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  1. #1
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    Dot brake fluid and mineral oil differences?

    I am wondering if since brake fluid will eat out mineral oil seals, is is true for the oppisite. I thought mineral oil was enviromentally more friendly? The question arises in using other calipers with shimano dual control brake levers (say mono mini's). I know Hope and Shimano and others dont want us to do this for market control, but is mineral oil truly going to fry seals meant to deal with brake fluid? Are we being mis informed to keep us from creating possible brake setups and allowing us to customize our brakeing as we have always did. It just seems contrary to the spirit of indiviualization we have in MTB community. Like a Harley,none should be the same. Any chem engineers have any input? Thanks

  2. #2
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    Just a guess

    Quote Originally Posted by rjpstoked
    I am wondering if since brake fluid will eat out mineral oil seals, is is true for the oppisite. I thought mineral oil was enviromentally more friendly? The question arises in using other calipers with shimano dual control brake levers (say mono mini's). I know Hope and Shimano and others dont want us to do this for market control, but is mineral oil truly going to fry seals meant to deal with brake fluid? Are we being mis informed to keep us from creating possible brake setups and allowing us to customize our brakeing as we have always did. It just seems contrary to the spirit of indiviualization we have in MTB community. Like a Harley,none should be the same. Any chem engineers have any input? Thanks
    I think mineral oil would work in DOT brake fluid sealed systems in the short run. But there could be more rapid wear of the internal steel or aluminum pistons, etc., and then possible seal leakage.

    DOT fluid absorbs water into the fluid, dispersing the water throughout the fluid. While mineral oil does not absorb water, leaving water from normal condensation (of open systems) to puddle at the bottom of the fluid system which is usually down in the caliper. When the calipers get hotter than 212 degrees, which is common during longer downhills, the water boils and produces air in the system. Puddled water separated in the calipers with mineral oil will cause noticeable air bubbles and sudden brake loss, while the dispersed water boiled in the caliper using DOT fluid would be not produce much air at all nor loss of brakes, perhaps for years.

    The puddling of water with mineral oil would cause more rapid oxidation and corosion of internal metal parts that were not designed for the presence of water, and produce oil contamination and resulting leaky seals, even in a few months.

    Minerala oil systems are probably closed systems only so no water can enter.

    I don't really know, just a guess. (Bored at work).

    - ray

  3. #3
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    Thanks

    Good input. The xtr is an open system. I suspect there are additives to the mineral oil (shimano brand) that approaches those issues. Too bad there is no leadway in interchanging parts....or some data base that we could purchase "seals" and fittings to make system compatible.

  4. #4
    I should be studying...
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    One more thing

    about 'open' and 'closed' systems. Pretty much all of the popular brake systems are open systems--this does not mean they are open to the environment and therefore water contamination; it means that there is a resovoir attached to the master cylinder (the lever) that allows for fluid to move into as it expands when heated. Check out Hayes' website, they have some good explanations. This results in consistent braking performance regardless of the temp (within reason) of your fluid. In a closed system, you have to adjust the volume of your system manually (hopes C2 uses a thumb screw- and is the only closed system I can think of). Yes DOT fluid is meant to absorb water chemicaly so that in small amounts, it has a negligible affect on the coefficient of thermal expansion, but if absorbs enough water, it will degrade the properties of the fluid. I am certain that the seal composition for each respective fluid is not compatible with the other, although I am not sure what exactly happens. I would postulate that putting DOT in mineral oil system would produce catastrophic failure (seeing as how mineral oil is relatively inert compared to DOT which is known for its paint-stripping abilities). Hope this helps.

    -Amadeo

  5. #5
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    many real good articles can be found about the differences.... just let me say its not all black and white....

    just very short and important... brakes with DOT fluid CANNOT be filled with Mineral oil. It will eat the seals at about the same speed as vica versa ...

    Magura : use Magura own OIL
    Shimano : use SHIMANO own Oil

    all others : use a fresh can of the cheapest DOT 4 you can find all over the place

    brakemeister

  6. #6
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    So i accidently put dot fluid in my mineral oil brakes, and i have bled them about 3 times now to get it all the way out, and i was wondering if there was a more efficient way to get it all out. I think the majority of it still remains in the caliper.

  7. #7
    Dude...
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    bleed it with everclear.....

  8. #8
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    Quote Originally Posted by ajlempka View Post
    So i accidently put dot fluid in my mineral oil brakes, and i have bled them about 3 times now to get it all the way out, and i was wondering if there was a more efficient way to get it all out. I think the majority of it still remains in the caliper.
    Not efficient but thorough would be a complete dissemble to ensure absence of all oil.

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