4 motion front to rear ratio

[dvkent]

Hi all. So I've owned my 2011 CC for a few months now. Not long after I got it, I did a fairly hard launch from the traffic lights in wet conditions. I didn't just mash the pedal rather I got the car moving on light throttle and then after a second stomped it. It accelerated well with no noticeable wheel spin.
However on 3 occasions in the last week or so it has broken traction at the front wheels rather easily (once was in the dry powering out of a roundabout).
So my questions are: do these cars have any sort of coupling to transfer drive between front and rear axles? (is this what the Haldex is for?) If so does it vary according to grip available at each end of the car?

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[AdamD]

The CC uses a Haldex system, which can transfer at most 50% torque to the rear wheels, but is always sending at least 50% of torque to the front wheels. The system is essentially front-wheel-drive until it detects or anticipates that more torque should be sent to the rear wheels (up to that 50% maximum).

The Haldex system does comprise a centre differential (typically mounted near the rear diff behind the tailshaft I believe), which is essentially a clutch pack for disabling drive to the rear wheels when rear drive is not required.

[dvkent]

Thanks AdamD. So does the fact it spins the front wheels up fairly easily suggest a problem with either the diff or Haldex or is it more likely just exceeding the 50% torque?

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[AdamD]

Thanks AdamD. So does the fact it spins the front wheels up fairly easily suggest a problem with either the diff or Haldex or is it more likely just exceeding the 50% torque?

Is it always operating in FWD only (are you getting nasty wheelspin and axle tramp under heavy acceleration, particularly in the wet)? There are situations where the Haldex can fail without warnings displaying on the dash. But if we're just talking about a chirp of the fronts or a half-turn of wheelspin under heavy throttle (particularly if the front wheels are turned or on a loose surface), that's just the amount of time the Haldex takes to send drive to the rear once it detects wheelspin, assuming it's not a scenario where it's preempted the need for a greater rearward bias. The CC runs the 4th-generation Haldex IIRC, which isn't quite as rapid to respond as the latest version, but even the current system can be caught out pretty easily.

[dvkent]

Is it always operating in FWD only (are you getting nasty wheelspin and axle tramp under heavy acceleration, particularly in the wet)? There are situations where the Haldex can fail without warnings displaying on the dash. But if we're just talking about a chirp of the fronts or a half-turn of wheelspin under heavy throttle (particularly if the front wheels are turned or on a loose surface), that's just the amount of time the Haldex takes to send drive to the rear once it detects wheelspin, assuming it's not a scenario where it's preempted the need for a greater rearward bias. The CC runs the 4th-generation Haldex IIRC, which isn't quite as rapid to respond as the latest version, but even the current system can be caught out pretty easily.

I might have to do more tests, as I generally lift off the accelerator when it breaks traction. I will let you know. And I really appreciate you sharing your knowledge.

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[Bora Sport]

It definitely sounds to me like there is a problem there. I recall reading another post recently on this forum about an R36 Passat that had a problem with the haldex controller. Basically you should get any wheel spin.

[AdamD]

It definitely sounds to me like there is a problem there. I recall reading another post recently on this forum about an R36 Passat that had a problem with the haldex controller. Basically you should get any wheel spin.

Generally, you shouldn't observe any wheelspin unless you have a front wheel on a loose surface (gravel or dirt on the road), or if you've got loads of lock on around a slow tight corner on a wet road and give it a bootful while the inside wheel is unweighted. Sometimes you may be able to trigger the latter scenario through a roundabout if you're really chucking it around, although I've not managed to get anything like that aggressive in my father's CC.

To be honest, yes, it does sound like something may be amiss. Worth scanning the car for fault codes to see if the Haldex controller/clutchpack has a problem. However if the system were completely disabled, you'd see fairly effortless wheelspin in 1st gear in a straight line in the dry, with a bit of prodding. 220kw through the front wheels alone is a recipe for wheelspin.

[kamold]

In theory, the Haldex can transfer up to 100% of power to the rear wheels in the case of zero traction to front wheels (eg if front wheels were on ice and rears on tarmac) however in the real world this is pretty unlikely to happen.

Torque transfer can start in as little as 1/7th of a wheel rotation, so it shouldn'e be a case of the system not responding in time to a loss of traction to the front wheels.

