Russ Burns

I have been trying to find out if it disables when engine braking.
Digging around on the net, it seems the Bosch system may have a throttle postion sensor.
This may disengage the EDL system when engine braking, eliminating the issue.

If there are only wheel and speed sensors being used, engine braking safely on wet ice with bad tires may be impossible with EDL. The easy cure is to push the brake pedal very slightly which will turn on the ABS braking logic, or just push in the clutch and use the ABS brakes to slow down.

I drive on wet ice for fun, but I always expect to end up in the ditch.

Thanks again
Russ

mm

...I have experienced the phenomena of which you speak many times myself. On slick surfaces, engine braking is just like any other kind of braking, too much drag or "braking" force can cause the wheels to loose traction and slide. The reason engine braking is often preferred for slowing on slick surfaces is the fact that it tends to be more gentle and subtle than an application of the vehicles brakes, but one still needs to be VERY careful with it. I prefer it more for maintaining speed on a downhill or for gradually coasting/slowing down. Other than that I tend to use the brakes and rely on proper pumping or ABS. Engine braking downshifts on slick surfaces should only be attempted with great care in matching revs and controlling the throttle, and I'm not sure one can really accomplish much via a downshift that one could not be similarly/more safely accomplish via the brakes on slick surfaces.

Having said all that, I'm sure that on slick surfaces, it would be no trouble to initiate a slide via engine braking in an Audi Quattro as well. I'm just not at all convinced that such a slide would cause any problems in and of itself for the car's EDL system. I don't think engine braking would tend to generate the kind of wheel speed differences necessary to suddenly and erroneously activate the EDL system and put the car in a spin.

This seems to be borne out by the fact that although A4 Quattros have been available and equipped with EDL for quite a few years now, we haven't seen many if any verifiable experiences where EDL seems to have erroneously activated and caused a car to loose control. If this is what happened to Jim (and I doubt there will ever be any way to really know for sure), it would be one of the first such experiences I have ever heard of. I would also think that this is something that Audi and Bosch would have considered pretty seriously in their development of EDL. The last thing the public would want is a traction control system prone to putting a foot wrong and causing a loss of control under low traction conditions. While no system is perfect, I guess I have faith that Audi and Bosch would have given these sorts of scenarios the proper consideration in their development of EDL.

Uwe Ross

> I have never heard of abs system lsd's [EDL] ever wearing out,
> and the pads have to be replaced with normal driving.

Well, mine is "worn out". EDL on my car (a FWD VR6) has simply stopped working. ABS continues to work fine. I've been through every diagnostic procedure and can't find a reason for it. But I've never heard of a worm-gear LSD that mysteriously stopped working..:-)

However, I can't say it really bothers me that my EDL has stopped working. I found it very obnoxious when it did work. Further, the "hammering" that EDL subjects the differential to is suspected to contribute to the numerous, catastrophic differential failures that VR6 owners have experienced -- and VWoA almost always tries to weasel out of fixing these under the 10/100 powertrain warranty by claiming the owner "abused" the car...

I know one thing for sure: The first time I have reason to pull my tranny, I'm putting a Quaife in it! (Had one in a previous FWD VW and absolutley loved it!)<ul><li><a href="http://wso.net/ross/Uwe/VR6/index.htm">My car. Don't laugh, it's (almost) paid for..:-)</a></li></ul>

mm

In some cases ABS may not allow you to stop as fast on "loose" surfaces, but it does allow you to steer effectively while you brake. I think too many people loose sight of this significant benefit. Remember, the secret to maximum ABS utilization is to:

STOMP on the brake pedal,
STAY fully on the brake pedal even if/when it shakes or judders under your foot,
and STEER around obstacles that you cannot otherwise avoid.

It's worked well for me in a number of practice and real life emergency situations.

Bob

> If there are only wheel and speed sensors being used, engine
> braking safely on wet ice with bad tires may be impossible with
> EDL.

