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Hangar Flying / Re: Viton O-rings in Clevelands?
« on: February 03, 2009, 06:54:31 PM »
The failure mode was referring to the original Buna-N rings which came in the brakes.

A CFI friend of mine had a brake failure in the right brake of his RV-8A which caused him to leave a taxiway, fortunately with negligible damage.  He is very cautious about his brakes, but had recently given a checkout in the airplane. He has since upgraded to Viton/83282.

There have been a significant number of brake failures (almost always the right brake, because of engine torque) and a small handful of brake fires in nosewheel RVs.  I also follow the Cirrus lists, and there have been a handful of airframes lost to brake fires on the ground.  There was an AD in the Cirri requiring larger brakes, vent holes in the wheel pants, and "telltale" stickers on the brakes which change colors if they overheat.

The tailwheel RVs are less susceptible, because they have steerable tailwheels, and the TW configuration discourages heavy brake use anyway :-)  There was one RV-8 incident resulting from forcing the airplane onto the runway at high speed and braking heavily (very tired pilot making a round-the world flight being yelled at by foreign controllers at the end of a multi-hour overwater leg).

When I bought my O-rings, they were available in 75 and 90 durometer.  I bought a selection and have installed only the 75s so far.

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Hangar Flying / Re: Viton O-rings in Clevelands?
« on: February 02, 2009, 07:35:00 PM »
I have used them in the Cleveland brakes in my RV-8 successfully for a few years.  I have also given several sets to friends (I ordered a couple of dozen to make a minimum order).

Fair Warning--I am not an A&P, and engineer, or any type of expert in airplane brakes.  Do your own research, yadda. yadda...

I also switched to MIL-H-83282 brake fluid in place of the more common 5606.  This is a chemically compatible (with the 5606) fluid that can be added to systems that have had 5606 in them previously.  It does have a significantly higher flash point than the 5606 and is commonly used in larger turboprop/commuter aircraft.  You can mix the two fluids if necessary.  5606 is only used in small GA aircraft for legacy reasons as far as I can tell.

Google MIL-H-83282 and you will find a lot of info.

It is my (inexpert) opinion that switching to Viton O-rings and 83282 is cheap, easy, harmless, and reduces the risk of a brake fire.  I think this is especially important in aircraft like EZs or -A model RVs that are dependent on brakes for steering.

The failure mode seems to be that the O-rings overheat, and become relatively square in cross section.  Then, on the next brake application, brake fluid gets past the seal and on the hot brake disc.  With 5606, the flash point is only 250 degrees or so.  I think the disc gets a little hotter than that.....

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