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Brake fluids .... my dilemma

Lycosaurus

Lycosaurus

Well Known Member
I bought the EPDM o-ring kit from Charlie Kuss a while ago, and had upgraded my BUNA N caliper and master cylinder seals with these o-rings, as well as changing out the pilot brake lines with teflon-lined hoses. The intent was to use DOT 4 automotive fluid, since it would mitigate a fire should the aluminum lines or caliper seals rupture at the wheels.

I have since done a little more research, and see that DOT 4 is only used in a sealed system, due to issues with moisture absorption. This fluid is highly hygroscopic, and it is typically recommended that it be flushed out every year or two, when used in a sealed system. Even moist air permeating the pores of the hoses will supposedly degrade the fluid over this time.

In our RVs, the brake system is open to the air, with a breather located at the the top of the firewall forward fluid container. I believe that this fluid would deteriorate very rapidly (weeks), since it is recommended that once opened, the remains of a bottle of fluid be discarded.

Seems that the upgrade to DOT 4 fluid is not for me (unless somebody here can convince me otherwise).


A compromise is the use of mil-h-83282 fluid, which is still flammable, but has a higher flash point than mil-h-5606. As it stands, it would seem that my EPDM seals are compatible with ester fluids (DOT 4, Skydrol), but not with the mineral base (5606) or synthetic hydrocarbon based (83282) fluids.

Here's a link for seal compatibility: http://www.lumaco.com/oringmat.htm

This leave me with the choice of using Skydrol and keep the present EPDM seals (I hear Skydrol is quite a skin irritant, though MSDS downplays this), or change the seals out to Viton (anybody sell a seal kit?) so I can use mil-h-83282. I would prefer not to go back to BUNA N, as it has a low temperature rating.

Skydrol is mildly hygroscopic (has an ester formulation), but also acidic (not sure this is really compatible with our aluminum lines.
Skydrol FAQ: http://www.skydrol.com/pages/faqs.asp

Not sure where to go from here. Leaning towards changing seals to Viton and going the mil-h-83282 route.

Comments?

Edit:

Skydrol seems to be compatible with aluminum.... see http://www.skydrol.com/pages/materials_chart.asp

also from http://www.skydrol.com/pages/faqs.asp
The basestocks of Skydrol hydraulic fluids are blends of phosphate esters, which are mildly hygroscopic. In order to keep moisture in the air from absorbing into the fluid, fluid containers should remain closed when not in use. Vent holes on reservoirs should fitted with dessicant breathers to absorb moisture from the air.​
 
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<<Comments?>>

Interesting chart. EPDM seals are only good to 300F? For reference, note 225F for Buna (the stock caliper seal) and 400F for Viton.

I think there are two views here. One desires a very fire-resistant fluid, and that approach says go with DOT4. You must change all the seals, master cylinders too. And yes, DOT4 is for sealed systems only, at least if you operate in a humid part of the world. Water in the system is a risk for corrosion pitting. You may or may not get fluid temperature high enough for a steam bubble problem. Add regular drain-n-fill to your maintenance list.

The other approach says the problem is simply keeping the fluid contained within the system in the event of a hot caliper. You make a simple switch; just change the caliper seals to Viton. If the fluid doesn't escape, it doesn't burn. 5606 is fine, 83282 has a higher flash point just in case.

If EPDM seals only gain the user an additional 75 degrees of operating range, I think the DOT4/EPDM choice starts looking less desirable, in particular on an RV-A. And the Viton caliper seal swap is so easy.

However, I notice you live in Canada, and there lies a catch. I had a conversation with a Cleveland engineer a few years back. He felt there was a lot of merit to Viton caliper seals, except in places where it got real cold in the winter....and Cleveland products are used world-wide. Viton may not seal as well at very low temperatures. Yes, I'd love to hear from somebody who tried Viton caliper seals in the Arctic.

So, you choose. It is all a matter of considered compromise. I live and operate where it is hot and humid, so I'll go with Viton and 83282. It may not be your best choice.

Side story; a few weeks ago a friend chose to abort a departure in his A-36 just before liftoff. He got it stopped on the runway. However, both calipers got hot, cooked the Buna O-rings, and started leaking almost immediately. My friend is not an A&P and it was not his home airport, so it turned into an expensive AOG deal....and he got the same components. Kiss your experimental airplane next time you see it.
 
Viton nicks easily, not for moving parts

DanH;244399...I'll go with Viton and 83282. It may not be your best choice. [/quote said:
Thanks for the background info, Dan.

I had noted that Viton was not recommended for use on a moving seal (don't have the link for that one). Seems it nicks easily and more readily loses its seal with use (probably in cold weather, and with some contamination).

