H.

I've been the happy owner of an A6 2.7T since October. At this site and on Edmund's, I've seen posts stating the superiority of one AWD system over the other. I believe both deliver power to the wheel/wheels that have traction and both will brake a spinning wheel that has lost grip. So, are there any real differences between the Mercedes 4-matic and Audi's Quattro? What advantage would one have over the other?

April

Hydraulic pump on 4matic can overheat and revert to RWD - oh, costs abt 10K more

Bob

EDL can overheat and shut off too ;-)

Steve Bollinger

The 4Matic has EDL also, and it can shut off on their car also. Plus, on the Audi, even if you lose EDL, you still have the Torsen working front to back.

On the 4Matic, you have a fixed front/back torque split under all conditions. The Audi Torsen can send up to 80% to the front or back if necessary.

Under such conditions though, I would imagine its little solace.

Bob

> The Audi Torsen can send up to 80%
> to the front or back if necessary.

I believe you mean, the Gleason Torsen can handle up to a 4:1 torque differential between the front and rear axle before showing slippage properties of an open diff.

Bob
96 A4QM
86 4KCSQM

Bob

similar to the M class, the X5, and Quattro without the center Torsen.

Bob
96 A4QM
86 4KCSQM

Steve Bollinger

>I believe you mean, the Gleason Torsen can handle up to a 4:1 torque
>differential between the front and rear axle before showing slippage properties
>of an open diff.

No, I don't. I've read up now.

I meand the Audi Torset, as opposed to the M-B fixed split. I was not attributing invention of the Torsen to Audi.

As to the diff showing properties of an open diff. I've read up, and it isn't true. Yes, it cannot send more than 80% of torque to one output, but if it reaches that point, it does not "open up" as you would suggest.

Instead the split just remains at 80%, and the slipping output does begin to spin (waste energy) somewhat. Still, the gripping output gets 80% of the torque, it does not reset to 50-50 or worse like an open diff would. Practical result: under all but the worst conditions, you are better off than with a locking-type diff. Under the worst conditions, you aren't too much worse off. Given that a Torsen doesn't limit steering, or have to get its clutches repacked, it seems like a good trade off to me.

You also were the one to tell me the EDL turns off at 25mph. Wrong. The manual says 50 (actually 80mk/h which is slightly lower).

Anyway, I was just pointing out that the M-B system has all the failures of the Audi system (EDL most notably) and also an inferior front/back split system. That makes the Audi the winner in my book.

I think both systems would serve very well in the kind of conditions these two on-road cars will encounter. Still, the Audi system is slightly superior. Actually, its even a little bit superior to the Land Rover Discovery II which does full off-road duty.

All 3 seem to use the Bosch EDL (or whatever) system.

On another note, the AMGeneral (now GM) Hummer uses Torsens for both left-right diffs. That vehicle is highly regarded for its off roadability, so I have to say I think the Torsen has proved itself under much more demanding conditions than Audi uses it for.

Bob

> As to the diff showing properties of an open diff.
> I've read up, and it isn't true. Yes, it cannot send
> more than 80% of torque to one output,
> but if it reaches that point, it does not "open up"
> as you would suggest.
> Instead the split just remains at 80%, and the slipping
> energy) somewhat. Still, the gripping output gets 80%
> of the torque, it does not reset to 50-50 or worse like an
> open diff would.

As I have said in the past, once the load bias ratio is violated, the Torsen acts like an open diff. All excess rotation or 'power' goes out the side with the least traction, as with an open diff. This is all I said. I never said it resorts to a 1:1 when slippage occurs.

> Practical result: under all but the worst
> conditions, you are better off than with a locking-type diff.
> Under the worst conditions, you aren't too much worse off.

Agreed. For a road car, I would not want to lock a diff. LSD's or open diffs are preferable for AWD street cars. Open diffs all around have an unobtrusive feel in comparison to the use of _multiple_ LSD's. Of course there is a feel vs. AWD performance tradeoff. I've built and driven quattros with multiple Torsens, quaifes and open diffs, and unless they are rebuilt with less aggressive bias ratios, they may not be appreciated by most owners.

> Given that a Torsen doesn't limit steering, or have to get
> its clutches repacked, it seems like a good trade off to me.

Sure. I disagree with your steering comment though. I've built a car with a Torsen up front and in the center, and I did not care for the feel. Multiple Torsens can bind.

Also, one more thing about the Torsen is that it is speed sensitive. It is not purely "torque sensing" as the literature says. The Torsen delivers more torque to the side or axle that is rotating slower, e.g. the inside wheel. The modern Quaife does just the opposite, it tends to transfer more torque to the outside wheel, which may be better.

> You also were the one to tell me the EDL turns off at 25mph.
> Wrong. The manual says 50 (actually 80mk/h which is slightly lower).

All EDL systems before '99 turn off at 25 mph as my manual says. Since then, Audi has changed this to 45-50 mph.

> I think both systems would serve very well in the kind
> of conditions these two on-road cars will encounter. Still,
> the Audi system is slightly superior.

Sure. The difference between the two systems, Quattro and the new 4matic full-time system, is the center diff. Audi's use of the Torsen center diff increases performance without sacrificing smoothness or road-car feel.

Steve, I've owned, built, driven Audis since 1980. I've owned countless Quattros through the years, including one UrQ, and have experimented with many diffs. Quattro IV has an edge in performance and "unobtrusive feel" when discussing sport luxury AWD road cars.

Bob
96 A4QM
86 4KCSQM