Tip of the day !! Over the past few months Ive had issues with my front brake, Doh - not good when you wanna stop.. I fitted a new master cylinder repair kit yesterday. Bled up the brake lines and found there was still micro bubbles feeding into my bleed kit, So a tip i found on the internet some years ago was to cable tie the brake lever as far into the handle bar as possible and leave as long as possible. Any air bubbles will then Travel back up into the master cylinder. Check all connection points for leaks and nip up where required.. This trick will firm up most spongy brake issues, well it worked for me.
I don't actually think the cap removal or loosening is actually required in this situation it may help tho but as the air rises up the pipe work and thought the MC (due to the lever being held open) fluid will take the airs place with the help of gravity. The air doesnt actually need to escape the reservoir it mearly swaps places with the fluid that was there. It would be a different story during bleeding the brakes as air needs to flow into the reservoir to replace the fluid thats removed from the system via the bleed nipple.
