Bora 4mo ESP kicking in at slow speeds

[djorkboy]

Here is my understanding of the setup of a Bora 4motion, feel free to correct where I am wrong (I'm used to it, I am married)....

It seems that a lot of people, including mechanics, use the word 'diff" when talking about the Haldex. I think this is partially because the Haldex is bolted to the diff housing.

The Haldex is a Viscous Coupling and contains clutches, but it is a totally separate unit from the Transaxle/Diff that the Haldex is merely bolted to. The diff contains no clutches, it is just a regular diff similar in concept to what you would find in any Commodore, Falcon etc.

In theory you could unbolt the Haldex, install a longer driveshaft connected directly to the transaxle and have a permanant 4 wheel drive system (well, it would be permanant until you drive it around a few corners and the transfer case blows up)

Here's a picture I knocked up in photoshop from a layout of an Audi TT..... (please don't think I'm trying to insult anyone's intelligence here, I know that everybody knows at least 90% of what this picture shows, if not more, I'm just trying to clarify my thoughts)

[djorkboy]

Now, having posted my previous tome, let me move onto my thoughts on this problem, and please bear in mind that I am an idiot and am usually completely wrong (as before, just ask my wife)

If it was the diff, which is purely mechanical, would there not be lots of crunching, grinding and whining if it had a problem bad enough to make the wheel skip?

If it was the Haldex would there not be an error code or light seeing as how the Haldex is so tightly monitored and controlled by the car's computer systems?

So that leaves the ABS. This to me seems most likely. The ABS can lock a wheel completely independently of the other systems. So if it were me I would be looking at the condition of my ABS sensors.

...oh, and I tried to replicate the problem a couple of times with my Bora and could not get it to happen. No matter how tight I turn or what speed I do it at I cannot get the wheels to skip, drag or chirp at all.

[popeclement]

Thanks djorkboy - your explanation v good. I started thinking ABS sensors but as the problem on my vehicle has only just started and can be reproduced doing either a RH or LH full lock turn, why would both sensors fail together - maybe its another common input to the Haldex?

[grtuned]

My understanding of the paragraph is at low speeds like taking of while turning the wheel speed sensors are not accurate so the
longtitudinal sensor compensates for speed input. Which if means if no signal is being transmitted to the abs unit from the wheel sensorsthe longtitudinal sensor may be causing ESP light to flash due to it being faulty. The only way to test would be to change it and see whathappens. like i said earlier post its an expensive test

And in English? lol

Is it saying it's a natural thing under certain conditions, or only if it's faulty?

In my car it feels as if just one rear wheel is dragging, not both the rear wheels. That's why I think it's the rear diff. Feels as if the clutch/spring packs are screwed and when going slow it doesn't have enough torque to over power the clutch in the diff to make it spin the same speed. Maybe I need to look from outside the car because I noticed when my wife dropped me off and turned tight it left skid marks (the rubber kind) but don't know which wheel(s) left them.

Also in regards to me removing fuse 31 to disable the haldex: I asked earlier.. If the fuse is removed then it is only FWD and takes the haldex AND rear diff out of the question?

[djorkboy]

My understanding of the paragraph is at low speeds like taking of while turning the wheel speed sensors are not accurate so the
longtitudinal sensor compensates for speed input. Which if means if no signal is being transmitted to the abs unit from the wheel sensorsthe longtitudinal sensor may be causing ESP light to flash due to it being faulty. The only way to test would be to change it and see whathappens. like i said earlier post its an expensive test

The VW Self Study document that covers the Haldex system says the following about the failure of the longitudinal acceleration sensor...

Without the additional measurement of longitudinal accelleration, it is not possible to determine the true vehicle road speed exactly in unfavourable conditions. The ESP and TCS functions fail. When ESP is activated, the Haldex coupling is opened.

