Originally Posted by
cxwrench
Bleeding is definitely necessary at certain intervals as the fluid (whatever it is) will get contaminated and/or absorb water. Contamination and moisture will both lower boiling temperature, sometimes dangerously. For people that do a reasonable amount of mileage or ride a lot of hills I'd recommend once a year. To put this in perspective when I raced motorcycles I bled the brakes every time the bike was on the track. That's obviously extreme, but they are your brakes.
I've bled a lot of brakes on motor vehicles and even aircraft. However only when it was necessary to open up the brake cylinders and allowing air to get into the system. Same for the airplanes I worked on and helped do annual inspections and other routine maintenance on. None had a requirement for regular changes of the fluid of any corporate jet, private aircraft or any motor vehicle that I worked on. Air in the lines shouldn't be there if there are no leaks and it was properly bled before.
And if there are no leaks, how will moisture get in?