blabla on AWD

[Rave Racer 2000]

----- Original Message -----
From: Jens <lukasdl at gmx.net>
To: quattrolist <quattro at audifans.com>
Sent: Wednesday, October 25, 2000 8:33 PM
Subject: blabla on AWD


> Systems:
>
> 1. Hollow shaft in gear box with integrated central diff: Can only be
> used with longitudinal mounted engines like pretty old and current
> Passat, real Audis ;> , or Porsche. With Audi: First it was a simple
> diff, then torque sensing (Torsen) which can transmit power to the axle
> where it is needed (not the one on ice ;)
>
> 2. Transverse mounted engine that drives the front diff, from there a
> special clutch, either Visco or Haldex transmits power to the rear. No
> real diff! If the slip (=difference) between front and rear is too
> large, the Visco gets locked more and more. This is achieved by a
> special fluid between discs mounted on the driveshaft coming from the
> front diff and some on the driveshaft going to the rear. The fluid
> thickens, if these discs revolute differently. The thicker fluid can
> transmit the power between the discs.
> A Haldex clutch is like a smart Visco (simply spoken) it is
> electronically actuated and controlled.
> However, both can only lock the diff, but not transmit more to the rear
> than to the front. Remember, the front diff is always driven by the
> engine!
> (Theoretically, the engine could be mounted longitudinal, but I know of
> no car with that system.)
>
        OK.....        I drive a 87 4k Q Sedan.  I had a blowout on the rear
and when I put on the spare, it didn't drive right?!  Of course it is the
Longitudinally mounted 2.2 five cyl.  The spare on the rear left and the
front right were blistering hot when I stopped.  I couldn't go faster than
30kph for fear of destroying my drivetrain.  I beleive the problem was that
the spare was a different size then the other tires and thus would turn at a
different speed at the outer circumference.
        Question:  What the F***!  Isn't there supposed to be someway the
drivetrain should be able to compensate for having one tire that moves at a
different speed than the others?  I can't see that after the thousands of KM
one might put on a brand new set of tires, that they could possibly stay the
same size all of the time.
                    Any insight?  TIA
                                                        RR