Disabling the Haldex?

[Neb]

Does anyone know if I can for sure disable the haldex system without causing long term damage to it? I think my new summer wheel setup is doing funky things (maybe it's too wide in the rear) so I wanted to try to disable the haldex to see if that changes anything. I've heard that you can pull the fuse as well as unplug it but I wasn't sure if it would cause damage if I did that for 4 or 5 months. Anyone have some insight?

[thekatt]

I read that the rear diff will still spin freely (although not engage the wheels) even if you unplug the haldex. People do it for a quick burnout or dyno, but not sure about long term effects. I can't imagine it being good in the long-term if you do it for extended periods... something about oil getting way too hot or something.

But i dunno, just guessing from what i've read - im sure someone will correct me.

+1 useless post

[wparsons]

Isn't the torque split on the TT 100/0 unless the fronts slip (or the haldex computer thinks theres slip)? If so, pulling the fuse shouldn't harm anything because its "functioning" just like it does the vast majority of the time.

[Neb]

I've read more along the same lines as what Jason was saying with the heat and such. Will, with the haldex, once you hit the gas it engages, not on wheel slip. If you're just cruising it's not really on but if you drop it down or punch the gas it engages. I think it's an 80/20 or 70/30 split with the OEM controller

[Punjabi_Dubber]

so why do you want to disengage it? how wide were your wheels before compared to now? I thought width shouldn't matter, only OD diameter does.

seems like you could do alot of damage.

[Neb]

The old wheels were 8/9 split. These are 8/9.5. The OD is still within spec but I think the extra weight is what is throwing it out of wack. That's 3" total of wheel width. I dunno. I would rather sell the wheels then risk damage to the haldex... want some twists?

[ipop07]

Ben, the width shouldnt matter at all its the tire overall circumference that is the picky one. What are your tire sizes? And what is the oem tire size? (assuming oem is same front and back)

[soundwave]

oem would be 225/45/17 if it came with say fat fives 17x7 et 38 i think

[Neb]

yeah OEM is 225/45/17

New ones are 205/40/18 front and 225/40/18 rear

[ipop07]

It may be due to your tire sizes:
This is your current setup:


As you can see, there is a difference of 2.571% in perimeter between front and rear. While this may be ok on some awd systems, the haldex may be a little more picky. A chat with some AUDI/VW technician who knows their stuff may be able to shine some light on what the exact limits of haldex are.

What I would suggest is you make one of the two following changes:
*1.056% difference front to rear*

*0.719% difference front to rear*



NOTE: while this may not be the exact or complete source of your issue, it will make it better.

[soundwave]

and if you think there is a chance you are out of spec stop driving it

this was @ 5% staggard









sauce

[Neb]

Those calculations 2 posts up, the diametre difference is actually only 1.65% (with my current setup) so not nearly as bad. Still getting me worried though.

The faster/slower speedometre part I don't really get though.

[Neb]

ok just did another offset calculator and I'm 2.6% difference in diameter. Not that crazy but maybe enough to throw things off?

[ipop07]

The faster slower was determining the sign of the difference. so in the first one you had positive difference (hence to fast) and the rear negative so total is 2.6%.

I'd say 3% is the limit, and 2.6 is getting close. Just think that one wheel has to spin 2.6% more in one turn than the other (if the diff was not compensating). So every 38 turns, that is a complete turn.
So in a kilometer, the front would spin 512.6 times and the rear 499.7 times (12.9 turns difference). While this means nothing on a 2wd on a awd it’ll make the diff work all the time instead of only when needed.
Just for comparison in the proposed setups the numbers look as follows:
1st setup: In 1km front spins 512.6 times and rear 517.9 times (5.3 turns difference)
2nd setup: in 1km front spins 496.2 times and rear 499.7 times (3.5 turns difference)
At 5% like liam posted the difference would be 26 turns, that is quite the difference when you travel 100km…

Keep in mind this may not be the only issue, but I definitely think it plays its part.

[Punjabi_Dubber]

Fairly certain they don't make 205/45/18 tires.


Have you tried throwing the winter tires back on in the rear and seeing if the problem goes away?

I would go 215/40 in the front but your losing stretch.

If you want to get rid of the 205/40s i'll take them for sure.

[ipop07]

You're right, that size is not available (should've checked before suggesting it). I guess that leaves one option only, that sucks.

[Neb]

You have 215/40's? Booked the car with Jason for Monday so he can do an inspection to make sure the car is safe. I'm going to swap the winters back on tonight and see if the problem comes back.

[soundwave]

The old wheels were 8/9 split. These are 8/9.5. The OD is still within spec but I think the extra weight is what is throwing it out of wack. That's 3" total of wheel width. I dunno. I would rather sell the wheels then risk damage to the haldex... want some twists?

fwd swap(summer mode)

[thekatt]

I think my new summer wheel setup is doing funky things

Just outta curiosity, can you describe the "funky"? Just want to know your symptoms in case it happens to me one day.

[Neb]

When it happens (it's happened to me 2 times since I put the wheels on) it feels like I have a flat tire. Weird, unnatural vibrations when I give it gas. I also notice it sounds like the exhaust is a bit louder (maybe another issue though?) Definitely loss of power and the second time it happened there was a whining sound coming from somewhere (but sounded like the front)

[EMSbyDay]

Dont forget that when dealing with fractions of percentages in tire differences, if you have stretched your tires that can affect OD as well.

[Neb]

Yeah for sure. I found that I'm actually running 2.6% OD between front and rear. Max that Audi says is 3% so I think that's playing a large factor. Swapped the winters back on last night so we'll see what happens this weekend. Car is booked to see Jason Monday either way though just to make sure.

If it's the tires, I guess I'll order some 225/35 for the rear. That'll bring the OD to 1% which should work.

[ipop07]

Keep us updated!.

Stretch doesnt play a large role...unless its extreme stretch, which i dont think is the case here..

[Neb]

No, but OD does between the two. I've been using this calculator to check the percentage..

http://www.miata.net/garage/tirecalc.html

[ipop07]

Yup. That one is good. The tire rack one is better a little, it gives you more info as well as brands and models for the sizes you pic: http://www.1010tires.com/tiresizecalculator.asp