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Mobil 1 ATF as brake fluid..

O-rings

Kinda an old thread, but as I'm getting close to finishing it up, just revisiting it as its time to load up the brake reservoir.

That said, with respect to Orings used in our systems, at least for my Matco brakes, those are Buna type seals. The below link is a good treatise on the Buna vs Viton in case one was thinking of changing.

https://www.humphrey-products.com/content/viton-vs-buna-which-seal-for-your-applications

In reviewing it, I knew Viton had a better high temp resistance (which goes nicely with ATF), but wasnt aware of the low temps. Despite high temp braking, I can see the trade off in sticking with Buna so no fluid leaks out at high altitudes (ie low temps) one might see there.

Also, heres a great table of all the typical oring materials and specs - note the compatible and non-compatible columns (I think the aircraft brake fluid note is wrong since we know those fluids are petroleum based (like ATF!), not glycol based as auto brake fluid is)
https://www.marcorubber.com/o-ring-material-quick-reference.htm

If you were so inclined to go Dot3 Glycol, Matco does sell an EPDM conversion oring kit for that. http://www.matcomfg.com/catalog.html?Tp=6&adv_search[4]=0&adv_search[keywords]=epdm&sbT=Go
 
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Off field repair

I had a brake line leak at a fuel stop with no help on the field. Had to go into town to get fluid and a fitting to fix the leak. Used ATF to fill the system and bleed the brake. Worked great to get home then flushed and refilled the system back up with 5606.

ATF will work when you get caught with no 5606 and then flush and fill when you get home.

Best of both worlds!
 
RV7A Flyer said:
I believe BMW recommends ATF in some of their power steering systems...

I wouldn't put so much stock in "approved fluid" lists from manufacturers as to *never* stray from them, albeit normally I'll abide by their recommendations for reasons as stated above.

But really...for brakes, as long as the fluid is compatible with the seals, what else is there? Aluminum lines, flared tube fittings, and such?
Click to expand...

My BMW uses ATF for the power steering. Many don't realize that auto transmissions are hydraulic systems. ATF works very well as a hydraulic fluid and is friendly to most type of rubber seals. It was designed to support both hydraulic applications as well as traditional gear lubrication. Hydraulic fluids of the day would not provide the gear lubrication necessary in an auto trans and traditional gear lube was too thick.

Larry
 
I have read this thread several times over the last year or so and so far I have one observation and one question.
The observation is that when I was in my teens back in the seventies I worked in a gas station and all of the cars I knew about used automatic transmission fluid in the power steering as well. As far as I know they did not even sell anything called power steering fluid.

Now the question. Why Mobil atf? Is it different somehow than others? I was always told that atf was basically hydraulic fluid.
 
I would rather use urine than 5606. Facetious overstatement. Flash point on ATF is 2X higher than 5606 and in no way is 5606 superior. It puzzles me why anyone even questions this anymore.
 
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Mobil ATF is synthetic. Just guessing, but it will almost certainly have a much higher flashpoint than traditional ATF, and will likely retain its other needed characteristics at a higher temp, too.
 
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I have been using Mobil 1 ATF in my rocket for 9 or 10 years now from -24C to plus 40C with no problems observed.

I also use Viton O rings in the grove calipers.

The first month I owned the bird following an electronic ignition that failed during run up, while on the mile long taxi back to the hangar, I nuked(melted & failed to leakage) a buna N
Oring. I made the switch to Viton Orings and Mobil 1 ATF.

There have been a couple of Cirrus AC that torched, from extended taxing in high cross winds, heating the calipers and O-rings allowing brake fluid to leak and ignite on the hot disks.

YMMV
 
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+1

I would definately want to learn how someone flying at -40 set up their heat muffs. -10 is about the tolerable limit on my 6 with two muffs.

Larry
 
rocketbob said:
I doubt many people are out flying in RV's at -40F.
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Not a materials scientist, but that seems to put it about the viscosity of ketchup, per Wikipedia :).

Doesn't seem like that'd be much of an issue even IF one were flying around at -40F.
 
RV7A Flyer said:
Not a materials scientist, but that seems to put it about the viscosity of ketchup, per Wikipedia :).

Doesn't seem like that'd be much of an issue even IF one were flying around at -40F.
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lol perhaps filling a brake system up with ketchup is in order to do a proper test. We can't have experimental planes with any sort of defect on the fringes of reality flying around.
 
rocketbob said:
lol perhaps filling a brake system up with ketchup is in order to do a proper test. We can't have experimental planes with any sort of defect on the fringes of reality flying around.
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Well, while you're at it, might as well try to find the flashpoint of ketchup, too! Wouldn't want those ketchup-filled brake lines catching on fire :)
 
rv7charlie said:
Mobil ATF is synthetic. Just guessing, but it will almost certainly have a much higher flashpoint than traditional ATF, and will likely retain its other needed characteristics at a higher temp, too.
Click to expand...

I don't know about that. The link posted shows Mobile ATF has a flashpoint of 356 f.
 
Robertc said:
Best I can tell looking at Mobil?s ATF spec that it?s about 32 times higher viscosity at -40 deg than 5606A.
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And yet cars in Alaska still have operational automatic transmissions in winter.

My flying-for-11 years -6 needed a 5606 flush when I noticed that the fluid in the plastic hoses had turned into jello when I added passenger master cylinders. Even with that 'goo' in the lines, the brakes still functioned just fine, and with no dragging when released. I now have flushing the brake system as a triennial maintenance item.
 
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