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not resolvedFollowing on from HST Thread Drift :)
We've been considering bike hanging storage for our garage and I'd wondered about these (or similar) from Decathlon:
https://www.decathlon.co.uk/1-bike-wall-rack-id_8512645.html?gclid=EAIaIQobChMI7aa0g_3b4AIVL7vtCh0KuwvyEAYYByABEgLvuvD_BwE
Husband is a bit concerned about hanging bikes with hydraulic brakes - is this a Thing? We could probably find several non-hydraulic bikes that we could hang up but thought I'd ask the Hive Mind for their experience.
I had my road bike hanging from one of those for years never did it any perceptible harm, however it was caliper brakes.
I've turned a few bikes with hydraulics upside down and left them for a while.
It took quite a while for adequate braking performance to return once the bikes were ridden.
Hanging will be much less extreme however, depending on the hanging angle, you might find the brakes are poor.
I don't know if it's time, vibration or repeated braking that restores normal function, as I went for repeated braking as I cycled along an Edinburgh road surface - normal service was resumed eventually!
Robert
@LivD: I presume his concern in this case, then, is the unusual orientation of the hydraulic system rather than load on the wheel rims.
I'm by no means an expert on such things but my initial take on this would be that it shouldn't be an issue since the hydraulic system is (or should be) sealed.
One piece of advice I've seen is not to store bikes fitted with hydraulic brakes upside down. The reasoning being that if there is an air bubble in the master cylinder reservoir* then it might migrate to the caliper while the bike is upside down, causing the brake to go soft. I suppose this could suggest that you should only hang the bike by the front wheel, since that will keep the master cylinder reservoirs higher than the calipers (or at least more or less on the same level).
* There shouldn't be if the brakes have been properly bled.
I hang my MTB with hydraulic brakes from the front wheel and it's usually pretty much fine. I did hear if you end up with a bubble in the brakes you are able to cable tie the brakes levers on overnight and that allows air to escape. Not sure about that though!
You need to open the reservoir as well, the air should come out of solution, then close the reservoir and before releasing the brake lever.
Erm... surely basic physics says that it will make absolutely no difference at all to brake functioning if it's turned upside down.
I'm nor replying to be argumentative - but because actually I've never quite got to grips with a full understanding of the system and I'd like to fix this if I'm wrong...
It's a sealed system isn't it? Air is compressible. But it's compressible no matter where the bubble is.
The only difference it would make is if you're trying to get rid of the air - you want to open a hole where the air is to let it out, not where the air isn't. Beyond that, the position of an air bubble is completely irrelevant.
I suppose - if I'm understanding the mechanism correctly - if you can get the air (which shouldn't be there at all) into an expanding reservoir (which is normally sealed from the rest of the fluid, and is used to automatically top up the fluid somehow) then it'll stop causing an effect on the breaking. But the real solution to this would be to get rid of the air completely, not to worry about which way up the bike is.
I await correction :-)
@rbrtwtmn
There has to be air in a hydraulic brake system somewhere. Otherwise the extra fluid can't advance from the reservoir into the master cylinder as the pads wear.
Motorcycle brakes have a telescopic gasket that concertinas out as the pads wear. Shimano brakes do not have that, nor Magura. I'm not quite sure what happens when you turn Shimano brakes upside down but they really don't like it.
The problem is air between the master cylinder and the pistons. No compressible fluid belongs there. Tying the lever back allows the air to rise and exit that part of the system, to be replaced with brake fluid from the reservoir when the lever sweeps forward.
EDIT
Thinking about it Magura rim brakes don't have a reservoir, just a big adjuster piston.
Or just bleed the brakes properly. Straightforward, if a little tedious, with Shimanos if you have the right kit (I use the Epic kit, their syringes are preferable to Shimano's plastic cup on the reservoir IMO). Best done at room temperature rather than in a cold garage so the brake fluid is less viscous and the bubbles rise quicker. Can't speak for other brands.
Or just bleed the brakes properly.
Shimanos go funny upside down when they are perfectly bled.
