I bought a bottle of Aeroshell fluid 41 from Aircraft Spruce as it is labled as 5606 compliant. I know a guy using auto transmission fluid without any problems and an Aeroshell serviceman recommended it also because our Matco/Grove system uses hydraulic fluid not brake fluid. I don't think it matters which you use but fluid 41 meets the Matco/Grove specs and is as cheap as auto transmission fluid.
Hope this helps some.
Automotive ATF (Automatic Transmission Fluid) is the ONLY thing close to spec we can get hold of here... it is red in colour, goes in nicely and does the job - hundreds of landings - generally short and hot on the brakes, with no issues. BUT we are in Africa... We were even recommended it from a friend in Canada who has set up different hydraulic aircraft brakes across Africa... Only issue is that it can lose its colour in the sun making it harder to see in the lines.. but the lines need changed every 5 years tops here, and the fluid too, so no biggie...
No complaints from using Automotive ATF here... but each must make his own choice in the wonderful world of bringing to life the creation from snips of metal and rivets....
Do not use automotive brake fluid -- not compatible with seals and parts. Do not use the airline hydraulic fluid (commonly known as Skydrol) for the same reason, not compatible. Also, Skydrol is very nasty stuff, the only positive virtue it has is that is does not burn. It causes chemical burns, it blinds you, it is bad stuff.
Good old 5606 will work well and we are talking so little of it in a brake system that the fire aspects do not bother me highly. I was not aware of the new generation of 5606 replacements that Grove discusses in their article, thanks for posting it. Since my plane and I live in New Hampshire, I am a little concerned with the fact that it thickens up a lot in cold temps, I will have to find out what they consider cold. 5606 is used in hydraulic systems of planes that fly in the Stratosphere where temps are fifty below zero. If they say the new stuff gets thick at twenty below, I am not worried. If they say it gets thick at twenty above zero, I need to know more.
ATF will work (I have known people who use it and Jonathan has verified it in his post) but why bother? You are building an airplane and aircraft hydraulic fluid is very reasonably priced. Brakes are a very important system, I recomment using aircraft fluid in aircraft brakes unless you just plain cannot, as is Jonathan's case. My two cents.
Good points - it would be interesting if everybody were honest about what they put in. I have come across DOT3 and DOT4 which are FAR worse than ATF.... as you say the seals take the beating... and brake failure on a short strip may be interesting ---- even expensive... As always, when one is in the 'grey zone' it is important to check more regularly all systems (for example change oil more often, change sparks more often, change lines, etc. EVEN if they look good... 1/2 life changes!
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