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  1. #1
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    Switching between mineral and synthetic oil (rainy day)(no TL;DR)(no chlamydibrah)

    So since it's raining outside and my saddle rails have been shot to chit, I've been doing some reading.




    There have been a number of such threads in the past, and the conclusion in almost every one is that synthetic DOT 4/5.1 will destroy seals in Shimano / Magura systems which use mineral oil and vice versa... leading to catastrophic failure, you flying down the mountain faster than everyone else, etc.

    Well, after reading a bit more on the subject, there seems to be no conclusive evidence supporting this conventional wisdom in the mtb community. Some car manufacturers recommend the use of mineral based hydraulic oil but do not prohibit usage of synthetic oil, which further adds to the mystery (read about this in some car forum regarding nissan/honda/toyota cars, anyone can confirm?)

    ==============================================


    Advantages of synthetic hydraulic fluid in brake systems:

    -Higher dry boiling point.
    -Relatively high wet boiling point (Absorbs moisture to prevent loss of brakes or brake lever lock when temperature of braking systems exceed boiling point of H20).

    Advantages of mineral based hydraulic fluid in brake systems:

    -Not abrasive, more environmentally friendly.
    -Does not absorb water, less spongy feel at the lever due to less air bubbles.

    Disadvantages of synthetic hydraulic fluid in brake systems:

    -Difficult to purge this water out hence corrosion (can be handled by additives) and spongy lever feel.

    Disadvantages of mineral based hydraulic fluid in brake systems:

    -Relatively expensive/not as accessible.

    ============================================





    Question 1: Is it OK to mix mineral oil and DOT 5.1 fluid?

    From Car Bibles : The Engine Oil Bible PAO oils will mix with normal mineral oils which means you can add synthetic to mineral, or mineral to synthetic without your engine seizing up.
    From same url as above: There was a time, years ago, when switching between synthetic oils and mineral oils was not recommended ... ... but changes in additive chemistry and seal material have taken care of those issues. And that's an important caveat.

    From same url as above: There is no scientific data to support the idea that mixing mineral and synthetic oils will damage your engine. When switching from a mineral oil to a synthetic, or vice versa, you will potentially leave a small amount of residual oil in the engine. That's perfectly okay because synthetic oil and mineral-based motor oil are, for the most part, compatible with each other.

    (The exception is pure synthetics. Polyglycols don't mix with normal mineral oils.)
    So I googled polyglycol and the first result (wiki, as always) that came up was polyethylene-glycol, i.e they're pretty much the same. DOT 5.1 fluid is polyethylene-glycol based. Most oil manufacturers say that their synthetic oil is compatible with mineral oil though, so I guess it depends on the bases. Conclusion: Do not mix the 4/5.1 and mineral based fluid.






    Question 2: But would it work if you flushed the system of all mineral hydraulic fluid and replaced it with DOT 5.1 and vice versa?

    Background info on esters:

    Swells and reduces the inner diameter of seals, softens rubber and elastomer seals but are used for their higher lubricity properties. Esters also combat the shrinking and hardening properties of Polyalphaolefins (PAO), which are used in synthetic oils for some favourable properties. More info here - What Are Synthetic Lubricants - In Depth.

    Some guru (molakule) on BITOG forums conducted an experiment. The goal is to determine fluid effect on common fluorocarbon elastomer seal materials using two dissimilar synthetic base oils. Seals were all new Flourocarbon elastomer seals from various seal manufacturers.

    Read more here: Seals - Bob Is The Oil Guy

    post #530790

    Results:

    III. Test Results

    1. Di-Ester
    A. Durometer - 5.3% (toward softness)
    B. Flexibility increased slightly
    C. Peeling, cracking, or any other physical damage none.
    D. Dimensional change + 7%; increase in lip height and decrease in radial dimension.
    E. Wetting and Fluid cling good.
    F. Effects on Steel core none; no rusting, no scale or discoloration.
    G. Fluid Color and opacity change showed a slight change in color toward a darker amber and a slight increase in cloudiness.
    H. Weight Change no detectable change.



