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Half water half brake fluid in brakes?

Old 06-03-20, 10:30 AM
  #26  
mr_bill
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Originally Posted by elcruxio
I'll actually revisit this immediately.

A cute finnish couple did a youtube video about bicycle disc brake vs lathe. The fluid only boiled well after the rotor had been red hot (so around 1000 degrees celsius?) for quite some time. I've only ever gotten my rotor brown and my wife who has worse braking habits than me has gotten her rotors blue.

There's also the brake force one H2O brake system which uses a water and glycol mixture as fluid.
Glycol is hygroscopic. (Even so, anyone who willfully adds water into a DOT3-4 brake fluid is an idiot.)

Mineral Oil is hydrophobic. (And please don't add water or egg yolk to your mineral oil braking system.)

-mr. bill
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Old 06-03-20, 10:37 AM
  #27  
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Originally Posted by mr_bill
Glycol is hygroscopic. (Even so, anyone who willfully adds water into a DOT3-4 brake fluid is an idiot.)

Mineral Oil is hydrophobic. (And please don't add water or egg yolk to your mineral oil braking system.)

-mr. bill
Yeah true. The Brake Force One H2O uses 80% water 20% glycol and glycol functions as antifreeze. But to my understanding it doesn't significantly raise the boiling temperature.
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Old 06-03-20, 11:13 AM
  #28  
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Originally Posted by Kapusta
I have GOT to see the video of this.
I think you mean the filmed bike edit.
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Old 06-03-20, 11:19 AM
  #29  
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Originally Posted by mr_bill
Feel free to do a kitchen experiment. You will not get mayonnaise with water and oil, no matter how long you blend.

You also don’t need a blender to make mayonnaise.

A whisk will do quite nicely, though if determined enough a fork will do, or if really determined a spoon or chopsticks.

You do need an emulsifier such as lecithin found in egg yolk. A soluble thickener (such as the mucilage found in mustard) is wise too. Finally, lowering the pH with a bit of acid from lemon juice or vinegar helps too.

-mr. bill
Still seems like using actual brake fluid would be easier...

Originally Posted by mr_bill
(And please don't add water or egg yolk to your mineral oil braking system.)
You tell me this now?
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Old 06-03-20, 11:26 AM
  #30  
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Originally Posted by Kapusta
I have GOT to see the video of this.
I see them all the time on failarmy
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Old 06-03-20, 12:17 PM
  #31  
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Maybe OT - but in case the OP needed to flush their brake system, could they use alcohol? It's hygroscopic, so it will blend with the water?
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Old 06-03-20, 01:04 PM
  #32  
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Originally Posted by elcruxio
I don't get the whole death and destruction attitude here. Using water and glycol in shimano brakes used to be a thing on another cycling forum. They did in with DH bikes if I recall correctly. Worked great, didn't go all stiff in the cold, didn't boil etc.
I donít know anything about the post you are referring to but mixing water with mineral oil is not the same as mixing water with glycol. Iím not sure what the benefit of mixing water with glycol would be for a brake system but putting water into an oil system is definitely going to change the characteristics of the braking system.

Originally Posted by elcruxio
The reality of the matter is, that it requires some serious work to get bicycle brakes boiling hot. Or rather, you'll easily hit hundreds of degrees celsius at the pads and rotor. However in order to transfer that heat through the caliper body into the fluid in large enough quantities and continuously enough to heat up enough fluid (a significant amount) to cause a boiling event even with water would require some monster hills and very irresponsible braking habits. ​​​I'm sure it'd be possible, but not with a dirt jumper in its natural habitat.
Itís difficult to get bicycle brakes to the point of boiling either DOT fluid or mineral oil but thatís because both have a boiling point of around 280įC. It would not be difficult to get the brakes to the boiling point of water at 100įC. 280įC is enough for a really good head of steam.

With water in the system and with the water phase separating at the bottom of the brake column, it wouldnít take much heat to get the water to boil...i.e. convert to a vapor...which, as I pointed out above, introduces a gas into a system that abhors gases.

Originally Posted by elcruxio
As to flushing it out? Empty the system as good as you can, put new oil in, presto. Good as new.
Hydraulic systems have a lot of nooks and crannies that can hold up water at the bottom of the system as well as other places in the system. The water at the bottom is the most concerning. Are you certain that draining the system would remove all the fluid from the pistons? Iím not. The bleed valve is on top of the piston and any oil injected would just force out any water that is around that valve. Thereís nothing driving emptying the piston itself, especially if just mineral oil is used. The oil will just flow over the top of the water in the bottom of the piston.

There is also a problem with residual water in the system which is why I said a full tear down and cleaning would be warranted. Residual water will expand a lot if the brakes get hot enough to boil the mineral oil and you are back to trying to compress a gas.

