'Don't mean to imply that mine was this same problem - it certainly was not,
but I'm reminded of the '81 300D that I bought from a 94-year-old friend in
'01. I remembered when he bought the car new and was a bit envious - his
ivory 123 looked much better to me than my cactus green 123 (240D). When I
bought it from him, the brakes squealed so badly that I thought it was metal
on metal. I immediately bought new pads and was ready to purchase discs if
necessary. When I removed wheels, though, to replace the pads, I found
nearly-showroom pads and discs. I asked him the next day at lunch when he'd
had the brakes replaced. He denied any knowledge of having done so, and
replied, "Aw, I don't ever use the brakes." A few days of my regular
driving and maybe even some extra braking cleared up the squealing fairly
quickly.
Wilton
----- Original Message -----
From: "Rick Knoble" <rickkno...@hotmail.com>
To: "Mercedes Discussion List" <mercedes@okiebenz.com>
Sent: Thursday, August 29, 2013 9:07 PM
Subject: Re: [MBZ] Brake fiasco
----------------------------------------
From: dsereta...@yahoo.com
Date: Thu, 29 Aug 2013 18:33:09 -0400
To: mercedes@okiebenz.com
Subject: [MBZ] Brake fiasco
What could be going on? Literally everything was replaced!
Clipped from the referenced article.
The obvious question now is "is there a "cure" for discs with uneven
friction material deposits?" The answer is a conditional yes. If the
vibration has just started, the chances are that the temperature has
never reached the point where cementite begins to form. In this case,
simply fitting a set of good "semi-metallic" pads and using them hard
(after bedding) may well remove the deposits and restore the system to
normal operation but with upgraded pads. If only a small amount of
material has been transferred i.e. if the vibration is just starting,
vigorous scrubbing with garnet paper may remove the deposit. As many
deposits are not visible, scrub the entire friction surfaces thoroughly.
Do not use regular sand paper or emery cloth as the aluminum oxide
abrasive material will permeate the cast iron surface and make the
condition worse. Do not bead blast or sand blast the discs for the same
reason. The only fix for extensive uneven deposits involves
dismounting the discs and having them Blanchard ground - not expensive,
but inconvenient at best. A newly ground disc will require the same sort
of bedding in process as a new disc. The trouble with this procedure is
that if the grinding does not remove all of the cementite inclusions,
as the disc wears the hard cementite will stand proud of the relatively
soft disc and the thermal spiral starts over again. Unfortunately, the
cementite is invisible to the naked eye. Taking time to properly
bed your braking system pays big dividends but, as with most sins, a
repeat of the behavior that caused the trouble will bring it right back.
Rick
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