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Brake fluid and FAA approval

bob turner

Registered User
I started this on another thread, but the title is misleading. I have checked everywhere, and cannot find anything that restricts me to Mil H 5606. In fact, I found that one can purchase DOT 5, an automotive product with superior characteristics, under MIL PRF 46176B.

So if the only thing that makes 5606 ok for aircraft is its Mil Spec, then I am guessing that DOT 5 would likewise be OK. My 5606 cans say nothing about PMA.

The advantages of DOT-5: non-hygroscopic (no more corroded master cylinder parts; no more pitted caliper bores), non-flammable (5606 is highly flammable, not sticky when it sits around (5606 clogs valves on light plane brakes) and it won't eat paint. I think it is compatible with any kind of rubber, but I know for sure that it works in those Scott and Hayes products, and the Cleveland O-rings seem to handle it just fine.

Any opinions as to what's actually legal?
 
DOT-5 sounds just like Silicon Brake fluid that I had to use in a foreign aircraft because the rubbers would melt in a years time with 5606. Silicon Brake fluid is the best as far as I am concerned. Causes no moisture, wont hurt paint, wont hurt if you drink it. Palhal
 
I had experience with silicon-based brake fluid years ago. It worked great except for one thing. When a small amount leaked on the brake pads, the coefficient of friction went to "nil", and I couldn't get it out of the pads with anything. Wound up replacing the pads, and going back to 5606.
 
That's the opposite of my experience, both with Hayes and Cleveland-type brakes. Fluid just wiped off, and pads/blocks seemed to work normally. They would lock a wheel up just fine, or modulate smoothly.
 
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