Rotors should be machined or replaced if they are cracked or unevenly worn
or warped, it retards breaking performance.
However, if each time you machine the rotors you take off 1mm, then they
will get very quickly below the specified limit. The DBA sport rotors have
the stamp MINTH 9.4MM on the edge of the rotor.
That means a minimum thickness of 9.4mm so a rotor's life could be as
little as 2 skims.(they start at about 11mm) - now is a good time to buy a
cheap plastic measuring caliper and check the thickness of your rotors.
Think of the mass removed when you take 1mm off 11mm - nearly 10 per cent -
that might be about 10% less heat absorbed.
A lot of guys who turn rotors for $20 are butchers and wont give them a
light skim say 0.5mm or less, then check them. (it takes more time to do
that) give specific instructions for disk machining and ask for them to
tell you the thickness at the end.
The disks should not bend - the calipers grab them in a sandwich - unless
you have very unevenly worn pads. You can loose pressure between the rotor
and the pad but this is the combination of pad wear and disk thickness -
scary though. If you go below 8mm thickness it starts to become a real
worry.
Thickness ultimately is a safety issue - the disks could heat and shatter
if they are thin and develop deep cracks, I once saw a 930 Porche with
cracks that looked about .5mm wide (and probably 3mm deep) all over racing
disks - sitting in a race track car park with Targa Tasmania stickers on it
- the driver must have had a death wish.
You brakes inform you at the worst time that they are saying bye-bye - down
a mountain road where there are heaps of bends and probably a 1000 foot
drop at the next corner.
Regards
Howard,
2 Datsun roadsters (one to race on next weekend)
-----Original Message-----
From: Daniel E McHatton [SMTP:hallosb@juno.com]
Sent: Tuesday, 14 November 2000 3:21
To: datsun-roadsters@autox.team.net
Subject: Re: brake rotors
Excessive heat is another reason. Rotors turned too much do not
dissipate heat as well. Anyone who has ever experienced over heated
brakes can tell you it's not a comforting experience.
On Mon, 13 Nov 2000 11:16:38 -0600 "Terry and Donna Cost" <tcost@vvm.com>
writes:
> I looked up the past threads on turning rotors. The "gurus" have not
> issued
> their usual warning. From what I read, when you turn rotors you add
> to the
> distance a brake pad has to travel to put pressure on the rotor, and
> when
> you turn them too much, you cannot put enough pressure on the brakes
> to stop
> the car. Additionally, the pads can travel far enough that the
> piston
> bottoms out on the caliper frame, and you get no brakes at all.
> That's why
> you don't turn rotors past the minimum thickness. Someone else jump
> in with
> a few facts.
>
> Leisure Suit Terry
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