Re: Questions on AWD, ABS, and locking the rear differential

[Eliot Lim <eliot@u.washington.edu>]

hi, just caught up reading this thread.. a couple of comments:

- ABS relies on speed differences between wheels to detect a locking
condition.. a solidly locked diff or a viscous coupled diff will inhibit 
the speed sensor's ability to detect speed differences.  those cars using
VC's have them set up with a lot of slack to enable ABS to work.  ugly
and hacky...

- the V8Q has a torsen diff in the rear.

- humvees use torsen diffs front and rear;  some sporty rover turbo hatch
fwd (not imported to US) use a front torsen diff.

- Q's with slushboxes use multiplate clutches (not torsen) in the center 
diff for locking, controlled entirely by electronics.  as with the torsen,
applying the brakes would unlock the diff, allowing uninhibited
speed sensing.

- '92 100Qs were available with slushboxes, but they were very very
sluggish cars.

- the new A4Q uses VW's traction control implementation for the front and
rear axles.  cheap, simple, reliable and effective and does away with the
manual lock for the rear.  no need to disable ABS because the system
automatically switches off if you hit the brakes. 

- the reason for the torsen diff being called what it is is because it is
torque sensing as opposed to rotational sensing.  viscous coupled diffs
are rotational sensing, as are traditional LSDs.  rotational sensing
LSDs will lock even if you are in a braking situation, while the torsen
and the computer controlled diffs will not...  significant in terms of
implementing ABS.


i will be rejoining the list soon since i have figured out how to redirect
the voluminous Q-list messages to another folder automatically!

ciao,

eliot