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Haldex Upgrades - questions

Discussion in 'A3/S3/Sportback (8P Chassis)' started by George K, Apr 20, 2008.

  1. George K
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    George K Hill Climber

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    [Apr 20, 2008]
    Haldex Upgrades – Questions

    I am trying to obtain feedback from anyone who has used one of these or has access to a more detailed technical spec than is available on most websites.

    Let me explain my understanding of the Haldex, as this will then set my questions into perspective.

    The Haldex is a part-time four wheel drive system , consisting of a normal front wheel drive system, with a part time connection to the rear wheels made by the Haldex clutch pack. This connection is basically triggered by a speed differential between the front and rear ABS sensors. This means that the system is at its best in muddy or snowy conditions. Similarly it should cut in when front wheel spin occurs from a standing start. This arrangement means that, despite PR artistic licence, without front wheel spin it is impossible for more than 50% of the torque to go to the rear wheels. Similarly this also implies that it will only help to combat understeer once a front wheel starts slipping (much too late).

    By contrast a true 4WD first feeds power to a centre diff and then to the front and rear axles – this normally gives a 50/50 split. In the case of the rightly much praised RS4, not only is there a centre diff with a limited slip function (Torsen), but it also incorporates an epicyclic gear which gives a rear bias of 60/40. For circuit use an even more extreme bias is often used (I have seen 72/28).

    The only way in which I can see the Haldex function being more performance orientated is by supplementing the ABS sensors with Yaw sensors and accelerometers, some of which I believe are now fitted to the current generation of Haldex systems as fitted to the TT. I would guess that the after market upgrade simply takes this one step further.

    Now to my specific questions:

    - Has anyone used one of these upgrades (Haldex or MTM) and if so does it reduce understeer?

    - What are the conditions under which it will activate the clutch pack?

    - If it completely locks the clutch pack, does it create any problems by forcing the front and rear axles to run at the same speed? Normally in cornering the rears run slightly slower as the corner radius is normally less at the rear – possibly only an issue on tight corners.

    - If it does not completely lock the clutch pack, then the plates will slip which can cause overheating or premature wear – any known problems?

    Apologies for such a long post, but any help will be much appreciated.
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  3. julians
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    julians Member

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    [Apr 20, 2008]
    Which haldex are you talking about? you're in the 8p section and I beleive the 8p version does indeed use various inputs (throttle positon, accelerometers etc) to send torque to the back at any time and not just when wheelspin is detected. I beleive the only time when wheelspin is the primary reason to send torque backwards is from a standing start. As you say if this were the only time when torque were sent backwards it would be a bit pointless, for two reasons, firstly, its too late, and secondly the ESP system will have killed the power to stop the wheelspin, and hence removed the need for torque to go to the back.

    The official haldex upgrade (HPP) appears to send power to the back in a more aggressive manner, ie sooner than the standard car, but it'll never send more than 50% to the back.

    You can see I've caveated that quite substantially as its just my interpretation from driving the car and reading things on the web, there appears to be precious little official info on under what conditions torque is sent backwards, the main focus being on wheelspin.
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  4. warren_S5
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    warren_S5 Moderator Staff Member Moderator VCDS Map User

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    [Apr 20, 2008]
    Based on the points raised above, why do Haldex make 2 variants of controller (standard & performance). As you can only ever send a max of 50% to the rear, is the upgraded controller going to deliver enough benefit to make it worth the cost / to be noticeable over the standard one? WOuld the average driver be able to feel that the power was being delivered to the rear wheel more quickly?
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  5. phantom
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    phantom On Boost

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    [Apr 20, 2008]
    As i read it ( i'm also thinking/looking into the HPP controller ) the 8p/MKV controller is superior to the 8L/MKiv version of Haldex.

    I was under the impression that even the STD unit can send up to 100% power/torque to the rear if needed?

    The new HPP for the 8P/MKV give you the option to have 3 settings if you choose to have the switch fitted, STD, sport, and race modes, if you don't choose to have the switch you can choose which mode you want it in sport or race as STD is pointless!

    There are some threads knocking around on it R32 owners club , ect.

    Std = does what it says on the tin
    Sport = 50/50 split ( my choice )
    Race = 30/70 not recomended for road use.

    I could have read it all wrong on the above^^^^^^if so i stand corrected!

    People who have had it done say it's better than STD and it's worth it if you drive your car hard or else you may not notice it!

    Thanks

    p
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  6. George K
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    George K Hill Climber

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    [Apr 20, 2008]
    I am asking about the latest version - I am a prospective owner.

    Julians does raise an interesting point about the ESP - complicated algorithms to say the least!

    I do agree that my question is almost irrelevant for road use - I am looking at the occasional bit of competition when a more aggressive lock up strategy might be helpful, but want to understand the implications and any downsides.

    Irrespective of what any blurb says it is a scientific impossibility for a Haldex to send more than 50% torque ot the rear wheels unless the front wheels spin - this is the artisitic licence to which I was referring. The most that can be achieved is permanent lock-up (50/50) and that would have all sorts of nasty side effects.
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  7. julians
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    julians Member

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    [Apr 20, 2008]
    Yep, it can never send more than 50% of the total torque to the rear (unless the fronts are spinning on a frictionless surface -icey?).

    It is very good, but for fullon/spiriting driving it could do with sending the torque backwards sooner, it could also do with a proper LSD on the front and back, but then thats probably taking things a bit far.
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  8. PNH80
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    PNH80 Low life livin' the high life.