Oooooft, I have five bikes on hooks but the hydraulic one sits proud on the floor via its kickstand
This is the standard warning from Shimano technical specs site for hydraulic brakes;
The disc brake is not designed to work with the bicycle upside down. If the bicycle is turned upside down or on its side, the brake may not work correctly, and a serious accident could occur. Before riding the bicycle, be sure to operate the brake lever a few times to check that the brakes operate normally. If the brakes do not operate normally, stop using the brakes and consult a dealer or an agency.
Motorcycle brakes have a telescopic gasket that concertinas out as the pads wear. Shimano brakes do not have that, nor Magura.
I grew up with Hope hydraulics, which definitely do* have the telescopic gasket on the reservoir. I thought it only worked because there was a pinhole on the reservoir cover (e.g. Hope Mini) to allow atmospheric pressure to the unsealed side of the gasket, but my motorbike front brake reservoir has no such pinhole as far as I can recall.
* An "open" system, in that it has an expansion reservoir that also provides fluid as the pads wear. The old Hope C2 and XC4, and old Maguras, were "closed" systems, with spring-retracted pistons and on-the-fly adjustment to fine tune fluid volume and thus pad-rotor distance and lever feel.
I think I'm going to need to see a picture... I had in mind that the reservoir would work like the one on a standard central heating boiler - there's no air in the system, the expansion/contraction which takes place when the water heats/cools is into/out-from an expandable reservoir. There's air used to compress this reservoir, but the air isn't mixed with the water at all - it's on the other side of a cylinder or something.
Don't hydraulic brakes work something like that too - or is there a reservoir with air sloshing around in it too. That seems like an odd design. What pushes/sucks extra fluid into the main bit of the system?
@rbtwtmn, during recent boiler service the engineer used a track pump with a long tube to pump up the pressure in the expansion tank.
In Shimano brakes the master cyclinder is open to the reservoir until the lever is pulled. That's why the oil falls out of the lines if you turn it upside down.
Suggests that if you have to invert the bike you should tie the levers back.
@rbrtwtmn: "I think I'm going to need to see a picture..."
Here's a couple of photos of the brake lever from theShimano M315 brakes that I replaced on my eMTB. (Sorry, the photos are a bit too big to display properly within the post - right-click and open in a new tab to see the full photo).
The first one shows the rubber diaphragm which seals the master cylinder reservoir:
This is also clearly shown in the exploded view on Shimano's technical docs web site. Note that there is a hole through the diaphragm for the bleed port which is sealed by the bleed bolt and o-ring in normal use ie when the brake is not being bled. The holes for the bolts that secure the reservoir cover are sealed by the diaphragm being squished between the reservoir body and the cover when the securing bolts are torqued up (those are torx head bolts, because they shouldn't need to be removed as part of normal servicing, only if you're having to e.g. replace a torn diaphragm - using torx head bolts reduces the risk of someone inadvertently trying to undo them instead of the bleed bolt, which has a normal hex socket head).
The second photo shows the breather hole that allows air to pass to and from the "dry" side of the diaphragm so that it can flex to accommodate changes in the volume of the brake fluid in the reservoir:
The reservoir doesn't need to be pressurised like a central heating system - the pressure required to operate the brakes comes from the brake lever acting on the piston in the master cylinder.
The hydraulic system in that brake is definitely closed - there is no way for air to get in to the system provided that none of the components is distorted, damaged or has been manufactured out-of-tolerance and all the relevant bolts etc are secured correctly. Any sponginess in the brakes can only come from:
- air that has been left in the system i.e. the brakes haven't been properly bled;
- vapourisation of the brake fluid due to elevated temperatures (this can happen under heavy/prolonged braking, especially if the brake shoes aren't thermally isolated from the caliper piston - hence the use of ceramic pistons in fancy-nancy brakes);
- leaks in the system (see caveat above).
Given that there are ways in which air can get in to the system - including through mechanisms which are beyond the manufacturer's control - it makes sense for them to reinforce the message that it's best to keep the reservoir above the caliper (because that allows any bubbles that do get in there to migrate upwards out of the actual brake line) and to check the operation of the brakes if you have to temporarily do otherwise. (Shades of the "idiot-proof" fork QR dropouts, before everyone started using thru axles.)
Note: I'm not saying that all Shimano brakes have these features, but it's clearly incorrect to suggest that none of them do.
