Brake lever sponginess

[mickwinf]

I had problems bleeding my brake last year, just could not get a good firm lever, in the end I left it in disgust, went back a few days later and had a good brake! I think the air bubbles just rise to the top over time, too much bleeding keeps agitating the fluid and adds more air.

[fisjon]

Brake fluid sucks in air, that's why you shouldn't leave the cap off for any length of time. If there is air in the system and you compress the system the air will ingress into the fluid instead of rising to the top causing the fluid to flex before pushing the piston.
if you can't bleed the air out it is best to let it rise to the top of the system and filter it out by wiggling the lever gently. You will be surprised how effective this method is.
It was the only way I could get the air out of my VF750FD clutch.