Brake issue

[MarkD]

Hi all. This topic is general, regarding a brake issue for a friend in Belgium. He has a Moto Guzzi cafe, and said his rear brake is 'as weak as a kitten'. I copied part of his email here: (The rear brake is still as weak as a kitten and I have no clue as to why: I have already changed the rear master cylinder, the caliper is new, stainless hoses... The mysteries of pneumatics or just a case of having been sold a poor rotor? But then: what can possibly be wrong on a rotor??) He also said he has bled the air out 5 times. He is an excellent mechanic. If anyone has a thought, I'd appreciate it, as I said I would ask the forum guys. Thanks in advance. Here is a link to his bike-- it's a cool one. https://www.returnofthecaferacers.co...t3-cafe-racer/

[MarkD]

Sorry for the dead end link-- here is the live one: https://www.returnofthecaferacers.co...t3-cafe-racer/

[jetmechmarty]

AFAIK, the Goose has linked brakes, essentially the same as the XS1100LH. That link opened a pic of a highly modified 850T3. Are the brakes linked? It appears the calipers may be updated. I expect he may have tampered with the piston ratios. That's my best guess with the very limited information given.
A closer look and reading the description of the bike makes me believe he's probably got the wrong master cylinder bore for the caliper, assuming he has removed all of the air from the system.