[s-cars] Cold start issue, brake fade

Tue Oct 10 17:37:03 EDT 2006

the stock calipers are rather flexible, which translates into more
pedal travel.  the pedal is mushy and the effort is high, which is a
bad combination.

braided steel lines do help, but the problem is that the stock brakes
are pretty small for a 4000 lb car that's capable of 150+ mph.
you'll get pad fade, which will require more pressure on the pedal to
stop the car, which means more pedal travel.  you can run more aggressive
pads, but then you'll have the tradeoff of noisy brakes and relatively
poor cold stopping performance.

i upgraded the front brakes to porsche 996 calipers on euro A8 rotors
using BIRA brackets (www.bira.org), and it was well worth the money.

i use valvoline synthetic brake fluid for my street cars, by the way.
it has a higher boiling point than castrol LMA, and it's cheap ($7 for
a quart at pep boys).  the race cars get motul 600, but that's overkill
for a street car.

i bleed my brakes without any assistance or brake bleeder tools.  i
jack up one side of the car, attach tubing to the brake bleed screws
with jars underneath, top off the master cylinder reservoir, pump the 
pedal 8 times, top off MC, pump 8 times, close the bleeders quickly, 
repeat on the other side.

-teddy

--- Mark Rivera <mrivera at webcats.net> wrote:

> Thanks for the tips.  Sounds like I should really find a belly pan now...
> I'm fairly certain the fluid is the major culprit.  I'll get it back up on
> jackstands and start over.  This time I'll use someone besides my pregnant
> wife as a pedal pumper.  :)
> 
> So tell me, what is it about the stock calipers that makes the pedal feel so
> bad?  Sorry, I'm just trying to understand how they can be a factor.
> 
> Mark
>   -----Original Message-----
>   From: Vincent Frï¿½geac [mailto:s.sikss at gmail.com]
>   Sent: Tuesday, October 10, 2006 2:21 PM
>   To: Mark Rivera
>   Cc: S-Car-List; Theodore Chen
>   Subject: Re: [s-cars] Cold start issue, brake fade
> 
> 
>   Mark,
> 
>   As you mentionned your pedal was close to the floor, I suspect the fluid
> you used was contaminated with water. I suggest you flush it again, using
> fresh Castrol GT LMA or ATE, both high boiling point and reasonnably priced,
> flushing the calipers and also the master cylinder, in fact in reverse order
> IIRC, MC first then calipers. I personnaly use the Castrol and never had a
> problem with it, even when I forgot to reinstall the belly pan after
> servicing the car (BTDT a few times).
> 
>   Beside, with the mushmallow pedal feel of the stock calipers, bad pad
> fading can also lead to a pedal going to the floor with almost no braking.
> In fact, the pedal would also go to the floor with good pads, it's just that
> your S4 will be up on its front wheels way before the pedal reach the floor.
> I personnaly use Pagid for pads, street savour (good initial grip, no fad,
> reasonnable dust), because my usual part suppliers always have them stock,
> but there's a lot of other good options.
> 
>   You can also install Paul's Frankenduct, which is simply a dryer duct vent
> installed in the wheel liners so the air coming from the intercooler and oil
> cooler flows directly on the brakes, I mean, when the belly pan is installed
> and some air is actually flowing through the intercooler and oil cooler.
> BTW, for the belly pan, you can contact Force 5 or Shokan. They should have
> a few used ones.
> 
>   Regarding the pedal feel, the braided lines are a pure waste of money with
> the stock calipers, IMO. These calipers create a pedal feel which is so bad
> you won't notice any difference changing the brake lines. The only advantage
> is they will make your wallet lighter, thus slightly increasing the power to
> weight ratio of your S4 with driver with wallet (BTDT, but with an S6).
> 
>   Now, servicing the rear calipers can make a difference. If the hand brake
> mechanism in the rear calipers is jammed or partly jammed, it can have an
> impact on the pedal feel. When the rear calipers will be nice and shinny,
> just get used to pull the handbrake once a day to keep the rear pads close
> to the rotors (BTDT on three Audis).
> 
>   My 0.02$
> 
> 
> 
>   Vincent.
> 
> 
>   2006/10/8, Theodore Chen <tedebearp at yahoo.com>:
> 
>     --- Mark Rivera <mrivera at webcats.net> wrote:
>     >
>     > I flushed and bled the brakes last night, and while it firmed up the
> pedal a
>     > little, it's still softer than I'd like.  I'll probably invest in some
>     > braided lines soon.  I took the car for a spin after I was done, and
> tried
>     > some heavy braking from about 80-45mph.  After about 3-4 applications
> like
>     > that, the brakes were fading really bad.  My foot was almost to the
> floor, I
>     > was almost out of my seat standing on the pedal, and could not get the
> ABS
>     > to activate.  Matter of fact I've never had the ABS step in yet, and I
>     > haven't locked a wheel yet either.  I cruised for about 5 minutes to
> cool
>     > things down, tried again, and most of the braking had returned.  I
> know the
>     > brakes are sorta weak on these cars, but I didn't know it could be
> this bad.
>     > I don't wanna pony up for a caliper/rotor upgrade just yet, but would
> like
>     > some pad suggestions to replace what I think are stock pads with wear
>     > sensors.
> 
>     mark, what kind of fade?  did the pedal soften and go lower?  or did
>     it stay firm, and just feel like higher effort?  the former suggests
>     brake fluid fade, the latter suggests pad fade.  you could also have
>     both.  did you use fresh brake fluid from a sealed container?
> 
>     the stock brakes aren't very good, but braking 120-0 on a steep downhill
>     worked fine although the effort got noticeably higher (pad fade).
> 
>     -teddy
> 
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