Originally Posted by elcruxio
It's bicycles, not rocket science.
It may not be rocket science but it is not that simple.
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Old 06-03-20, 01:07 PM
  #33  
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Originally Posted by phughes
Not even close to surprising. Johnson's Baby Oil is mineral oil.
Yes, but as pointed out in the video the viscosity of the oil is unknown. I donít know how important viscosity is to the brake operation but as also pointed out in the video, donít go back to the manufacturer and try to put in a warranty claim.
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Old 06-03-20, 01:11 PM
  #34  
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Originally Posted by Reynolds
Maybe OT - but in case the OP needed to flush their brake system, could they use alcohol? It's hygroscopic, so it will blend with the water?
Ethanol, acetone, 20 year old Scotch, yes. But none of those are all that soluble in mineral oil. And, if you donít dry out the system, you have something that has an even lower boiling point. Acetone would be a questionable choice as well because it could damage seals.
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Old 06-03-20, 01:22 PM
  #35  
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Originally Posted by njkayaker
Still seems like using actual brake fluid would be easier...
Mineral oil is unpleasant tasting and has a strong laxative effect.

Mayonnaise some find unpleasant tasting, but....

While there are food grade glycols, DOT brake fluid isnít. POTUS might disagree, but if I were you avoid ingesting.

-mr. bill
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Old 06-03-20, 01:59 PM
  #36  
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Originally Posted by cyccommute
I donít know anything about the post you are referring to but mixing water with mineral oil is not the same as mixing water with glycol. Iím not sure what the benefit of mixing water with glycol would be for a brake system but putting water into an oil system is definitely going to change the characteristics of the braking system.
I did some quick googling and apparently water gives faster braking response and a more accurate feel. However I haven't tried a water brake so I don't really know. It'll change the characteristics sure but not necessary for the worse.


Itís difficult to get bicycle brakes to the point of boiling either DOT fluid or mineral oil but thatís because both have a boiling point of around 280įC. It would not be difficult to get the brakes to the boiling point of water at 100įC. 280įC is enough for a really good head of steam.
The interesting thing is though, that compared to mineral oil, water has almost three times the thermal capacity. So getting to a hundred centrigrade is going to take far longer than with mineral oil. With Glycol (DOT) water still has the advantage with almost double the thermal capacity.

I'm also not sure it is that easy to get bicycle brakes so hot that the fluid inside is at 100 C. Parts of the brake? sure. Rotor and pads? Most certainly. Pistons? Well, maybe part of the piston. However, getting enough heat transferred to get the fluid to reach 100 C is going to take some doing. I mean there is on the market a bicycle hydraulic brake system that uses water as brake fluid. I also know that it used to be done with Shimano hydraulic brakes. Water laced with glycol doesn't freeze easily. Granted mineral oil doesn't either, but I used to suffer from the mineral oil turning solid thus making braking a bit difficult.


With water in the system and with the water phase separating at the bottom of the brake column, it wouldnít take much heat to get the water to boil...i.e. convert to a vapor...which, as I pointed out above, introduces a gas into a system that abhors gases.
Well that's just it isn't it? It'll take about the same amount of energy to heat water to a 100 C than it takes to heat mineral oil to 280 C. Weird I know but that's physics I guess.

I do not know a single person who has ever had a boil event. I haven't had a boil event and I used to do DH with mineral oil brakes. And I was bad at it so I was on the brakes a lot. The routes I did were easily long enough to overheat brakes, which I did etc etc. Really the only place I could imagine a boil even could occur would be with a loaded touring bike, kilometers of fast descent and abhorrent brake practices.

Hydraulic systems have a lot of nooks and crannies that can hold up water at the bottom of the system as well as other places in the system. The water at the bottom is the most concerning. Are you certain that draining the system would remove all the fluid from the pistons? Iím not. The bleed valve is on top of the piston and any oil injected would just force out any water that is around that valve. Thereís nothing driving emptying the piston itself, especially if just mineral oil is used. The oil will just flow over the top of the water in the bottom of the piston.
The point I was trying to make was that I simply do not care if there's a bit of water left inside. It'll get out eventually with future bleeds and it doesn't really matter does it? OP was talking about a dirt jumper. It's not exactly a discipline where heat buildup is an issue. In dirt jumping you could use... I coming blank about substances that boil at 30 degrees celsius...

There is also a problem with residual water in the system which is why I said a full tear down and cleaning would be warranted. Residual water will expand a lot if the brakes get hot enough to boil the mineral oil and you are back to trying to compress a gas.
Try it. Try to boil you brakes. Actually I might try it. I have enough stuff in my parts bin to give water brake a go. I wonder if I should even do a preheated test where I preheat the whole system so I'd get better info on how much dragging brakes on steep descents really heats up the fluid.

