Anatomy of a failed hydro caliper

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NATURAL ANKLING
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Re: Anatomy of a failed hydro caliper

Post by NATURAL ANKLING »

Hi,
In practice I do it every two years BUTTTTTTT if I miss a year no problem like fully synthetic oil...........if you miss a year it dona mater. been using fully synthetic oil for over 35 years.................

Goes to the recycling centre along with anything else fluid.......but admit it will end up in same container :oops:
Not sure how you green dispose of it.

If you change the brake fluid often then it matters less if you forget etc for a few years.

Obviously some people buy cars every few years, never lift bonnet etc.

I understand that northern counties with more road salt and more rain ice etc will have an effect on servicing.
When maintaining on / off road motorcycles I would work on for 7 hrs and ride for 6-8 hours, maintenance is chronically time consuming but necessary, the mud in water would get every where, and would dry every thing out and seize up, left without work you could quickly find that big daddy 14 pounder is your freind :?
NA Thinks Just End 2 End Return + Bivvy - Some day Soon I hope
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Brucey
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Re: Anatomy of a failed hydro caliper

Post by Brucey »

MikeDee wrote:
SRAM thinks DOT fluid is better than mineral oil https://sram.zendesk.com/hc/en-us/artic ... neral-oil-.


well SRAM would say that, they make brakes with DOT fluid in.... :roll:

SRAM says the following:

Heat/moisture management: DOT fluid manages heat better. While pure mineral oil and pure DOT fluid both have boiling points around 280C, DOT fluid is much better at managing water, which, over time, always finds its way into any brake system. DOT fluid makes any water in the system part of the fluid, while mineral oil pushes water to the edges. If a fair amount of water migrates into a mineral oil system, water’s boiling point, 100C, becomes that of the system. Our tests showed that even old, “wet” DOT fluid the boiling point never gets below 180C, while a bike brake system rarely sees temperatures over this point. The result: DOT fluid offers more consistent braking performance.


I know for a fact that no system filled with DOT fluid has anywhere near the stated boiling point for dry fluid because water always gets in at the seals, and diffuses through/past rubber parts. If you had and used a moisture tester on your brake fluid you would know this too. Water gets in very easily because the brake fluid is 100% miscible with water. You will get water vapour entering all the time (via diffusion) and liquid water will get past the seals very easily too because the wetting angle is so low; surface tension doesn't help you at all, and there is a strong driving force for the brake fluid to dissolve water. Wet fluid soon starts the inside of the system corroding (which isn't what this thread is about but is arguably even worse). For a supposedly standardised product, the corrosion inhibitors in DOT fluid seem to vary quite a lot.

Water does not get into an oil-filled system anywhere near as easily, (which is good, the consequences might be worse) because surface tension fights it all the way (you need a very high pressure to get water through a small gap if the wetting angle is unfavourable) and there is no driving force (in fact quite the reverse) for water vapour to enter the system. I am not saying that it never happens but it is unlikely. I have seen liquid water inside an oil-filled system once and for it to get there the master cylinder pushrod had to be submerged whilst the brake was being used, and the pistons were mechanically jammed so that they wouldn't return properly.

To equate the rate at which water will enter a DOT system vs a mineral oil system is not sensible; the former is guaranteed and the latter is quite unlikely.

I use castrol LHM in brakes that use mineral oil; it is a well proven product that has been manufactured and used to good effect for at least sixty years. No problems to date and none reported by others either.

So many of the arguments for one fluid over the other (in bicycle commuting use) are spurious or irrelevant, until the system starts to leak, at which point you are definitely worse off with DOT fluid. IME leakage is (in some uses) more likely with DOT fluid too.

You keep mentioning UK winters, salt on the roads, etc. Why don't you keep your good bikes for a sunny day and ride your beater bikes in crappy weather, if you even have to, and clean/wash your bikes if they get dirty? Riding in the rain is something I avoid. Riding an expensive bike in the rain doesn't make sense to me either. People in the US also live in cold and wet climates where salt is used on the roads in winter, so this type of weather is not unique to the UK. I don't get the obsession with corrosion.