    2. Polyol Ester
    A. Durometer 3.7% softer after test.
    B. Flexibility increased slightly
    C. Peeling, cracking, or any other physical damage none.
    D. Dimensional change + 5.7%; increase in lip height and decrease in radial dimension
    E. Wetting and Fluid cling Excellent.
    F. Effects on Steel core none; no rusting, no scale or discoloration.
    G. Fluid Color Change - ! No darkening and no change in transparency. No color shift.
    H. Weight Change no detectable change.
    So while there is some seal swelling and softening involved, modern synthetic oils have been engineered to be pretty much compatible with all modern elastomer seals by reducing seal swell/shrinkage and other signs of degradation. The exceptions are synthetic oils that have been specially engineered to do otherwise.


    But



    Isn't DOT 4/5.1 fluid polyglycol-ether based? Well, according to an article from Honda Performance List on importnut, DOT 4 contains borate esters in addition to what is in the polyglycol-ether based DOT 3. Therefore, conclusion: DOT 4/5.1 fluids can be used on modern elastomer seals without any significant changes or detrimental effects. [

    I]So using DOT 4/5.1 fluid in mineral oil based systems should not be a problem[/I]... But since no one's conducting a proper experiment on this, we don't know if there are some unseen side effects, such as poorer braking power, slower return of brake levers, etc.

    Edit: But it is my belief from reading some stuff on the internet that it is highly unlikely that DOT 4/5.1 will destroy your seals.

    Some weird shiz coming right up:

    This test (Mineral oil test for clutch slave cylinder seals]The Car Maintenance Bibles) shows that seals designed to be compatible with synthetic brake fluid will swell in mineral oil but the material does not show any signs of degradation even after 18 months.

    The swelling is on the seal submerged in mineral oil is about 25%, while the swelling on the seal submerged in DOT 4 is about 2%. While seal swell between 18 - 30% is acceptable in aerospace applications, I don't think it would work out great in bicycle brake applications.

    Conclusion:

    Don't know how to add in-text citations and stuff so here are my sources:

    Car Bibles : The Engine Oil Bible
    Esters In Synthetic Lubricants - Bob is the Oil Guy
    Mineral oil test for clutch slave cylinder seals
    DOT 5.1 - Wikipedia, the free encyclopedia
    Additives II - Seal Swell - Bob Is The Oil Guy
    Seals - Bob Is The Oil Guy
    Brake Fluid Basics

    Thank you for reading.

    Flameshield on.
    Last edited by Jag Brah; 06-06-2013 at 04:47 AM.

  2. #2
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    Much like reading your post and understanding it, changing DOT fluid to mineral oil (and vice-versa) yields too little return for the effort expended.
    I may or may not be laughing at you.

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    If the claims Shimano makes are true, their mineral oil actually has a higher boiling point temperature than the DOT fluids. At that point, why switch to an "inferior" product.

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    Quote Originally Posted by wv_bob View Post
    Much like reading your post and understanding it, changing DOT fluid to mineral oil (and vice-versa) yields too little return for the effort expended.
    Thanks for reading anyways. Was just curious abt the myths, read up on it and shared my findings. Knowledge is always good, and is particularly interesting when it proves conventional wisdom inaccurate

    Dot fluid can be had for really cheap and is very accessible though, so it might work out fr the frugal in the long run.

    Quote Originally Posted by scottap2003 View Post
    If the claims Shimano makes are true, their mineral oil actually has a higher boiling point temperature than the DOT fluids. At that point, why switch to an "inferior" product.
    Dot fluid absorbs water by design, and some contain corrosion inhibitors (or so i've read) to combat the absorbed moisture. The b.p of mineral oil might be higher than dot fluid, but the unmixed water in a mineral oil brake system might boil and turn to air bubbles during a long dh run, causing sudden loss of brakes.

    Now even if the wet boiling point of dot fluid may be lower than the boiling point of mineral oil, it still is a lot higher than the b.p of water so there won't be sudden loss of brakes.

    I think this is why mx bikes use hygroscopic synthetic oil for brake fluid.

