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Brake Master Unit replacement for M10

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26 Jun 2022 09:37 #1 by Laurent Crombet
Replied by Laurent Crombet on topic Brake Master Unit replacement for M10
Hi Scott,
Sorry for the long time but at least I come with a solution!
First of all forget mention of rubber coating supposedly damaged. Wrong track.

A friend of mine very experienced in aircraft maintenance looked at the "composite" seal found around the pistons, it combines a conventional O-ring and a very flat section seal probably made of Teflon (on the photo this one has been cut to disassemble it without damaging the edges of the piston groove).
He supposes that this system allows to limit the wear of the joint, Teflon having a better glide than synthetic rubber.
Both seals have therefore been replaced by a single O-ring MS29513-11 in NBR (rubber butadiene-acrylonitrile), as in the Cleveland master cylinders of the same class. See reference at Aircraft-Spruce . This saved the problem including parking brake.

It remained to drain the pipes, which was not simple because the outlet elbows are arranged (unfortunately!) upwards, so it is necessary to use a bench with a hand-pump connected to the drain screws on the wheels.

'Hope this helps.
Laurent
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26 Sep 2021 15:42 #2 by Scott Engelhart
Replied by Scott Engelhart on topic Brake Master Unit replacement for M10
Gordie,
That's interesting, we'll see if I experience that as well. Like you, I will gladly trade good brakes for a parking brake.

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23 Sep 2021 19:28 #3 by Gordie Meade
Replied by Gordie Meade on topic Brake Master Unit replacement for M10
We replaced the O-rings in mine but were never able to get the parking brake to work correctly. The brakes work fine and the parking brake engages. Problem is that once engaged, it stays engaged. I finally just marked it inop and carry wheel chocks with me.
By the by. The wheel chocks I have are 3D printed plastic and weigh almost nothing, particularly compared to the ones I got from Sportys. Unfortunately, I cannot for the life of me remember where I got them. Anybody that's handy with a 3D printer can make them pretty easily and I would guess there's a market for them.

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17 Sep 2021 11:35 #4 by Scott Engelhart
Replied by Scott Engelhart on topic Brake Master Unit replacement for M10
    After realizing that there is NOTHING available for replacement or cross reference substitute for the M10 MC I removed and disassembled mine. An aluminum casting with stainless steel sleeves in the piston bores. No measurable wear in the bores or the pistons themselves. The O rings on the pistons however, were hard and were virtually flush with the piston, they are 46 years old. I have replacement O rings coming from Aircraft Spruce.This morning I had a phone conversation with Richard Pedersen, author of "Last of the Ercoupes, The Mooney M-10 Cadet" who describes the restoration of his M10. I asked him, in your book you stated that you rebuilt the master cylinder, just what did you do? He replied, "well, I cleaned it up and replaced the O rings, that's all you can do". I will report my results when things are reassembled.  
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15 Sep 2021 05:51 #5 by Michael Hainen
Replied by Michael Hainen on topic Brake Master Unit replacement for M10
You guys might check out this URL and it's link to Parker Hannefin .

lasar.com/seal-kits

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14 Sep 2021 19:38 #6 by Scott Engelhart
Replied by Scott Engelhart on topic Brake Master Unit replacement for M10
Laurent,
BOY are we in the same boat. I had requested an M10 master rebuild from Skyport and receive a kit with two O rings which don't appear to relate to our Gerdes master cylinders. I have not removed the cylinder rod/pistons yet, however I have a fair amount of master, wheel and caliper experience, I expect the bores in the master to be smooth aluminum,..... could you expand on the "damage rubber coating" and what seal(s) did your guy replace?? LET'S KEEP IN TOUCH ON THIS ISSUE.
Scott Engelhart
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608-526-9199
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