Solution To Brake Freezing?

[mata22]

adam--> i am from croatia and it can be wery cold here, so i have same problems as i am running water. could you please explain me more about mix for marura you were talking about,

thanks in advance

[AdamR28]

Yes, add a few drops of anti-freeze (the stuff you put in a car in winter to stop the water cooling from freezing) to the water and it will help a lot

[mata22]

and that,s it? thanks alot

[MikeCottTrials]

What 'problems' do you have?

Sticky pistons, slow lever and it needs re bleeding more often than I should like

he is from hull.....

Oi, Hull is no worse than any other place in this country. I'd say these days its fairly nice

Different state of matter = not really comparable as gravel reduces the friction by a totally different mechanism.

I disagree. The only reason water on the road reduces traction is because it prevents the tyre from making contact with the road, same for gravel

Either way water isn't a lubricant

[Mark W]

Sticky pistons, slow lever and it needs re bleeding more often than I should like

I've had sticky pistons with a mineral oil bleed too. Also had slow lever feel with it too, and not just 'cos oil bleeds suck Sticky pistons are easily remedied anyway as I said earlier, as is a slower lever action. I don't really understand why it would need more bleeding with a different fluid in either. Unless your brake's leaking, it shouldn't need bleeding more with one fluid than another. Think I got about 9 months at least out of a water bleed before - only had to re-bleed it 'cos I was adding anti-freeze to it...

Hull was also named the worst place to live in the UK a while back too

[Matt Vandart]

Id only buy it if it was drilled

[AdamR28]

I disagree. The only reason water on the road reduces traction is because it prevents the tyre from making contact with the road, same for gravel

Either way water isn't a lubricant

Bit off topic now, but... in a Magura, if the fluid (blood or otherwise) prevents the rubber seal from making contact with cylinder bore (thus 'lubricating' it), the brake will leak... so... theoretically, neither fluid will actually lubricate the system? Thus making water fine to use?

[Matthew62]

It lubes the piston though not the seal surely? Wouldn't be much of a seal if id didnt seal the system. So surely the royal blood lubricates the piston and theres enough tolerance to allow the tinniest of amounts to do their job? Oui or non?

[Matt Vandart]

Adam:-

That sounds good but is in reality bollocks.

In hydraulic seals it is the pressure on the back of the lip seal that causes the sealing effect, so up to it's failure pressure it seals more, the more pressure you put on it.

When it is under no pressure a tiny wennie amount of oil will "leak" around the seal and to an extent lubricate it.

Take for instance when you undo the shroud nut and pull the tube out, what happens?

The oil doesn't piss out the lever or the tube.

The system is in balance.

You require an imbalance for it to leak.

i.e a squeeze of the lever or opening the bleed screw or air passing from the outside past the seal.

So when you have the system closed up again, as soon as you apply pressure to the seal it seals tight against the cylinder wall and stops any passing.

Now taking the two fluids, and gravel too behave as a fluid, as can be seen when digging in sand dunes and dying as it collapses on top of you, try digging someone out of that! No way, once the sand is acting as a fluid you may as well be digging water.

Anyway back to the point, oil and water.

Oil is well known and used as a lubricant, and in fact water is also used as a lubricant in some applications, but oil tends to be used in situations such as described due to its stability under pressure and the fact that you can control the exactness of the oil more easily than tap water and its alklinity/acidity.

The problem with sticky pistons is more likely to do with water being:

A: To Acidic

B: To Alkaline

Both leading to corrosion of the cylinder wall.

C: The water having a high mineral content. These minerals will come out of solution under pressure and in turn fur up the cylinder wall, just like in yer kettle.

Thus the reason why I use totally demineralised water with a PH of exactly 7 and no mineral content.

That is all.

Now we wait for Cormac....................

By the way I am no expert on hydraulics

Edited October 30, 2009 by Matt Vandart

[Mark W]

It lubes the piston though not the seal surely? Wouldn't be much of a seal if id didnt seal the system. So surely the royal blood lubricates the piston and theres enough tolerance to allow the tinniest of amounts to do their job? Oui or non?

