Questions on installing ABS in a 4000Q

[Huw Powell]

> I asked this group before about putting ABS in a 4000Q.  A few people replied
> it was do-able.  Get all the parts and bolt them in, was the general
> consensus.

Yup, seems so easy.  Maybe simpler than a well done turbo engine swap,
but harder than a dashboard swap.  Remember it is the equivalent of a
complete suspension and brake overhaul (well, I exaggerate slightly)
along with various electrical system installations.

>
> So I bought Bentley manuals for 80,90, 100-200, and 5000, just to study what
> was out there.

Smart, vey smart.

> Here is an observation I made: the ABS in the 90Q (Torsen center diff) is a
> 3-channel system.  But, the ABS in a  80/90 non-Q, as well as a 5000Q (non
> torsen) is a 4-channel system
>
> So, here is my question: should I use the ABS system out of a 90Q, or should
> I use the four-channel (four is better than three, right?) out of a 90-non-Q?

four may be better, but your *car* has a "3 channel" brake system - one
line for each front wheel and one that gets split between the rears.  I
can't attest for that 5kq thing, but 2wd Audis have a "dual diagonal"
system, ie one line for each wheel, and the LF/RR are driven off one
section of the master, RF/LR off the other.  Q's, as far I thought I
knew, were set up with the front running off one section and the rear
off the other, for some reason.

So... if the 5k*Q* truly has a four channel ABS system, that means it
must also have four separate brake lines leaving the master.  You could
run another line to the rear of your 4kq and.... ok, so use the system
from a 90Q.  You're gonna need the strut housings anyway.

>  Also, should I rig my system to be
> defeated whenever I lock one or both differentials?  (It is my understanding
> that the ABS is defeated in this way on the 5000 Quattros).  Is it true that
> he ABS can't function properly with a differential (even just eh center one)
> locked?

I think that is true.  You lock a diff, and now the wheels can't turn at
different speeds, so ABS is not getting good information any more.
Locking both diffs must be a lot like "brute force" ABS anyway!

--
Huw Powell

http://www.humanspeakers.com/

http://www.humanthoughts.org/