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From: donch@tekirl.UUCP
Newsgroups: net.cycle
Subject: Re: Brake repair (was Re: New pads = squeaky brakes)
Message-ID: <264@tekirl.UUCP>
Date: Mon, 27-Oct-86 15:53:09 EST
Article-I.D.: tekirl.264
Posted: Mon Oct 27 15:53:09 1986
Date-Received: Wed, 29-Oct-86 01:22:34 EST
References: <1630@drutx.UUCP> <8800042@uiucdcs> <229@atux01.UUCP>
Organization: Tektronix Inc., Beaverton, Or.
Lines: 30


Something I've been doing for several years is to "exercise" the
brake pistons on my front disc brake.  My brakes are by Brembo,
of the dual piston type.  Whenever I remove the pads, I find a suitable
tool and fork the pistons back into the brake housing; then I carefully
squeeze the brake lever to work them out again.  Doing this several
times causes a noticeable improvement in the free-movement of the pistons.

I began this treatment when I noticed one of the brake pads was wearing
much more than the other.  On a dual piston (opposing pistons, that is)
system, that means only one piston is moving and the disc is being
pushed from one side more than the other.  So a quick investigation
revealed a stuck piston, which freed up using the above-mentioned technique.

Mechanics tell me that corrosion is likely in both the master cylinder
and brake piston parts where close tolerances are the rule.  Water entrained
in the brake fluid (which is hygroscopic, hence the source of the water
with any significant exposure to the atmosphere or from leaky seals)
won't get flushed very efficiently out of the close-tolerance spaces
and will collect there and corrode the parts.  I switched to a DOT-5
silicone brake fluid to eliminate the hygroscopic fluid, only to find
that it doesn't lubricate as well as the old stuff, and I get sluggish
return on my master cylinder piston after brake actuation.  

Oh, well.  At least the corrosion should be eliminated.

Hope this is helpful.

Don Chitwood
Tektronix, Inc.