Non?

The problem with sticky pistons is more likely to do with water being:

...again, I've had sticky pistons with mineral oil, and I've seen other people with sticky pistons with mineral oil. It is in no way limited to people using water.

[Matt Vandart]

Agreed.

The clue is in the name:-

Mineral oil

[TROYston]

Sounds like a lot of effort when you could just run water and it'd be absolutely fine 99% of the time. I never had a single issue with a freezing hydraulic brake when I used to run them.

That said, I'd take a vee every time so it's not even an issue anyway

+1

I have never had the freezing brake problem ever, but i did find my brake wnt odd in the cold a while back, though i was using a raceline maggie, which are poo anyway imo.

[MiuSliS]

Ride indoors.

[psycholist]

O-ring seals tend not to be strongly pressure energised seals (that is the higher the pressure they resist the better they seal), but up to a point they behave this way in terms of being shoved to one end or other of the slot the o-ring sits in by the pressure they're seeing and being flattened by the brake fluid pressure, which forces the o-ring to press harder against the inner and outer sealing surfaces. I'm guessing (I haven't measured) for most bike applications where an o-ring slides in a given piston bore diameter, the pressure it can resist is more of a function of the difference in diameter between the piston and the o-ring pressed into it without having to worry about dynamic effects. As you go to higher performance o-rings at higher pressures I think the pressure energising behaviour will become important though.

What this means though there's always a sealing pressure between the o-ring and the surfaces it touches, so no leaking occurs in static conditions either except through diffusion, which is very very slow. If the seal rolls slightly as it changes direction it will carry very small amounts of oil onto the piston surface, and I'm guessing this is what o-rings rely on to stay lubed. This provides part of the restoring force that helps retract disk caliper pistons when the lever is released (This is the case where the o-ring doesn't slide when the deflection is small, instead being able to roll on the piston surfaces).

Pressure energised seals are found in the oil seals on suspension forks/rear shocks, where cutting friction/stiction is more beneficial to performance (As well as the seals needing to resist sudden high peaks in pressure). These seals can be recognised by their 'u' shaped cross section with the open end of the 'u' exposed to high pressure from within the fork, forcing the seal to expand inwards onto the sliders and outwards onto the fork legs to improve the seal (At the expense of higher sliding friction) but only when there is a high pressure to be sealed out.

For braking systems on bikes the pressures and movements the seals see are small enough that there's no great benefit to cutting seal friction and considerable expense in trying to make small enough pressure energised seals to fit lever pistons, so o-rings are the chosen solution.

Water is an excellent lubricant due to its strong surface tension and low viscosity (Low viscosity means it supports higher shear rates, and therefore allows bigger speed differences between lubricated surfaces for a given force applied to move them and a given gap filled with lubricant - think the difference between using oil and heavy grease in a Chris King). The low viscosity is also what makes a water bleed brake feel more responsive as it takes less energy to drive water through the narrow orifices within a brake system than it takes to drive mineral oil through.

Water is let down by the fact it evaporates when left in air, so its lubricating effect is short lived unless it keeps getting replenished (Which would require a sustained leakage from the brake seals and is therefore a bad thing for a consistent brake). This is why it's a bad idea to completely clean all the oil out of a Magura before a water bleed. The oil will stay coating the surfaces, including sealing surfaces without evaporating away, keeping everything lubricated regardless of what fluid is used as well as providing a barrier the water has to diffuse across before it can get through the gaps in a seal to evaporate out. The other down side to using water is that drops of water on a surface can form part of a galvanic cell, leading to accelerated corrosion - a major issue if it's used in contact with non-stainless steels for example, as well as a cause of crevice corrosion in aluminium.

Gravel behaves in exactly the same way as all fluids used as lubricants, but at a scale we can see more easily. It allows two surfaces to slide over each other with less friction by allowing the gravel to roll between the surfaces (Gravel behaves in a manner more like a rarified gas flow than a liquid flow, but the principles are the same). In liquids the rolling is less evident unless you're dealing with turbulent flows, but the idea of supporting a difference between the speeds of two surfaces using a velocity gradient in a fluid held between them is the same (Look for Couette flow on Wikipedia for this behaviour).