If you are talking about engine braking while driving around on the ice, the axle will behave like any other axle with an open-diff. For the _most part_, EDL will not engage since wheel speed variation will be under the threshold. Driving dynamics has much more to do with the characteristics of a open-diff than with EDL, in this situation. Any other 2WD vehicle would have the same concerns in this situation although an argument can be made concerning the added problem of the front open diff. Using open diffs though is the best tradeoff when considering that the car is also driven on pavement. Nothing can beat the feeling of open diffs on pavement. There are issues when using Torsens, quaifes, viscuous diffs , and of course lockers as front and rear diffs.

> The easy cure is to push the brake pedal very slightly
> which will turn on the ABS braking logic, or just push in the
> clutch and use the ABS brakes to slow down.

Pushing the clutch in and using the brakes is the "controlled" way to do it on ice. Open diffs are the culprits here, so pushing that clutch in is important. As an aside, experienced quattro drivers use the brakes and hand brakes (and gas) to apply a load to the Torsen and open diffs to alter spin and torque delivery.

Regards,
Bob
96 A4QM
86 4KCSQM

Ben Broder

I wish Audi had done a quaiffe or torsen rear lsd from the factory.

I find it very easy to get EDL in the wet. One place it always does it: my parents have a fairly steep driveway with a small bump at the transition from street to driveway. I turn in from street and hit gas to go up driveway. As soon as rear tires go over the bump, I get corresponding kick from the EDL. I am not talking about a full throttle run into their garage, any more than feathering the gas is enough to provoke it. And regardless of whether you call it a bang or a clunk, it is apparent enough that I've had passengers mention it.

Russ Burns

But since you threw in the handbrake technique, do you use that to correct understeer?

Russ

Bob

> I wish Audi had done a quaiffe or torsen rear lsd from the factory.

You may not like the feel of that on a street car.

EDL provides thet most torque transferring capability with the least amount of bind. And multiple Torsens or Quaifes, especially in the front, amplify binding. To reduce this effect one would have to design a low load bias ratio but unfortunately this would degrade traction performance.

Also, under most conditions, the feel of an open diff cannot be beat. And for those infrequent low-speed situations, EDL works the best. A Torsen or Quaife requires 1/4 the traction on the slipping wheel to work. If this load bias ratio not maintained, the Torsen will act as on open diff.

I apologize for the terse answers and spelling errors. I'm leaving the office right now...

Regards,
Bob
96 A4QM
86 4KCSQM

Graham

Dunno what value this has in realtion to all the informed speculation on this thread, but I would like to relay real life experience of this.

One of the exercises we went through in a quattro experience day was exactly that, differential braking, ie braking with wheels at opposite end of the axles on differnt surfaces.

Wet concrete was used for one surface, and wet vinyl sheeting used for the other (about if not more slippery than ice )

The cars were EDL/EBD equiiped A4's, and the exercises werec onducted with and without ABS.

With ABS all that was required was to let off the gas and stomp on the brake pedal. The cars would, without fail (and even without hands on the steering wheels) all pull up in a straight line...Remember, two wheels on concrete, two on the other side of the car on vinyl(ice). No problmes at all with EDL/EDB/ABS, worked perfectly.

Withoput ABS it was a fun game of trying to catch the inevitable slide, opposite lock, depress clutch, foot off brake, foot off gas, line up in a straight line, not over correct, then drive off through the exit 'gate'.

That may not be as scientific as some of the theorising in this thread, all I can say is it what was experienced by my butt (any many other butts) and seen with my eyes (and many others too).

Graham

ErikR

Nope, torsens do not fail mysteriously. When you find out what failed on your edl let us know, maybe some of the anti folks could use that to disable it. FWD and quaife is definitely the way to go. That is one of the many caveats posted earlier in this thread. Now, as Bob mentions, it will handle quite differently, so your driving style may have to change slightly.

VW is notorious for putting cheap (read wrong) bolts and clips in the diff. The 02's even had a fixit kit from the dealer, while they were still making the junk and putting them on cars.