It may not be rocket science but it is not that simple.
It's still bicycles. The forces and energies we deal with are tiny. The cooling effects however are actually pretty close to motor vehicle levels because bicycles are just that fast. I mean if boiling fluid was such an issue it'd happen all the time with people riding Honda Gold Wings. Those things are heavy and the brakes are tiny compared to the potential heat buildup.

i did mention in my other comment the youtube video where they put a bicycle brake on a lathe. The fluid boils only after the rotor has been glowing red hot for fifteen seconds.
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Old 06-03-20, 02:08 PM
  #37  
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Originally Posted by mr_bill
Feel free to do a kitchen experiment. You will not get mayonnaise with water and oil, no matter how long you blend.

You also donít need a blender to make mayonnaise.

A whisk will do quite nicely, though if determined enough a fork will do, or if really determined a spoon or chopsticks.

You do need an emulsifier such as lecithin found in egg yolk. A soluble thickener (such as the mucilage found in mustard) is wise too. Finally, lowering the pH with a bit of acid from lemon juice or vinegar helps too.

-mr. bill
My recipe is a bit simpler:

Take one jar of Hellman's. Open it.
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Old 06-04-20, 08:21 AM
  #38  
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Originally Posted by elcruxio
I did some quick googling and apparently water gives faster braking response and a more accurate feel. However I haven't tried a water brake so I don't really know. It'll change the characteristics sure but not necessary for the worse.
You are still missing the point. anze_awesome mixed two immiscible liquids. That’s what changes the characteristics. The brake you are talking about doesn’t use immiscible liquids.

Originally Posted by elcruxio
The interesting thing is though, that compared to mineral oil, water has almost three times the thermal capacity. So getting to a hundred centrigrade is going to take far longer than with mineral oil. With Glycol (DOT) water still has the advantage with almost double the thermal capacity.
It’s not that simple. The higher heat capacity of water means that more heat is retained in the system. The water takes more heat but it will hold that heat for longer. If you heat them up, they are going to be hotter the next time you apply the brakes than if the brakes were filled with mineral oil or DOT fluid. And they’ll be hotter the next time you apply the brakes, and the next time.

Mineral oil won’t hold heat like water can. The heat radiates away and the brakes cool more quickly.

Originally Posted by elcruxio
I'm also not sure it is that easy to get bicycle brakes so hot that the fluid inside is at 100 C. Parts of the brake? sure. Rotor and pads? Most certainly. Pistons? Well, maybe part of the piston. However, getting enough heat transferred to get the fluid to reach 100 C is going to take some doing. I mean there is on the market a bicycle hydraulic brake system that uses water as brake fluid. I also know that it used to be done with Shimano hydraulic brakes. Water laced with glycol doesn't freeze easily. Granted mineral oil doesn't either, but I used to suffer from the mineral oil turning solid thus making braking a bit difficult.
Some pads come with cooling fins to move heat away from the pistons. The fins aren’t there to cool the pad. The pistons on a bike are pretty small and the volume of liquid pushing them is also small. Small volumes are easier to heat.

Mineral oil freezing is another good argument for using DOT fluid (or mechanicals). DOT doesn’t freeze until -40įF. Water suffers from the same problem.

Originally Posted by elcruxio
Well that's just it isn't it? It'll take about the same amount of energy to heat water to a 100 C than it takes to heat mineral oil to 280 C. Weird I know but that's physics I guess.
But, again, water retains heat better and longer than oils do. It would be easier, especially in heavy braking situations to get the water system to boiling than an oil system.

Originally Posted by elcruxio
Try it. Try to boil you brakes. Actually I might try it. I have enough stuff in my parts bin to give water brake a go. I wonder if I should even do a preheated test where I preheat the whole system so I'd get better info on how much dragging brakes on steep descents really heats up the fluid.
I’m not going to try to boil my brakes because it would mean installing hydraulic brakes. To borrow a phrase, this is bicycling, not rocket science. Hydraulic brakes push bicycling towards the rocket science side. Cables have none of the issues that hydraulics have. anze_awesome wouldn’t have even been tempted to add water to his brake system if they were mechanical. He might have been tempted to use rubber cables instead of steel ones but that would be even dumber than adding water to an oil system.
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Old 06-04-20, 08:23 AM
  #39  
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Originally Posted by cyccommute
Ethanol, acetone, 20 year old Scotch, yes. But none of those are all that soluble in mineral oil. And, if you donít dry out the system, you have something that has an even lower boiling point. Acetone would be a questionable choice as well because it could damage seals.
I only use 15-year old Scotch for flushing out my brake lines. 20-year old Scotch is for drinking.
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