So much for EDL!!

It so happened that as I got to the restaurant of my choice yesterday the car park was full and so I decided I would make full use of Quattro to park
by driving up onto a slope (about 12% steep) with only the two right wheels onto a grass fringe (wet with hail from a recent storm) while keeping the two left wheels on the road's tarmac. I was pretty confident Quattro would have no problem in driving up along the fringe for about 4 m so that the car was out of anyone's way. Well, I was totally disappointed to get a bitter taste of the old days when we used to get stuck without Quattro. Still refusing to believe this, I got out to check that there was enough clearance all the way up and there certainly was. Then I made sure the car did not nosedive into the fringe. Everything was OK but the car still refused to start off uphill. My only resort was to shily reverse onto the tarmac and try to find a more traditional parking space.
I was taken aback in such a way that on coming out of the family reunion meal I asked both my father in his A6 2.5TDI Q and my brother-in-law in his 02 A4 1.8T Q (on winter tyres) to try the experiment, as they were telling me it must have been a case of my EDL not working properly. Well, they got the same identic result: the front right and rear right wheels kept spinning to no avail while the other two did not move an inch.
My conclusion is that while Torsen works flawlessly, EDL (Electronic Differential Lock) is no less than a big fiasco, at least when there is a big difference in terms of surface friction coeficient between the two sides of the car alongside.
I remember reading once that Jeep's Quadradrive and BMWs x systems had been the only ones to pass a certain traction test on rollers, while Quattro and the rest had failed, but I refused to believe this. However after this, I think I'll have to warm up to better systems which have evolved with the times.
A totally disappointed Quattro ex-believer,
JP Roberts
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JP, Not to rub it in, but I'm sure my '87 5ktq (Quattro I) would have made it without problems. Of course, I'd have to reach down and switch the locks on by hand ;-) Which car is this? IIRC, something like this is addressed by ESP (applying brakes to the spinning wheels) is it not? Cheers! Steve Sears 1987 Audi 5kTQ 1980 Audi 5k 1962 and '64 Auto Union DKW Junior deLuxes (SPAM Blocker NOTE: Remove SHOES to reply)

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Hello,
My 2 cts:

sides
EDL is not actually lockking the diff's but activates the brakes on the spinning wheel. ABS is used to detect the slip. There where some constraints in the manaual iirc about heating up and disengagement. But if I read how it was tested I don't think that was the case. Probably the brake could not handle the power coming from the engine in the tested circumstances (slope to steep?). It would be interesting to know if after the test the spinning wheel was hot, if not the the conditions where not detected and brake was not engaged at all (or something was broken) . If hot then at least someting was working. I assume that you did not decativate ABS during this test (don't knwo if thats possible). On my 03 allroad I actually have EDL seen working but circumstances where different. (Left - right traction was unequal but It was not on a slope).
-Reijer-
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Yep, I was totally aware of that.

I'd been driving very slowly and not touching the brakes since the start of the journey, because it was all uphill basically. The other two cars had been sitting at the restaurant's car park for some 3 hours, so the brakes had had an equally long rest before the test.

I did not check disk temperature after the test - I should have thought of that - but from what I saw when looking at the other two cars, I would have suspected the brakes were not slowing the spinning wheels at all. Judging from rev drop on clutch disengagement I did not feel any impressive brake activity either (I was able to disengage at around 1,500 rmp repeatedly). On other occasions, though and with snow under the four wheels I have felt the brakes actuate, so I can sort of tell. Also, because I tried to be as gentle as possible when disengaging the clutch pedal, and to keep revs as low as I could, I don't think the torque was very impressive either, at least not enough to override brake actuation. My car does not have an ABS button so this cannot be disabled at will.
If I were given a second chance I would now try revving the engine to about 3,000 rev and then gently push the brake pedal while keeping the gas on to see if that made any difference at all. Maybe that would have done the trick of transferring torque sideways? I seem to remember having read something about this?
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JP Roberts wrote:

Another possibility would be to slightly engage the handbrake. That would slow down the rearwheels and should transfer more torque to the front.
Sounds strange though.
Regards
Wolfgang
--
1999 Audi A6 Avant TDI

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Both the front and rear right wheels were spinning all of the time, so it was not a front-to-rear, or rear-to-front issue. It was a side-to-side transfer issue, rather.
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JP Roberts wrote:

I read that. But by braking _both_ rear wheels with the handbrake you'd be also braking one happily spinning wheel on the slipepry side.
So you'd have "grip" on 3 of four wheels. That might transfer enough torque to the wheels on the dry side.
Regards
Wolfgang
--
1999 Audi A6 Avant TDI

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Or you might be successful in transferring more torque to the front "sadly" spinning wheel only? I have always read that the result of applying a braking force to a wheel on a given axle will translate into more torque being transferred to the wheel opposite on that same axle, but not being knowledgeable about diffs or how they work I still fail to see that. And in the best of cases I would have grip on only 2 out of four wheels, not three - remember it was both right wheels that were spinning out of grip. I'm not saying you aren't right as I have not tried this but can you clarify your reasoning?

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JP Roberts wrote:

I was basically transfering my experience with RWD and handbrakes to AWD. By using the handbrakes you could get some grip on the gripping side of the car.
I would just try it, I didn't have time to think it through completely for AWD (hence the long time until I replied) but my gut feeling is that you'd be having some grip on one axle. Maybe enough to get you going. If the middle differential is working, you could really end up spinning the remaining free whell even faster. But I'd be curious what it does in reality.
I truly think quattro is not a substitue for an all terrain vehicle AWD with difflocks et all.
Regards
Wolfgang
--
1999 Audi A6 Avant TDI

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Thank you for your answer Wolfgang. I am always pleased to read your highly instructive postings.
I'll try that as soon as I get the occasion to.
Cheers,
JP Roberts

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JP
pls try same again in better conditions and report progress?
I'm interested as ordering A4 3.0TDi Quattro having had 4 years of Merc ML. I need to set some parameters for "on-road awd" versus what i can do now with "off-road 4-wd". Understand they will be different of course.
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charles blassberg wrote:

I read from an A4 cabrio quattro manual that....
To prevent the disc brake of the braked wheel from overheating, the EDL cuts out automatically if subjected to excessive loads. The car remains operational and will behave in the same way as a car without EDL.
EDL will switch on again automatically when the brake cools down
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Charles, I still haven't been able to go back to the same spot for testing. Don't think I've dropped your request.
In my case I'm positive the system had not overheated because the other two cars had been sitting in the lot for more than 3 hours. So the disks were as cool as a cucumber, though I did not check their temperature after the test.
Anyway, the 3.0TDI seems to be a hell of an engine, and it certainly does also offer considerable tuning potential - main stream tuners offer between 275 and 300 PS for this engine, though you'd be well advised to check the price of turbo replacements if you're planning to go this route.

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