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  1. #1
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    DOT fluid, how caustic is it?

    i sometimes fiddle with my magura brakes, which means a lot of mineral oil on my hands. what happens if i get DOT fluid on my skin? if its dangerous, why not replace it with mineral oil?

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  3. #3
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    Quote Originally Posted by brake jack
    why not replace it with mineral oil?
    Because the seals, and system overall isn't designed for mineral oil.

  4. #4
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    Here's Material safety data sheets for DOT Brake Fluid

    http://www.championbrands.com/MSDS/1400.PDF DOT 3

    http://www.spectro-oils.com/images/m...GSBF%20MSD.pdf DOT 4 and 5.1

  5. #5
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    Its no problem at all as long as you wash your hands/affected bike parts fairly soon.

    Dot fluid is easily diluted in water.

    However, leave it on the bike and you can kiss your paint job goodbye
    Last edited by Icantthinkofaname; 06-17-2007 at 02:07 PM. Reason: added to txt

  6. #6
    SLX
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    Ive spilled it on Anodized surfaces never cleaned it up and seems ok.

    Seen it semi desolve electrical tape.

    One Question, how does this stuff hold up in contact with epoxy? Im fixing the cap in for the reservior part of a disk brake.

  7. #7
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    Quote Originally Posted by brake jack
    i sometimes fiddle with my magura brakes, which means a lot of mineral oil on my hands. what happens if i get DOT fluid on my skin? if its dangerous, why not replace it with mineral oil?
    DOT brake fluid has a higher boiling point than mineral oil so your brakes will perform consistently longer under hard use with DOT than with mineral oil.

  8. #8
    pbj
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    Dont Use DOT w/Magura

    Quote Originally Posted by brake jack
    i sometimes fiddle with my magura brakes, which means a lot of mineral oil on my hands. what happens if i get DOT fluid on my skin? if its dangerous, why not replace it with mineral oil?
    There are several version of DOT brake fluid, 3,4 and 5. All are designed around good low temp viscosity, high boiling point and the ability to handle a certain amount of moisture <3%. All contain corrosion inhibitors to help prevent rust in the presence of moisture. Type 3 & 4 are basically ethylene glycol and very similar to antifreeze. Type 5 is way more advanced and is actually silicon fluid, which has the highest boiling point of most any fluid and the best chemical compatibility. None are particulatly toxic with occasional skin contact, obviously ethylene glycol is toxic to ingest. Mineral is still probably the least irritating to the skin. None of these brake fluids are corrosive otherwise they'd eat up your brakes insides. All are organic/inorganic solvents of some sort or another. As for compatibility with your Magura brakes, I would not recommend using any thing except mineral oil as that is what the seals have been designed to be compatible with. If you do use one of the other fluids there is a very good likelihood the seals and orings will swell causing sticking and eventual leaking requiring complete replacement.

    Good with your decision..

  9. #9
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    You forgot about DOT 5.1. 5.1 is still glycol based.

    DOT 5 is not hygroscopic like the glycol based DOT 3, 4, or 5.1. DOT 5 also often results in a "spongey" feel.

  10. #10
    pbj
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    Quote Originally Posted by XSL_WiLL
    You forgot about DOT 5.1. 5.1 is still glycol based.

    DOT 5 is not hygroscopic like the glycol based DOT 3, 4, or 5.1. DOT 5 also often results in a "spongey" feel.
    ----
    Your are right, for bicycle brakes I did not think the distiction was that important. Also why should DOT or any brake fluid feel spongy? All fluids are incompressible,unless they contian air. Does one intrain air (foam) more that the others?

  11. #11
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    The fluid absorbs moisture from the air. Even though they seem sealed every brake has breather holes. When the temp goes up the water boils, bubbles, and then the bubbles of air are what compresses. The more moisture absorbed the lower the boiling point vs.what's stamped on the bottle.

  12. #12
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    Water accumulation leads to corrosion.

    DOT fluids absorb water which inevitably leads to corrosion, then stuck pistons or other moving parts. I prefer mineral oil for that reason alone. DOT fluids really need to be flushed annually, especially if you are running a brake system with minimal fluid (lightweight systems for example).