Frankly I would rather hammer nails through soft parts of my anatomy than take some of my bikes out in the winter weather but plenty of other people do exactly that, and (say) find the prospect of using hydro brakes on their commuting bike appealing. I think they are usually inherently unsuitable in that use for the reasons I describe. Serial brake failures back this view up. In this case I don't think washing will be 100% effective against road salt because it has hours of riding/standing to penetrate the crevice around the pistons, and of course won't easily be displaced by mere minutes of washing.

Looking over your photos, it would seem that the corrosion was caused by external influences, not internal. Is that correct? If so, discussing the merits of different fluids in preventing internal corrosion would appear to be moot.


Yes indeed, I didn't really mention internal corrosion until you started raised the subject of DOT fluid. DOT systems often corrode from the inside but that isn't likely to be the thing that stops a brake on a commuting bike from working first. DOT brakes barely enter into this discussion I'm afraid; they are far less commonly seen (there is a reason for this...) and they typically corrode and fail so much faster than ones filled with mineral oil, in all-weather/commuting use.

FWIW for typical MTBing I don't think there is a lot in it between DOT fluid and mineral oil but for other uses (and any prospect of road salt) my views have changed somewhat. However even mineral oil systems can have an unacceptably short life because of salt water corrosion, and that is what this thread is really about.

cheers
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Jezrant
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Re: Anatomy of a failed hydro caliper

Post by Jezrant »

One thing that would be useful to know is which are the most reliable hydro brakes. I would have assumed the real reason DOT brakes are "far less commonly seen" is simply because Shimano dominates that market? I've heard it said by a couple of LBS bike mechanics that Sram and Hope hydros are more reliable, but I wonder if there's any truth in it. And if anyone knows a good source of replacement O rings for Avid bleed screws (including the right dimensions), please let us know. :)
Brucey
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Re: Anatomy of a failed hydro caliper

Post by Brucey »

Jezrant wrote:One thing that would be useful to know is which are the most reliable hydro brakes. I would have assumed the real reason DOT brakes are "far less commonly seen" is simply because Shimano dominates that market? I've heard it said by a couple of LBS bike mechanics that Sram and Hope hydros are more reliable, but I wonder if there's any truth in it. And if anyone knows a good source of replacement O rings for Avid bleed screws (including the right dimensions), please let us know. :)


Well it comes to folk saying brand X is more reliable, one has to take it with a pinch of salt. They could mean that they have seen fewer failures (which may or may not be a reflection of the proportion in similar use that fail), or that they get better results when setting them up, or that they prefer to sell such brakes for their own reasons (like they have invested in all the kit that goes with them or that they make more money out of them or something).

Hope brakes are pretty good but most folk don't use them on commuting machines or others that see the worst of the winter road salt, so this dramatically reduces the chances of failure. SRAM/Avid brakes are OK (and unlike many others you can at least (in theory) buy spare parts for the calipers and MCs) but for good or ill they are another DOT brake. Dunno if there is a strong argument about the type of usage profile that these brake see, but let's put it this way, I have never seen a set of these on a winter commuting bike either.

In fairness I don't know for sure that any manufacturers don't apply a corrosion resistant coating of some kind to the caliper bore and/or the seal groove. If they do then this could skew the choice of brake for some conditions.

Re Avid bleed screw seals; £4.99 for ten on ebay, eg
https://www.ebay.co.uk/itm/AVID-Hydraulic-Brake-Bleed-Screw-O-ring-Elixir-Jucy-Etc-/282672588007

If you start trying to independently source rubber parts for brakes, you need not only to worry about the physical dimensions of the part, the shore hardness, etc but also the rubber chemistry. You cannot swap fluids and rubber parts between systems willy-nilly; so for example it is OK to use nitrile rubber with mineral oil brake fluid but for DOT systems something like EPDM rubber is a better material to use. There are oils (like LHM) which appear to work OK in all systems that use mineral oil but that is not to say that it is definitely OK to use magura fluid in shimano brakes or vice versa. Get this wrong and the seals may swell, fall apart, or otherwise give trouble.