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    Isn't that one of the major positives of mineral oil though, that it doesn't attract water? How would it get in there if you didn't introduce it into the system at that point?

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    ^^This. This is what I'm wondering too. Kinda sorta sounds like a fix to an issue that really actually does not in fact need fixing is being belabored with those "findings".

    Also, Shimano mineral oil is pretty easy to get too, and not terribly expensive. I just went ahead and bought the big jug of it. Cost around 22 bucks if I'm not mistaken. I have as much as I will ever need (unless I open a bike shop) and it isn't going to absorb the ambient humidity in the air once I open it...like DOT fluid will, no matter how tight you try to close that cap.
    Stay aware of those who hide in plain sight.

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    I think you're confusing your terms. A lot of the references you've quoted pertain to synthetic oil vs. traditional. NOT brake fluid vs mineral oil. Brake fluid is made from petroleum stocks, polyglycol and glycol ethers. Synthetic brake fluid just substitutes synthetic petroleum for natural oils.

    Brake fluid and mineral oil generally require different sealing rubbers. Generally speaking, what works for one doesn't work for the other. This is why people say replacing DOT with mineral oil or vice versa will result in bad things happening. Ultimately, the question is: What are you trying to achieve by changing the fluid? The performance of either in the context of a mountain bike is more than adequate. It seems like you're spending a lot of time trying to fix something that isn't broken. Other than a full on downhiller running weak brakes, I've never even heard of someone boiling the brake fluid on a bike. Brake fade perhaps, but that's an issue with pads.

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    Quote Originally Posted by scottap2003 View Post
    Isn't that one of the major positives of mineral oil though, that it doesn't attract water? How would it get in there if you didn't introduce it into the system at that point?
    I'm not trying to preach the advantages of DOT 4/5.1, just sharing some info on whether DOT 4/5.1 will destroy seals as most claim.

    Air and moisture seeps through seals, hoses, pistons, reservoir caps over time. One major con for those who don't service their brake fluid often is that once the DOT 5.1 fluid absorbs moisture, you have to flush and replace with new DOT 5.1 fluid, whereas you can just bleed out the air and top up the fluid in mineral oil systems.

    But there's a higher risk of sudden brake loss with an improper brake bleed of a mineral oil brake system. I would say that (theoretically) DOT 4/5.1 it's the better choice if you go on really long DH runs and change fluid often.

    Quote Originally Posted by jochribs View Post
    ^^This. This is what I'm wondering too. Kinda sorta sounds like a fix to an issue that really actually does not in fact need fixing is being belabored with those "findings".

    Also, Shimano mineral oil is pretty easy to get too, and not terribly expensive. I just went ahead and bought the big jug of it. Cost around 22 bucks if I'm not mistaken. I have as much as I will ever need (unless I open a bike shop) and it isn't going to absorb the ambient humidity in the air once I open it...like DOT fluid will, no matter how tight you try to close that cap.
    People should not be afraid of destroying their seals when using DOT 4/5.1 in a mineral oil brake system because that's just inaccurate.

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    Quote Originally Posted by car_nut View Post
    I think you're confusing your terms. A lot of the references you've quoted pertain to synthetic oil vs. traditional. NOT brake fluid vs mineral oil. Brake fluid is made from petroleum stocks, polyglycol and glycol ethers. Synthetic brake fluid just substitutes synthetic petroleum for natural oils.

    Brake fluid and mineral oil generally require different sealing rubbers. Generally speaking, what works for one doesn't work for the other. This is why people say replacing DOT with mineral oil or vice versa will result in bad things happening. Ultimately, the question is: What are you trying to achieve by changing the fluid? The performance of either in the context of a mountain bike is more than adequate. It seems like you're spending a lot of time trying to fix something that isn't broken. Other than a full on downhiller running weak brakes, I've never even heard of someone boiling the brake fluid on a bike. Brake fade perhaps, but that's an issue with pads.

    Brake Fluid

    Most brake fluids today are made from mixtures of polyglycols, glycol ethers, borate esters and corrosion inhibitors.
    The references discuss synthetic oil VS mineral oil and whether using synthetic oil will render your 'mineral' system useless due to seal swell, leakage, physical deterioration.

