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Re: Quattro Differentials?

>From my understanding, when not using the diff locks at all, the car 
isn't really all wheel drive on the 4000q, it is mostly front wheel 
drive. while the car is running,some momentum in the drive shaft travels 
back to the rear wheels allowing the car to have some power in the rear, 
it is not until you lock the center diff that power is actually 
tranmitted back to the rear wheels. You can run the car like this pretty 
much as long as you want(I think) it just means there will be 
accellorated wear on your drive train. Try it, set the knob on the first 
setting on dirt road or when it is raining heavily, you will notice a 
difference in handling( at your own risk, because I don't know what 
shape your car is in, and I don't want to be held responsible if 
something goes wrong) it is a cool learning experience though.

 turning the knob to the second setting Locks the center diff and locks 
the rear diff allowing all wheels to spin at a constant rate, not 
allowing the tranferring of power to a combo of two wheels. That is why 
if you put your diff lock knob on the second setting and try to go in a 
really tight circle or turn your car seems to skip, laws of physics the 
outer wheels have to turn fast/farther than the inside in order to 
travel around the same turn..........phew.........confusing? you can try 
this too(at your own risk!!!), but disengage after as this is not really 
good for the drivetrain at all.

 Since all the wheels are locked they all spin at the same rate which is 
good in really bad situations like being stuck, when all the wheels are 
spinning the car gets confused at where to send the power. so locking 
them all, sends constant power to all of them. I think the 4000q used a 
slip diff. which to me, didn't make sense. 

The newer cars, early 1990's and up have a newer quattro system, they 
use a torque differential, which makes more sense, which is monitored by 
the cars computer system and is engaged by the system when it deems 
useful. Although you still can lock the rear differential manually, but 
this is turned off when the cars speedo reaches 30mph. This is how I 
think the quattro system works, or at least the best theory that I can 
come up with. I know that you said brief but ........sorry!!! anybody 
else have a different theory please let me know. I am always wondering 
about this myself.

----Original Message Follows----
From: tturse@ps-b.com (Thomas Turse)
To: "quattro list" <quattro@coimbra.ans.net>
Subject: Quattro Differentials?
Date: Wed, 12 Aug 1998 14:58:47 -0600

I know this has probably been mulled over hundreds of times, but can 
give a brief summary of when you can and/or should drive w/ the center 
rear diffs locked (85 4ksq), and the handling effects of each.  Also, is 
the car actually 4wd all the time?  I noticed that the 85 manual differs
from the 86 and 87's in the do's and don'ts and when to use the locked
differentials.  I'm particularly interested in their use in driving on 
and ice.  I have been unable to lock the center because of a bad vacuum
switch, but used the rear lock to get out of the snow when the car was 
a few times.   Just curious about the benefits of having a locking 
differential.  As always, thanks for your thoughts.
BTW, my two labs like my car or any car they can get into for that 
but my back seat is covered in black and tan hair and the windows are 
crusted w/ drool.  I usually try to vac it once a month so it doesn't 
too bad- in my GLI, I went about 6 mos. before cleaning up the hair and 
took hours and a few rolls of duck tape to get it out!


Thomas C. Turse
Boulder, CO
85 4ksq

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