Originally Posted by
vredstein
Shimano makes both a 7800 and 7900 down tube shifters. They use non-interchangable SIS unit, lever, fixing screw and cap. Is the indexing different? Is the indexing different on the 7800 and 7900 STI levers?
The 7800 and 7900 rear shifters and rear derailers are compatible from everything I've seen. My understanding is that the major changes were made to the front shifting and 7800 STI is not compatible with 7900 STI for front shifting. But since DT and bar-end are friction for front, they should still be compatible.