    Esters cause seal swell, but modern fluids have been engineered to counter this swelling by adding other components, such as PAOs. The test results I found on BITOG show that ester-based fluids will not cause significant swelling of elastomer seals and for the most part, the seals remain unaffected.

    What I got from the findings: a polyglycol and esters combo (basically DOT 4/5.1) will not destroy your elastomer seals. I don't know the itty bitty details but this is what I got from the sources and from what I've read, Molakule seems like a rather reputable guy on those forums.

    Losing pressure in brakes is a big deal in mtb, remember what happened to Aaron Gwin in Leogang.
    Last edited by Jag Brah; 06-05-2013 at 11:20 PM.

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    I will be honest from the start, haven't read the thread fully yet, but think that you are on the wrong track.

    My understanding (and I'm happy to be proved wrong) is that the seal material used in the two systems DOT 3/4/5.1 and Mineral oil, are different (EPDM and Nitrile) and are NOT compatible.

    This is based on feedback from seal suppliers and the following web pages

    http://www.goodyearrubberproducts.co...g1.Page011.pdf

    Petroleum based hyd oils need Nitrile seals, and Non-Petroleum Brake fluids need EPDM

    and

    Rubber Compounds of O-Rings - Viton, Neoprene, EPDM, Nitrile

    Confirmed here

    So whilst I'd love the opposite to be true, I don't think it is.

    My wish for it to be true is adapting some Avid calipers (DOT 5.1) to a mineral oil based master cyder (TRP Parabox).

    If I'm wrong, please let me know where !!!
    Last edited by MichaelB; 06-06-2013 at 12:38 AM. Reason: fixing link

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    I don't know how to put this politely, but you don't know what you're talking about. You're also messing with something that could get you seriously hurt. DOT brake fluid has no business being in a system designed for mineral oil and vice versa. Period.

    The synthetic vs mineral oil discussions you've linked to are a discussion about MOTOR OILS that are produced using natural petroleum stocks vs synthetic. DOT brake fluid is NOT a simple oil and is not what they were discussing. When synthetic MOTOR OILS were first introduced they had some effect on seals which had long term exposure to MOTOR OILS which were produced using natural feedstocks.

    As mentioned above by myself and others, the rubber stock selected for DOT brake fluid vs mineral oil is typically mutually exclusive for what would be used in these applications.

    Quote Originally Posted by Jag Brah View Post
    Losing pressure in brakes is a big deal in mtb, remember what happened to Aaron Gwin in Leogang.
    Aaron lost his front brake because of a sealing issue within his prototype brakes. This had nothing to do with what kind of fluid the system was designed for.

    But, you are absolutely correct about how serious a brake failure can be. Which is why this ongoing nonsense (from others as well, not just yourself) about switching fluids needs to end now. Sorry to be blunt, but others reading threads like this might get it in their head to give it a try. There is absolutely NO benefit to filling your mineral oil designed brake system with DOT. Period.

    You also have not given one single problem that you are trying to solve by doing this. Have you boiled the fluid in your brakes before?

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    You said in response to my post...

    Quote Originally Posted by Jag Brah View Post
    People should not be afraid of destroying their seals when using DOT 4/5.1 in a mineral oil brake system because that's just inaccurate.
    I just don't agree. Like I said before, I feel like these "findings" are belaboring an issue that really does not need fixing. I don't mean to sound unsupportive of your inquisitive mind, but I just don't quite get why you'd even want to humor and research this.

    I'm using Mineral Oil in my Shimano's happily, and I am using DOT in my wife's Avids somewhat less happily, but that is what they call for, and that's what I'm going to use. Until the manufacturers tell me that I can use some other fluid in their respective brakes systems, (and I don't think that will ever happen) that is how it's going to stay.
    Stay aware of those who hide in plain sight.

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    Thanks for the links MichaelB.

