On request of skodaw and for anyone else interested, here's a rundown of VAG's 4WD systems and brand names used over the years.

Brand names

Audi: quattro

VW: syncro, followed by 4motion

Seat: 4

Skoda: 4x4

Systems

Quattro I: open front diff, open center diff (manual lock), open rear diff (manual lock). No ABS when locked.

Full-time manually engaged four-wheel drive.

Was on: original Audi quattro (also named "Urquattro"), Audi 80/100 quattro.

Syncro: open front diff, viscous coupling acting as the center diff, open rear diff.

Part-time automatically engaging four-wheel drive.

Was originally developed by Audi, but sourced to VW as "syncro". Similar line of thought to the Haldex system, with the VC engaging rear drive when needed. Crude system with serious drawbacks, such as a lack of ABS integration, which needed the 4WD system to be switched off under braking, using a secondary clutch. Volvo also went on to use it on their earlier Cross-Country models, adding a TC system at the front and an LSD at the back - complicated and flawed. Also on 911 Carrera 4, but then that's originally a RWD car...

Quattro II: open front diff, torque sensing ("torsen") center diff, open rear diff (manually lockable for "those" situations in the rough). No ABS when rear is locked, auto de-lock when speed exceeds 15mph.

Full-time automatically engaged four-wheel drive.

Was on: the Audi quattro ('88-'91, still nicknamed "Urquattro"), Audi 80/90 quattro, Audi 100/200 quattro, Audi Coup

Originally posted by ncarring in this post

So what's a Haldex? and why does it matter? Are you saying your 4x4s are really FWDs masquerading as 4WD?

And especially for you too, Nick...

to a maximum torque split of 60/40

Are you sure about that? My manual clearly says 50/50.

Quattro IV was the 'grippiest' 4wd road car system I have ever owned (out of 14 4x4's) with more grip than my Subarus and Haldexed Octavia.

Not the most fun, but definitely the safest in feel

so what does the word "open" mean when referring to a diff

Stuart

Spoke to someone in a pub last night who has a 4WD Golf Rallye. He's only gone and put a FAT turbo and supercharger on it, to welly it out to 400BHP!! As he said, he doesn't drive it often as it can't cope with long journeys. I reckon he probably just keeps it in his garage 99% of the time, and fiddles with it!

PS: He recommended I use a company in Bridgwater, instead of Jabbasports. I don't know of this firm, but apparently he's a VW/Skoda specialist tuning bloke. If I can find the name, I'll post it to see if anyone knows of them.

Cheers

Originally posted by Stuart_J in this post

so what does the word "open" mean when referring to a diff

The opposite of locked...

Originally posted by otheos in this post

Are you sure about that? My manual clearly says 50/50.

Ah, you could be right. Let's see...

I dont know all this talk of 4x4, feels like I should be chewing straw down on the farm!

Seriously though... I hadnt realised there were so many different versions...

Open diffs are the most common type of diff. Wheels (or axles on a 4 X 4) can turn freely relative to each other. They have no means of balancing power delivery if one wheel has less traction than the other.

Limited-slip diffs allow the two wheels turn relative to each other, but limits the rate at which they are allowed to do so (usually either by some sort of friction or fluid coupling). This ensures that, even if one wheel loses traction, some power is still delivered to the other.

Lockable diffs (not to be confused with EDL) physically lock the two half-axles together. This is fine for off-road travel, but can cause problems when trying to turn on high-grip surfaces - one wheel gets "dragged" around.

EDL is not - as the name suggests - a differential lock at all. Sensors monitor wheel speeds, and if one is rotating substantially faster than the other (i.e. slipping) the EDL system momentarily brakes it. This effectively transfers all the power to the other wheel.

I'm a bit vague about Torsen and Haldex diffs.

Yeah - what's a Torsen diff, Mattijs? And a VC?

Great precis though, thanks. BTW did Skodaw really ask first?

Nick, I can tell all about those, but I'll oblige when given some time off work - no chance of that now... :(

And yes, I know it's Friday afternoon, but our office motto has, for the past six months now, been "Crisis? What crisis?"

First a bit of history on (racing) 4WDs:

http://8w.forix.com/4wd.html

Now the techie stuff:

Viscous coupling

Invented by Ferguson Formula (FF). Silicone liquid in a casing. Increased slip will lead to increase in the liquid's viscosity, thus locking up the coupling. Used by Subaru in conjunction with a regular center diff, so only as a locking device, as opposed to the syncro system, in which it was used as the center diff itself, creating a part-time system. The main problem with VC locks is that they work by sensing rotational differences. Thus they risk not allowing the wheels to run free and seperately under braking. You can see that the integration of ABS, which is relying on precisely that characteristic, has been an engineer's nightmare. The syncro system was simply disconnected during braking. Others reduced the viscosity of the fluid, but this rendered the system less effective, though good enough for 4WD performance road cars. It is much cheaper than torsen, and that's where its main attraction lies.

