Dot 4....Dot 5.1 and mineral oil???Oh Why??

Discussion in 'Downhill & Freeride' started by RMboy, Jan 3, 2008.

  1. RMboy

    RMboy Monkey

    Rep/Likes:
    0 / 0
    Joined:
    Dec 1, 2006
    Messages:
    879
    Location:
    England the Great...
    SO you have all of the above, i cant seem to find out what the difference is between them... As in what advantages each would have over the other

    I know that Mineral oil does not eat you paint and It apparently does not absorb water...?(is this true?) So this must be a bonus over the Dot fluids.... But then there must be a reason to use them...

    Also heard that Avid and hope changed to Dot 5.1 this year which has a much hight boiling point....

    Pleas help a poor boy understand:busted:
     
    #1 -   Jan 3, 2008

    Please register to disable this ad.

  2. chriscarleton

    chriscarleton Monkey

    Rep/Likes:
    0 / 0
    Joined:
    Aug 4, 2007
    Messages:
    366
    Location:
    Portland Maine
    there's a thread in here somewhere about that, do a search on it, it's pretty informative.
     
    #2 -   Jan 3, 2008
  3. davep

    davep Turbo Monkey

    Rep/Likes:
    0 / 0
    Joined:
    Jan 7, 2005
    Messages:
    3,279
    Location:
    seattle
    DOT 3, 4, and 5.1 are glycol based (same as anti-freeze). They are water miscable and thus absorb water out of the atmosphere (if open to the atmosphere). these are all (for the most part) interchangable.

    DOT 5 is silicone based and does not absorb moisture.

    mineral oil is a petrol based oil. It does not absorb moisture.

    The problem with fluids that do not absorb moisture is that any moisture in the system (due to condensation via temp or pressure changes) is not absorbed and left as water droplets within the system. This water not only boils at a MUCH lower temp that the fluid, it can also cause rust/oxidation within the brake system. Water is also heavier than the fluids and thus will migrate to the caliper (the hottest point in the system) increasing the possibility of boiling (and loss of brake force)


    It is true that the glycol fluids absorb moisture, and this in-turn lowers the boiling point of the fluid (look at 'wet boiling point')..BUT because the moisture is integrated into the fluid, rust and corrosion is prevented (think coolant/anti freeze in a cast iron block engine). The boiling point is lowered as the % of moisture goes up, but usually the wet boiling point is high enough to prevent boil if you change fluid on a regualr basis (and it is certainly significantly higher than the boiling point of the free water in a non-miscable fluid).
     
    #3 -   Jan 3, 2008
  4. FrontRangeDH

    FrontRangeDH Monkey

    Rep/Likes:
    0 / 0
    Joined:
    Sep 12, 2007
    Messages:
    591
    Location:
    15 sq. miles surrounded by reality
    Keep in mind that brakes specifically designed for Dot cannot use Mineral oil and visa versa. I have been using brakes with DOT since I started riding but am switching to Shimanos for the year which use Mineral Oil. Aside from bleeding technique, anything different in how they actually work, any specific tricks to make them run well?
     
    #4 -   Jan 3, 2008
  5. General Lee

    General Lee Turbo Monkey

    Rep/Likes:
    0 / 0
    Joined:
    Oct 16, 2003
    Messages:
    2,872
    Location:
    The 802
    just curious, but i always read that DOT fluid can 'ruin your paint.' Having spilled it all over every bike i've owned since 1998 i've never experienced any damage to the paint (or thermoplastic in the case of my Lobo).

    obviosly it is--or was--a hazard to some kinds of paint, but i wonder if it's fairly innocuous to modern day paint jobs; the warning being akin to the 'clearcoat safe' label we see on car wax.


    i've had different brakes that ran on one or the other with no noticeable difference. Rotors get hot, but not nearly as hot as those on a car or motorcycle. I'm a fan of DOT though, for the simple reason that--it being a staple of every gas station and convenience store--i can find a fresh bottle of it on about every corner. you can be out of luck if you run out of mineral oil or spill it on the ground. last i checked the mineral oil sold a drug stores is thicker than the stuff used in brakes. But, in its defense if you use mineral oil you'll always be prepared in case you need a laxative.
     