This is a little ambiguous but, it might mean that in "unfavourable conditions" a failed longitudinal sensor could cause an ESP failure. But could this in turn cause the ABS system to get confused and lock a wheel? Is turning a really tight slow corner unfavourable enough for a failed longitudinal sensor to freak out.

Failure of a wheel speed sensor results in "No ABS control" and "No four-wheel-drive control" with the note that "The failure of a wheel sensor does not cause any restrictions to four-wheel drive" which sounds a bit like a contradiction to me. If four-wheel-drive control is lost does that mean the car can still operate in four-wheel-drive but just can't control it? That just doesn't sound right.

The more I read about this the more I agree with grtuned that it is a failed or faulty sensor that is causing the ESP or ABS to lock the wheel.

[grtuned]

It is difficult even at dealerships to narrow down problems that are so sporadic in respect to this issue everyone is having.
And due to the age of the car no dealership has any new cars so its not possible to swap parts from another car to try and diagnose.
Best way to do this is if you have a mate which you could swap parts from car to car and then drive and see what happens.
This i'm afraid may be the only way of diagnosing this issue with no cost lay out. Very difficult issue to pinpoint when no faults are
present as the vehicles ESP system thinks everything is behaving normally which we all agree is not during special circumstances.

[kapowww]

Latest thing I did was to remove the ABS fuse (#9). The ABS light pops up so does that mean it's disabled? The problem still occurs so I'm guessing this rules out an ABS sensor issue? ...or is the ABS sensor still operational and sending faulty messages to the haldex but ABS doesn't kick in?

[Shadow_Rusty]

Is it possibly that the haldex isn't disconnecting properly??
Is it possible the wrong consistancy oil has been used in the haldex? (Causes similar wierd issues in auto trans)

I have read that the 'Race' Haldex controller is alot more aggressive in that it will be active at lower speeds and does the wheel chirp when parking and doing a u-turn...

It's possible that your controller has upgraded itself... lol.

[kapowww]

The haldex oil was changed so it can't be that.. I wish all my car parts upgraded themselves. I doubt it has an updated controller but how do I check?

***********************************

I have just a few weeks left until my warranty runs out so I just want to gather all the info I've had so I can work this out..

PROBLEM:
When turning in a tight circle (pretty much full lock) at low speeds going forward or in reverse it feels like the outside wheel isn't keeping up with the inside wheel, either by braking (ESP light flashes) or dragging as a few mechanics think it's a screwed diff. This causes the car to feel like it's bunny hopping. When turning faster the problem doesn't occur. It's hard to reverse as I normally reverse slowly to park and sometimes the car doesn't want to move at all.

SUSPECTS:
1. Haldex controller
2. Diff
3. ESP/ABS sensors

TESTS:
1. Haldex and rear diff oil and filters were changed, problem still there and might have gotten temporarily worse.
2. Removed fuse 31 (Haldex) and car works fine in FWD mode.
3. Turned off ESP at the console and the problem is still there.
4. Removed fuse 9 (ABS) and the problem is still there.

Anyone have a spare haldex controller I can try out in Melbourne? I really want to isolate the problem..

The culprit must be hiding somewhere...

[djorkboy]

Is that your diff and Haldex or a spare one?

I really need a diff!!! I am seriously considering importing one from the UK

[kapowww]

Is that your diff and Haldex or a spare one?

I really need a diff!!! I am seriously considering importing one from the UK

Nah that's just a pic off eBay Germany lol. How much are they usually?

[Shadow_Rusty]

Is that your diff and Haldex or a spare one?

I really need a diff!!! I am seriously considering importing one from the UK

Don't know how good they are for VW parts, but you could try Find A Part
Just submitted one for my missing lower front valance...

ps. Still searching for the Haldex Comp thread for reference here...

[Shadow_Rusty]

Still can't find the exact thread I'm thinking of, (as I thought it was here or MK-IVs.co.uk), but this thread has tons of interesting info about the operation of the haldex units...