Torsen

Invented by Gleason. Mechanical device of worm gears and a worm wheel that will split torque 50/50 in a no-slip situation. When one axle slips, the gears will send more torque to the axle with most grip, thus working in the opposite way of a conventional diff. Locking is instantaneous because it's a fully mechanical device. The gears work by sensing differences in torque instead of differences in rotation. This means it will prevent wheelspin instead of reacting and curing it. Also, it won't inadvertently lock under braking, as it will only lock under power. So torsen had all the advantages of the VC but none of its disadvantages.

Haldex

Developed by Swedish firm Haldex. Electronically controlled multi-plate clutch. Part-time, but fully automatic solution, directing torque to the rear axle when slip occurs. Compared to syncro, it negates the need for an extra clutch to disconnect the system under braking, so it's much simpler and lighter. Acts within 1/8 of a wheel rotation. Electronics control the precise distribution of torque split. Easy integration with ABS - in fact, ABS is an integral part of the system.

BTW I think Torsen stands for TORque SENsing differential (IIRC)

Duncan, you have recalled correctly...

I was wondering about the haldex and the edl/esp type systems.....

Does the esp/edl work at all speeds? What would happen if your car has 3 wheels on snow and one with grip. Would the esp allow it to move at all or would the power spin away on the other axle?

In my naive world, I imagine that the electronics would brake the slipping wheels in order to transfer the torque to the gripping one.

Mike

2002 Octavia 4x4 estate

Mike, good to see yet another Octavia owner with taste! The experts will answer shortly...

Originally posted by jenko in this post

Does the esp/edl work at all speeds? What would happen if your car has 3 wheels on snow and one with grip. Would the esp allow it to move at all or would the power spin away on the other axle?

In my naive world, I imagine that the electronics would brake the slipping wheels in order to transfer the torque to the gripping one.

Your naive world sounds perfectly realistic to me...

That's exactly what will happen. In this respect it's no different from Quattro IV. The difference is full-time (50/50 without slip) vs. part-time (100/0 without slip).

What say you guys if I sling most of this stuff together into a nice and neat one-post package? Would it be FAQ-worthy? If so, am I allowed to create such a thread or is this strictly moderator stuff?

AFAIK, everyone can post a FAQ. It mnight need approval from a moderator before it appears, but creating a FAQ should certainly be possible by all.

Right, I'll try and fix something up and will have the mods decide... I'll go and do the same for the 1.8T engine facts.

Originally posted by Dutch4x4 in this post

Now the techie stuff:

Viscous coupling

Invented by Ferguson Formula (FF). Silicone liquid in a casing.......

Torsen

Invented by Gleason. Mechanical device of worm gears and a worm wheel that will split torque 50/50 in a no-slip situation.......

Haldex

Developed by Swedish firm Haldex. Electronically controlled multi-plate clutch. Part-time, but fully automatic solution.......

Terrific descriptions thanks Dutch! I wish I had seen them a couple of weeks ago. I didn't ask the question here (didn't want to appear ignorant) so I just plugged Torsen and Haldex into Google and got straight to their sites. Talk about information overload.....

How about this for a 4WD FAQ? (Based on my own input and that of KLB.)

"What four-wheel drive system is used in my Octavia 4x4 and how does it compare to Audi's quattro system?"

Since the launch of the original Audi quattro (also known as "Urquattro"), the Volkswagen-Audi Group have developed, tested and deployed various four-wheel drive systems for their cars.

For years, the systems and the brand names were interchangeable. This changed when VAG introduced the Swedish Haldex clutch as a part-time 4WD solution for their smaller cars with transversely mounted engines. From that moment on, "quattro" was no longer a system but a brand name for Audi 4WD cars. Conversely, "4motion" was introduced as a brand name for VW's 4WD cars. Depending on engine lay-out, "quattro" and "4motion" can now point to both Quattro IV and Haldex systems.

Here's a rundown of VAG's 4WD systems and brand names used over the years. This is followed by a brief explanation of the various types of differentials used by 4WD car manufacturers.

Brand names

Audi: quattro

VW: syncro, followed by 4motion

Seat: 4

Skoda: 4x4

Systems

Quattro I: open front diff, open center diff (manual lock), open rear diff (manual lock). No ABS when locked.

Full-time manually engaged four-wheel drive.

Was on: original Audi quattro (also named "Urquattro"), Audi 80/100 quattro.

Syncro: open front diff, viscous coupling acting as the center diff, open rear diff.

Part-time automatically engaging four-wheel drive.

Was originally developed by Audi, but sourced to VW as "syncro". Similar line of thought to the Haldex system, with the VC engaging rear drive when needed. Crude system with serious drawbacks, such as a lack of ABS integration, which needed the 4WD system to be switched off under braking, using a secondary clutch. Volvo also went on to use it on their earlier Cross-Country models, adding a TC system at the front and an LSD at the back - complicated and flawed. Also on 911 Carrera 4, but then that's originally a RWD car...

Quattro II: open front diff, torque sensing ("torsen") center diff, open rear diff (manually lockable for "those" situations in the rough). No ABS when rear is locked, auto de-lock when speed exceeds 15mph.

Full-time automatically engaged four-wheel drive.

Was on: the Audi quattro ('88-'91, still nicknamed "Urquattro"), Audi 80/90 quattro, Audi 100/200 quattro, Audi Coup

So everyone agrees?

Right, I'll stick it in the FAQ.