Message-ID: <003301bec1a8$ce5fbd80$bb818ed1@pavilion>
From: "J. N. Cameron" <CIC@centuryinter.net>
To: "Lancair List" <lancair.list@olsusa.com>
Subject: SDR: Frozen pistons on Parker Brakes  (LNCE)
Date: Mon, 28 Jun 1999 15:40:23 -0500
Mime-Version: 1.0

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    Over the weekend I was putting my ES back together after its paint job
(see below).  When we tried to roll it a little to get at the inflation
stems in the tires, we found that both main wheels were nearly locked up.
Inspection of the brake piston assemblies revealed that the pistons were not
fully retracting into their housings, but were protruding maybe 0.020" to
0.030", which was enough to bind the shoes against the rotor.  There
appeared to be a combination of crud and corrosion (C&C) around the rim of
the pistons, which prevented full retraction upon release of brake pressure.
Thorough cleaning of the piston housings, plus some careful polishing of the
edges with 2000 grit 3M wet-or-dry cured the problem.  [This takes two
people: one in the cockpit to work the brakes, the other crawling around
underneath to do the dirty work.]  The causes of the C&C were probably a
combination of sanding dust from the body work, priming, wet-sanding, etc.,
and a period of about 6 weeks of not being used.  After working on them each
of the pistons retracted to below the flush position, and the two could be
pushed up and down alternately with moderate thumb pressure.  While we were
at it, we thoroughly cleaned the rods that ride in the bracket, making sure
that the whole brake assembly "floats" properly when reassembled.

    An attempt to take off with the brakes in this condition could have had
serious consequences.  Extreme heating would be a likely result, possibly
resulting in tire failure and/or loss of control.  I recommend that anyone
whose plane has Parker brakes and has sat for a while pay particular
attention to brake drag when rolling it out.  It's easy to notice the
increased effort needed to roll it, and there is usually quite a bit of
noise when the brakes drag.  So -- if your plane seems hard to pull out
after a period of disuse, and you hear some dragging noises from the mains,
check out the brakes to make sure they're working properly!

    Incidentally, the piston assembly came off easily on one side, but
lacked about 0.010" clearance on the other side, hitting one of the bolts
that attach the axle backing plate to the gear leg.  I had to file the marks
on the bolt head off, which was enough to allow the brake assembly to slide
out.  Filing more might compromise the bolt strength, but I didn't want to
remove the bolts and take a chance on changing the wheel camber or toe-in,
however slightly.

    Paint:  Imre Fratilla did a great job, and N82500 has collected a crowd
in every ramp on its way home.  The way home was rather tortuous, as I spent
an extra day dodging weather across the Florida Panhandle.  Imre painted Tom
Giddings' 360, and Bob Stia's ES (Best Composite, '99 SNF).  You can contact
him at fantasy6@gate.net if you're interested in having your plane painted.
I'll try to post a jpeg pic later in the week.

Jim Cameron,  LNCE N82500


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