There have been a few recent cases of R36 owners having the Haldex oil pump fail, causing the Haldex to effectively become disengaged and leaving only a front-wheel drive setup which will very happily break traction.

I'd have the Haldex checked for faults first, if you can't get to someone I guess you could experiment by removing the Haldex controller's fuse from the fusebox and see if there is any difference in behaviour. Checked your tyres? What sort are they?

[AdamD]

In theory, the Haldex can transfer up to 100% of power to the rear wheels in the case of zero traction to front wheels (eg if front wheels were on ice and rears on tarmac) however in the real world this is pretty unlikely to happen.

That's incorrect Kamold - distribution of torque to the front wheels cannot drop below 50%. The haldex actuator is mounted by the rear diff housing and transfer to the front wheels and the tailshaft is permanent.

Loads of detail here:

https://www.youtube.com/watch?v=CDRVTjMPK9Q

http://www.billswebspace.com/HALDEX.pdf

[kamold]

It's a theoretical discussion of which I cannot claim any full understanding, let alone authority

Here is a more detailed explanation of the 'front wheels on ice' scenario

[AdamD]

It's a theoretical discussion of which I cannot claim any full understanding, let alone authority

Here is a more detailed explanation of the 'front wheels on ice' scenario

For the purposes of this discussion, the statement is wrong, and suggesting that a Haldex can (by design) send 100% torque to the rears is misleading. Let's not spread misinformation on the Internet - there's enough of that already.

That theoretical is discussing the nature of torque transfer and mechanical differentials, and their disposition to send more torque (in some cases 100%) to the output shaft with the least load. However, it's not about the ability of a Haldex AWD system to apportion torque across specific axles. If we want to apply the same semantics, a Haldex-equipped vehicle is 'mostly' 1-wheel drive (one of the two front wheels), and at other times usually 2WD (one front, one rear depending on the wheel on each axle with the greatest load).

Torque is a tricky thing to measure (just look at the huge complexities and variations involved when measuring it on a dyno), but when discussing any real-world operating condition - when all four wheels are touching the ground - a Haldex-equipped vehicle is essentially FWD, and at most sends 50% of engine torque to the rear axle (which means usually one wheel on that axle).

[dvkent]

Thanks everyone for contributing to this thread.
So it was a wet day today so on the way home from work I tried a hard(ish) launch from standstill and to my dismay was greeted with buckets of front wheel spin and axle tramp. Houston we have a problem! I did notice when I was doing this that the little 'traction control' light flicked on.
So I guess I am off to the VW specialist...

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[kamold]

For the purposes of this discussion, the statement is wrong, and suggesting that a Haldex can (by design) send 100% torque to the rears is misleading. Let's not spread misinformation on the Internet - there's enough of that already.

That theoretical is discussing the nature of torque transfer and mechanical differentials, and their disposition to send more torque (in some cases 100%) to the output shaft with the least load. However, it's not about the ability of a Haldex AWD system to apportion torque across specific axles. If we want to apply the same semantics, a Haldex-equipped vehicle is 'mostly' 1-wheel drive (one of the two front wheels), and at other times usually 2WD (one front, one rear depending on the wheel on each axle with the greatest load).

Torque is a tricky thing to measure (just look at the huge complexities and variations involved when measuring it on a dyno), but when discussing any real-world operating condition - when all four wheels are touching the ground - a Haldex-equipped vehicle is essentially FWD, and at most sends 50% of engine torque to the rear axle (which means usually one wheel on that axle).

Thanks for the clarification Adam, makes more sense to me now

dvkent please report back to the thread on the outcome as it's always good for anyone else who may have a similar issue to know what happens. Nothing worse than finding a thread which sounds like your issue only to have the poster disappear without reporting the resolution...

[AdamD]

Have a read of this thread dvkent:

http://www.vwwatercooled.com/forums/f234/uh-oh-v6-passat-without-awd-=-balls-111358.html

I wouldn't be surprised if this is the issue you're experiencing too.

[dvkent]

Thanks for the clarification Adam, makes more sense to me now

dvkent please report back to the thread on the outcome as it's always good for anyone else who may have a similar issue to know what happens. Nothing worse than finding a thread which sounds like your issue only to have the poster disappear without reporting the resolution...

Will do. I am taking it in on Tuesday for someone to check.

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