matronics(at)bob.brennan.
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 Posted: Sat Sep 20, 2008 6:02 am Post subject: Give me a brake! |
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Follow up to conclude this thread...
I received 2 master cylinder rebuild kits from Matco for $8.88 each, found
and bought a tiny tube of Black Max adhesive on the net for about $15
including shipping, and scored some aviation brake fluid at a local FBO
through shear luck.
I disassembled both cylinders to find the ineffective left brake had a
Buna-N plug that looked like a donut, hole in the center, and not attached
to the piston shaft. The right (working) brake had an unattached plug with
nearly-a-hole worn in the middle.
Lessons learned from the rebuild:
1. Don't used the recommended "small drill bit" to punch out the roll pins,
it only enlarges the end. One pin on mine came out with a hammer and pliers,
the other I had to cut both sides with a Dremel grinding wheel and then use
the other pin as a punch in a vise.
2. The "Buna" material supplied is enough to rebuild about 10 cylinders, so
must be first cut to size, glued and left for 24 hours, and then shaved down
to working size. I found the recommended 220 grit sandpaper was ineffective
so used the Dremel to get it close and a fine metal file to adjust.
3. Don't take the 1/16" +/- thousandths recommendation seriously, I did, and
did the whole roll-pin and snap-ring assembly/disassembly too many times to
remember. According to final experience and George at Matco - the piston
should wobble freely on the shaft, and most importantly you should be able
to blow air into the outlet (past the plug) or it won't work.
4. I ordered new calliper bleeder nipples rather than risk breaking old ones
- replaced and you *must* fill the system with fluid from the calliper
bleeders until it leaks out of the fill screw in the cylinder. Until Matco
set me straight on the size of the Buna plug I wasted a *lot* of time and
fluid trying to pump into the cylinders.
Biggest lesson learned = send the whole cylinder to Matco - they will
rebuild and test it for the absurdly reasonable price of $15 + parts.
Hope this helps someone in future.
Bob Brennan - N717GB
1991 UK Model 2 ELSA Kitfox
Rotax 582 with 3 blade prop
Wrightsville Pa
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