Originally Posted by
Briareos
I don't think a 7400 derailleur would take 10 speed cassettes?
Correct. To run a 10 speed cassette you'd need the 10 speed shifters, 10S chain, and a rear derailer that will be compatible (Ultegra, 105, 9-speed or newer DA, etc.) You current derailer would not work.
Originally Posted by
Briareos
If I use a 9-speed shifter I can index 8 of them and either the highest or lowest gear becomes friction as long as the limit screws keep it from going too far?
You'll actually just have an extra click somewhere. If you set it up like you would any other shifter, the extra click will be locked out by the lower limit screw, and you will never notice it when riding.