    #5 -   Jan 3, 2008
  6. Transcend

    Transcend My Nuts Are Flat

    Rep/Likes:
    3 / 0
    Joined:
    Apr 18, 2002
    Messages:
    18,062
    Location:
    Towing the party line.
    Pretty sure it's the clear protecting your paint. It's much harder than the actual paint itself. On bare paint it does a pretty good job.
     
    #6 -   Jan 3, 2008
  7. davep

    davep Turbo Monkey

    Rep/Likes:
    0 / 0
    Joined:
    Jan 7, 2005
    Messages:
    3,279
    Location:
    seattle
    The vast majority of bike frames are not painted...they are powder-coated...essentially plastic powder/dust that is melted onto the frame. I think this is one of the reasons you see little damage from short term exposure to glycol fluids.
     
    #7 -   Jan 3, 2008
  8. jvnixon

    jvnixon Turbo Monkey

    Rep/Likes:
    3 / 0
    Joined:
    May 14, 2006
    Messages:
    2,327
    Location:
    SickLines.com
    I think its almost safe to say that we've all seen what dot brake fluid can do to a set of older hayes brake levers. We've all seen it at least once i'm sure.

    Davep i think covered a lot of the reasons why its not so prevalent on your frame.
     
    #8 -   Jan 3, 2008
  9. General Lee

    General Lee Turbo Monkey

    Rep/Likes:
    0 / 0
    Joined:
    Oct 16, 2003
    Messages:
    2,872
    Location:
    The 802
    mineral oil is a lot less toxic too. lick the DOT off your fingers and you can get sick, lick the mineral oil off and you just poop.:biggrin:
     
    #9 -   Jan 3, 2008
  10. RaID

    RaID Turbo Monkey

    Rep/Likes:
    0 / 0
    Joined:
    Oct 27, 2001
    Messages:
    1,393
    Location:
    Not the real North Shore (Sydney), Aus
    Officially that is the case

    However mineral oil wont destroy seals because it is less toxic/reactive (whatever you want to call it) than DOT fluids.
    I have seen mineral oil been used successfully in a DOT system for an extended period of time without any problems

    Definately DONT run DOT fluid in a Mineral Oil System

    The fluid type doesnt have anything to do with the difference in bleeding technique and setup of the brakes. That is governed by the design of the brake system itself.

    Shimano brake systems are bled like car systems ie from the reservoir (ie your brake lever) to the caliper. You put fluid in the reservoir, pressurise the system by pumping the lever then release the bleed valve in the caliper.

    unlike Hayes for example which are bled from caliper to reservoir ie you put fluid in calliper and push it up through the system to the reservoir in the lever.
     
  11. DirtyMike

    DirtyMike Turbo Fluffer

    Rep/Likes:
    51 / 542
    Joined:
    Aug 8, 2005
    Messages:
    13,721
    Location:
    My own world inside my head
    Clear coat is protecting the paint, or with Powder coating its just tough enough not to eat up right away, It was the older style laquers and acryllics that would get eaten up when brake fluid would get on them
     
  12. FrontRangeDH

    FrontRangeDH Monkey

    Rep/Likes:
    0 / 0
    Joined:
    Sep 12, 2007
    Messages:
    591
    Location:
    15 sq. miles surrounded by reality
    All it takes to dilute the DOT fluid is a little rubbing alcohol and then you dont have to worry about your paint burning up
     
  13. DirtyMike

    DirtyMike Turbo Fluffer

    Rep/Likes:
    51 / 542
    Joined:
    Aug 8, 2005
    Messages:
    13,721
    Location:
    My own world inside my head
    Not on older paints, it was like paint stripper, took about one minute and your paint was done, newer paints yet, just was it down and your good to go, and with glycol fluids, just hit it with some running water. No need for alcohol
     
  14. RMboy

    RMboy Monkey

    Rep/Likes:
    0 / 0
    Joined:
    Dec 1, 2006
    Messages:
    879
    Location:
    England the Great...
    Cool that was a informative post...so there is no real advantage over each system?
     
  15. Rover Nick

    Rover Nick Monkey

    Rep/Likes:
    0 / 0
    Joined:
    Oct 17, 2006
    Messages:
    280
    Ideally you shouldn't be licking any kind of brake fluid off your fingers.
    But I will say that I have gotten DOT fluid on my tounge and it tingled really badly. Not very fun