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Thread: DOT brake fluid

  1. #1
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    DOT brake fluid

    This might be a dumb question but is all DOT brake fluid the same? Is the brake fluid you get with a MTB bleed kit the same fluid that you can buy from an autoshop? I want to bleed my Avid brakes and wonder if I can use DOT 4 brake fluid from an auto supply shop?
    Thanks

  2. #2
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    Yes it's the same. Car branded fluid is usually cheaper than bike branded stuff too.

  3. #3
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    Not all brake fluid is the same.

    DOT 3,4,5.1 are all hygroscopic fluids (they have the abilitly to absorb moisture) technically you can mix them together. As the number increases you the boiling point increases when you mix them that number will drop. Avid uses this fluid shimano and magura uses the fluid below.

    DOT 5 is a silicone-based brake fluid. Unlike polyethylene glycol based fluids, it is hydrophobic. Its chief advantage over other forms of brake fluid is that silicone exhibits a more stable viscosity index in extreme temperatures. It is widely used in the antique automobile arena as well as it does not damage paint.

    Using DOT 5 in a DOT 3 or DOT 4 or 5.1 system without proper flushing will cause damage to the seals and cause brake failure.

  4. #4
    fua
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    shimano and magura don't use dot, they use mineral oil.

  5. #5
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    You aren't supposed to use DOT 3 in Avid brakes though, only DOT 4 and 5.1.
    I wasn't able to find DOT 5.1 in auto shops (they had never even heard of it), but you can use the DOT 4 from an auto shop. Though keep in mind that 5.1 has a higher boiling point then 4 and if you mix them it will sink to the lowest level of performance.
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  6. #6
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    Car shop hasn't heard of it....wow, avoid that place for advice.

    Motor bike shops tend to be better.

    I would say that hygroscopic is better as it removes any water you get in the lines meaning more tolerant to a bad bleed, but each to their own I guess.

  7. #7
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    Any brake that uses Dot 5.1 can also use dot 4, even mixed together. However, as Monk-Knight says, 5.1 is better especially if you're going to be doing long downhills.
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  8. #8
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    Just restressing the point, don't get dot 5 mixed up with 5.1.

    You want 5.1

    5 will cause you brakes to fail and may result in serious injury or death.

  9. #9
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    I'm using 5 in brakes designed for 5.1


    Haven't died yet. No leaky seals or poor performance of any sort, a year or more running it as well. It won't attack seals, but you shouldn't mix it with 5.1 or the other grades, you should bleed all the old fluid out thoroughly.
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