FWIW I once dismantled a seized car brake caliper set using a grease gun to push the pistons out (which BTW works really well; you can get nearly 10000psi out of some grease guns which makes them a truly 'unstoppable force' :shock: :shock: ) . However I didn't immediately clean the grease out of the second caliper and a week later I came back to the job only to find that the (DOT compatible) rubber seal had swollen badly by being exposed to the oil in the grease. Just for fun I left the seal soaking in DOT fluid to see if it might recover; after about two years it hadn't done so, meaning that some types of seal swelling may be regarded as permanent. The first seal I cleaned promptly and this one didn't swell at all, BTW.

cheers
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NATURAL ANKLING
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Re: Anatomy of a failed hydro caliper

Post by NATURAL ANKLING »

Hi,
I had a M/cycle my first after a vespa :) The fuel tank filler cap seal was cork or similar and leaked, after market cap on a resprayed tank.
The paint was peeling and fuel leaked back onto me.
I cut a piece of rubber to make a seal.............latter I cut it small to allow for swell :)
The leak tended to persist..................brazed a tube onto top of metal cap for a breather...job done.

Be careful with rubber / rubber type / plastic seals etc as said.
As with all mechanical assembly's, clean up well, finishing after a solvent if used with hot soapy water rinse well and dry, AND a good visual on mating parts.

Always problematic sourcing OEM quality after market parts, the bane of my life as you find out later down the road.
NA Thinks Just End 2 End Return + Bivvy - Some day Soon I hope
You'll Still Find Me At The Top Of A Hill
Please forgive the poor Grammar I blame it on my mobile and phat thinkers.
Jezrant
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Joined: 14 Dec 2007, 8:11pm

Re: Anatomy of a failed hydro caliper

Post by Jezrant »

Brucey wrote:
Jezrant wrote:One thing that would be useful to know is which are the most reliable hydro brakes. I would have assumed the real reason DOT brakes are "far less commonly seen" is simply because Shimano dominates that market? I've heard it said by a couple of LBS bike mechanics that Sram and Hope hydros are more reliable, but I wonder if there's any truth in it. And if anyone knows a good source of replacement O rings for Avid bleed screws (including the right dimensions), please let us know. :)


Well it comes to folk saying brand X is more reliable, one has to take it with a pinch of salt. They could mean that they have seen fewer failures (which may or may not be a reflection of the proportion in similar use that fail), or that they get better results when setting them up, or that they prefer to sell such brakes for their own reasons (like they have invested in all the kit that goes with them or that they make more money out of them or something).

Hope brakes are pretty good but most folk don't use them on commuting machines or others that see the worst of the winter road salt, so this dramatically reduces the chances of failure. SRAM/Avid brakes are OK (and unlike many others you can at least (in theory) buy spare parts for the calipers and MCs) but for good or ill they are another DOT brake. Dunno if there is a strong argument about the type of usage profile that these brake see, but let's put it this way, I have never seen a set of these on a winter commuting bike either.

In fairness I don't know for sure that any manufacturers don't apply a corrosion resistant coating of some kind to the caliper bore and/or the seal groove. If they do then this could skew the choice of brake for some conditions.

Re Avid bleed screw seals; £4.99 for ten on ebay, eg
https://www.ebay.co.uk/itm/AVID-Hydraulic-Brake-Bleed-Screw-O-ring-Elixir-Jucy-Etc-/282672588007

If you start trying to independently source rubber parts for brakes, you need not only to worry about the physical dimensions of the part, the shore hardness, etc but also the rubber chemistry. You cannot swap fluids and rubber parts between systems willy-nilly; so for example it is OK to use nitrile rubber with mineral oil brake fluid but for DOT systems something like EPDM rubber is a better material to use. There are oils (like LHM) which appear to work OK in all systems that use mineral oil but that is not to say that it is definitely OK to use magura fluid in shimano brakes or vice versa. Get this wrong and the seals may swell, fall apart, or otherwise give trouble.

FWIW I once dismantled a seized car brake caliper set using a grease gun to push the pistons out (which BTW works really well; you can get nearly 10000psi out of some grease guns which makes them a truly 'unstoppable force' :shock: :shock: ) . However I didn't immediately clean the grease out of the second caliper and a week later I came back to the job only to find that the (DOT compatible) rubber seal had swollen badly by being exposed to the oil in the grease. Just for fun I left the seal soaking in DOT fluid to see if it might recover; after about two years it hadn't done so, meaning that some types of seal swelling may be regarded as permanent. The first seal I cleaned promptly and this one didn't swell at all, BTW.

cheers


I had similar thoughts about skewed findings. I just assume, again, that the folklore about Shimano hydros is based not simply on their tendency to leak but mainly on their bigger market share. When was the last time you saw a touring/commuting bike with Hope hydros?

