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DOT fluid confusion

stayhigh65stayhigh65 Posts: 611
edited July 2012 in MTB workshop & tech
Morning All

Just a quick question here for you. Do I need to use DOT 4 or % fluid for my Formula Oro K24 brakes.

My lbs told me it was 5 however after checking through the manual last night it says only use 4?
Wow great ship man. Looks like a fish, flies like a fish, steers like a cow.

HECKLER
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Posts

  • nicklousenicklouse Posts: 50,675 Lives Here
    you can use DOT4 or DOT5.1

    Do not use DOT5
    "Do not follow where the path may lead, Go instead where there is no path, and Leave a Trail."
    Parktools :?:SheldonBrown
  • Dot 5.1 is higher spec than Dot 4 and is more expensive.

    You can use either, but if you don't know what is in your brakes now, it would be best to completely replace all the fluid for new.
  • nicklousenicklouse Posts: 50,675 Lives Here
    Dot 5.1 is higher spec than Dot 4 and is more expensive.

    You can use either, but if you don't know what is in your brakes now, it would be best to completely replace all the fluid for new.

    you dont need to replace all the fluid.
    "Do not follow where the path may lead, Go instead where there is no path, and Leave a Trail."
    Parktools :?:SheldonBrown
  • AlexAlex Posts: 2,086
    It's <10mls of fluid. We're not talking cars here. IF you're bleeding your brake, all the fluid is getting replaced, like it or not.
  • I'll be bleeding the brakes and replacing the pads on thursday so all the old fluid will be gone so it doesnt matter what I put in then? Whats the difference between DOT 4 & 5.1?
    Wow great ship man. Looks like a fish, flies like a fish, steers like a cow.

    HECKLER
    exercise.png
  • AlexAlex Posts: 2,086
    The difference between 4 and 5.1 is the boiling point. 5.1 has a higher boiling point and is theremore more suited to motor racing than Dot 4.
  • stayhigh65 wrote:
    I'll be bleeding the brakes and replacing the pads on thursday so all the old fluid will be gone so it doesnt matter what I put in then? Whats the difference between DOT 4 & 5.1?

    Unless your brakes get red hot in use then there is no need to worry about the difference . http://www.millersoils.net/1_downloads/ ... _FLUID.pdf
  • So would I be right in thinking then that as long as all the fluid is either one or the other it doesnt make much odds which you use?
    Wow great ship man. Looks like a fish, flies like a fish, steers like a cow.

    HECKLER
    exercise.png
  • Whats the difference between DOT 4 & 5.1?

    DOT 5 is a later release than DOT 4. DOT 5.1 is essentially DOT 5 but has more bugs ironed out. FACT.
  • pte1643pte1643 Posts: 518
    Alex wrote:
    The difference between 4 and 5.1 is the boiling point. 5.1 has a higher boiling point and is theremore more suited to motor racing than Dot 4.

    Doesn't the higher number mean it's also less prone to absorbing moisture/condensation that can form inside the hoses?
  • nicklousenicklouse Posts: 50,675 Lives Here
    pte1643 wrote:
    Alex wrote:
    The difference between 4 and 5.1 is the boiling point. 5.1 has a higher boiling point and is theremore more suited to motor racing than Dot 4.

    Doesn't the higher number mean it's also less prone to absorbing moisture/condensation that can form inside the hoses?

    nope.

    also the viscosity is different.

    and a few other things.
    "Do not follow where the path may lead, Go instead where there is no path, and Leave a Trail."
    Parktools :?:SheldonBrown
  • Department Of Transportation DOT (in the USA) sets standards that brake fluids have to pass.
    The DOT 4 has been superseded by DOT 5.1. Both DOT 4 and 5.1 are highly flamable (glycol) and can be washed off with water (readily absorb / dissolve water).
    DOT 5 is for the US forces to use in extremes of climate without having to change (going from artic conditions to the Gulf etc). DOT 5 does not mix with Glycol or water.
    DOT 4 does mix with 5.1.
    In the very small volume required for bike hydraulic brakes it hardly matters what the fluid is as long as it does not freeze, does not damage the seals and is bleed properly.
  • pte1643pte1643 Posts: 518
    nicklouse wrote:
    pte1643 wrote:
    Alex wrote:
    The difference between 4 and 5.1 is the boiling point. 5.1 has a higher boiling point and is theremore more suited to motor racing than Dot 4.

    Doesn't the higher number mean it's also less prone to absorbing moisture/condensation that can form inside the hoses?

    nope.

    also the viscosity is different.

    and a few other things.

    Earlier (older type DOT 3 and 4) Brake fluid is Glycol based and therefore Hygroscopic.

    DOT5.1 is Silicon based and therefore NOT. :wink:
  • pte1643 wrote:
    nicklouse wrote:
    pte1643 wrote:
    Alex wrote:
    The difference between 4 and 5.1 is the boiling point. 5.1 has a higher boiling point and is theremore more suited to motor racing than Dot 4.

