[s-cars] Brake pedal firmness

Taka Mizutani t44tqtro at gmail.com
Wed Jul 5 20:36:31 EDT 2006

Are you driving with the stock brakes?

The reason I ask this question is because the G60 calipers used on the S4/S6
a lot of fluid, requiring a fairly large diameter master cylinder and then
there is the hydraulic
servo to consider.

The G60s' master cylinder has to be large to move all that fluid to move the
pistons- this results
in fairly wooden pedal feel, but that's better than having a really long
pedal travel- that would
be scary to drive.

The hydraulic servo system doesn't seem to feel as linear as a vaccum assist
servo, that may be
the second part of the equation.

Finally, a large sliding caliper like the G60 doesn't have the caliper
stiffness of a fixed caliper, obviously.

Comparison between a Porsche caliper equipped car and the stock car is very
interesting- even
a small caliper like BIRA system 1 makes the pedal feel better- the fixed
monoblock caliper has much
less movement (just the pistons themselves move, everything else is fixed),
feel more precise.

Someone in the industry like Keith should be able to explain this better
than me, I'm giving the very
basic overview without really explaining how and why, hopefully someone else
can supplement this info.

My old 200 with the 996 calipers has a pretty nice feel to them, but still
very wooden and nonlinear compared
to the brakes on my Subaru- I think that is due to the servo, considering
that the caliper construction and
everything else is pretty similar.

If this really concerns you, the cheapest way to make the brakes feel more
linear (if you're complaining about
lack of response) is to switch to a higher friction, more "grabby" brake
pad, along with SS lines of proper construction,
helps take some of the flex out of the system. I've driven a 200 10v with SS
lines, good pads and stock G60s
and it felt way better than another car with rubber lines and stock pads.

The more expensive way is to install a fixed caliper system like the Porsche
calipers and other similar calipers-
Brembo branded, Stoptech, etc.


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