VWVortex.com - Orange Haldex Controller - excessing wearing of Haldex clutch kit

The binding in a MKIV R32 (or most Haldexed cars actually) has nothing to do with the rear axle differential, since it is an open differential and allows the rear wheels to rotate with different speeds.

The "problem" is the same as for a fully locked rear differential when turning, but it is the difference in distance covered by the front axle compared to the rear axle. If the Haldex is fully locked (50-50 front to rear) it creates the same situation as for when a RWD car with a locked rear differential is turning.

In the Haldex case it is somewhat harder to understand, but rear and front wheels are not covering the same distance in the same period of time, forceing them to either turn at different speed (which is ok with an open center differential, say FWD or RWD car) or with a LSD (limited slip differential) coupling. The Haldex is a LSD coupling allowing front and rear axle to rotate with different speeds with stock software (ECU). The performance controller locks the LSD to a 50-50 state and thus forces the front and rear wheels to rotate with the same speed.
To be able to turn, something has to give, and normally the tires would "skid" towards the road surface unless you have a lot of traction. Going slowly in a sharp turn (parallel park for example) means you have lots of traction. This is why the binding phenomena occurs.

I assume this phenomenon forces the clutch discs in the Haldex to slip even though it is in full lock. They are designed to slip and the oil helps the slipping by reducing the friction (and cooling) but when in full lock the forces on the clutch discs are a lot higher - so it would wear the discs to a greater extent than intended by the engineers initially. However, the clutch discs are engineered to cope with massive torque, so I think it will only be a problem after a long time.

Haldex has a system on the market (Saab 9-3 XWD was the first car with this) with a eLSD coupling between the rear wheels as well. Working the same way as the center Haldex in the R32 but between the rear wheels, it always puts the torque where it makes the most power. This is great for track driving. The inside rear wheel in a corner will have less traction (or even none being in the air..) and in a car with a fully open rear differential, all power will be lost through that wheel. With the eLSD rear Haldex, more or all power will be transfered to the other wheel with lots of traction. Since it is a limited SLIP differential, it copes with turning issues by allowing both rear wheels travelling at different speeds. When not needed, it can also open up fully, just like our "normal" center LSD coupling.
The same goes for the R32 between front and rear with a stock controller..

I hope this helps you guys understanding..


One more thing, correcting some posts here:
Haldex transfers torque even without wheel slip, also with a stock controller. The only thing needed for torque transfer to happen is different axle speeds front to rear. This occurs a lot more often than just when wheels slip (which is difficult to understand).
Acceleration, retardation, turning and even more cases adds to the Haldex function, and it transfers torque to the rear wheels.
When going at a constant speed, straight forward, it is at minimum torque transfer, and only ~5% of the torque goes to the rear wheels.

And even though the maximum lock is 50-50 regardning how fast the wheels can turn, almost 100% (minus some friction in losses turning the front axle) of the torque can be transfered to the rear axle.
You can try this at home by putting the front axle on axle stands and drive away. (I do not take responsibility to damages underneath your cars when doing this, your car will drive forward!!) The force driving the car forward comes from 100% torque on the rear wheels. This is of course a stupid example, but the same thing occurs when the front wheels loose traction in real life situations. On ice, wet or other places.. If they only loose some traction, just some more torque is transfered, but it is the same principle.

Sorry for a long and maybe "nerdy" post, but I hope this clears some misunderstanding and adds to some more knowledge regarding the Haldex unit.

[Shadow_Rusty]

Still not the right one, but is exactly the same issue as here...

http://www.vwwatercooled.org.au/forums/f14/bora-4-mo-full-wheel-lock-problem-51179.html

[kapowww]

Still can't find the exact thread I'm thinking of, (as I thought it was here or MK-IVs.co.uk), but this thread has tons of interesting info about the operation of the haldex units...

Very good read. It'll take me a while to digest all this. That test he explains at the end sounds like fun!