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Auto brake fluid or not

hcccs

hcccs

Well Known Member
I started filling the brake reservoir on my RV-4 with standard auto brake fluid, DOT4+ type. A friend told me to only use the special MIL specified fluid and that got me wondering. If the fluid is good enough for a car where the brake caliper can get really hot would it not be good enought for the RV brakes which you use sparingly, at the end of a landing, at engine run-up? What is so special about the aeroplane brakes?
 
Dont know

I cant offer much help on that, but I did ask a similar question a long time ago and the answer was something along the lines of do what you want..but when the company that made the plane kit says to do this or do that or use this or use that....your a dumb a$$ if you just decide to ignore their specific instructions. So I bought a couple pints of the good stuff and life has been good since. Why not use what they tell you to use:confused:
 
Dot 4 is NOT compatible with aircraft system seals or rubber hoses.
 
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DOT 4 fluid WILL cause the rubber components to fail. I made this mistake years ago, and my brakes failed as I was attempting to stop short of the active at MSP with a 727 in short final. Was invited to never come back -- and I landed back home with no brakes.
 
Brake Fluid

I once spent nearly 3 days replacing all the rubber parts in a Cherokee 6 brake system after it was serviced with Dot 3 automotive fluid. Some of the "O" rings that came out were gummy and others looked and felt normal but were swollen up a size or two.


Don B

RV-9 Rebuild in Progress
 
hcccs said:
I started filling the brake reservoir on my RV-4 with standard auto brake fluid, DOT4+ type. A friend told me to only use the special MIL specified fluid and that got me wondering. If the fluid is good enough for a car where the brake caliper can get really hot would it not be good enought for the RV brakes which you use sparingly, at the end of a landing, at engine run-up? What is so special about the aeroplane brakes?
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A few searches will return a ton of info. After doing my due diligence I switched to Mobile 1 synthetic automatic transmission fluid for my brakes and have had no problems for the past 400 hours or so. As always, YMMV
 
Another problem with auto fluid is the cold temps a wheel can experience at height. the fluid may be frozen or nearly so when you most want the brakes.
 
Brake fluid

Yen said:
Another problem with auto fluid is the cold temps a wheel can experience at height. the fluid may be frozen or nearly so when you most want the brakes.
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Not an issue, the stuff is similar to antifreeze. Cars are tested at colder temps than our planes experience at altitude.
I switched out all the seals and hoses in my brake system when I built and use DOT4 fluid. No problems in the 5 years I've been flying.
Be careful with it around painted surfaces, it is a great paint remover :eek:
 
I have set up my -6 for use with Dot 3/4. That involved new seals in the masters, parking valve, and calipers. A new sealed reservoir, plus all hoses are teflon. Sounds like a big job, but really isn't. The new brake reservoir was the biggest change, but I like the new one better anyway.
 
Just about any liquid will work as a hydraulic fluid. Once upon a time a 172rg ran out of hydraulic fluid, the pilot filled the resevoir with urine and got the gear down. Synthetic ATF works well, is red, and is visibly indistinguishable from 5606. No need to make it any more complicated than this. The red stuff is easy to see in clear lines.
 
Auto brake fluid?

Walt said:
Dot 4 is NOT compatible with aircraft system seals or rubber hoses.
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Thanks Walt, that is the answer that explains it. I have now drained the system and will fill it with the right stuff.
 
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