Re: Subject: Re: Question: 80Q "limited slip" center diff doesn't limitslip...

["Avram Dorfman" <dorfman@est.org>]

Yes, when he locked the rear diff, it was no problem.

Hmmm... You guys seem to think this is normal behavior of a torsen center
differential. It seems to me that if his rear wheel had been on ice with a
small hill, he'd have been in the same position as in the test we did. I'm
having trouble seeing where this would be any more beneficial than a full
slip diff in the center. It seems that my 4kcsq is better off b/c at least I
can lock the center diff.

Does anyone else have an experience out there they could share where they
could actually tell that the torsen was kicking in?

-Avram
-----Original Message-----
From: C1J1Miller@aol.com <C1J1Miller@aol.com>
To: quattro@audifans.com <quattro@audifans.com>
Cc: dorfman@est.org <dorfman@est.org>
Date: Friday, June 18, 1999 3:43 PM
Subject: Subject: Re: Question: 80Q "limited slip" center diff doesn't
limitslip...


>"Avram Dorfman" <dorfman@est.org> wrote:
>---------------------------
>>> He went into a 2 level parking lot with a steep ramp, and drove up on
>>> the edge of the ramp so that the right rear wheel came off the ground,
>>> but all others were firmly planted. The wheel in the air spun free as
>>> the care came to a stop and started rolling *backwards* until the fourth
>>> wheel hit the gound again (and then made a lot of noise and smoke 8-)
>
>>> This doesn't match my understanding of "limited slip" which is this: It
>>> allows only a certain percantage difference in rotational speed between
>>> it's two sides. Namely, for the rear shaft to spin at 100 rpms, the
>>> front "shaft" must be spinning at some percentage of that, e.g. 60 rpms.
>
>>> Well, if the rear axle is spinning forwards and the car's not moving,
>>> that's pretty much full slip, right? And if the car can go backwards,
>>> then it's really full slip, right?
>
>Phil Payne <quk@isham-research.demon.co.uk> replied:
>------------------------
>>The Torsen senses _torque_, not rotation.  It was probably applying more
>>toque to the front axle than the rear, but you were artificially not
>>applying enough to overcome gravity and so didn't see the fact.  The
>>Torsen Audi used in these cars doesn't go as far as a 0-100 split, so
>>there's always about a fifth going even to the slipping axle.  The
>>rear differential is (relatively) normal, so it spins the free wheel.
>--------------------------
>"Avram Dorfman" <dorfman@est.org> next posted:
>--------------------------
>::Hmm... I'm still not sure if I understand. You're saying that 4/5 of the
>::engine's torque was going to the front wheels, and that wasn't enough to
get
>::up the hill? He gave it quite a rev while the wheel was in the air, I
don't
>::think it's a question of not being enough torque.
>
>::The question remains, can the "limited slip" mechanism wear out and start
>::allowing full slip?
>================
>Can they wear out? yes, I suppose they can, although it has not been
reported
>on the list or elsewhere to my knowledge.  Can they transfer full power?
Not
>likely.
>
>Phil's right.  If the car was in gear, and you hit the throttle, the engine
>will quickly rev up, and not produce much horsepower.  If all four wheels
>were in the air, you'd have more resistance, and the engine would produce a
>couple more HP, but still quickly rev up.  Now, you're on the ground, the
>engine's producing more hp, but most of it goes into spinning the wheel
with
>no resistance.  So, as the engine quickly spun up, you put out a couple hp,
>20% of the torque went to spinning the rear wheel, and the rest was applied
>against the ground through the front wheels; he didn't move because the
>torque wasn't enough to go up the ramp.  Again, not enough to move the car.
>Now, try locking the rear diff; different story altogether.
>chris
>