[s-cars] Re: Big Red Rear Brakes

[Leigh Anderson]

Good clarification/refinement Scott. Certainly for the earlier three-channel
years like my car, that makes a lot of sense.

Leigh
----- Original Message -----
From: <QSHIPQ at aol.com>
To: <leigha at teleport.com>; <s-car-list at audifans.com>
Sent: Monday, October 20, 2003 5:39 AM
Subject: Re: [s-cars] Re: Big Red Rear Brakes


> Two things to note Leigh.  First, the 3 channel abs have a brake prop
valve
> located at the rear control arm.  This is modifyable by preloading the
prop
> valve (I used to do this for track events - zip tie the rear valve).
Also, IME,
> most 3 channel
> prop valves need to be serviced about every 2 years to function properly
> (chicago comment).  It's exposed to the elements, and they freeze up all
the
> time..  Those with the 4 channel abs (95 S6 without locking rear) don't
have to
> worry about a proportioning valve, cuz there isn't one.  IME, the 95 4
channel
> abs can handle big brakes without a safety problem, rear bias is impending
> lockup. So, YMMV.
>
> As a rule, I completely agree that upgrading the rears prior to 95 isn't
> really a good idea.  Proportioning valves pretty much show anyone that big
rear
> upgrades requires the lowest bias rear you can dial in (assuming Big front
> upgrades).  Proportioning valves also have some legal ramifications on a
street car
> (too much rear bias can cause loss of rear end control).
>
> WARNING:  DO NOT PUT BIG REARS ON A STOCK 3 CHANNEL ABS CAR!  I was
running
> behind ex Qclub Prez Mike Fisher (91 v8 5spd - alcon 4piston x4) 72
degrees,
> dry track.  Coming into 6 I watched in awe as his rear brakes locked up
putting
> his black beast completely 90 degrees to the front end of my TQC.
>
> I asked Mike about this a couple years later, when I saw the rear delete.
He
> said he was using the stock prop valve, and "we couldn't get it dialed in
> right" ABS on OR Off.  Duh?
>
> HTH
>
> Scott Justusson
>
> Second, those with a proportioning valve have to know that
> In a message dated 10/19/2003 12:09:47 PM Central Daylight Time,
> leigha at teleport.com writes:
> Hi Todd,
>
> I have a few thoughts, btdt for putting big brakes on back of an UrS6...
> I'm skeptical of the performance benefits for such a front-heavy car as
> ours, but if motivation is 'cause they look great... thats cool, go for
it,
> being a big brake fanatic myself.  But I just couldn't justify the expense
> for myself for functional reasons.
>
> btdt/background: For hard braking anywhere/track use especially, i predict
> the best setup will be to use a brake bias control and defeat almost all
of
> the BR rear brake's capability. my BTDT is an UrS4 track car with mov'it
> BR's up front (works great and much better than smaller P-car (968) brakes
> that PO put on), and P-car brakes on rear (968) installed by PO, smaller
> than the 993tt rears, but much bigger than stock UrS rears. When i tried a
> few laps set even 1/3 to rear, it was truly scary/dangerous, the car was
> skittering/jittering all over, very un-nerving, with lots of
quick-steering
> inputs to keep it semi-straight and ABS helping as much as it could but
not
> nearly enuf. As soon as i slapped the control back to full-front, the car
> was rock-solid, much more usable/powerful straight-line braking resulted.
I
> experimented a few more laps doing a-b testing and came to a firm
> conclusion, at least for that car.
>
> Also note the usual pad life (long) of rear pads vs. front pads under
street
> or track condition. My R4S street compound pad lasts a long long time at
> rear thru street and track use.
>
> so my 2cents is... if function is the goal, consider not to do it, save
> money for a more functional perf upgrade.  If aesthetics is the goal, go
for
> it, but most likely expect to be defeating the rears with a
> brake-positioning valve for safety reasons.
>