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Of all the things to argue about on this forum, this has to be one of the more pedantic.
Two relevant/amusing experiences from my past. When I was in the AF stationed in England, my Jaguar had a bad front seal leak. Being a poor airman at the time, I did not have the resources to keep throwing ATF into it every day nor the motivation to spend the weekend dropping the tranny and replacing the seal. What I did have though, was access to an unlimited supply of 5606. So that's what I filled it with. Every day for months. I'll bet I ran 50 gallons of the stuff through that tranny before I finally installed a new seal. Was still running fine on 5606 when I transferred back home a year later. When I picked up my Tri Pacer and serviced the brakes, I found that the previous owner had serviced it completely with DOT 3 (automotive) brake fluid. The Certified Cleveland brakes didn't seem to mind one bit. (Yes, I went with 5606) I have a lifetime of 5606 around, but I'd have no trouble at all adding ATF out on the road if required. Power steering systems use it as do convertible top systems. Is it just a slow week on the forum? |
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Neither Van's nor any brake manufacturer I'm aware of has tested or approves using ATF in their brake systems, but I guess you're just smarter than they are. Until they do, thank you very much but I'll stick with the "approved" fluids. |
Brake Fluid.
When I picked up my Tri Pacer and serviced the brakes, I found that the previous owner had serviced it completely with DOT 3 (automotive) brake fluid. The Certified Cleveland brakes didn't seem to mind one bit. (Yes, I went with 5606)
For what its worth: It was years ago, but I once spent days replacing parts and rebuilding the brake system on a Cherokee 6 that had been operated for a couple months with automotive (Dot 3) brake fluid. Many of the ?O? rings were very soft and gummy. On my 9 I will use the higher flash point Aviation Grade Fluid or ATF. Only 5606 in the Pacer. Don Broussard RV9 Rebuild in Progress 57 Pacer |
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Flash point of Royco 782 (MIL-PRF-83282) and Mobil 1 ATF appear to be about the same 445F/220C. http://www.qclubricants.com/royco/royco_782.htm So unless you're just "very frugal" (I'm being nice here), or just want to be different, there's really no good reason not to use what the brake manufacturers recommend. |
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It's like the rest of aviation, there are standards we follow in the industry that are considered accepted practices, like manufacturers manuals and AC 43-13, you don't have to do it that way but those are considered "approved" methods of aircraft maintenance and repair. Can you do it any way you want because it's experimental, sure... but please don't imply I am being "morally superior" because I choose to use accepted aviation materials and practices and not the methods "approved" by some folks on VAF. Ok I'm done. |
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the technician's manual for Parker (Cleveland) brakes says: Hydraulic Applications - Use fluids compatible with the system MIL-H-5606 / MIL-H-83282 (Red Oils) Skydrol ? Only compatible with itself So...is ATF compatible with aluminum? I'd guess so. Is it compatible with the o-rings? Depends on the o-rings, I guess, but evidence is that it is compatible with the ones we're using. What else is in the brake system for it to be incompatible with? |
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Did a bit of Googling trying to find out the chemical differences between 5606 and ATF and didn't find much. I did find that people are using it interchangeably in automotive lifts, sailboat autopilot systems, industrial hydraulics and other stuff - some of it with claimed manufacturer endorsement of interchangeability. So I guess if we want to ignore the empirical evidence offered by those who are using ATF in their brakes, a simple test would be in order. Cut a "certified" O ring in half and drop a chunk in a jar of 5606, the other in ATF and let it sit for a while. Once the soak period is over, compare each half and see if there is any sign of distress from the ATF half. Swelling, durometer, and general appearance, should be readily apparent. |
ATF
I don't know what all the fuss is about on using ATF in aircraft brakes. The O rings are compatible with petroleum based oils. ATF is such; any hydraulic oil will work.
I have been using ATF for over 40 years. An engineer friend used ATF in his 310 Cessna for 35 years. I probably have close to 4,000 hours (different airplanes) using ATF in my brakes. Never had a problem! Thank goodness for experimental aircraft. |
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/co...r-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-m...-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...5D=epdm&sbT=Go |
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! |
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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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Best I can tell looking at Mobil’s ATF spec that it’s about 32 times higher viscosity at -40 deg than 5606A. This may be more important for winter brake operations.
As info. The 5606 spec is older/obsolete, but it’s still available. Newer versions are equal or better. https://www.mobil.com/English-US/Pas...XXMobil-ATF-DM http://everyspec.com/MIL-SPECS/MIL-S...06A.044544.pdf |
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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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 |
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Doesn't seem like that'd be much of an issue even IF one were flying around at -40F. |
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5606:
https://www.noe.jxtg-group.co.jp/eng...4021-1704e.pdf and traditional ATF: https://www.acdelco.com.au/pdf/speci...s_dexronVI.pdf vs Mobil 1 synthetic ATF: https://mobiloil.com/en/automatic-tr.../synthetic-atf |
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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. |
Does anyone know if the ATF turns into sticky goo when it evaporates like 5606 does?
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