Aircraft brake fluid?

[PapuaPilot]

There are definitely areas we cans save $ on building our planes, but this wouldn't be one that I would choose. Brakes are one of the things I want to work properly with out any doubts. You don't want you brakes to fail at an inopportune moment, especially if the third wheel happens to be at the back of your plane.

Aircraft Spruce has a quart of Philips brand 5606 for less than $7. That should be enough to do your entire brake system. It's not worth the $4 you MIGHT save here.

[Paul Z]

I concur Phil, especially with the third wheel is where it belongs. You could have some serious aaaw cr@@ moments!

[jiott]

Just FYI, the 5606 is different than ATF fluid: The 5606 is a high quality mineral based hydraulic fluid. ATF is also a mineral based fluid with different additives for automatic transmissions, such as friction modifiers for the clutches, but some times is also used as a hydraulic fluid. It is just not optimized for hydraulic use as the 5606 is.

[cgruby]

A little late on the reply, but I was just looking through the MATCO specs and they indeed do authorize DOT 5 brake fluid. All others are not usable due to incompatibility with the seals.

[PapuaPilot]

I haven't heard of DOT-5 so I did a quick search for it online. NAPA Auto doesn't show it. Then I checked Amazon and found it. DOT-5 is a synthetic brake fluid and it looks like the price would be around $12 for 12 oz. That is 5x more expensive than 5606 from Aircraft Spruce.

[Paul Z]

I use DOT 5 on my Triumph TR6, it is tough on paint.

[jtpitkin06]

The MSDS for 5606H lists it as

Distillates (petroleum), hydrotreated light naphthenic

Whatever that is it sounds nasty.

The MSDS for ATF lists it as

highly refined mineral oil

I'd probably wash my hands in ATF without worrying.

DOT-3 is a mixture of Glycol and Glycol Ethers. Not alcohol. Don't breathe the fumes unless you want to go to sleep, permanently.

DOT-5 is Polydimethylsiloxane... Huh???? Some art of silicone. Unpronounceable but it doesn't kill rats.

As for substituting one fluid for another by definition we are experimental aviators. But that's not the real issue here. Neither is cost.

The real issue is availability. So you fly into a small GA airport and your brake goes flat due to a slow leak and lack of fluid. You ask around and most line boys will give you a blank stare when you ask for "MIL SPEC 5606H"

Last I checked there were only two outlets for Aircraft Spruce and they are not open on Sundays.

Scour your airport after 6 PM on a weekend and see if you can find 5606, and really, I don't know of anyone that carries a spare pint of hydraulic fluid in their airplane.

But a trip to the local Wal-Mart will be successful in a search for "brake fluid". DOT 3 is everywhere. DOT 5 is a bit hard to find. My local Autozone and Oreilly's do not carry it, but the New Holland tractor dealer does.

Both DOT-3 and -5 have some nasty habits of eating some seals and paint. ATF is easy on paint and seals but I have no clue as to how it resists the high temps in brake pucks. My Case 480 backhoe uses general purpose hydraulic oil for the brakes and a placard warns against using DOT -3. go figure...

I think the simple test is to put some chosen fluid into a jar with some old brake seals and set it on the shelf for a month. What the hey... You may find that Wesson oil is the answer.

John

[cgruby]

Dot 5 is used in Harley Davidson motorcycles, so you should be able to find it there. "MIL SPEC 5606H" is pretty much the standard hydraulic fluid used in a lot of airplanes, so I would think it would be plentiful around any maintenance facility.

[jiott]

Yes 5606 is not that hard to find. I find it in most all aircraft maintenance and supply dealers in the Portland area. It is also available in many tractor supply houses since it is often used in mobile equipment hydraulic systems, especially in colder climates (it is lower viscosity than most common hydraulic fluids). It is almost exclusively used in military and civilian aircraft hydraulic systems where a mineral oil is called for rather than a synthetic. It is known as military "red oil". Very high quality and not much different than ATF fluid in toxicity. I am a retired hydraulic engineer and worked with the stuff for many years. It is NOT compatible with brake system seals designed for DOT 3 fluid, not sure about DOT 5, but would carefully check first. The 5606 is not hard on paint like most brake fluids. It is flammable at hi temps which is why it is not used in cars where brakes are generally used harder and hotter than most airplanes. I would stick with what the aircraft/brake manufacturer specifies.