    I would say almost all compatibility tables say the same thing: glycol base is not compatible with nitrile, mineral oil is not compatible with EPDM. But I came across this yesterday while doing some reading on mtbr: eFunda: O-Ring Materials Compatibile with Chemical Glycol, General

    And looking through the test results from BITOG I posted earlier, the seals were made of fluorocarbon, also known as "Viton". Viton is not compatible with glycol based brake fluids
    (Viton Chemical Compatibility Results says otherwise).

    Is polyethylene glycol different from other glycol based fluids?

    On the other hand, EPDM seals (which are used in DOT4/5.1 systems) are not compatible with mineral oil. This runs in line with the findings of the test conducted here: Mineral oil test for clutch slave cylinder seals so I guess that's that.


    Part of me thinks that since we're talking about synthetic oils here, there are additives added to counter balance the swelling and shrinking properties of the agents in brake fluid so that they can be used across the board with almost all types of seals without any significant adverse effects...?

    One more question... How does one tell a nitrile seal from a viton seal, neoprene, etc? I've never opened up my brakes, and I don't think it's possible to tell the type of seal just by visual inspection.

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    Quote Originally Posted by car_nut View Post
    I don't know how to put this politely, but you don't know what you're talking about. You're also messing with something that could get you seriously hurt. DOT brake fluid has no business being in a system designed for mineral oil and vice versa. Period.

    The synthetic vs mineral oil discussions you've linked to are a discussion about MOTOR OILS that are produced using natural petroleum stocks vs synthetic. DOT brake fluid is NOT a simple oil and is not what they were discussing. When synthetic MOTOR OILS were first introduced they had some effect on seals which had long term exposure to MOTOR OILS which were produced using natural feedstocks.

    As mentioned above by myself and others, the rubber stock selected for DOT brake fluid vs mineral oil is typically mutually exclusive for what would be used in these applications.


    Aaron lost his front brake because of a sealing issue within his prototype brakes. This had nothing to do with what kind of fluid the system was designed for.

    But, you are absolutely correct about how serious a brake failure can be. Which is why this ongoing nonsense (from others as well, not just yourself) about switching fluids needs to end now. Sorry to be blunt, but others reading threads like this might get it in their head to give it a try. There is absolutely NO benefit to filling your mineral oil designed brake system with DOT. Period.

    You also have not given one single problem that you are trying to solve by doing this. Have you boiled the fluid in your brakes before?
    The problem (from what I've gathered) with earlier oils is they got the composition (ester vs PAO) slightly skewed, which in turn degraded the seals by causing excessive swelling or shrinkage and leakage.

    The Aaron Gwin comparison was meant to show the danger of losing pressure during a DH run, which is why some favour DOT 5.1 instead of mineral oil.

    I'm not trying to solve anything. My XT brakes work just fine and I intend to keep it that way. But there seems to be a certain think-tank, go-with-the-majority mindset, in forums (not just mtb forums) and I found some info that MIGHT prove otherwise, so I was just asking for the community's thoughts on the subject, instead of just repeating what everyone else has said without any knowledge on the subject nomsaiyan?


    Quote Originally Posted by jochribs View Post
    You said in response to my post...



    I just don't agree. Like I said before, I feel like these "findings" are belaboring an issue that really does not need fixing. I don't mean to sound unsupportive of your inquisitive mind, but I just don't quite get why you'd even want to humor and research this.

    I'm using Mineral Oil in my Shimano's happily, and I am using DOT in my wife's Avids somewhat less happily, but that is what they call for, and that's what I'm going to use. Until the manufacturers tell me that I can use some other fluid in their respective brakes systems, (and I don't think that will ever happen) that is how it's going to stay.
    I've pretty much summed it up in my response to car nut. I don't want to switch to DOT 5.1, I was just interested in seeing what sorta damage DOT 5.1 would do in a mineral oil system. I've seen a lot of posts regarding destroyed seals but no personal, first-hand testing experience.

    'M just presenting another side of the argument, not forcing others to go and change over to DOT 5.1.

    I]So using DOT 4/5.1 fluid in mineral oil based systems should not be a problem[/I]... But since no one's conducting a proper experiment on this, we don't know if there are some unseen side effects, such as poorer braking power, slower return of brake levers, etc.

