Self bleeding brakes

TBH I think they’re having me on.

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Some bloke on another forum swears this is a thing, though for all my time servicing brakes I’ve never heard of such a thing.

I take it this is utter boollocks. But im open to new things and in the brake world i’d be interested to know if this is possible, or fantasy.

sounds like BS to me….

All* brakes will self bleed to some extent as the air slowly makes it’s way up back to the lever.  You can speed it up by leaving the lever ziptied to the bar overnight to compress any air bubbles and expand the hose a bit.

I wouldn’t really call it self bleeding though?

*open systems with a reservoir above the master cylinder like shimano or hope. It doesn’t work so well with ambidextrous designs which rely on a bladder type reservoir like SRAM.

Sure, you can have a perfectly operable Shimano brake without a completely full master cylinder (I.e. with air space in it). Assuming any bubbles migrate from caliper or hose into the reservoir then the system has technically bled itself.

I suppose.

You can speed it up by leaving the lever ziptied to the bar overnight to compress any air bubbles and expand the hose a bit.

I think this is going to slow it down, because the bubbles get smaller and more dense under pressure but the fluid does not. So they’ll be less buoyant.

All brakes can self bleed to some extent but the trouble is bike brakes have to be sealed because bikes get turned upside down. So any air that comes out of the hoses and pistons, is still in the reservoir waiting to **** you up. Not sure what they’re talking about, I’ve never seen any brake that is more or less self bleedy, ie they’re all ever so slightly but not really usefully.

molgrips
Free Member

I think this is going to slow it down, because the bubbles get smaller and more dense under pressure but the fluid does not. So they’ll be less buoyant.

TBF I’ve no idea why it works, but it does work.

TBF I’ve no idea why it works, but it does work.

Isn’t it because it resets the pistons in their seals, rather than anything bleed related?

Nah, it can definitely get air out. I’ve always thought it’s something to do with air rising to the top combined with whether or not it can escape, like, maybe undoing the tied back lever encourages the gathered air to come up into the reservoir and come out of the “working fluid” . But that’s pretty much just magical thinking, I have no idea at all if it’s true 😉

It would probably be possible to make a self-bleeding hydraulic system, but it would be expensive and complex and not worth it for bikes or cars.

I think this is going to slow it down, because the bubbles get smaller and more dense under pressure but the fluid does not. So they’ll be less buoyant.

Yea…… but it works.

I think it’s probably got something to do with surface tension.  Big bubbles cant move up the line because they can’t actually form a bubble around which fluid can flow.  It’s the inverse effect of capillary action, the liquid cant flow down the tube because to do so requires more energy to crate the surface of a bubble than it gains from gravity.