2018 S3 Haldex / rear drive (contains tale of woe)

The Cardinal

For the love of cars
As covered in my thread here, I have a 2018 S3 S-Tronic. I've never been convinced that it had proper working 4WD when compared to my previous cars, so had it inspected in the last few days. As suspected (and despite new fluid earlier this year), the Haldex pump gauze was gunked-up.

Unfortunately, replacing the Haldex pump and doing the VCDS pump re-learn procedure doesn't seem to have improved things. I'm told that the rear transfer box still isn't getting sufficient oil flow. The garage is going to try a final flush of the system from the pump onwards in case the gunk has gotten that far, but otherwise they say the next step is a new rear transfer box at c.£5k fitted!

I'm obviously a bit unsettled at that prospect. :blue: It certainly doesn't seem like great value compared to all the other things in my life and at that price I'd consider the alternatives. Sadly, the car is out of warranty.

I guess I'm just asking for any experience or opinions on this. One option is to have a second garage or Haldex specialist look at it, though I'm already racking up a fair bit of labour charges just getting this far. :(
 

A3SBQ

A3 SportBack 2TFSI quattro DSG
There have been other reporting issues like you are describing.
The outcome was the angel gear/transfer box being the problem.
The ring gear is pressed on to the out going shaft to the back to the rear diff (Haldex)
This ring gear has detached it self from the shaft and now is spinning when torque is applied!
No one has experienced nor reported any noise from this...
All have tried everything with the rear diff even bought a new one with out any better solution!
In the end it was the transfer box...

Good luck.
Please report back...

Sent fra min SM-N975F via Tapatalk
 

The Cardinal

For the love of cars
Yes, my garage have diagnosed the transfer box... that's what's behind the £5k estimate. I'll update what they say...

If the diagnosis remains the transfer box then I'm minded to pause things there and make no quick decisions. It's pretty driveable even in its current state.
 

Harvey

VAG Convert
Could be worth speaking with a a few companies who have a fuller understanding of the haldex/rear diff to hear what they recommend. A couple that spring to mind are these but there are more out there. If you were closer and obtained a known good second hand unit I'd happily help swapping it out as it doesn't look difficult ;)

Might also be worth having a poke around the world of Golf R mk7.5 forums as they use the exact same kit as your FL S3. See if there are any similar symptoms and what their fix was.

Just found this place that offer replacement rear clutch plates.

Another interesting read for you as it's more than likely the haldex side of the whole rear unit that is your issue and nothing at all to do with the rear diff. So basically you require the haldex clutch plates inspecting.

Video of how the haldex gen 5 clutch pack works.
 
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The Cardinal

For the love of cars
Well, this tale took an unexpected turn and not one I've seen reported elsewhere online.

20210917-133323.jpg


Firstly, a proper VCDS scan did show a fault code. I haven't checked which the code was, but it's not one that came up via my Carista app and that's worth noting in itself. The mechanic removed the original Haldex pump and found it to be working, though with shards of metal and gunk present. I guess this is what many other people are finding and, following a clean / new oil / reset this is usually enough to solve the issue.

[I should add that my Haldex oil was changed 2,500 miles ago by the same people...]

This might normally have been enough to restore satisfactory performance. However, in my case, there was another issue.

This second issue was a manufacturing defect in the Haldex unit itself - where several of the oil reservoir chambers were insufficiently machined and this meant that the unit was unable to create sufficient pressure. The mechanic's view was that this was present at the time of manufacture and that the rear drive had quite probably never worked from new. :shrug:

The solution of shortening the drain plug to create more space for the oil flow. I was instructed to tell whoever does the next Haldex oil change to make the same adaptation to the drain plug. I'm a little confused about this and it seems slightly bodge-ish. Nonetheless, it's worked!

Finally, the Haldex pump was replaced as it was found to be underperforming - probably a legacy of the first issue.

Just... wow. The transformation of the driving experience is immense. I challenge anyone to drive one of these cars in the state mine was in and then not to notice a *massive* improvement. Even at very low speeds there's an huge difference, while on the open road / out of bends etc it's nothing short of breathtaking now that full torque is being put down by all 4 wheels. Now I know why I persisted in solving this and it reminds me how well-suited these VAG 4WD hatches can be for me and my preferences.

I drove the car for 5 months and 2,500 miles in its pre-fixed state. To think that the first owner probably drove 22,000 miles like that seems amazing to me.

I suppose the final bill was somewhat steeper than I'd like, caused by more investigate labour and two flushes of the Haldex fluid - but right now it seems worth it.

20210917-122945.jpg
 

Harvey

VAG Convert
Fantastic news and what a strange fault, so glad someone has finally got to the bottom of it and you've fell in love once again with your :s3addict: . I had wondered why the drain plug was so long in the first place but there must be a reason for this. At least you now have the full package.
 
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Damo S

Registered User
Out of warranty or not Id be pushing Audi to supply a new Haldex as that is NOT acceptable. Had you reported traction issues before the warranty ran out?
Clearly it was never fit for purpose and how would perhaps a non-car nerd know anything was wrong with the car from new if they didnt know what it was meant to feel like? If I was you I'd be on it like a car bonnet. This drain plug bodge is just that, a bodge. But its great to read that you don't need to fork out for a new transfer box at least.
 

-Ju-

Well-Known Member
VCDS Map User
Out of warranty or not Id be pushing Audi to supply a new Haldex as that is NOT acceptable. Had you reported traction issues before the warranty ran out?
Clearly it was never fit for purpose and how would perhaps a non-car nerd know anything was wrong with the car from new if they didnt know what it was meant to feel like? If I was you I'd be on it like a car bonnet. This drain plug bodge is just that, a bodge. But its great to read that you don't need to fork out for a new transfer box at least.
100% agree with this.
If the original casting is still untouched and the diagnosis is correct I'd be taking it up with your local dealer and Audi uk as ultimately it should be replaced FOC
Who knows what damage has been caused from new
 

Mr Freeze

Registered User
Happy to read the car is back working as it should a 5k bill would of been a disaster .

This is why I always keep my cars in warranty you never know what's round the corner with cars especially high performance ones .
 

The Cardinal

For the love of cars
The mechanic explained to me that the reservoir inside the Haldex unit is quite small and relies on a reverse waterfall (i.e. pushing fluid up and over an obstacle) to create the required pressure to drive its clutch. I was told the lack of gallery machining is quite fractional and must obviously have been so for a slightly shorter bolt to create the required space, but it was sufficient for the new pump to then generate enough pressure and give full(er) rear drive.

I don't think it's likely that damage has been done. In fact, you could argue the opposite. The front has been working harder than the rear arguably since new, but the rear setup has been lubricated and working... it's just not been working very hard. This is the default for a Haldex 4WD unit anyway.

You would expect this sort of thing to be a claim under Audi warranty if it had been continuously covered. However, the car was bought just after the 3rd year from an independent dealer and their own sale warranty has also since expired. The car would have been eligible for extension of the Audi warranty but I chose not to because I run a remap on the car. A TD1 flag would give the warranty company a get-out clause for most of the expensive stuff. My feeling is that an Audi workshop would have replaced the whole Hadlex unit and that I would have been asked to pay!

So, it's a bit painful - not ruinous, though - and I think the chances of someone else coughing up are limited. To put things in perspective, it's about a third of the cost of maintaining my van and other car this year and I could sell this S3 for more than I bought it for in this current market.
 
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