Found that Skydrol is compatible with aluminum (updated my post above with a link), and being mildly hygroscopic, requires just a dessicant at the vent line. Something I certainly can cobble together. Wondering about local availability ... Airlines should make lots of use of this, but wondering if I can get it in less than 45 gallon drums :rolleyes:
Click to expand...
 
You don't want to have anything to do with skydrol, it burns your skin on contact. Nasty stuff.

8 years on my RV with Mercon ATF in the brake lines, and have yet to have to top off the resevoir.
 
"Sealed System"

Although I'm content with good old 5606 in my application, I have a couple of thoughts on how to use automotive brake fluid. The term "sealed system" is based only on the way the reservoir is vented. Go outside and look at the cap on almost any modern (or not so modern) car. There is a vent in the cap to the outside air but there is a rubber bellows to separate the air and the fluid. Seems to me that if you want the isolation in an aircraft installation, you just need to adapt that technology. Find the smallest rubber bit you can and fabricate a reservoir to match.

John Clark
RV8 N18U "Sunshine"
KSBA
 
Rocketbob is right- Stay away from Skydrol!
How about silicone brake fluid? It's non-hygroscopic and won't remove any paint it accidentally gets on. Pedal feel can be slightly mushy, but might be a good choice. I like Bob's idea about ATF, or maybe good old 5606 just to keep it "airplane like".
http://www.skygeek.com/royprod756pe.html
 
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Obviously your airplane, so what matters to you most of all is what is most important. I have been trying to make the final call myself. I think the best choices are either DOT5.1, 4 or Mobile ATF.

Moisture is not that big of a concern given the real world moisture measurements. You must, again IMHO replace the fluid on a yearly basis to be cautious. That is what I would do anyway as to flush any contaminants, no matter the fluid. I think it is a big plus that DOT fluid does not burn. So even if you have a leak, no fire. This fluid is also in the cockpit again same reason it is a plus, for me.

Reference:
http://www.bobbyarchermotorsports.com/pdf_2848_2.pdf

http://www.xs11.com/tips/maintenance/maint1.shtml

Good luck in your choice.
 
Buna and Mil-H-83282

I have made my decision, and will convert back to Buna N, and use Mil-H-83282 fluid. If I were to do this over, I would just leave in the original seals, and just use the better 83282 fluid. Can always be topped off with 5606 if in a bind.

At this point, I don't feel comfortable with the DOT brake fluid and open-air vent that entrains moisture. Heat the brakes, and vapor lock may become the issue. Last thing I want is my brakes locking up on a -9A.

May still consider use of Viton on caliper seals, however they are not rated for as low a temperature as the BUNA N, and I live in a fairly cold region. Also, they require more lubrication, and may abrade the cylinder walls. We'll see...

Thank-you all who chimed-in.
 
Gary Bricker

Let me start by saying I am the Wagner Brake fluid factory Rep for north Texas. I sell a lot of it. The reason the automotive mfgs. use Dot 3 or 4 fluid it its ability to absorb mosture. This cuts down on rust and corroson. If you use Dot 5 which is silicone based the mosture stays seperate and causes problems. The difference between 3, 4, and 5.1 is the boiling point. Most later model cars have aluminum cyl's and we don't sell 1/4th the Master cylinders that we did when they were cast iron. For several years some of the auto mfg's were really pushing flushing after about 30,000 miles. Some have backed off this. When the fluid gets dark change it. When the fluid gets mosture in it the boiling point goes down. With out looking it up, I think 3 boils around 350, 4 around 425 and 5.1 around 500. We sell mostly 3 for cars and 4 for medium duty and off road. Very little 5.1 is sold. Some of the high end imports use 5. (silicone). There is not a large market for 5 so we don't sell it. That is my 2 cents worth on BF.
 
Cleveland has been building certifed wheels and brakes for many years. I think I will go with their recommendations for seals and fluid.
 
83282 Brake Fluid

I have 83282 fluid in my 9A. I have used it from the start and I did not change any seals. I have had two brake line failures with no fires. Both were on taxi out so the brakes were not too hot. I have since replaced the hard aluminum lines with flexible lines on the main gear.

I have 1150 hours on the airplane and use the brakes more than I should and the brakes are doing well with no leaks at the calipers. I had a hard time sealing the pipe thread fittings at the master cylinders on the pedals for the first hundred hours. I found a high temp/pressure thread sealant at the local auto parts store that worked.

I did email Matco to confirm the seals in the cylinders were compatible with 83282. I can't remember how I confirmed the caliper seals were OK.

Blue Skies.
 
Lycosaurus said:
I bought the EPDM o-ring kit from Charlie Kuss a while ago, and had upgraded my BUNA N caliper and master cylinder seals with these o-rings, as well as changing out the pilot brake lines with teflon-lined hoses. The intent was to use DOT 4 automotive fluid, since it would mitigate a fire should the aluminum lines or caliper seals rupture at the wheels.

