[s-cars] Re: Big Red Rear Brakes

[QSHIPQ at aol.com]

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.