From Wiki:

"Haldex is a Swedish company manufacturing for example the Haldex electro-hydraulic limited-slip "coupler" or clutch, used in vehicles with automatic all wheel drive systems to engage and disengage a secondary axle when needed. "Haldex" refers to the aforementioned differential system — its most prominent use is in all transverse engine 4x4 models of the Volkswagen Group: (Audi A3 and TT, and Volkswagen Golf ), making them non-permanent 4x4s, unlike longitudinal engine models (Audi A4, A6, A8, previous-Volkswagen Passat) which use a Torsen centre differential. However, its short reaction time (only a seventh of a wheel spin) relative to systems like a viscous coupling, and ability to fully lock mitigate its theoretical disadvantage to a full-time AWD (like Torsen) setup. The Haldex LSC has been used in AWD models of VW by the name "4motion", and Audi cars under the name of "quattro". The same labels have also been applied to Torsen-based, full-time AWD systems from both VW and Audi which has led to confusion and some amount of heated debate as to the relative merits of each system. This is nothing more than confusion over nomenclature; due to the fact that the original Audi Quattro coupe did use a torque-sensing center differential (not Torsen, however), many fans believe that "quattro" refers to said type of AWD system, not realizing that it is simply a trademark (It is interesting to note that "quattro" is also used on the Audi Q7 SUV, which uses neither Torsen nor Haldex; instead, it uses a BorgWarner system."

Haldwx webby: http://www.haldex-traction.com/

 

I posted this elsewhere, but since I don't know if it will ever make it to a sticky, I'd post here too.
Installed the Haldex Blue controller. The install really isn't that bad. Just be prepared to spend about 2 hours to do it right. From the start, be prepared to drop the exhaust from the cat back. That's to remove the heat shield over the rear muffler. That's makes it much easier to unplug the wiring. Also, remove the plastic stone shield covering the gas tank. That gives you a couple more inches to work on getting the controller out. Also, get a small 4mm hex (allen) key. Other than that, take your time.
Been driving it for the last 2.5 hours. As others have said, not much difference during normal driving. However, the car seems faster off the line, boost is smoother (don't know why), and turns are awesome. Why it doesn't come from the factory like this I can't understand!

Here's the link: http://forums.vwvortex.com/zerothread?id=3665625

And install instructions: Neuspeed Haldex Blue Install Instructions

 

I'll agree with the stone shield over the gas tank, I'll say you can skip the exhaust removal part, it didn't take 2 hours to do, probably because I wasn't screwing around with the exhaust.

 

I won't argue that point. I have found in the past that sometimes it's easier to go ahead and do things that take a little longer than spend more time trying to figure out how to work around doing something. The exhaust probably added a half hour to the whole process. But having done it once, I can probably get away with not doing it again.

 

How long have you been running the blue controller now?

Dunno if you've seen any of my other posts, but my haldex clutchpack is presumed to be burned out. No basis for/against it, but curious if the blue had anything to do with it. Car has 136,000+ miles, I figure that might have more to do with it.

 

Is there a differencial or something to make the split more to the rear or atleast 50/50 just curious...I see aftermarket differenials all the time such as this one:
http://www.mjmautohaus.com/catalog/p...oducts_id=2657

 

That's the idea of the Blue Controller.

 

My ESP light comes on as soon as I start driving and do get the odd noise on tight steering, so pretty sure it's the Haldex Control Unit.

What's the issue if I don't change the controller? I had a quote of around £800 for a new one fitted at Audi in West London.

Cheers,
Lee

 

Gotta give us a little more info. Do you have the stock controller or the Blue? Any DTCs? Have you checked your fuses?

 

It's a 2001 Audi TT Roadster 225 - I've only done 21,000 miles - Fuses all looked ok, is therea specific fuse I should be looking for?

In terms of the controller, it'll be the one that is fitted by default - I assume that's the stock controller??

Cheers