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    [Apr 20, 2008]
    It is also my understanding that no more than 50% of the power can ever be sent to the rear with a Haldex system. By upgrading the system it basically becomes more predictive, aggressive and responsive at delivering power to the rear. You may not really notice a massive difference in 'normal' dry conditions but under ANY loss of traction or during a spirited drive on a twisty road you should see a very noticeable difference.
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  9. phantom
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    phantom On Boost

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    [Apr 20, 2008]
    Maybe i was getting mixed up between " before and after slipage" about the amount of torque transfer.

    p
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  10. phantom
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    phantom On Boost

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    [Apr 20, 2008]
    Not long after 2pm everything was finished and I was handed the keys along with the original Haldex system for safe keeping. I remember looking at the car and getting a little kick out of knowing that although it looked standard, it no longer was! The switch (used to change between Normal, Sport and Race) is quite big and does stick out next to the OEM push buttons but it’s good quality and has a tactile, silent click when turned. It’s nicer to use than the mirror adjustment knob and being large, you’re able to operate it without braking concentration.

    The drive home was uneventful, I was tired and it was raining heavily so I drove like a little old lady (but with observation and indication). This morning however was a different matter. I’ve been out and had a play on some well known roads. In normal cornering and acceleration there’s no difference which is to be expected but if you turn off ESP and find a deserted roundabout it’s a different story! When you’re pushing it, the difference between “Normal/Stock” and “Sport” mode is obvious. The car is far more balanced, understeer is dramatically reduced (unless it’s very tight) and when loss of traction occurs, it’s progressive and all four wheels are involved. I went over the same ground multiple times in Standard and Sport modes comparing the two and it really is so much better (and faster) in Sport. The best way of describing it is simply to say that the car now feels like a true AWD. I didn’t think I’d be writing that two months ago! Why it doesn’t come like this out of the box is a mystery to me.

    I have tried Race mode but if I’m honest, I’m a little apprehensive about testing it as I still don’t know the car anywhere near as well as I did my Peugeot and I don’t fancy over-steering into the middle of a roundabout or over correcting and flying into someone waiting at a junction! I’ve never been to a track day, never had an advanced lesson and the only experience I have was gained years ago rallying a pickup on my friends farm. I’m sure it will become a firm favourite but maybe it’s safer to explore on a track.

    So, is it worth the money? I guess it depends on your priorities and how much you value £850. If you tend to drive your car well within its limit and see it as a long distance cruiser with the ability to overtake slower moving cars then I wouldn’t say so. It’s only when you’re loosing traction in a corner that you feel the difference so it’s really geared towards someone who enjoys a very spirited drive and/or goes to track days. I’m sure on a circuit you’d really see the true potential of this modification. I would be astounded if it didn’t shave a noticeable amount of time off your lap.

    I’m still yet to gain a full understanding of this mod but the first signs are encouraging. I’m a happy chappy and glad I went for it. I wonder if a set of ARB’s would further enhance the handling…

    Stay tuned!


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    Taken from the R32 owners club thread.

    I'll try and find more tech info

    p
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  11. phantom
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    phantom On Boost

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  12. Relaxitscool
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    Relaxitscool Member

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    [Apr 20, 2008]
    I was also under the impression that the Haldex system took readings from steering input, and that at anything over 15 degrees wheel turn Haldex started to feed power to the rear wheels, so ineffect the only time the car is front wheel drive only is in the dead straight ahead with no traction issues.

    Regards

    Rob
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  13. Relaxitscool
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    Relaxitscool Member

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    [Apr 20, 2008]
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  14. George K
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    George K Hill Climber

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    [Apr 20, 2008]
    Relaxitscool - I had a look at the link, sadly it is technically incorrect in saying:

    'The haldex is the centre differential and is responsible for dividing torque between the front and rear axles. It is used in VAG AWD cars that have a transverse mounted engine (Golf/A3). The longitudinally mounted engines (Passat/A4/A6) use a torsen centre diff and this is the traditional quattro setup. Audi muddy the waters by calling the haldex setup in an Audi "quattro" (A3/S3)and the torsen setup in a VW "4motion" (Passat).'

    If you refer back to my opening notes, you will see that the haldex is a clutch pack to make the connection from the front to the rear wheels, but the main difference from a true 4WD system is that there is not a centre differential! Oops!

    It is this lack of a centre differnntial that led to my questions in the first place.

    Still an interesting post - keep looking!

    Thanks
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  15. phantom
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    phantom On Boost

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    [Apr 20, 2008]
    A Bugatti veyron uses Haldex

    I would have a guess at it not being the same one found in a S3 though LOL

    p
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  16. Dandle
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    Dandle Member

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    [Apr 20, 2008]
    The way in which haldex works can be found by searching through previous posts for an explanation. To be short it isn’t front wheel drive until wheelspin is detected and any time the car is moving fwd with a throttle input and no brake input the clutch pack will be engaged and transmitting power aft, with varying degrees depending on throttle position, speed and steering etc. All the HPP controller does is act more aggressively to move more power aft quicker than the standard controller does. Never tried it though so cant comment on how much better it is, although i've never heard anything negative about the upgrade.
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  17. phantom
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    phantom On Boost

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    [Apr 21, 2008]
    So the only bit that is incorrect are the STD , Sport and Race figures i put down ( i must of read them somewhere , i don't make figures up for fun ) but you decided to miss out the bit where i said " i could be wrong on the above if so i stand corrected " from your qoute.

    p
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  18. inigoj
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    inigoj Member

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    [Apr 21, 2008]
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  19. Dandle
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    Dandle Member

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    [Apr 21, 2008]
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  20. inigoj
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    inigoj Member

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    [Apr 21, 2008]
    I didnt see a problem with it, the brief description must be taken as a whole, and is an short overview of the system as oposed to the torsen or Borg-werner, it describes the basic shift of potential power to the axles, and depends what you class as 'normal driving conditions'. lol

    In reality, just pootling along in the flat at low constant speed, you will have around 3% of troque to rear (for a given value of 'pootling')
    #19

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