Brake Master Unit replacement for M10

So I thought it was best to add the following to this discussion.I believe this brake master cylinder and reservoir is only applicable to the Mooney M10.  Possibly a few later production A2As, but I do not know.  It is a nice, compact unit that for some reason not very popular despite how popular Gerdes brake systems are.  Good luck finding any sort of literature about this unit, let alone a rebuild kit. I recently rebuilt this master brake cylinder a few months ago, and found the following o-rings to be the correct ones:MS28775-006 quantity two for the parking brakesMS28775-008 quantity one for the reservoir cap boltMS28775-009 quantity two for the piston seals (most important ones)MS28775-010 quantity two for the exterior of the piston rodsI was surprised how “dirty” the accumulation of gunk within the cylinders despite changing some of the hydraulic fluid over the last 5 years.  If you are having some brake issues and have already changed out the caliper piston seals and fresh hydraulic fluid, I suggest removing this unit and cleaning it.  Take your time and take pics because there is no reference literature, but it is not really that complex.The reservoir cap, I just used a very light coat of RTV as a gasket, and let it set for 20 minutes before assembling.  Let it sit overnight before adding fluid. 
Hope this helps someone….Mike

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Both seals have therefore been replaced by a single O-ring MS29513-11 in NBR (rubber butadiene-acrylonitrile), as in the Cleveland master cylinders of the same class.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

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.

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.

    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.  

You guys might check out this URL and it's link to Parker Hannefin .

lasar.com/seal-kits