Audi 4WD Systems

[charlie]

BS. It can never transfer more than 50% to the rear axle as the unit is at the rear axle!

I stand corrected. No need to grind ur axe
Obviously i was missinformed by Audi maindealer
when i span TT 225 twice
and was doing donuts in the snow at a "T junction" :mischeif:

[4WheelDrifter]

Porkkis is right. The Haldex unit is at the end of the propshaft, just ahead of the rear diff.

There is a lot of BS flying around surrounding this. Some even say torque split is 50:50, and can be shifted 100:0, and even 0:100. Witchcraft maybe?
I Guess Keeper of The Kitten is correct, in the fact that if the Haldex can be disconnected, then I cannot be classed as Permanent 4WD.
I will defend it does seem to be a good system.

As for "Is it a real quattro?". Well, at the end of the day 'quattro' is Audi's marketing tool. In the same way as Volkswagon's is now '4motion'. These terms obviously cover both Torsen systems and Haldex systems.

Now. Where do I put the spot welds to make my Torsen permanently 50:50 torque split?

[yoggi]

Having owned both driven systems i can confidently say;

Haldex:
- it's a swedish invention which is alot lighter and more compact
about 100 kgs compared to Torsen.
- It's normally 95% to front wheels, 5% to rear
- It uses an electric engaging clutch which is activated
when either front wheels start to spin as read by ABS sensors
- Their is software that allows u to have 50/50 split at all times
or can be fine tuned to any % ur heart desires.
- Can transfer up to 95% of power to rear wheels
-very quick and instantanious transfer rate compared to Torsen
_ very dangerous to dry quickly in snow
_ same system used by Volvo S70, V70 , AWD.

Torsen:
- Derived from TORgue SENsing and is controled by torque output
of engine ( not ABS sensors or bhp)
- Slower to react than Haldex.
_ consumes more power than Haldex
- only effective only effective when powering through corners
i.e slow in, fast out. with practice you can get your back end out
using the pendulam technique.
- slowing down using gears still engages 4wd system but dipping clutch
or braking disengages 4wd system in order for ABS to be active
- alot safer to drive in snow and more fun its just a shame audi
dropped the ABS switch found on 3B cars

Everything of this is true except one thing, torsen reacts faster than the haldex because its a mecanicsystem, it doesnt need electronics telling it a wheel is slipping!

[Henka]

Having owned both driven systems i can confidently say;

Haldex:
- it's a swedish invention which is alot lighter and more compact
about 100 kgs compared to Torsen.
- It's normally 95% to front wheels, 5% to rear
- It uses an electric engaging clutch which is activated
when either front wheels start to spin as read by ABS sensors
- Their is software that allows u to have 50/50 split at all times
or can be fine tuned to any % ur heart desires.
- Can transfer up to 95% of power to rear wheels
-very quick and instantanious transfer rate compared to Torsen
_ very dangerous to dry quickly in snow
_ same system used by Volvo S70, V70 , AWD.

Torsen:
- Derived from TORgue SENsing and is controled by torque output
of engine ( not ABS sensors or bhp)
- Slower to react than Haldex.
_ consumes more power than Haldex
- only effective only effective when powering through corners
i.e slow in, fast out. with practice you can get your back end out
using the pendulam technique.
- slowing down using gears still engages 4wd system but dipping clutch
or braking disengages 4wd system in order for ABS to be active
- alot safer to drive in snow and more fun its just a shame audi
dropped the ABS switch found on 3B cars

Hey hey hey... You need to explain what you mean here. What do you mean by the following:

Slowing down using gears still engages 4wd system but dipping clutch or braking disengages 4wd system in order for ABS to be active

Not true. The 4wd is NEVER diengaged. It is... in lack of a better word... permanent.

How do you mean it is "controlled by the torque output of engine"? I mean, it is not "controlled" by anything, it is a mechanical differential that splits the torque to front and rear axle.

You also state that torque transfer on Haldex is instantanious compared to Torsen. As the torque split between the front and rear axle of a Torsen system is continous, it is even faster than "instantanious"... It does not wait for anything to happen, it is happening ALL the time, at any given time.

Oh and... Why would Haldex be hazardous to drive in the winter?

Saying that a Torsen has a 50-50 torque split is not true. It is true only in the "static" case, where each wheel has exactly the same friction to the ground and has the same speed. As soon as one wheel starts to spin, the torque split will be different. Therefore, you can NOT describe any Haldex system as ANYTING else that 95-5 split. On a Haldex, the front axle is alwas driven. What varies is how much torque that is put to the rear wheels. The torque split will vary between 95-5 to 50-50 - but this is only relatively thinking. The front wheels always get the same amount of force/torque and correlating wheel speed.

The reason that the torque-split is 95:5 in "static" mode is that the front and rear axle have different gearing. Reason? Well, no matter how "instantanious" the system is on paper and in theory, the reality always catches up. The 5% difference in gearing is there to ensure that the rear wheels actually are engaged in decent time. Had it not been for that, well then the Haldex systemwould have been slow - no matter how instantanious the electronics would have decided it was time to react. This trick was also used in the old Syncro system, the system found in Golf 2 and Passat with transverse engine.

Volvo using Haldex is only true when it comes to later cars. The early AWD's used the old Syncro style system, tey actually "bought" that from VW. When VW widely went over to Haldex, Volvo still used the Syncro system. Later, they incorporated a Haldex unit. This is the main reason that the early Volvo AWD cars were terrible. The Syncro sausage was even slower that the Haldex unit to engage... Horrible.