[s-cars] RE: Confessions

[QSHIPQ at aol.com]

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Ok guys:
I've enjoyed this thread, maybe more than most.  However, it's digressing
(guilty me) from where it started, and  really my main concern is Big Red rear
brakes on a 3 channel ABS car.  As I suspected, Hap's install did NOT include
removing or modifying the stock rear bias valve.  IME running big brakes in the
back of type 44 chassis (as close to miss piggy as you can get), the 3 channel
cars can overload the rear brakes in hi brake loading situations, possibly
causing loss of control in the rear.  I experienced it in the 5ktq race car I
service and drive (unlocked center - abs on or off), as well as, WATCHED it from
1 back as Mike Fisher almost lost his v8 using Alcon x4's going hot into turn
6 at Mid-OH.  In subsequent discussions with him upon noticing the deletion
of the rears, my suspicions confirmed my experience.

Those with 4 channel abs (95> S6) and those with locking center diffs, have a
closer to ideal (the latter the accepted definition of ideal) brake force
distribution in all braking environments.  So where does that leave the "others"?
 I suspect that a bias valve mounted pre abs MIGHT help address the problem,
but I am also concerned by a couple issues with that.  If the propensity of
big rear brakes is to lockup before fronts, there will always be a crossover
point based on brake loading, car loading, cf, cof, etc...  Which means that one
must pay extra attention to conditions and the crossover point.  The second
is, three channel abs systems in audi quattros use a check valve over the rear
axle.  This is to help prevent inside wheel lockup in chassis side loading
under braking.  My concern is the character of that valve adding big rears,
especially with audis "select low" rear abs software.  Most don't even know the
valve is  there, and very few know how it or abs S-L is going to act with a
hardware change.  Hopefully in concert.

Alarmist?  Very much so.  I knew we'd get here eventually, those little
weenie rears don't look right with bright red paint on the fronts, and a tea cup vs
a frisbee sized disc comparo.  But I will say without question, that Big Rear
brakes aren't the same dunk and go, as the fronts.  The compromise COULD be
complete loss of control of the vehicle, especially on track where it matters
most to you and yours concerned about you.  I've had in my shop, a set of big
red rear brakes for over 3 years now (the actual rear caliper off a 993tt), but
after my experiences, observations and investigation, am most reluctant to
take the install step.

I have contacted Hap's installer directly, as well as contacted Hap offline
sharing my concerns and recommendations before Hap goes to his next track
event.  I highly suggest that you all become intimately familiar with HOW rear
brake systems work on 3 channel systems before you dunk big reds on the back of
your ride.  It could be, the very best mod you could do here, is just nothing.

Scott Justusson
QSHIPQ Performance Tuning