Van's Air Force
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Brake fluid?
- Thread starter rvator9a
- Start date
John Clark
Well Known Member
Brake fluid
This is yet another topic that has flogged before. You might want to search "brake fluid" and read the posts. The bottom line is some prefer aircraft fluid (mil 5606) becuse it is compatable with the seals provided and in not hydroscopic (wil not mix with water,) The other side of the discussion is automotive fluid which is "fire proof" but will absorb water. Automotive fluid is good for higher temperatures and is an excellent paint remover.
In my experience, bleeding most RV systems is best accomplished by pumping fluid from the calipers up. Conventional bleeding will not clear the air from some of the "loops" of tubing in the system.
John Clark
RV8 N18U "Sunshine"
KSBA
This is yet another topic that has flogged before. You might want to search "brake fluid" and read the posts. The bottom line is some prefer aircraft fluid (mil 5606) becuse it is compatable with the seals provided and in not hydroscopic (wil not mix with water,) The other side of the discussion is automotive fluid which is "fire proof" but will absorb water. Automotive fluid is good for higher temperatures and is an excellent paint remover.
In my experience, bleeding most RV systems is best accomplished by pumping fluid from the calipers up. Conventional bleeding will not clear the air from some of the "loops" of tubing in the system.
John Clark
RV8 N18U "Sunshine"
KSBA
randylervold
moderator
"Standard" brake fluid for GA aircraft is MIL-H-5606. This fluid has been around forever and works fine, but can be improved upon. MIL-H-83282 was introduced a few years back and is a semi-synthetic upgrade. It performs better in every regard, but of special interest is the flash point. 5606 has a flash point of around 225? whereas 83282 is around 425?. This can be a factor with RVs because there have been several reported cases of brake fires on RVs and some have taken the whole aircraft with it. Do yourself a favor, upgrade the standard MIL-H-5606 to MIL-H-83282: Royco 782 or Aero Shell 31
rocketbob
Well Known Member
Mobil 1 synthetic ATF specs are almost identical to Aeroshell Fluid 31 (I've checked). Available at Walmart.
Best way to bleed is to connect a tube to the reservoir which goes into a container of fluid to capture overflow and use a pressure can to bleed the system with a significant volume of fluid, from the bottom up. I made a pressure can with a valve and some fittings on an old solvent can. It connects to shop air, turn the valve on and go. Just used this setup on a J3 last weekend on which I swapped the expander brakes with Grove disc brakes. It took me about 30 seconds to bleed each side. Completely foolproof.
Best way to bleed is to connect a tube to the reservoir which goes into a container of fluid to capture overflow and use a pressure can to bleed the system with a significant volume of fluid, from the bottom up. I made a pressure can with a valve and some fittings on an old solvent can. It connects to shop air, turn the valve on and go. Just used this setup on a J3 last weekend on which I swapped the expander brakes with Grove disc brakes. It took me about 30 seconds to bleed each side. Completely foolproof.
FredMagare
Well Known Member
I seem to remember someone writing about how they used an ordinary plastic garden sprayer (for fertilizers/weed killers, available at any home improvement store) as a pressure vessel by attaching an appropriate hose to the end. Fill it with fluid, connect it to the nipple, pump it up, and squeeze the trigger. What a GREAT idea!
Mobil 1 Syn ATF--Risks?
I'd like to use Mobil 1 Synthetic ATF as brake fluid. I just pulled the technical specs on both mil spec 83282 and Mobil 1 Synthetic ATF. I used ExxonMobil's website. Mobil's trade name for 83282 is Mobil Aero Grade(1) HFS.
I'm no engineer. I'm listing these particular specs just because I was able to find these particular specs for BOTH fluids.
Viscosity at 40 deg C is 14.2 cST for the 83282 equivalent. Viscosity at 40 deg C is 34 cST for the ATF. At -40 deg C it's 2000 vs 5190. I don't know if that's significant or not.
Flash points are quite similar at 224 deg C vs 236 deg C. Pour points are quite similar at -60 deg C vs -54 deg C.
The ASTM D 2270 viscosity index seems acceptable at 128 vs 199. For reference, mil spec 5606 has an index of 370.
The specific gravity/density (ASTM D 4052) seems similar at 0.851 vs 0.837. For reference, mil spec 5606 is 0.881. There may be some temperature differences here in the testing at 60 deg F/ 60 deg F vs 15 dec C kg/l.
What risks are involved in using Mobil 1 Synth ATF in RV brake systems?
I'd like to use Mobil 1 Synthetic ATF as brake fluid. I just pulled the technical specs on both mil spec 83282 and Mobil 1 Synthetic ATF. I used ExxonMobil's website. Mobil's trade name for 83282 is Mobil Aero Grade(1) HFS.
I'm no engineer. I'm listing these particular specs just because I was able to find these particular specs for BOTH fluids.
Viscosity at 40 deg C is 14.2 cST for the 83282 equivalent. Viscosity at 40 deg C is 34 cST for the ATF. At -40 deg C it's 2000 vs 5190. I don't know if that's significant or not.
Flash points are quite similar at 224 deg C vs 236 deg C. Pour points are quite similar at -60 deg C vs -54 deg C.
The ASTM D 2270 viscosity index seems acceptable at 128 vs 199. For reference, mil spec 5606 has an index of 370.
The specific gravity/density (ASTM D 4052) seems similar at 0.851 vs 0.837. For reference, mil spec 5606 is 0.881. There may be some temperature differences here in the testing at 60 deg F/ 60 deg F vs 15 dec C kg/l.