I have since done a little more research, and see that DOT 4 is only used in a sealed system, due to issues with moisture absorption. This fluid is highly hygroscopic, and it is typically recommended that it be flushed out every year or two, when used in a sealed system. Even moist air permeating the pores of the hoses will supposedly degrade the fluid over this time.
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Comments?

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ALL brake systems are open to the atmosphere! If they were not, a partial vacuum would be generated in the reservoir. This would inhibit the fluid's ability to flow freely through the system. Don't fret that the fluid will degrade more quickly because your RV has an "open to the atmosphere" system. The vent hole in most automotive systems is very small, but it IS there.
Flushing DOT 4 type fluids is recommended every two years. However, most automobile owners don't flush their fluid at all (at least not till the master cylinder, wheel cylinder, or caliper fails). This generally takes about 8 to 10 years to happen here in very humid SE Florida.
Castrol manufactures a DOT 4 fluid which they call LMA. LMA stands for Low Moisture Affinity. That's just a fancy way to say that it does not have as great a moisture absorbsion rate.
Charlie Kuss
 
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Yukon said:
Cleveland has been building certifed wheels and brakes for many years. I think I will go with their recommendations for seals and fluid.
Click to expand...

I've spoken at length with one of Cleveland's engineers. He admitted that the reason they haven't changed anything is due to the small GA market size and the large cost of getting stuff re-certified by the FAA.
Charlie Kuss
 
DOT 4

N258RE said:
so what would the draw back be of using DOT-5 ? other than mushy pedal

I found this but it applies more to auto's than aircraft :

http://www.xs11.com/tips/maintenance/maint1.shtml
Click to expand...

Mushy pedal is not a certainty with DOT 5, only a possibility during "pumping" of the pedal. As mentioned in the web link you quote above, any water will sink to the bottom of the system. I've had extensive experience with what happens to water trapped in the bottom of a brake caliper. It will cause rapid corrosion of the piston bore in the caliper, thus rendering the entire caliper junk. While flying at altitude, you also face the possibility of that water freezing into ice. A rapid let down "might" put you into a situation where your brakes do not operate correctly upon landing. This would be more of an issue when landing up north during the winter.
DOT 4 fluids with the previously mentioned (by another lister) 3% water entrainment still have a freezing point of nearly -60F. Dry DOT 4 has a freezing point of -74F. See

http://www.amsoil.com/msds/bf4.pdf

More info on DOT 4 can be found below

http://www.shotimes.com/SHO3brakefluid.html

The link you provided was posted back in 2002. It is my understanding that the US Army is now moving away from DOT 5 fluids. Anyone else have any info on this?

Charlie Kuss
 
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<<ALL brake systems are open to the atmosphere! If they were not, a partial vacuum would be generated in the reservoir.>>

Most DOT4 systems have a diaphram in the master cylinder reservoir.

<<It is my understanding that the US Army is now moving away from DOT 5 fluids.>>

Don't know about the Army, but when roadracing in the 80's a bunch of us tried the stuff and hated it. Never could get decent brake feel at the front brake lever, critical for motorcycles. Most attributed it to silicone fluid being hard to bleed properly; I don't know for sure if that was truly the problem.
 
Brake Fluids

I have been flying my 6 for 4 years/400 hours and have been considering changing out the 5606 brake fluid to the higher spec version, but it is hard to get in this part of the country. Recently I noticed that the brakes were dragging so decided to strip the calipers and see if the pistons were sticky. At the same time I popped a pair of Viton O-rings onto the pistons and replaced the 5606 fluid with Amsoil Synthetic ATF. Like Dan, I had experimented with DOT 5 fluid in my race bikes - Harley uses DOT 5 but I am sure that is so that it doesn't lift the valuable paint when it leaks or is spilt - but went back to DOT 4 somewhat unconvinced. Now, after some 35 hours on the synthetic ATF, the RV brakes have not dragged, the seals have not swelled and everything in the garden is rosy.

Martin
 
DanH said:
<<ALL brake systems are open to the atmosphere! If they were not, a partial vacuum would be generated in the reservoir.>>

Most DOT4 systems have a diaphram in the master cylinder reservoir.

snipped

Dan,
Your age is showing! :) Back in the 1970s, most American automotive master cylinders DID have diaphrams. That is no longer the case. Check out almost any modern master cylinder reservoir. It's made of plastic. It's secured to an aluminum master cylinder via grommets (and perhaps a split roll pin or two to keep the lawyers happy). The top is plastic and screws on. No diaphram seal.
Charlie Kuss
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Viton Caliper Seals

Can anyone give me a source and part # for the Viton o ring seals that fit our RV brake calipers. I plan on popping in a set and going with 83232 or Mobil 1 Syn ATF fluid as opposed to the stock aviation brake fluids----for the higher flash point.