Interesting. Of course if your taking your hydraulic disc braked bike on a Scotrail West Highland train you are 'encouraged' to hang your bike from back wheel. (Other thread)
I've experienced upside down bike leading to spongy brakes and it's definitely A Thing (10 mins going in circles in the car park and braking on and off sorted it out, thankfully). Til that point I'd been intending to use hooks for storage but that scared me off. So when @BikeFan offered bike pulleys for sale on here, I jumped at 'em.
Edit: I've been told that many suspension forks can have leak issues from hook storage too.
I think my understanding is gradually increasing...
Is this right - as follows?
In at least some models of hydraulic brake with a reservoir (if I'm understanding some lack the reservoir)...
- it is helpful to understand that there's an active 'braking' side of the hydraulic system, and a passive 'reservoir' part of the system.
- there is free movement of fluid to/from a sealed from the air but expandable reservoir, until the brake lever is pulled
- when the brake lever is pulled it seals this reservoir from the braking side of the system so that pressure is applied through the fluid (rather than squeezing fluid into the reservoir)
- fluid is allowed into the braking side of the system once the levers are released, either because the reservoir is very slightly pressurised (basically the diaphragm above acting like a balloon) or through gravity - once the brake levers are released there should be no remaining pressure in the braking side of the system so even a small amount of pressure from the diaphragm would be enough.
There should be no air in this system.
There is no air (shouldn't be) in the reservoir.
This is fundamentally different from the central heating expansion system - because the central heating system remains pressurised at all times. The braking system has no pressure in it once the levers are released. (Gembo - despite the bike pump, air isn't being introduced in with the water in the central heating - the water expands into a balloon like system, but rather than relying on stretchy rubber to keep the water under pressure, the balloon sits in a sealed vessel, with the air in this under pressure which has been introduced by the bicycle pump. Air and water are strictly separate).
*IF* there is air in the system it would be good to get it into the reservoir, because that would improve braking performance - it being sealed off from the braking side of the system as soon as the brakes are applied. But the solution is really to get rid of this air completely - it shouldn't be there. In this circumstance then it would be bad to turn the bike upside down - simply because the air might get trapped somewhere rather than returning to the reservoir.
If there is air on the braking side of the system then it makes absolutely no difference at all where it is.
Brake performance may decline if the bike is upside down, with the levers released, because fluid drains into the reservoir, with a corresponding retraction of the brake pads away from the disk. This isn't a permanent problem - the solution is simply to turn the bike the right way up - the fluid should return to the braking side of the system. It may be that working the levers helps to prompt the fluid to return into the braking side of the system.
(If I've said 'breaking' rather than 'braking' somewhere in all that verbiage I hope you'll forgive me).
How much of that is right?
Well, I certainly enjoyed it.
Me too! Thank you :)
fluid drains into the reservoir, with a corresponding retraction of the brake pads away from the disk
I doubt it - suspect air replaces the brake fluid and the slave cyclinder pistons remain where they are. The brakes don't then work because air is compressible. Leave the bike sitting and it bleeds itself as the air rises and exits the master cylinder into the reservoir.
I've to assemble and fill the rear brake on the Scaffolding Bike's replacement (to be named the Lavender Menace?) soon so I will actually check this.
Nice one. THe dial on the expansion tank looks like the dial on a track pump but I should know this is different as I have opened the valves to increase the pressure without a pump.
The disc brakes on the lecky bike were squealing today.
Went onto bike station was given excellent info went out they squealed one more time and without me doing anything, they are now silent
My goodness (being polite) there's a lot of junk information out there when you go looking for information on how hydraulic bike brakes work...
Park Tools seems reliable.
From the first article - a solution to one of the questions I had:
Hydraulic disc systems use a reservoir system that contains a bladder to allow for the expansion of the brake fluid. Some models use an enclosed bladder in the lever, while others use an “open system.”
In other words - some systems ("open") have air in the reservoir - and therefore (I conclude) turning the bike upside down clearly means air can rise from the reservoir into the active braking part of the system. Whereas other systems "bladder" don't - and assuming they are set up correctly turning the bike upside down (I conclude) can't introduce air into the system.
This would explain why some people report that the bike upside down causes issues, and others report that it doesn't.
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