    Doesn't the higher number mean it's also less prone to absorbing moisture/condensation that can form inside the hoses?

    nope.

    also the viscosity is different.

    and a few other things.

    Earlier (older type DOT 3 and 4) Brake fluid is Glycol based and therefore Hygroscopic.

    DOT5.1 is Silicon based and therefore NOT. :wink:

    DOT 5 is silicone based.
    DOT 5.1 is glycol based.
  • nicklousenicklouse Posts: 50,675 Lives Here
    pte1643
    Please get your facts right.
    "Do not follow where the path may lead, Go instead where there is no path, and Leave a Trail."
    Parktools :?:SheldonBrown
  • pte1643pte1643 Posts: 518
    nicklouse wrote:
    pte1643
    Please get your facts right.

    Oooo, that told me didn't it.

    OK, so I got a little mixed up between 5 and 5.1, for which I apologise.

    But the moisture absorbing properties arguement between Organic (Glycol) and Synthetic (Silicon) fluids is still a valid one.
  • AlexAlex Posts: 2,086
    Except on mountainbikes which all use Mineral oil, 4 and 5.1, never 5.
  • pte1643pte1643 Posts: 518
    Alex wrote:
    Except on mountainbikes which all use Mineral oil, 4 and 5.1, never 5.

    Accepted. :wink:
  • Magura and Shimano use mineral oils.
    HOPE, Formula etc use glycol-based DOT 4 or DOT 5.1 (non-mineral).
    DOT 5 is silicone based.

    But as the title of the thread says: "DOT fluid confusion"

    However the environmental, and health and safety hazards of glycol-based fluids are probably more important.
  • I'm still confused but perhaps my question can attract some more definitive answers...
    I have formula rx brakes on my Mtb with dot 4 fluid
    I live in Thailand so I'm having issues with water absorbtion due to the high humidity.
    My question is... Can I change to dot 5 (silicon based) fluid?
    Is dot 5 compatible with all dot brake systems?
    Some mistakes are too much fun to make only once 
  • nicklousenicklouse Posts: 50,675 Lives Here
    yes you can but is increases wear and water can be a greater issue due to the fact you mention. the water can not be absorbed so sits at the loest point and then as soon as the brakes warm up it boils. I would just buy a bleed kit and continue with DOT4 or DOT5.1

    this sums it up niceley but is from an MC company
    Since DOT 4 fluids were developed, it was recognized that borate ester based fluids offered the potential for boiling points beyond the 446F requirement, thus came the Super DOT 4 fluids - some covered by the DOT 5.1 designation - which exhibit a minimum dry boiling point of 500F (same as silicone, but different chemistry).

    You can go ahead and mix or flush (replace) any DOT 3, DOT 4, or DOT 5.1 brake fluids, no problem. So there are no special bleeding procedures and you don't need to run anything in the lines. The only one to watch out for is DOT 5 (silicone brake fluid).

    DOT 5 does not damage paint like other brake fluids do, but is not recommended by AP Lockheed for use in their systems due to higher wear than with other type fluids.

    Brake system contamination:

    The single most common brake system failure caused by a contaminant is swelling of the rubber components (piston seals etc.) due to the introduction of petroleum based products (motor oil, power steering fluid, mineral oil, etc.) A small amount is enough to do major damage. Flushing with mineral spirits is enough to cause a complete system failure in a short time. I suspect this is what has happened when some owners change to DOT 5 (and then assumed that silicone caused the problem). Flushing with alcohol also causes problems. Brake systems should be flushed only with DOT 3 or 4.

    If silicone is introduced into an older brake system, the silicone will latch unto the sludge generated by gradual component deterioration and create a gelatin like goop which will attract more crud and eventually plug up metering orifices or cause pistons to stick. If you have already changed to DOT 5, don't compound your initial mistake and change back. Silicone is very tenacious stuff and you will never get it all out of your system. Just change the fluid regularly. For those who race using silicone fluid, I recommend that you crack the bleed screws before each racing session to insure that there is no water in the calipers.
    "Do not follow where the path may lead, Go instead where there is no path, and Leave a Trail."
    Parktools :?:SheldonBrown
  • The RookieThe Rookie Posts: 27,804
    pte1643 wrote:
    But the moisture absorbing properties arguement between Organic (Glycol) and Synthetic (Silicon) fluids is still a valid one.
    Except on bikes as we run sealed systems (unlike cars and motorbikes) so there is no moisture to be absorbed once the system has been bled and re-sealed.
    Current steed - Whyte T129, 2013 frame, mongrel Revelations, Giant dropper, Stans S1 wheelset. 12, Magura Trail Sport brakes, 1x11. 12.8Kg
  • Nick thanks for your input. Much appreciated :)
    Some mistakes are too much fun to make only once 
  • mikewoodsmikewoods Posts: 135
    I heard theyre making a DOT 6.3 which stops you in half the time and helps with bunny hops!
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