Any help would be appreciated.

Cheers,

db
 
How often should I change out 83282 fluid?

This seems to be a good place to ask:

I put the 83282 into my brake system when I built the plane - anyone know of a recommendation on how often I should refill?
 
DanH said:
<<

Don't know about the Army, but when roadracing in the 80's a bunch of us tried the stuff and hated it. Never could get decent brake feel at the front brake lever, critical for motorcycles. Most attributed it to silicone fluid being hard to bleed properly; I don't know for sure if that was truly the problem.
Click to expand...

My understanding of DOT 5 is that it contains more dissolved gases, mostly air, and is therefore more compressible. This is what gives it the mushy feel. I have heard of motorcycle riders pulling the lever right to the grip, that would have scared me during my riding days, cars can have the pedal go right to the floor. Bleeding does not help this as the air will not come out.

The only people I know that use it consistently are the show car people as a spill will not damage an expensive paint job, and the car seldom goes very fast or far.

Bob Parry
 
Anybody know where to get MIL-PRF-87257?

Grove has a good writeup on brake fluids in aircraft:
http://groveaircraft.com/fluid.html
MIL-H-5606 hydraulic is a mineral-oil based fluid with excellent operating properties over a temperature range of -65?F to 274?F. A major deficiency of MIL-H-5606 is its high degree of flammability... The military led the way in developing a more flame resistant hydraulic fluid that is compatible and miscible with MIL-H-5606. As a result, a synthetic-hydrocarbon based fluid MIL-H-83282 (now MIL-PRF-83282) was developed which is superior to MIL-H-5606 (now MIL-PRF-5606) in fire resistant properties, but lacks good qualities in low temperature viscosity.

More recently MIL-PRF 87257 was introduced in order to address the concerns over the low temperature viscosity weakness of MIL-PRF-83282.

Bottom Line: MIL-H-5606 has been replaced with MIL-PRF-83282 and MIL-PRF-87257. Each of these fluids, and their associated systems, are compatible and miscible with each other. You can mix any combination and/or amount of these fluids together without any ill effects.
 
Noah, a quick search turned up this: http://www.radcoind.com/index.html

A thread on the PPrune forum also pointed to them, possibly they are the only ones packaging small quantities.

For anyone interested in DOT 4, I converted my Matco master cylinders & Cleveland brakes, including a diaphgram-equipped reservoir. I used a small remote reservoir from CNC Brakes (www.cncbrakes.com), which has the requisite integral diaphragm, vented to the atmosphere on the back side. Viton o-rings are compatible with either fluid. I have fairly extensive experience using Viton o-rings in motorcycle and automotive braking systems in contact with DOT 3/4 fluids, and have never had leakage issues even at somewhat low temps (-15°F). In hindsight though,the whole exercise was probably silly, as MIL-PRF-83282 or its equivalent would no doubt have served me as well without the reservoir hassle or the need to swap all the other o-rings in the system (all EPDM except the the more hi-temp tolerant Viton caliper piston seals).
 
I am also converting my system over to DOT brake fluid. I already installed the o-ring kit mentioned by the OP. I bought a reservior from Scotts Hotrods in CA.

Upsides:
1)It is a solid machined part, so no welds to crack.
2) It has ports on the back and the bottom.
3) The size and volume are pretty close to the Vans unit.
4) it has the diaphram under the cap to prevent moisture from getting in the system.
5) It looks cool and should be easier to fill.

Downsides:
1) It is heavy, just over 7oz not including the cap. I romoved some excess material and got it down to around 7.5 total, but more needs to be done.
2) the mounting holes are tapped for course-thread 1/4" bolts, which is overkill. I'll have to use course-thread engine bolts rather than standard AN bolts.

FP14042012A0004R.jpg


FP14042012A0004T.jpg
 
Careful with that diaphragm and altitude changes. Not sure what sort of effect pressure changes would have on a sealed reservoir like that. Or maybe I'm worrying about something that's a non-issue....
 
krw5927 said:
Careful with that diaphragm and altitude changes. Not sure what sort of effect pressure changes would have on a sealed reservoir like that. Or maybe I'm worrying about something that's a non-issue....
Click to expand...

Every car made in the last 50+ years or so has a master cylinder reservoir with a rubber diaphragm, just like that one. Its purpose is to keep air away from the glycol-based brake fluid, while allowing the fluid level to drop as shoes/pads wear. Drive your car from low elevation to high, same thing. Non-issue.
 
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