Slow and wobbly wrote:......Over to the boffins to explain how this works. It is a method I have seen used in workshops where they also do not have time to wait overnight. It works......
Yep, its using basically the same principle as the cable-tie to bars method.......just applied quickly and in several dozen lever pulls instead of just one long one ....
Brake fluid in a sealed hydraulic system, when the brakes are applied, only moves a tiny distance compared to the overall length of the entire system. Air bubbles will *always* rise in a hydraulic system, so even though you are putting pressure on the fluid itself by pumping the piston, if the only place for pressure relief is at the m/c piston bypass valve.....thats where the air will eventually make its way to, and it will bubble up higher, every time you let the pressure 'drop' for a fraction of a second when you let the lever all the way out. The air bubbles rise at a faster rate (and over a longer distance) than they move down when the lever is pulled in.
Much the same effect can be seen if you only partially pull the brake lever in - its often possible to see a whole lot of air bubbles appearing in the fluid resevoir, and the lever pressure will immediately increase.
Here endeth todays lesson.
