I'm borrowing my friend's Kestrel Evoke on a long term basis. I'm not as strong as him, and the 39t/23t gearing wasn't enough for me to go up hills, so I changed the cassette to a 12-27. It wouldn't shift to the big gear, so I lengthened the chain by two links. I now have two problems
1) When on the biggest gear, the derailleur gear and the cassette gear interfere.
2) When on the small chain ring, the small gears have a slack chain.
I read that the "B" screw on the derailleur is supposed to move the derailleur farther from the casette, but on the bigger gears, it doesn't seem to do anything. On the smaller gears, it changes the angle of the derailleur, and on the small/small gearing, can make the chain rub against the chain [the cage tilts up instead of down], or provide some clearance.
It seems like both problems could be solved if I can convince the top gear of the derailleur to move back/down. Then it moves away from the big gear, and also picks up the slack on the small gears. Unfortunately, I can't find an adjustment for this.
Is there one, or do I need to buy a new derailleur? If so, how do I know the new one supports the 27t gear?
Components are Shimano Ultegra.
thanks for your help,