datsunmike wrote:
> Supposedly its main pupose is for outgassing of the pads which is no longer
> true (pads haven't had that problem in almost 30 years) BUT they are also
> used to dissapate water in wet conditions.
>
> Personally I think its another kind of snake oil and just looks better if
> you like that racy look. However I could be wrong.
>
> Grassroots had a long article about brakes and in particular a long
> discussion about rotors. They said what I feel but maybe what I feel came
> from their article as well as others.
>
> Those drilled rotors are particularly bad unless manufactured by a very
> reputable company and even then you have to keep your fingers crossed. I
> have heard of several stories about the rotors cracking under pressure as
> the holes caused stress risers. Yes, Porsche uses them but those are Porsche
> parts made under strict guidelines.
>
> Mike
Slotted rotors do work, and *if* you have a problem related to pad
outgassing (which does still happen with comp parts but is nearly
unheard of in *normal* street use with street pads - some of us do
experience it even on the street however) :-) they will help. And unlike
crossdrilling, slotting is generally harmless and will not cause
accelerated failures. It does reduce rotor mass a bit (not much, but if
you are marginal to start with on the rotor mass, this may kick you over
the edge) and that can mean rotor overheating under certain conditions.
It does not aid in cooling, but then neither does crossdrilling really,
despite what companies are claiming. It can help with hydroplaning if
you brakes suffer from this in the wet.
Crossdrilling is a whole other thing, and not something I recommend. Not
because it can't be made to work, but because almost no one knows how to
make it work, and/or is willing to do what it takes. In 99.9% of the
cases I've seen, the crossdrilling did nothing to improve the brakes and
resulted in premature brake failures. Porsche crossdrilled rotors are
*not* drilled. Those "drilled" holes are created during the original
manufacturing process. The problem with drilling is the stresses put
into the material by the drilling itself. You can correct their effect
to some degree, but never completely eliminate it. And I know of very
few people who properly stress relieve rotors after drilling. It costs
too much for most of the people who want those "cool" crsossdrilled
rotors. It is a selling gimmick and not a real problem solver.
Go with good new rotors that have been properly balanced, shotpeened,
surfaced, and then cryotreated. Cryotreat your pads (there is good cryo,
bad cryo, and pointless cryo; you want the good cryo which can be hard
to find). Get good quality pads. Break in the rotors and pads properly
(this is one of those areas where almost no one knows how to do it right
for some reason - pads and rotors get broken in differently, and in most
cases you should not break in new pads on new rotors). And then if all
that isn't enough, then try slotting the rotors, but only if it looks
like that might solve your problem. But remember, all slotting can
possibly do is aid in keeping the pads in contact with the rotors when
they are both running at the top of their heat ranges. The better
solution is bigger, more massive rotors with better cooling capabilities.
If you are running good pads and your brakes overheat after repeated
hard braking (ie it takes a while) and once hot they stay overheated,
you probably need both better cooling and more mass in your rotors. And
you may also need a different pad compound. If the brakes overheat after
a single hard brake (be it the first such incident, or if it is just a
particularly hard brake in the midst of many - the key being that the
brakes overheat specifically during a single hard braking effort), then
come back until used very hard again, then you probably do not have
enough mass in the rotors, but the pad compound and cooling are probably
adequate. Rotor mass acts as a heat storage buffer. Cooling can only
have an effect between braking events, not during. So if the brakes get
hot and stay hot you likely have multiple problems. Whereas if the
brakes only get hot when actually used hard, and then cool off fairly
quickly thereafter, the issue is likely that there is insufficient rotor
mass (heat storage buffer is too small).
Has anyone on the list ever looked into or played with modifying the hat
section of a stock Roadster rotor to enhance the "fan" effect and get
more air blowing over the rotors/hats to aid in cooling? This was an
area I thought could be played with for very little $$ and *might* net
some measurable results. Of course your rotors would end up being
directional, but then how often do your "rotate" your rotors? :-)
--
Marc Sayer
82 280ZX Turbo
71 510 Trans Am vintage racer
no Roadster (yet) just a desire, and insatiable curiosity.
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