    The fact is, it is highly unlikely that DOT 4/5.1 will destroy your seals.
    Maybe I should change this last line though...

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    Perhaps I'm not being clear enough. The term "mineral oil" is being used with two different meanings here. First, you have a class of fluids. For example: Water, milk, OJ etc:
    Motor oil: Obviously, the oil that is used to lubricate an engine. This is what is being discussed in most of you links.
    DOT Brake fluid: A glycol-based hydraulic fluid used in brakes
    Mineral oil brake fluid: A petroleum distillate based hydraulic brake fluid

    Now, when discussing anything petroleum based, we have two major categories:
    Synthetic: Oils created by any number of processes which create consistent, low variation feedstocks.
    Mineral oil: liquified dino bits from the ground.

    You are confusing the two uses of the term "mineral oil".

    Now, as to whether or not you can substitute one for the other, here is the reason why NOT:
    DOT brake fluid systems are most commonly spec'd with EPDM seals. Why? It's the only one of the cheap, widely available materials that works with it. I've never designed a mineral oil system, but Parker says Nitrile would be the choice for the same reason. Nitrile does not work with DOT. Now, maybe Shimano spec'd in $12 o-rings that are compatible with each, but I don't think anyone should be willing to bet their face on it since there is absolutely no reason why they would have done so.

    Go here: http://www.parker.com/literature/ORD...g_Handbook.pdf
    Chapter 7, compare DOT brake fluid vs mineral oil.

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    Quote Originally Posted by Jag Brah View Post

    But there's a higher risk of sudden brake loss with an improper brake bleed of a mineral oil brake system. I would say that (theoretically) DOT 4/5.1 it's the better choice if you go on really long DH runs and change fluid often.
    It doesn't matter what brake fluid you use, if you get a bad bleed, the risk of sudden brake loss is the same. If Shimano's claims of a higher temp boiling point are to be believed, then you would have LESS risk of sudden brake loss based solely on that. If DOT boils at temp X and Shimano fluid boils at X+10, then you are going to reach that boiling point sooner on DOT and have that type of brake failure. I don't understand where you're coming from saying DOT would be better in that instance.

    Besides all that, if you have water in you system and it "boils" you're going to have issues other than brake fade. In a closed system, like we run on bikes, there is no room for expansion caused by the boiling of water. That psi increase has to go somewhere, which is going to do one of two things, push the pistons of the caliper out and against the rotor, causing even more heat and probably a sudden stop, or your hose is going to pop loose and squirt you with scalding hot liquid. Have you ever seen that happen? There's a reason for it, we don't boil the fluid or the water in it. The pad compounds we use for bikes fail long before the fluid reaches that point.

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    Everyone knows that mineral oil will work with mineral oil compatible seals, DOT 4/5.1 will work with DOT 4/5.1 compatible seals. But what makes them compatible/incompatible with ea other is in the chemical properties, doesn't matter whether they came from cows, dinosaurs or men in labs.

    All you're doing now is shoving me with info already posted earlier in the thread and being real condescending about it.

    Do take time to read all my points below...

    From my point of view:

    DOT 4/5.1 are borate-ester, polyethylene glycol based, yes? Yes.
    Seal swell/shrinkage is bad, yes? Yes.
    Swelling due to ester kept in check with PAOs in synthetics, yes? Yes.
    Nitrile compatible with glycol, yes? Yes.

    eFunda: O-Ring Materials Compatibile with Chemical Glycol, General

    If that link doesn't work, use http://www.balseal.com/files/tech_li...0707133101.pdf and scroll down to Nitrile.

    So assuming that seals in mineral oil brake systems are nitrile,

    1. What is it about nitriles that make them incompatible with glycol-based brake fluid?
    2. How is polyethylene glycol different from "general glycol based fluid", rendering it incompatible with nitriles/vitons?
    3. Is it even the glycol in the brake fluid that is causing incompatibility or a common property shared between all glycol based brake fluid that's causing it?
    4. Or were "anti-swell" agents deliberately left out of glycol based DOT 4/5.1 fluids to induce this swelling of nitrile seals?