What risks are involved in using Mobil 1 Synth ATF in RV brake systems?
terry_georgia
Member
I seem to remember someone writing about how they used an ordinary plastic garden sprayer (for fertilizers/weed killers, available at any home improvement store) as a pressure vessel by attaching an appropriate hose to the end. Fill it with fluid, connect it to the nipple, pump it up, and squeeze the trigger. What a GREAT idea!
I use an even simpler method - an old fashioned pump type oil can (harbor freight - $1.99 special) with a short piece of clear plastic hose (Home Depot Aviation Department $0.20) that runs from the oil can to the bleed valve. Simply pump the oil and watch in the clear tube that no air bubles get into the system.
I'm sorry to seem so dense.
If there are no obvious risks in using Mobil 1 Synth ATF as brake fluid in an RV, then great! I just thought I might be jumping into another situation where I create my own problems--like when I had HC pistons forged and bought an electronic ignition before knowing enough to even wonder about prop vibration and resonance. Now, I know and accept certain risks in running my particular engine/prop combo.
With regard to brake fluid, I was curious whether others knew about certain risks in using Mobil 1 Synth ATF as brake fluid and accepted those risks? Or, in the alternative, whether there are no obvious risks in using Mobil 1 Synth ATF as brake fluid? I should have just asked that, huh?
Just to clarify my earlier post, I don't know what properties are significant when selecting a brake fluid. The ones listed above, in my previous post, may or may not be significant. And, there may be many other more significant properties to consider when selecting a brake fluid than the ones I listed.
Thanks in advance! I learn a lot here.
rocketbob
Well Known Member
In a lot of instances that will work fine, as I have one just like you describe. The problem arises when you have master cylinders upside down like on the -4 and Rockets, or where you have high points in the system where the supply is not upstream gravity-wise. You literally have to blow oil thru quickly to get all the bubbles out. That's where a pressure can bleeder has the advantage. AC$ sells a similar setup and its just a garden sprayer.
f1rocket
Well Known Member
I'm sorry to seem so dense.
I just thought I might be jumping into another situation where I create my own problems--like when I had HC pistons forged and bought an electronic ignition before knowing enough to even wonder about prop vibration and resonance. Now, I know and accept certain risks in running my particular engine/prop combo.
With regard to brake fluid, I was curious whether others knew about certain risks in using Mobil 1 Synth ATF as brake fluid and accepted those risks? Or, in the alternative, whether there are no obvious risks in using Mobil 1 Synth ATF as brake fluid? I should have just asked that, huh?
Just to clarify my earlier post, I don't know what properties are significant when selecting a brake fluid. The ones listed above, in my previous post, may or may not be significant. And, there may be many other more significant properties to consider when selecting a brake fluid than the ones I listed.
Thanks in advance! I learn a lot here.
Sorry Monte, I was being cute.
I'm unaware of any downsides. I have been using it most of the year and the other guys here in Indy have been using it for years without any known effects. It's even red like the the other stuff so your friends won't know unless you tell them.
No worries, Randy. Thanks for the info. I appreciate your willingness to help me.
rv9av8tr
Well Known Member
Use of DOT 5 silicone fluid
I am ready to bleed my RV-9A brakes for the first time!!
RV-9 plans, pg 10-4, specifically says to NOT use 100 silicone automotive brake fluid. BUT.... in the 1980's, there were several cases of EZ's having brake fires when using the traditional "ruby red" hydraulic brake fluid.
Burt Rutan published in his RAF newsletter, Canard Pusher 54-Pg4, July 1987: "We highly recommend the 100% silicone brake fluid (must be Dot 5). Since it is completely inert, compatible with any type "O" rings and seals. It is not flammable and it does not destroy your paint as normal aircraft brake fluid does. We bought it at a Hot Rod-type auto parts store locally."
I personally changed the brake fluid in my Long-EZ from "ruby red" to DOT 5 purple fluid and never had any trouble in 20 yrs of running the fluid in my EZ.
Question is.... does Van's know something about silicone fluid in Cleveland brakes that others are missing????? Anyone else out there with DOT 5 experience?
I am ready to bleed my RV-9A brakes for the first time!!
RV-9 plans, pg 10-4, specifically says to NOT use 100 silicone automotive brake fluid. BUT.... in the 1980's, there were several cases of EZ's having brake fires when using the traditional "ruby red" hydraulic brake fluid.
Burt Rutan published in his RAF newsletter, Canard Pusher 54-Pg4, July 1987: "We highly recommend the 100% silicone brake fluid (must be Dot 5). Since it is completely inert, compatible with any type "O" rings and seals. It is not flammable and it does not destroy your paint as normal aircraft brake fluid does. We bought it at a Hot Rod-type auto parts store locally."
I personally changed the brake fluid in my Long-EZ from "ruby red" to DOT 5 purple fluid and never had any trouble in 20 yrs of running the fluid in my EZ.
Question is.... does Van's know something about silicone fluid in Cleveland brakes that others are missing????? Anyone else out there with DOT 5 experience?
I have a 'mixed' brake set-up, old-style Rosenhan master cylinders (with automotive seals) and Grove brake units. For compatibility reasons I went with the silicone fluid and have used Dot 5 for the past five years.
Have not had any problems whatsoever using silicone. The fluid is benign if you spill some or have a leak. Initially I was concerned that moisture might settle to the bottom of the calipers (since apparently unlike regular brake fluid, Dot 5 does not absorb water) but to date I've found no corrosion or indeed any water at all.
Have not had any problems whatsoever using silicone. The fluid is benign if you spill some or have a leak. Initially I was concerned that moisture might settle to the bottom of the calipers (since apparently unlike regular brake fluid, Dot 5 does not absorb water) but to date I've found no corrosion or indeed any water at all.
