Bleeding Hydraulic Brakes?

[figbat]

No I asked why it works, I do not think it does. Your second idea maybe in fact the first idea could be what is happening the same. Compressing air in a hydraulic line does not make is go away.

On motorbikes my take on it is that compressing the bubbles makes them smaller and more able to move through the orifices and lines - they can then migrate to the highest point, hopefully the master cylinder. Of course with the brake lever pulled the fluid port in the cylinder is closed but when you release the lever the air should then exit the cylinder into the reservoir. Of course this requires there to be a reservoir and fluid port - I'm not sure many or any bicycle brakes have a reservoir, other than the master cylinder itself, so the above method won't work on its own, but may then allow you to expel any air at the cylinder bleed/fill port.

 

[Levo-Lon]

On motorbikes my take on it is that compressing the bubbles makes them smaller and more able to move through the orifices and lines - they can then migrate to the highest point, hopefully the master cylinder. Of course with the brake lever pulled the fluid port in the cylinder is closed but when you release the lever the air should then exit the cylinder into the reservoir. Of course this requires there to be a reservoir and fluid port - I'm not sure many or any bicycle brakes have a reservoir, other than the master cylinder itself, so the above method won't work on its own, but may then allow you to expel any air at the cylinder bleed/fill port.

The Res is in the master cylinder, the fluid above the port.
A tied off lever when released opens the port and any air simply rises up through the pin hole.
Used this many times on a motorcycle brake.

 

[Electric_Andy]

No I asked why it works, I do not think it does. Your second idea maybe in fact the first idea could be what is happening the same. Compressing air in a hydraulic line does not make is go away.

um yes it does. COmpressing the whole system (overnight) will force any air bubbles to rise, and therefore come up to the top of the air space in the reservoir. If it doesn't work, it means that you've bled it correctly the first time around. But always worth doing just to make sure.