness

[peasant]

I am not a lone voice in the wilderness

I happen to like the much improved driving characteristics of a 4WD T3 over a 2WD T3 ON THE ROAD and I really can't understand why somebody would deliberately want to spoil that / miss out.

Especially as off road a working VC is still doing a pretty admirable job, all things considered

[syncropaddy]

so in the end there is no need for a decoupler unless your vc is tight, evan then the front end and prop is still turned by the wheels so is still wearing. A decoupler wont save you fuel or wear unless you could also fit free wheeling hubs to the front and as such leave the front drive shafts, diff, vc and prop stod still your not going to gain anything. If some one designs free wheel hubs for a syncro then i MIGHT concider a decoupler but till then i would rather put my hard earned into a new vc when the time comes. mine is a little tight but i dont do a lot of motorway miles so for now its good enough

Not trying to upset any one, more thinking alowed

99% correct .... if your VC is tight then its not a de coupler that you need, its a new VC. Simples ....

[syncrosimon]

Oh boy!
Cant I have something because I want it?
Decoupler racism

Course you can have it ...it's just that wanting it makes about as much sense as wanting a set of fake boobs (for yourself) ...nice idea in principle ...but kinda pointless in the end and not neccessarily an improvement

Thanks for letting me have my decoupler. I feel much better now, maybe one day you will actually see one.

[syncrosimon]

Oh boy!
Cant I have something because I want it?
Decoupler racism

Of course you can but dont give us 'fact' based on opinion. Fact: de couplers do sometimes fail to function ( when you need them most)

Course you can have it ...it's just that wanting it makes about as much sense as wanting a set of fake boobs (for yourself) ...nice idea in principle ...but kinda pointless in the end and not neccessarily an improvement

I am not a lone voice in the wilderness

Paddy it is you that is spouting the fact based on opinion, who's to say that your vc isnt failed open. When did VW last test your VC and give you a report on it's performance.

I have never ever stated that anyone should buy a decoupler, but for me it is perfect. Is that not enough?

[HarryMann]

Now, shake hands and be good boys

kissing and making up sounds too much to ask