I too was referring to drilling, not slotting!
Greg
Marc Sayer wrote:
> 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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