Thanks for the fleabay linky. I’ve seen listings like this before and wondered whether the size and material were right or just elementary guesswork by somebody buying packets of a thousand o rings at a time from somebody like Simply Bearings and then flogging them on in marked-up small amounts to unsuspecting punters. Nowhere can I see in that particular listing any reference to the dimensions or EPDM rubber. Isn’t it more likely those o rings are nitrile rubber in which case, according to your argument, they would not be ideal for DOT brakes? Or maybe it doesn’t matter that much anyway for seals like these?
Brucey
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Re: Anatomy of a failed hydro caliper

Post by Brucey »

best to ask the vendor about the type of rubber they are made from. It may not be critical like you say, for these (static in service) seals; if they swell but don't fail you just replace them next time round, I guess.

cheers
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MikeDee
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Re: Anatomy of a failed hydro caliper

Post by MikeDee »

Brucey wrote:best to ask the vendor about the type of rubber they are made from. It may not be critical like you say, for these (static in service) seals; if they swell but don't fail you just replace them next time round, I guess.

cheers


DOT systems use EPDM and mineral oil systems use nitrile rubber. One source I found said "Nitrile rubber’s biggest drawback is that it can suffer from exposure to sunlight, general weathering or ozone from electrical equipment unless specifically compounded to resist them." Another reason why DOT brake systems are superior.
Brucey
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Re: Anatomy of a failed hydro caliper

Post by Brucey »

so what? Such conditions are not that likely, because seals are in dark corners covered in oil. EPDM swells up horribly if it sees any normal oil; this is quite likely to happen which explains why I've seen many such swollen seals on DOT systems and hardly any nitrile seals that failed prematurely.

Like water ingress the supposed vulnerability of nitrile seals is a largely imaginary problem in mineral oil systems.

cheers
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MikeDee
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Re: Anatomy of a failed hydro caliper

Post by MikeDee »

Brucey wrote:so what? Such conditions are not that likely, because seals are in dark corners covered in oil. EPDM swells up horribly if it sees any normal oil; this is quite likely to happen which explains why I've seen many such swollen seals on DOT systems and hardly any nitrile seals that failed prematurely.

Like water ingress the supposed vulnerability of nitrile seals is a largely imaginary problem in mineral oil systems.

cheers


That's why those piston seals in your teardown photos were hard/failed, exposed to the environment. Isn't that obvious?

Of course you can't use EPDM seals in a mineral oil system and nitrile rubber in a DOT system because of fluid compatibility. I didn't think I had to explain the obvious.

On your second paragraph, why does Shimano go to great lengths to keep the heat out with gimmicky stuff like cooling fins on their pads, ceramic pistons (dumb idea using a brittle material for that), and ice tech rotors (dumb idea to use aluminum in a rotor, by the way) if there wasn't a heat management issue? If they used DOT fluid, maybe they wouldn't have to resort to all that nonsense.
Brucey
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Re: Anatomy of a failed hydro caliper

Post by Brucey »

MikeDee wrote:
That's why those piston seals in your teardown photos were hard/failed, exposed to the environment. Isn't that obvious?


actually the seals were in good condition. I thought the body seal O rings were slightly hard but in fact they seemed about right once compared with others. They (and the main pistons seals) de-wrinkled themselves once they had been out of the cruddy corroded grooves they had been sitting in.

Of course you can't use EPDM seals in a mineral oil system and nitrile rubber in a DOT system because of fluid compatibility. I didn't think I had to explain the obvious.


yes, if you had read what I wrote you would see that I mentioned that upthread.... but equally obviously folk oil their bikes (lever pivots etc) and chain oil often gets on brakes too. This sort of thing often causes contamination from the outside and thus problems in DOT systems with seal swelling. A squirt of WD40 in the wrong place can be fatal. The brake manufacturers don't mention this or recommend compatible lubricants for lever pivots, AFAICT.

