[W126 Coupe] Brake upgrades

[Daryl Armstrong]

Sam,

Thanks for the kind words.

If you send me your address I will answer your post with details. I haven't
read the forum rules recently (sorry), but I would guess no one wants me
pushing product, and it's not my intention to do so.

Thanks.

Daryl
Black Euro 500 SEC

----- Original Message -----
From: "Sam Sisic" <ssisic at Antunovich.com>
To: <mbcoupes at mbcoupes.com>
Sent: Friday, August 12, 2005 2:47 PM
Subject: [W126 Coupe] Brake upgrades


Daryl,

Thank you for the very informative comments!  Great web site by the way
too!!
I would love to see a brake system developed for the SEC... Doesn't need
to be extreme because these are not race cars, they are just great
driving automobiles!
As many people are upsizing the wheel diameters for these cars and
installing lowering springs, which are definite improvements to an
automobile without much room for improvement, brakes would be a natural
progression.
I don't think the stock brakes are bad at all, considering they are
confined to a 15" dia. stock wheel, aside from the incredible amount of
dust they generate on the front wheels and not much to look at with a
more open type wheel upgrade.
It would be great to see the dust minimized and braking improved with an
appropriate handsome brake kit.
I would definitely be interested in seeing the 560SEC on your "What Big
Brake Systems are currently Under Development?" list!

Sam
Chicago



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Message: 4
Date: Thu, 11 Aug 2005 10:56:14 -0700
From: "Daryl Armstrong" <daryl at precisionbrakescompany.com>
Subject: Re: [W126 Coupe] Brake upgrades
To: "Mercedes Coupes Mailing Lists" <mbcoupes at mbcoupes.com>
Message-ID: <012e01c59e9d$f7311410$6c01a8c0 at daryl>
Content-Type: text/plain; charset="iso-8859-1"

Hi,

I am involved in the business of design and manufacture of big brake
upgrades for race and street applications. As of a year ago, we no
longer supply direct replacement (stock size) brake components. I do
have opinions which I am happy to share.

I'd like to start out by saying that I did NOT join this list with a
view to pedaling my wares and this should not be construed as an attempt
to promote the company.

Some people like the appearance of cross drilled rotors, they look
pretty cool. Most of the time they work pretty well. Many people condemn
them for their tendency to crack and in many cases it's justified. There
are factors which influence the rate of crack development, these are
primarily hole configuration, heat and to a lesser degree, placement of
holes.

Most rotor manufacturers chamfer the surface of the rotor around the
holes. If the holes were not chamfered the edges of the holes at the
rotor surface would be quite sharp (90 degrees). The sharp edges heat up
and cool down rapidly during the braking cycle which causes rapid and
repeated localized expansion and contraction and so, fatigue. Repeated
severe brake applications result in small fractures growing into big
cracks and I suppose if no one notices the problem developing (?)
catastrophic failure could result.

The chamfer angle is typically 45 degrees which means, in round numbers,
that the 'sharpness' of the friction surface transition into the cross
drilled hole is half that of an un-chamfered hole. This significantly
reduces the rate of crack development. A gently "radiussed" transition
from the rotor friction surface into the cross drilled hole seems to
just about triple the crack development time over chamfered holes (all
other variables remaining the same).

Our experience with normal street driven vehicles indicates that cross
drilled (or cross drilled and slotted) rotors usually wear out before
cracking makes it necessary to replace them. If your daily drive
includes 14 miles of 6% down grade through a winding mountain pass, in a
4000 lb car and you like to double the recommended corner approach
speeds, drilling probably is not for you. I have such a drive, but of
course, I don't know anyone who drives that way ;).

Slotted rotors exhibit many of the positive characteristics of cross
drilled rotors without such a tendency to crack. One feature which makes
slotting attractive is the tendency of the slot to 'wipe' the pad clean.
Slots keep pad glazing to a minimum under severe conditions and pretty
much guarantee sustained friction coefficient for the life of the pads.
Frequently, on plain rotors, we find the friction coefficient falling
off as the pad wears. This seems not to be the case with slotted rotors.
The same can be said for pads used with cross drilled & slotted rotors

My recommendation: If you think you will use your brakes to capacity
(you experience brake fade) on a regular basis, use plain or slotted
rotors. If you like the idea of cross drilled rotors, use them and keep
an eye on the surface condition. Tiny hairline cracks are usually no big
deal. If they become really obvious, you might trade the rotors out. If
you like drilled rotors, you might consider drilled and slotted rotors
for the benefit the slots provide. If possible, try to get "radiussed"
holes.

In terms of brake effectiveness, our tests have shown little or no
difference in stopping distances using plain or drilled / slotted
rotors. I would modify that statement to include "within our ability to
accurately test....", considering we use real life conditions and 'G'
meters as scientifically as real life conditions permit. Also, rotors
that look like Swiss cheese are just as effective as plain rotors in
terms of stopping distance. This dispels the myth that surface area has
a lot to do with how well brakes work. The same applies to pad area....
Big pads last longer than small ones, but they do the same job.

There are other advantages to cross drilling that don't really apply to
standard sized replacement parts for street use, but they typically come
with the need for some compromise. Actually, compromise seems common to
all walks....

Although we no longer deal in direct replacement parts, we have access
to a variety of direct replacement parts. I would be prepared to make
rotors and pads available to list members on a, cost plus a small bit,
basis if it is of interest. Again, not wishing to be a 'vendor' here.

Regards,

Daryl.
  ----- Original Message -----
  From: Rockymiranti at aol.com
  To: mbcoupes at mbcoupes.com
  Sent: Wednesday, August 10, 2005 2:18 PM
  Subject: [W126 Coupe] Brake upgrades


  Looking into slotted and drilled roters for the 560, anyone have
advice and expertise in this area?


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