    One thing I have been trying to figure out lately is if mineral oil can be safely used in brakes designed for DOT fluid. The other way around seems like trouble for sure, but since mineral oil is less "reactive", I wonder if it would be OK in systems designed for DOT?

  13. #13
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    probably not. systems that use mineral oil, from what i understand, have ways of keeping the heat from the rotor / pads boiling the mineral oil (such as maguras brake pads that have a heat shield i think?). if you put mineral oil into a system that uses normal brake fluid, you would probably boil the mineral oil in no time, which is not a good thing obviously.

  14. #14
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    Why I don't think heat dissipation is a problem.

    I thought about heat, but found that Magura Royal Blood, for example, has a boiling point of ~383 degrees F. Since it doesn't absorb moisture, the boiling point won't degrade much as the fluid ages, unlike most DOT fluids. The minimum wet boiling point of most DOT fluids is quite a bit less than Royal Blood.

    Some manufacturers specify DOT 5+, but many allow 4 or even 3. I haven't seen any manufacturers specify a minimum boiling point, although most want you to use their brand of fluid (minimum boiling points definitely vary between various brands of the same DOT # fluid). Hope specifically states mineral oil will damage their braking systems, but doesn't offer any details.

    Also, the heat dissipation is proportional to the amount of fluid & weight (mass) of the system. Most brake systems are too close in these respects for it to matter much - at least for any common intended use.

    So unless some manufacturers are really pushing the limits (which I doubt), heat isn't obviously the issue. That's why I've always thought seal compatibility must be the issue, but I can't find any reason to believe seals that are DOT compatible wouldn't be fine with mineral oil.

    Has anybody experimented with mineral oil in DOT brake systems?

  15. #15
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    Don't Do It!

    OK, middle school science class time as an example of what will happen if you switch fluids between systems.

    Take a gummy bear and throw it in a glass of water. What happens? Your bear swells up a couple sizes and becomes fragile, falling apart at the lightest touch. The same thing happens to seals formulated for DOT fluids when exposed to petroleum distillates (i.e. mineral oil) or when seals formulated for mineral oil are exposed to DOT fluids. Then you're looking at a heck of a costly rebuild as ALL rubber, pistons, and hose of the brake will need to be replaced due to chemical damage. May as well buy a new brake due to those costs. No good!

    Also, make a point to differentiate between DOT 5 and DOT 5.1. 5.1 is compatible with MOST DOT formulated systems (check with the manufacturer, follow their instructions so you don't void any warranties). DOT 5 can cause the same kind of seal damage as mineral oil, so again, follow manufacturer's instructions and save yourself some grief.
    The biggest thing I've seen between the two fluids is that DOT fluids have a more consistent feel across a broad temperature range, with the major change in lever feel coming from the temp of the seals. It gets cold up here and all hydros feel heavy in the winter, but my experience is the Shimano/Magura systems feel heavier due to the viscosity of the fluid changing in temps. I could be off base here, but it's my experience, yours could be different.

    The ability to absorb heat is one thing, but the main point with brake fluids is to control the thermal expansion of the fluid. They take up less volume for a given temperature increase than, say, water or motor oil, so they don't pump up as much, and the reservoir doesn't need to be as large. Heat dissipation is primarily a function of the mass at the caliper/rotor interface. The more pad contact (and ergo the more metal at the caliper) combined with larger rotors serve to dissipate the heat to the ambient atmosphere, away from the brake system as a whole. Hence, you don't rock Hope Minis on a V-10. Wrong tool for the job, like throwing the brake from a Festiva on a F-350 with a 30' trailer. Which is why all the major players are coming out with DH/FR specific brake sets. Bikes have evolved, and now the component manufacturers are evolving along with them.

  16. #16
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    You must have went to a good middle school.

    Your analogy is amusing, but not very convincing. I'm not a chemist, but it surprises me that a seal formulation that can withstand DOT fluid cannot withstand mineral oil. So do you know for a fact that the seal materials of bicycle brakes could not possibly be compatible with both types of fluid? Can you provide a reference?

    PS. I have also noticed better brake performance from better DOT fluids.

