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Old 09-18-2023, 08:08 AM
moetzmoet's Avatar
moetzmoet moetzmoet is offline
Join Date: Jun 2022
Location: Sacramento
Posts: 6
Default What do you think on brake fluid

Howdy again,
I can't find anything in the instructions of what type brake fluid to use. I have dot 4 Motul high temp fluid that I use on motorcycles.What do you think?
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Old 09-18-2023, 08:30 AM
swjohnsey swjohnsey is offline
Join Date: Nov 2018
Location: Kingsville, TX
Posts: 602

Most aircraft use hydraulic oil similar to automatic transmission fluid. I use Mobil 1 ATF, easily available at car parts stores.
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Old 09-18-2023, 09:02 AM
JDA_BTR JDA_BTR is offline
Join Date: Dec 2013
Location: Colorado Springs, CO
Posts: 1,663

Aeroshell 4 is good when mineral oil is compatible with the brakes.
Ser 140142, RV-14A flying - N1463
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Old 09-18-2023, 09:26 AM
Taltruda Taltruda is offline
Join Date: Oct 2017
Location: Las Vegas, NV
Posts: 1,805

Royco 782 is the answer. Also 5606 Hydraulic fluid, but the latest Vans Service Instruction is to use the high temp synthetic Royco 782. It is compatible with 5606, but due to the nature of the nosewheel models and that most pilots that I’ve seen who taxi a free caster noose wheel plane tend to abuse and overuse their brakes, you have a risk of a wheel fire if you still use nylon brake hoses and the heat causes the line to slip out of the fitting.
Vans also recommends upgrading the internal caliper O-rings to their Teflon (edit: VITON, not Teflon) versions.
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Last edited by Taltruda : 09-19-2023 at 10:24 AM.
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Old 09-18-2023, 09:40 AM is offline
Join Date: Jan 2017
Location: Battle Ground WA
Posts: 738

Oh this is a topic fresh in my mind as I just three days ago I replace the o-rings in my calipers in my RV-6A.
Didn't have any "aircraft" brake fluid.
Upon popping the pucks out of my calipers I found water in one of them. It was a holy ^#&# moment. There is not supposed to be water in the brake system as far as I know.
I bought the plane 4 years ago and never had a problem
BUT, I am sure the previous owner put in DOT 3 or 4 as it is a Glycol based fluid (I.E. water)
I did a bunch of research and found Royco 782 has a flash point of 445F
BUT guess what? The Toyota synthetic auto trans fluid I had on the shelf has a flash point of 440F
Well, that just solved my problem.
Fluid in stock and I do not own the Toyota any more so it was a win win win.
If you go the trans fluid route make sure to stay with the synthetic as non-synthetic has a lower flash point in the range of 250-300F
Mobile-1 is very available and good stuff.
Just realize that brake fluid is just hydraulic fluid used in a touchy place.
Being a mechanic for 55 years I used to think that there was something special about the stuff.
My luck varies. Fixit

Last edited by : 09-18-2023 at 09:49 AM. Reason: missing info
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Old 09-18-2023, 10:49 AM
RheinRivets RheinRivets is offline
Join Date: Jan 2023
Location: Langenlonsheim, Germany
Posts: 19

As vehicle brake fluids were mentioned here: One of the major differences between any hydraulic oils and DOT brake fluids is, that DOT3 or DOT4 are strongly hygroscopic, i.e. brake fluid is designed to absorb any water which made its way into the braking system - up to a certain amount, of course. This way, it will effectively inhibit internal corrosion inside the braking system. However, the more water the brake fluid absorbed, the lower gets its boiling point. When brakes heat up, the fluid may then (partially) evaporate. Steam or gas won't transfer the hydraulic pressure very well which can cause brake fading. It is therefore essential to regularly drain and replace DOT brake fluids - in road vehicles not later than in 2 years intervals. This may not be the only reason why I haven't seen much DOT brake fluid use in aircraft.
Not sure how internal corrosion prevention will work with hydraulic oils or ATF and which replacement intervals are needed here.
Best wishes,
Member of the RV-10 QB team at Aero-Club Rhein-Nahe (EDEL)
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