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Haldex Gen II Owbers/Advise

Discussion in 'A3/S3/Sportback (8P Chassis)' started by A3_3.2_S-Line, Dec 10, 2007.

  1. A3_3.2_S-Line
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    A3_3.2_S-Line Member

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    [Dec 10, 2007]
    After a couple of hours driving in the wet over the weekend I am seriously thinking about get this mod ASAP.


    I don’t know if you guys have noticed on your cars, but my car goes around corners much better in the wet then in the dry.

    There is noticeably less under steer and I can really notice the rear wheels pushing the car around the corner as the front wheels start to slip.


    I have done a load of research into this and from what I can work out, it will give my car similar characteristics in the dry.


    For all you guys that do have it installed, is this the sort of results I can aspect from this mod or am I way off? Also have you noticed better acceleration due to better traction?
    #1
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  3. killa_z
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    killa_z Couped Out

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    [Dec 10, 2007]
    am also looking very seriously into this mod

    basically, as far as i know it transferrs more power more aggressivly to the rear wheels, if installed with a switch you can choose from race,sport or stock modes

    courtesy of Ben who is able to shed more light on it

    #2
  4. s3mike
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    s3mike Member

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    [Dec 10, 2007]
    I haven't quite worked this out but I'm sure others have said the Haldex can only apply power to rear when the fronts start to spin ( as it works of difference in driveshaft speeds or something ). It's only meant to take a 1/4 turn more for a front wheel than back before it starts working but the fronts still need to be turning faster than the rears to engage the clutch pack.

    If this is the case what difference would the controller make? It still cannot provide power until the fronts start to spin, which probably wouldn't happen in the dry.

    Could be totally wrong on this, if somebody could explain how the system works I'd be grateful!
    #3
  5. boggysv
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    boggysv Member

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    [Dec 10, 2007]
    less than quarter turn needed, just 15degrees is enough.

    read this site for more info how the haldex controller applies power to the rear more aggresively (though the pictures show a gen1, it's concept is similar)
    http://www.wak-tt.com/mods/haldexpp/haldexpp.htm

    slow-mo video of a r32 launching
    http://s113.photobucket.com/albums/...view&current=r32-launch-gravel-turbo-slow.flv
    #4
  6. JohnS3
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    JohnS3 Active Member

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    [Dec 10, 2007]
    Ouch, paintwork!!
    #5
  7. Dandle
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    Dandle Member

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    [Dec 10, 2007]
    It doesnt quite work like you have mentioned. The system will be working and transfering power all the time the car is moving fwd with some throttle input. Slip isnt wheel spin it is a difference in torque sensed between the front and rear diffs(in effect). The wheel degrees you see quoted about is the amount of front axle rotation needed from a standstill for the haldex clutch pack to be transfering maximum power aft, not for it to start transfering at all times(im not sure on how many degrees the gen 2 system needs though). There is a slight pause before it works from standstill before it transfers power as it needs the input shaft to build up pressure to close the clutch pack. Gen 2 pre-x eleminates this with the use of an electric pump to always supply pressure but thats only used by vovlo at the moment.. The pressure is always there if the car is moving and then its up to the Haldex ECU how much it closes the clutch pack to vary the power aft. With less being sent aft while high speed driving but more with agressive driving, cornering and parking.

    The HPP will send a larger amount of power aft alot more of the time to give the car more of a RWD feel compared to standard.

    Hope that helps somewhat :).
    #6
  8. magnus911
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    magnus911 R8GGA

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    [Dec 10, 2007]
    But the thing to remember is that because of the way the gearing is connected to the front axle, no more than 50% of the power can ever go to the rear axle, so you'll never get a true RWD experience...right Dandle?
    #7
  9. julians
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    julians Member

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    [Dec 10, 2007]
    That post by Dandle explains a lot and makes total sense.

    I guess (now I know) its obvious really as otherwise it would be purely front wheel drive for 99.99% of the time apart from when setting off violently or understeering badly round a bend under excessive power.
    #8
  10. Dandle
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    Dandle Member

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    [Dec 10, 2007]
    Thats correct the haldex unit can only move power from the front diff aft. It can be 100% rear drive but only if the front wheels are in the air or on ice etc. It will nearly always be front biased though like you say.
    #9
  11. A3_3.2_S-Line
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    A3_3.2_S-Line Member

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    [Dec 10, 2007]
    So is it going to handle in the dry like it does in the wet with the upgraded?
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  12. Dandle
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    Dandle Member

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    [Dec 10, 2007]
    I would think it would be alot more agressive all the time. I have never driven a HPP equiped car but people who have it rave about how much better it is all the time.
    #11
  13. s3mike
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    s3mike Member

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    [Dec 11, 2007]
    Your description makes a lot more sense.. thanks Dandle.

    I was kind of wondering how it would work if power could only go to the rear when wheels are spinning. If that was the case accelerating from a standstill through puddles would mean you keep getting small doses of wheelspin as the front wheels lose grip, which I'm glad to say isn't the case.

    Once moving I never get any wheelspin, sometimes you feel a small scrabble from the front wheels when driving off in the wet but as soon as the Haldex kicks in it stops. Only problem is the ASR kicks in a bit too much and brakes / cuts power, if you turn it off the car just spins all 4 wheels for a second and then takes off.

    I keep forgetting it's 4wd but then I remember what my Leon Cupra R was like in the wet!!
    #12

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