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  1. #1
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    Wink DOT brake fluid vs.Mineral oil.

    Does anyone even know the boiling point of mineral oil? I know DOT brake fluid is nastey stuff, removes paint, is posionous as hell but the stuff is avalible everywhere and is a proven product in Cars, automobile etc. I was looking at some new shmano brakes and they said mineral oil on the lever reservoir. A big turn off to me. It just seems hard to turn my back on the tried and true engineering of DOT brake fluid systems and known working seals and such. Is mineral oil less hydroscopic than regular DOT fluid? That could be a signiicant advantage.
    Big JuJu

  2. #2
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    Solution = DOT 5.1 or the new DOT 5.2 varieties. No hydroscopic characteristics. Motorcycle / Dirtbikes have been using them for a while now with great results.
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  3. #3
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    Now your Talkin

    Isn't that stuff synthetic? Id go for that.

  4. #4
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    So what I am interested in knowing is can you use DOT 5.1 or 5.2 in a mineral oil system without eating the tubes/seals & gaskets away? It is of interest to me as I use Shimano M555s with them little mineral oil labels on my reserviors too.
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  5. #5
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    Mineral oil is less hydroscopic than DOT fluid. That's the problem - it's lighter than water, so if any gets into the system it'll sit at the bottom near the pistons. This can get nice and warm, evaporate any moisture down there, and cause spongyness or failure. Regular fluid has two rated boiling points - wet and dry, so if you use good fluid then moisture absorbtion isn't a major problem (assuming you bleed 'em every so often).

    As far as mineral oil boiling points go, this was hard to find. Couldn't see anything written about Magura or Shimano oils directly, and that got me worried. If it's that good, wouldn't they be crowing about it? So I dug deeper and found the following:

    http://www.execulink.com/~dtierney/w...ra/geninfo.htm says Shell Naturelle is used by Magura in EU markets, and Finish Line No. 5 Shock Oil is used in the US market. I'll go out on a limb and guess that Shimano specs something similar.

    http://www.shell-lubricants.com/prod...php?code=65176 says that Shell Naturelle is rated for operation up to about 90* C. No boiling point seems to be listed.

    There is also a DOT 5.0 silicone based fluid that is supposed to be fairly safe on seals and paint and things. Again, any water in the system isn't good, and it's a litte more compressible than glycol based fluids. If you are having problems with your mineral oil brakes boiling then silicone DOT 5.0 might be worth a shot? I don't know if it'll be compatible in terms of viscosity, but it shouldn't destroy your seals. Not completely sure about the newer 5.1 or 5.2 fluids, but I understand that they're non-silicone so aside from being synthetic are just as chemically nasty as 4.0 fluids. I wouldn't use them in these brake systems.

    First thing I'd try is fitting some temperature stickers to your calipers to see how hot they actaully get. No point messing with fluids if that's not your problem.

    http://www.shotimes.com/SHO3brakefluid.html has some general info on DOT fluids.

    http://www.bicycle-forum.com/tech/Su...il_469506.html has some handy alternative oil options info too.
    Last edited by No I'm Spartacus; 09-19-2004 at 05:22 PM.

  6. #6
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    [burnsvoice]Excellent[/burnsvoice]

    No Im Spartacus;
    Thanks much for the detailed response. I haven't had problems yet, as I have not rolled down anything taller than 200m with these brakes yet, but I figured I would look into this before it becomes a problem, which at my skill level means its too late! So I think I will snoop around for specs on DOT 5.0...

    Cheers.
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  7. #7
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    dot 5 will make the brakes real MUSHY ,,,, plus it usually makes gunk out of everything dot 4 which remanis in the system ...

    5.1 is ok .usually higher dry boiling point but unneccessary and expensice

    dot 4 works best and its cheap.

    Dot fluid has MUCH higher boiling point than the so called mineral oil. Chemically it is almost as nasty as dor 4 fluid, as chemical additives like foam inhibitor and what else not make an interesting mixture..... Magura stains usually stay in clothing forever, even if you wash them right away.

    Magura uses organic pads versus the much better ( rain ) metalic pads, because metalic pads tramsfer heat better and get the temp much higher faster, which relatively fast gets to the boiling point of mineral oil based fluids. Metalic or semi metalic pads are also almost double the price..... usually last double as well, and again work better in wet conditions..

    When you search the board there were a few real good articles about the oil / dot differences. fact is that you do NOT want to make any mistakes and changing manufacturers recomendations for sure... warranty is gone, performance is gone, brakes are gone

    brakemeister

    About that paint stuff with dot 4 ... you need to put the painted surface in constant contact to make a mess, if you wipe spills off after a bleed job you are ok.

  8. #8
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    I dunno about 5.0 being real mushy... I tried it for a while in one of my motorbikes and had no problems. It's a little softer than 4.0, but not that bad. Still, I agree that changing fluids without very good reasons is a bad idea.

  9. #9
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    Good job! I'm gonna take my Raytek pyrometer and

    take a temp reading of the calipers after a long steep fast downhill. As an automotive technician I use the Reytech to se if a caliper is sticking of on a radiator but I think it my serve as a good tool to test the effectiveness of the brakes. The Mercedes Benz brake fluid that I have abundent access to has a dry boiling point of 512 degrees f . I've never used the DOT 5 stuff but I know that it has a high boiling point (a little higher than mercedes benz) and cannot be mixed with convertional DOT3 or DOT 4 brake fluid. I've heard that the DOT 5 has a spongier softer feeling pedal that sports car drivers and racers don't like. You can get the Mercedes Benz brake fluid from any mercedes dealership at the parts department. It's around 15 bucks a quart or liter and it's probably the best brake fluid avalible. For the record one of the first things I learned as an apprentice was DO NOT GET BRAKE FLUID ON THE PAINT.
    Big JuJu

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