    Results are cool and all, but an explanation of the results would be way better in edumacating inquisitive minds like yours truly.

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    Quote Originally Posted by scottap2003 View Post
    It doesn't matter what brake fluid you use, if you get a bad bleed, the risk of sudden brake loss is the same. If Shimano's claims of a higher temp boiling point are to be believed, then you would have LESS risk of sudden brake loss based solely on that. If DOT boils at temp X and Shimano fluid boils at X+10, then you are going to reach that boiling point sooner on DOT and have that type of brake failure. I don't understand where you're coming from saying DOT would be better in that instance.

    Besides all that, if you have water in you system and it "boils" you're going to have issues other than brake fade. In a closed system, like we run on bikes, there is no room for expansion caused by the boiling of water. That psi increase has to go somewhere, which is going to do one of two things, push the pistons of the caliper out and against the rotor, causing even more heat and probably a sudden stop, or your hose is going to pop loose and squirt you with scalding hot liquid. Have you ever seen that happen? There's a reason for it, we don't boil the fluid or the water in it. The pad compounds we use for bikes fail long before the fluid reaches that point.
    This should explain the part about open/closed hydraulic brake systems. Review: Brake Force One | Mountain Bike Review

    DOT 4/5.1 has a wet boiling point and a dry boiling point. Since it absorbs moisture, lets just assume that the fluid boils off at the wet boiling point. Boiling point of water is 100*C and boiling point of DOT 4/5.1 range from 160*C to 180*C (just for info, dry b.p is roughly 260*C) according to wiki.

    Air can be compressed. When the water boils, the air will expand until it cannot expand further due to the fixed volume of brake fluid in your system. I highly doubt that there's enough volume of air and that much pressure to cause a hose blow out or to jam your pads against your rotors. However, the air produced will be enough to cause increased lever travel which can cause problems with your braking. Losing pressure at your levers can happen, one way or another and this is just one of the many ways that can happen. It has happened to Aaron Gwin, but apparently that's due to some other technical fault.

    Personally, if I had my own personal mechanic and a mountain in my backyard, I would run DOT 4/5.1 fluid but that's just me, and has nothing to do with why I wrote the original post.

    I'm not sure what brake fade has to do with any of this though . If you can't get enough pressure at the lever, even with perfectly cool brakes, your levers will likely reach the bar first before you stop.

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    Quote Originally Posted by Jag Brah View Post
    This should explain the part about open/closed hydraulic brake systems. Review: Brake Force One | Mountain Bike Review

    DOT 4/5.1 has a wet boiling point and a dry boiling point. Since it absorbs moisture, lets just assume that the fluid boils off at the wet boiling point. Boiling point of water is 100*C and boiling point of DOT 4/5.1 range from 160*C to 180*C (just for info, dry b.p is roughly 260*C) according to wiki.

    Air can be compressed. When the water boils, the air will expand until it cannot expand further due to the fixed volume of brake fluid in your system. I highly doubt that there's enough volume of air and that much pressure to cause a hose blow out or to jam your pads against your rotors. However, the air produced will be enough to cause increased lever travel which can cause problems with your braking. Losing pressure at your levers can happen, one way or another and this is just one of the many ways that can happen. It has happened to Aaron Gwin, but apparently that's due to some other technical fault.
    Ok, so I see what you're saying about open/closed systems. The newer brakes that we're all using have very small reservoirs. Do you know what the expansion rate of a water molecule is when it turns to steam? 1600+ times the size. Air doesn't have anything on what you can do to water. It's the reason some power plants use steam turbines to generate power. That's my point on our brake systems. We don't get them hot enough to truly boil. You can have water at 700*F if you have enough pressure on it (roughly 400psi). Now, the inverse of this is true too. In a vacuum, you can create steam at much lower temps, roughly 100* steam in a 26inHg vacuum. So, if you create a void in your system, a vacuum, you can create steam at lower boiling points, which is one way of affecting your lever. There is some debate that this is what happened to Gwinny. Shimano said shortly after it happened that they were having to bleed the brakes after every run because they couldn't keep enough fluid in the system. They did not bleed them between his seeding and race run due to time constraints, so he was low on fluid. He created steam because high temperature in a vacuum, not because of a super hot temperature issue under pressure, and when he did, it pushed out even more fluid, and made the issue even worse, hence the brake failure.

