I have an 08 Arlen Ness Vision with 24,000 miles. I had this issue with the rear brakes come up last spring after sitting all winter. I tried the usual bleeding of the rear including using a hand vacuum pump to pull fluid from the master all the way back throgh the caliper. I went through 3 resevoirs of fluid and never pulled an air bubble, but only got meager pedal pressure. I only put on 4000 miles last year as the rest of the summer was spent on my new BMW R1200 RT.
This year the problem is back only worse, there is virtually no pedal pressure. I am glad to have found these suggestions from others, and will attempt bleeding the front right caliper, and if that fails will have to replace the brake line.
Thanks to all contributors.
What they all said I would do first......but check to see if the disk roter is bent. It has the same cause as air in the line due to pads being pushed deeper into the calipers. Best wishes and hope it is nothing but air.
Bill And Sarah
I have a similar problem with my '08 JP, I bled the rear brake twice but there seems to be air getting into the back brake system. No fluid leaks or need to add fluid - just additional air.