(20-08-16, 08:47 AM)Buzz link Wrote: In the past couple of weeks I've noticed that my brake lever is getting further out as I ride and the disks are really heating up, so much so that the last time I got home I could feel a real rolling resistance. I just went out to clean the pots but found it a real struggle to push all 4 back into the caliper...Having just had another read of the above and another think it still sound very much to me that the piston in the master cylinder is not returning fully.
Here is my reasoning. When you release the brake lever the master cylinder piston is helped to return by the spring behind it, and faster than the caliper pistons are pushing the fluid back. To prevent a vacuum forming, which could draw in a very small amount of air at the caliper seals, fluid can flow past the master cylinder piston seal as it is retracting. When the seal clears the little hole in the reservoir the fluid can return and everything is at zero pressure. All that is how it is designed to work. However if the piston does not come back far enough to uncover the little hole in the reservoir, the fluid that flowed past the seal each time you release the lever is trapped. This would gradually increase the pressure in the system and give the symptoms you describe.
I hope you could make sense of my theory but why the piston would suddenly stop coming all the way back I don't know.