blueprinTT

...after work I tried the emergency brake test to see if it would disengage the haldex and eliminate the binding I've been experiencing in tight turns. Sure enough, the binding seemed to go away, partially. So later this evening I pulled fuse 31 to cut power to the Haldex. The binding was COMPLETELY gone...and the car seemed like there was nothing holding it back at all...there was a big difference even in a straight line...no drag at all. I guess Haldex has been engaging the rear axles all the time over the last couple of months. Now if I can convince the dealer it's not the differential. Maybe I just shouldn't bother with them anymore at all. Strange they could not find this problem with all their diagnostic tools.

This sounds like the Haldex controller is bad, right? Hopefully it's not the Haldex clutch too.

With fuse 31 pulled, the yellow ESP light is on now....is that normal?<ul><li><a href="https://forums.audiworld.com/tt/msgs/1562418.phtml">Post from earlier today</a></li></ul>

TTagz

sounds like a good excuse for the haldex controller upgrade!

MCPaudiTT - DEFCON 1

<ul><li><a href="https://forums.audiworld.com/tt/msgs/1452481.phtml">https://forums.audiworld.com/tt/msgs/1452481.phtml</a</li></ul>

blueprinTT

...after Steve suggested it in response to my 9/13/06 post.

The Haldex coupling seemed to behave as it should in the roll-out test. There are no unususal grinding sounds coming from anywhere, just the binding sensation, which leads me to believe during turns, the difference in distance traveled between the front and rear wheels is causing the binding at the Haldex coupling, instead of between the right and left rear wheels in the rear diff.

It must be the controller that is causing the Haldex clutch/coupling to engage all the time for some reason. Or maybe a bad sensor somewhere is constantly sending a signal to the controller telling it to engage the Haldex coupling. It still seems strange the dealer could not diagnose a problem with the controller or elsewhere in the sensors. If I had to replace something expensive, the controller would be the easiest and least expensive thing to replace...so I'm hopeful that's what it is.

blueprinTT

....the car felt so much better with fuse 31 pulled, that I think I'll be real happy to just get it back to normal.

But the controller upgrade is definitely worth looking into...especially if the price is right.

MCPaudiTT - DEFCON 1

Still not cheap, though...<ul><li><a href="http://www.tcarbon.com/product_info.php?products_id=279">http://www.tcarbon.com/product_info.php?products_id=279</a</li></ul>

blueprinTT

...apparently the Haldex coupling and rear dfferential are contained within one overall part number...02D 525 010 D or J, called the "final drive" so the dealer was quoting the cost to replace both as $3200. Worldimpex.com lists the whole assembly for $2778.

Vagcat.com breaks down the parts and #'s further.

Hopefully the problem can be traced down to a more specific part that went bad, instead of replacing both the rear diff and Haldex coupling.

I'm still holding out hope that maybe it's just the controller, although that's not cheap either. Or maybe it's just one of the many sensors erroneously telling Haldex to engage when it shouldn't.

The car is still drivable without any symptoms other than a binding sensation when making tight turns, especially while backing and turning out of a parking place. Most people wouldn't even notice anything is wrong, but I'm still not going to drive it until I find out exactly what's wrong, which is proving difficult to diagnose with certainty.

See links to previous posts for my whole story.
Stay tuned....

Here are some diagrams which may be helpful to others...

The overall "final drive assembly:
<img src="http://pictureposter.audiworld.com/47675/final_drive.jpg">


The rear differential:
<img src="http://pictureposter.audiworld.com/47675/525120.jpg">

The Haldex coupling:
<img src="http://pictureposter.audiworld.com/47675/525150.jpg">

MCPaudiTT - DEFCON 1

open differential should be able to accomodate it... Have they visually check the rear differential gears yet?

blueprinTT

....allow me to see if the rear diff alone was causing the binding. While driving with Haldex disconnected, the rear wheels should cause the axles and pinion gears within the diff to spin normally both straight and in tight turns, and rotate the rear drive shaft all the way up to the Haldex coupling.

I did pose this question to a Haldex tech yesterday, and this was his reply:

"I am sorry to say that pulling the fuse do not help you investigate but rather the opposite.
Once the fuse is pulled all tension in the driveline/ptu is removed and it will not bind up wether
it is the ptu, the driveshaft, haldex, final drive or halfshafts that causing the problem."

"We will look into it as well but i do not believe it is a Haldex problem."

I haven't had it back to the dealer yet to check the diff gears, and dig into the whole thing deeper.

But I still think the binding occurs because Haldex is erroneously engaging all the time, and it is happening within the Haldex coupling due to a difference in speed between the front and rear wheels/driveshafts....and not at the differential due to differences in side to side wheel speed at the rear.

I could be wrong, of course. Anyway, thanks for tracking this post. :-) Hopefully the conclusion will eventually be helpful to others who might have the same problem.