Re: Defiant leaky brakes


Hi John,
My experience is with single puck Clevelands on my LongEz. My brakes use the MS28775 O-rings in a slightly smaller size. However, I replaced the originally spec'd Buna-N O-rings for Viton O-rings. Viton has superior high heat tolerance. When I did my research, others had reported contacting Parker-Hannifin and the tech there had no issues against using Viton.

Did you verify if the leak is from the O-ring, the bleeder, or the fittings? I suppose you use silicone based brake fluid because it is not hygroscopic and less flammable than the standard aviation 5606 fluid. Maybe that is why you have leaks since the system is designed for the standard fluid, not the DOT5. In my opinion, aircraft should not use DOT5 because it is not compatible (miscible) with the standard red fluid and, if getting help from an A&P away from home base, he may add standard fluid and cause a bad situation for you. I use a less common, but compatible aviation fluid, spec'd as #83282. Its also known as Aeroshell #31 or Rayco #782. It is red, 100% compatible with the standard 5606 aviation brake fluid, but has a much higher flash point.

On Sun, Jul 7, 2019, at 2:39 PM, john toelaer johntoelaer@... [canard-aviators] wrote:
  ... but I made a logbook entry that the o-ring is MS28775-222
Now I am ready to fly but one piston is leaking.   I replaced the Ms28775-222 with a new one from aircraft spruce but no joy. ...when I get back to the hangar I had overheated the good brake and it was leaking also.
additional info:
I use dot 5 silicone brake fluid.  Aircraft Spruce sells a Ms28775=222 for 65 cents and also a Parker -Hannefin equivalet for about 20 bucks.  I ordered both because the cheap one has a speck thickness of 0.125 but the expensive one is 0.139 thick (may be within the + or minus tolerance, don't know)
Any help would be appreciated.


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