On your second paragraph, why does Shimano go to great lengths to keep the heat out with gimmicky stuff like cooling fins on their pads, ceramic pistons (dumb idea using a brittle material for that), and ice tech rotors (dumb idea to use aluminum in a rotor, by the way) if there wasn't a heat management issue? If they used DOT fluid, maybe they wouldn't have to resort to all that nonsense.


I have no idea what shimano are thinking of tbh (it all seems a bit bonkers to me too; I think they want to make disc brakes as small and lightweight as possible, in fact) but I don't think that the fluid choice alters heat dissipation in any significant way, or the chances of a boil up much (in averagely well maintained systems), in reality. My main gripe with DOT fluids on bikes that are to be used in the winter is that it seems to encourage corrosion (worse than mineral oil) and it takes the paint off (everything...) when it leaks out.

Hydraulic brakes are not at all suitable for all weather UK use IMHO and those with DOT fluid are even less suitable for the task in hand than those with mineral oil. Banging on about supposed differences isn't going to make all the failed DOT calipers I've had pass though my hands (which greatly exceeds the number of failed mineral oil ones BTW despite the fact that there are fewer of them) all better again....

cheers
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MikeDee
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Re: Anatomy of a failed hydro caliper

Post by MikeDee »

A mechanical engineer for Hayes recently wrote the following on the MBTR forum:

"Mineral oil is fine in low performance applications. But get it hot and it releases gas. This is why open bath DH forks have air bleed buttons and it's why mineral oil brakes which get hot need bled all the time.

Hayes are now doing mineral oil in their Radar brake. It's a great brake, but has exactly the same limitation as other mineral oil brakes. Get them too hot and they go mushy as the fluid releases gas. A rebleed fixes it. Until next time.

DOT fluid brakes used on exactly the same rides stay rock solid. Which is why DOT is used for automotive."

First I've heard that mineral oil out gasses...
Brucey
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Re: Anatomy of a failed hydro caliper

Post by Brucey »

only the ill-informed would believe that suspension fluid is the same as that used in brakes or that the foaming that might happen in open bath dampers is in any way related to what might happen inside a brake.
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NATURAL ANKLING
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Re: Anatomy of a failed hydro caliper

Post by NATURAL ANKLING »

Hi,
I don't quite go along with a hydraulic system slave cylinders being contaminated by lube, if it is then they are as more likely to use something like WD 40 on the disc to eliminate the squeak :roll:
Discs are on the other side of wheel from chain, unless its cross contamination from careless maintenance.

I see the arguments but is this all about DOT being so corrosive to paint etc along with accelerated corrosion of cylinder parts in bad weather / or bad design of systems on bicycles :?:

All hydraulic systems need maintenance......bicycles are high maintenance like motorcycles.
Though I do maybe agree the fact that a mechanical disc will give less trouble.

I also wonder if we are talking off road MTB's not road.....OK so more road bikes now use disc with fluid.

Off road stuff tends to be owned by Xtreeme Freakeys who tend to pay more attention to fashion and looks wearing baggy shorts an all :mrgreen:

P.S. I junked WD 40 several decades ago, this is not an maintenance stuff you need at all.
NA Thinks Just End 2 End Return + Bivvy - Some day Soon I hope
You'll Still Find Me At The Top Of A Hill
Please forgive the poor Grammar I blame it on my mobile and phat thinkers.
Brucey
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Re: Anatomy of a failed hydro caliper

Post by Brucey »

NATURAL ANKLING wrote:...I don't quite go along with a hydraulic system slave cylinders being contaminated by lube...


folk will pick up a can of whatever and spray it over the lever pivots. The lube of course fairly easily penetrates to the MC seals.

It doesn't have to be WD40, most common spray lubes will have the same effect on DOT fluid seals.

This thread isn't meant to be about the difference between DOT fluid and mineral oil (an argument that has been done to death elsewhere and is frankly pretty tedious tbh) it is meant to be about the weather reistance of hydraulic calipers in general.

My basic point is that typical bicycle calipers that run mineral oil are prone to developing leaks because of corrosion if they see typical UK winter weather. [Running comparable DOT fluid systems just seems to make this even more likely to happen, because the fluid is miscible with water, but that is by the by.]

If anyone has anything useful to contribute to this thread (eg about different corrosion proofing in some brands of caliper, for example) I'd be glad to see it.

cheers
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