RE: Locking Brakes on Quattros?

[Paul Heneghan <paul.heneghan@bbc.co.uk>]

>From: "Buchholz, Steven" <Steven.Buchholz@kla-tencor.com>

>> I picked up that pulling e-brake turns can damage the quattro drive
train.

>... is that right?  I don't think so.  By definition, every time you
are
>running in anything other than a straight line, each of the four wheels
>covers a different distance!  I doubt that there are too many quattros
>driven in only a straight line!  Differentials are meant to make up the
>differences in rotation rates between the two sides ... I suppose that
when
>there is a difference in relative speeds the gears inside the
differential
>move relative to each other, but in my mind this should only be a good
>thing.  If there was no differential motion at all I would imagine that
you
>could get wear only on parts of the gears, while motion should cause
fairly
>even wear ...

>> If that is true, I assume that having less than all four wheels lock
at
>> the
>> excact same moment will cause the same type of damage? It's not like
I
>> ever
>> lock 'em up on purpose but I'd like to know if anything bad(besides
tire
>> damage) is happening when they do lock.
 
>Certainly for the short relative period that you would have the wheels
>locked as compared to the total amount of time that they are running at
>similar speeds I can't possibly imagine any damage at all being done
...

The handbook for quattros warns against towing them (by lifting the
front wheels off the ground) for more than 30 miles or more than 30mph.
I think its got something to do with the fact that the centre diff would
heat up too much and thin out the oil causing accelerated wear.  Apart
from that extreme case (and I think VAG are being very cautious with
their warning), the diffs are designed to cope with continuous small
amounts of speed differences between different wheels/axles.

If you're the sort of person who does handbrake turns you are unlikely
to be worried about the minute amounts of wear to the diffs (minute in
comparison to the wear to the tyres and your wallet when you hit a kerb
sideways at 30mph - BTDT).


>Steve Buchholz

>With an '87 5kCSQ into which someone installed a tranny from a
non-turbo ...
>given the 4.11:1 front FDR and the 3.89:1 rear FDR ... that center diff
is
>working all the time!  No apparent problems (with the tranny that is!)

Paul
paul.heneghan@bbc.co.uk

1980 Jetta GLi recently scrapped, but with totally rebuilt suspension
(driveshaft, bearing housing, bearing, disk, strut, wishbone, 2 wheels,
rear beam with training arms after a failed handbrake turn)
1984 Audi 80 quattro
1989 Audi Avant 2.2E