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A torque-biasing (a.k.a. automatic torque-biasing, torque-sensing, torsen, or geared) differential such as your Quaife cannot split torque between the axles when one wheel has zero grip. (This is, literally, a mechanical application of math: anything multiplied by zero equals zero.)
You can try tricking the differential into biasing torque to the wheel with grip by gently pressing on the brake with your left foot while pressing on the gas with your right. The drawback to this is that, if you try this during the conditions you describe in your post, then you'll also immediately freak out your ABS system! :-) (The technique is really for if you are stuck in the mud/snow and one wheel spins freely.)
To direct torque to a wheel with grip while the other has absolutely none would require a clutch-type diff*, which splits torque no matter what each wheel's grip level is, up until some pre-set breakaway torque value**. To the best of my knowledge, no one makes a clutch-type differential for 9000s, and there are several drawbacks to this type of differential that can make it problematic on a street-driven car, especially FWD.
FWD cars that come with LSDs from the factory (SRT-4, new Mini, Acura Type R, et al.) are usually fitted with torque-biasing differentials because they are well-mannered and unobtrusive on the street. (Some FWDs have viscous type differentials, but they are not especially effective.)
If it makes you feel any better, last year I tried to pull away from a curb in a Subaru Outback that had two wheels on ice. The car would not move. Even if the car had had torsen differentials (it did not), it still would not have moved. My point being, for the situation you describe, you're no worse off with 2WD than AWD, even if the AWD had Quaifes. I also have a Quaife on a c900 that's basically a weekend toy I tinker with. I like it so much in snow that I'm inclined to install one in my daily driver, also a c900.
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*There is a new diff out that combines the gearing of a torque-biasing diff with components that allow torque to be biased even if there is zero grip at one wheel. http://www.autotech.com/prod_drive_wavetracDiffs.htm. There is not much real-world experience on them, and they certainly do not make them for old, out-of-production Saabs.
**For this reason, rally cars will often use a clutch-type differential so that they can get to the end of a stage even if they wreck an axle along the way. A Quaife or standard open differential would leave them dead in the water.
posted by 98.247.137...
, Sun, 6 Dec 2009 22:08:40
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