Maybe so - but if you go to your local physics teacher and ask him/her the same
question,
after a long discussion on the subject of black body emitters with excursions
into the
subjects of surface area, boundary layers and turbulent vs. laminar flow, you
will come
away with the following facts: 1) black-colored surfaces emit and absorb
radiation
(including infrared - you know, heat) more efficiently than white or
lighter-colored
surfaces, 2) a matte finish increases the surface area (minutely, it's true,
but the
effect is measurable) over a shiny finish.
Now, all that having been said, it is true that most of the heat dissipation
from a brake
drum (or a radiator, for that matter) is by conduction - direct contact between
the hotter
metal surface and the cooler air that surrounds it. That is the exact reason
why the brake
drums on the 2000 (and your radiator and the cylinders and heads of air-cooled
internal
combustion engines) are finned - to increase the amount of surface area which
is exposed
to air contact and thus increase conductive cooling. The difference in heat
dissipation
between an unpainted and a properly painted (thin coat of flat black) brake
drum might
not be significant in terms of brake performance, but it is measurable and
positive for
the painted item.
Gary McCormick
San Jose, CA
'70 2000 (brakes emit NO heat - parked for 9 years)
"PATRICK P. CASTRONOVO" wrote:
> Well if you go to a radiator shop and ask them that question of will paint
> slow the dissapation of heat, the answer will be yes. I now have no paint
> on my radiators for that reason. I would think that same would hold true on
> a brake drum. Probably why the 2000 has finned drums, to dissapate more
> heat.
> -----Original Message-----
> From: Gary McCormick <svgkm@halley.ca.essd.northgrum.com>
> To: Teddy Seidenfeld <teddy@stat.cmu.edu>
> Cc: John F Sandhoff <sandhoff@compctr.ccs.csus.edu>; Victor Laury
> <vlaury@earthlink.net>; datsun-roadsters@autox.team.net
> <datsun-roadsters@autox.team.net>
> Date: Tuesday, October 12, 1999 2:05 PM
> Subject: Re: drun paint
>
> >A nice flat black finish should help (albeit in a small way) to dissipate
> heat because of
> >the increased heat-radiating capability of the matte black finish.
> >
> >Gary McCormick
> > -------------------------------------------------------------------------
> -----------------
> >
> >Teddy Seidenfeld wrote:
> >
> >> Dear John and Victor,
> >>
> >> On my 69 2000 I (spray) painted the rear brake drums with high-temp,
> black
> >> (high-gloss) engine paint: some ordinary, off-the-shelf stuff. I did
> that
> >> almost one year ago and it doesn't interfere with cooling or brake
> >> performance; however, I run (old-style) 14" Amer. Racing Libre wheels,
> >> which have generous open spaces between the 4 "coke-bottle" spokes.
> >>
> >> Best,
> >> Teddy
> >> Pgh PA
> >> OROC
> >>
> >> At 12:10 PM 10/12/99 +0000, John F Sandhoff wrote:
> >> >Victor asks:
> >> >> I want to do a rear after work tomorrow. I was looking at it and saw
> that
> >> >> the drums need repainting.
> >> >
> >> >Is it a good practice to paint the drums? Won't that impede heat
> transfer?
> >> >And if you do paint them, wouldn't it need to be hi-temp paint?
> >> >
> >> >-- John
> >> > John F Sandhoff sandhoff@csus.edu Sacramento, CA
> >> >
> >
> >
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