    Now, I'm not saying that there was water in his system, because IMO if it was a vacuum, that could have lowered the boiling point of the brake fluid very easily. I've never seen any information on what would happen to brake fluid in a vacuum, but if it behaves like water, it would be similar.

    Here's something else for you. DOT3 fluid boils 401*F dry, 4 boils @ 446*F dry, and 5 boils @ 518*F dry. Shimano claims their fluid boils @ 536*F. Now, based on that, which is best?

  20. #20
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    Quote Originally Posted by Jag Brah View Post
    .....So assuming that seals in mineral oil brake systems are nitrile,

    ......
    The reality is that MOST manufacturers will choose the cheapest option regarding the seal material. From what I know, Viton and Nitrile seals are more expensive than EPDM. Manufacturers WILL NOT select a meterial that adds cost that does not provide any performance advantage (i.e. speccing a seal that can cope with any oil, rather than the one that they use.

    This comes from my extensive background in Auto manufacturing.

    Some of the links provided have been great and very informative, and thanks to all those in the thread.

    At the end of it all, I need to chnage the seals for the work I am doing , but I knew that.

    I just hope I can get something OTS rather than custom made, as it will be a bit cheaper !!

  21. #21
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    Just thought I'd provide an update on my quest to get the seals for an Avid X0 Trail caliper that are compatible with Moneral oil.

    Well, today yielded success, and at a great price.

    Used a company called HyTech in Melbourne (Australia), and they custom manufactured the required piston seals for $3.00 ea + GST (10%). I got 12 of each size (differential pistons - 16mm & 14mm dia) shipped to Adelaide for $97.

    Then I went to the local bearing supplier on got the 3 different sized o-rings (had to get 25 of each to meet the minimum order value !!), and the three different o-rings (75 in total) cost another $8 all up. I also picked up a pair of seal picks to help with the disassembly whilst I was there.

    So, for all those caliper owners that want custom square seals, give Hytech ( Hytech: Hydraulic Manifolds, manifold designer and manufacturer - HYTECH ) a buzz. They made the seals and dispatched them within a day !!!!

    Now to swap the seals and get them on the bike !!!!

  22. #22
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    I prefer mineral oil because it doesn't strip the paint off my bike like DOT fluid and because it leaves my hands feeling soft and supple after I bleed my brakes.

  23. #23
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    Quote Originally Posted by MichaelB View Post
    Just thought I'd provide an update on my quest to get the seals for an Avid X0 Trail caliper that are compatible with Moneral oil.

    Well, today yielded success, and at a great price.

    Used a company called HyTech in Melbourne (Australia), and they custom manufactured the required piston seals for $3.00 ea + GST (10%). I got 12 of each size (differential pistons - 16mm & 14mm dia) shipped to Adelaide for $97.

    Then I went to the local bearing supplier on got the 3 different sized o-rings (had to get 25 of each to meet the minimum order value !!), and the three different o-rings (75 in total) cost another $8 all up. I also picked up a pair of seal picks to help with the disassembly whilst I was there.

    So, for all those caliper owners that want custom square seals, give Hytech ( Hytech: Hydraulic Manifolds, manifold designer and manufacturer - HYTECH ) a buzz. They made the seals and dispatched them within a day !!!!

    Now to swap the seals and get them on the bike !!!!
    Interesting topic. Very curious as to why you are completely rebuilding your brakes with new seals to be able to utilize mineral oil?

    Also, like car nut alluded to earlier.....the links in the first post are discussing motor oil for crankcases. Not brake fluid.

  24. #24
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    He's going to attach this brake caliper onto this master cylinder which uses mineral oil to try and get a more powerful brake system.

  25. #25
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    Quote Originally Posted by cobba View Post
    He's going to attach this brake caliper onto this master cylinder which uses mineral oil to try and get a more powerful brake system.
    Thanks.

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