As for the mineral content of water - I'm guessing after getting rid of the oil in sealing surfaces of the brake it's the single biggest contributor to the variation in people's long term results using water bleeds in their brakes. AFAIK acidic water is probably pretty ok with aluminium pistons as quite strong acid dips are used to passivate (oxidise) aluminium to stop corrosion in the first place, so an oxide covered aluminium surface won't really notice a weak acid (The seals are also likely to be fine with this).

However if you look at previous threads you'll see alkaline solutions (Caustic soda/NaOH) are used to strip anodising (Which is just a thick layer of dyed aluminium oxide) from bike components. Tap water is pretty much never acidic (The latin origin of the word acid is from 'acidus' (Or something similar), which means 'sour', which will probably explain why tap water tends to have a pH slightly above 7 or pretty much always between 6.5 and 8.5 to make sure it's not sour tasting, though apparently if water has too high a pH it starts to taste sour too). For this reason people in hard water areas may see damage in their brakes quicker than those in soft water areas, but I'd say it's still slow.

Carbonates carried in the water (Hard water) forming a scale in the brakes is less likely to be a cause of failure as there's a finite volume of water in the brakes, so unless they're bled repeatedly, there won't be enough of these compounds to leave significant deposits. Using boiled water is a good idea from this point of view as well as because it removes all the dissolved gases in the water, preventing them from being able to precipitate out of the brake fluid after the bleeding is done (Again this is rarely a problem anyway though may show up as spongy brakes that get better over time if you leave the bike in the car on a very sunny day for example).

Probably way too much for a Friday evening, but the weather's shit here at the moment ...

[Matt Vandart]

Sooper dooper explanation!

Knew you'd have some good input on this.

[MikeCottTrials]

thank you for the gravel explanation, people will now think when contesting my posts

[Ali C]

Water is let down by the fact it evaporates when left in air, so its lubricating effect is short lived unless it keeps getting replenished (Which would require a sustained leakage from the brake seals and is therefore a bad thing for a consistent brake).

If I'm reading what you're saying right, then surely pretty much every time you pull your brake you'd basically be lubricating those points? In any case, like I said before - you can lube sticky pistons wherever they may be on your brake using a spray of GT-85 or similar. It's easy to do, and works fine. Completely cured any problems I had with sticky pistons when I had them last (which was years ago now). Other than that, water isn't going to be any harm to your seals or virtually anything in your brake, so there's pretty much no reason to not use it...

Mike - re: contesting your posts, did you see the bit where Psycholist pointed out the lubricating properties of water, something you said it didn't possess?

[mata22]

i red what you all wrot, but i have one question, my friend ( while he rode trials) used WD40 in his magura. i dont have contact with him any more, so...what do you think about that?

[Ali C]

thank you for the gravel explanation, people will now think when contesting my posts

Either way water isn't a lubricant

Water is an excellent lubricant due to its strong surface tension and low viscosity (Low viscosity means it supports higher shear rates, and therefore allows bigger speed differences between lubricated surfaces for a given force applied to move them and a given gap filled with lubricant - think the difference between using oil and heavy grease in a Chris King).

[totaltrials]

i red what you all wrot, but i have one question, my friend ( while he rode trials) used WD40 in his magura. i dont have contact with him any more, so...what do you think about that?

He pulled his brake and it didn't work. So he died.

[MikeCottTrials]

thank you for the gravel explanation, people will now think when contesting my posts

Allow me to untwist your underwear

[psycholist]

I'm pretty sure the sticky piston problem in Maguras is more down to the wiper seals being contaminated from the outside than the o-rings that seal the oil into the brakes causing the friction or anything to do with the fluid used (Unless it eats aluminium or rubber).

A clean water bled brake will lose the water that gets to the outside of the seal through evaporation, and so will need topping up more often than an oil bleed or a water bleed with oil left on the seals.