    PPS. I did find one reference to support DOT seal incompatibility with mineral oil, but nothing specific to bicycle brake systems & seals. There are so many types of seal material. Perhaps the type of material used in DOT systems is very specific though?

  17. #17
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    well, i'm sure you could get a seal kit from whatever brake you're using, and test it by putting it in a jar of mineral oil and let it sit for a few months. what's wrong with spending a few bucks in the name of science!

  18. #18
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    When you do the test, also check and see if the seals and o-rings get a bit harder.

    We use the same seals (nitrile rubber) for ethylene glycol, and oil in my business and it does work well.

    So it must be the additive that can cause some of the issures.

    Big question I got is who cares, just use the right stuff.

  19. #19
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    Good idea.

    That's a good idea, but I'm not sure I could easily test all the important parameter. Swell would be easy to measure, but there could be other effect - hardening or other deterioration, for example. The other effects could be even more dangerous that seal swell. It is worth a try though if I can get a complete seal kit!

  20. #20
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    That's exactly my point.

    I don't know if nitrile is what is used in brake systems, but I do know there are many seal materials. I don't know what material fit the needs of bicycle brake systems. Bicycle brake systems are smalller than any other hydraulic brake system I can think of, so maybe it is possible a material compatible with both fluids is available for this specific application. It seems more likely that manufactuers would use the same materials found in traditional brake systems, but who really knows?

    I personally believe mineral oil is a better fluid for bicycle brake systems. It has a lower viscosity, absorbs less (if any) water, is less corrosive to what is around it (including me), & seems to have adequate heat characteristics in the right formulation. I agree most people just don't care, but I am curious & that's obviously why I am asking.

  21. #21
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    As a matter of fact, B R H,...

    yup, I do have experience with this matter. Another shop in the area that shall remain nameless bled up a a guy's Sole brakes on his Fisher with the same bleed system that they used for bleeding Shimano's brakes. The residual mineral oil was enough to cause the seal swelling as I described. Needless to say the cat wasn't too happy to have his brake crap out in the middle of a ride. Removed the res cap from the brake and the bladder just ballooned out of the reservoir. Master cylinder piston had to be blown out with compressed air. Call to Hayes and I was given the facts of what is termed a 'contamination', as well as the analogy I used. Other shop did fess up and cover the guy's expenses (props!).

    I bet the reason you don't see much more than the labelling of individual brake systems specific fluid requirements is that the manufacturers think we wouldn't be fool hardy enough to use a different fluid than recommended by them. Apparently not always the case however. This is where I totally agree w/ jeffscott. Use what's recommended and ask the questions to the manufacturers. They know the 'why' to these questions better than a bunch of us on a forum for sure. Heck, they make the stuff. Gives 'em a leg over us!

  22. #22
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    Quote Originally Posted by pbj
    ----
    Your are right, for bicycle brakes I did not think the distiction was that important. Also why should DOT or any brake fluid feel spongy? All fluids are incompressible,unless they contian air. Does one intrain air (foam) more that the others?
    little false there. All fluid is compressible to a degree yes including water. Some fluids are more compressible than others.
    Might like to point out that you can compress most fluids to the point where they will turn solid.

    General if the fluild feels spongy in the break line it is because water is in there and water turns into steam.

  23. #23
    SLX
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    Quote Originally Posted by juancancook
    Take a gummy bear and throw it in a glass of water. What happens?
    The wonders of our public education system......

  24. #24
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    Quote Originally Posted by juancancook
    Take a gummy bear and throw it in a glass of water. What happens?
    It drowns of course!

  25. #25
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    So it won't work with that model Shimano. That's good information. Thanks. Do you know approximately how much the repair parts cost?

    I agree the manufacturer should know, but often getting that information is not as easy as you might think. The design engineer will know for sure, but most likely anybody you can contact will not. Either way, most companies would rather just be safe & recommend their fluid for obvious reasons.

    I totally agree that this is not something people should take lightly & just go out & try.

    There is indeed a seal material suitable for brake systems that is also compatible with both fluid types. It is called TFE propylene. If my test seals fail, I may try to find appropriate replacements made of this material. It's expensive though & obviously won't work if bike systems use any proprietary styles or sizes. It might not be possible to replace the bladder/expansion membranes that most brake systems use though.

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