Hi guys, just giving my personal description of how Haldex work on our A3/S3s
Essentially, the front wheels are 100% driven directly from the transmission like any 2WD A3, but from the side of the gear box(I think?) is a prop shaft that goes to the rear of the car where the Haldex coupling is situated, which is actually a clutch that operates/controls the amount of drive the rear wheels get.
During normal driving, the Haldex is usually doing sod all, so the car behaves like a 2WD motor, with the rears disconnected from the fronts. When things start to get serious for the driver, and the car senses slip between the front and rear axles, then the Haldex is engaged to deliver power to the rears, and gives us 4WD.
Now here comes the technical bit with regards to power distribution, when the Haldex is fully engaged, the car will have 50:50 drive to the front and rear wheels, so the power distribution should only ever be 50:50 max between the front and rears. It is Impossible for any more than 50% of the drive to go to the rear axle with this setup, as the fronts are directly connected to the transmission as mentioned above! Now with regards to having the ability to transfer 100% of the power/torque to the rear wheels in extreme conditions, picture this, put the front end of your A3 Quattro on axle stands(lets say the axle stands have castors on them) and the rear wheels are on the ground. Now if you try to pull off in 1st gear, the fronts will start to rotate, then all the electrics come into play and engages the Haldex, and there is drive to the rear axles pushing your Quattro forwards. In this 'Extreme' condition, the front will be free wheeling(they are off the ground!), as they need to rotate to give drive to the rears, so the drive is still 50:50, but as only the rear wheels are pushing the car forwards, all the torque is going to the rear of the car!.
There we have it, It's been a long night, and I wanted to get this off my chest. /ubbthreads/images/graemlins/tongue.gif
Hope that has made it more clear to anyone whose read this far lol. /ubbthreads/images/graemlins/grin.gif
Any more questions on Haldex, form an orderly queue over here. ---->