Looking at your photos it appears as if you have an integrated shifter/ brake lever combination; the shifter is built in to the brake lever assembly.
If you have a 7 speed rear end with three sprockets up front, the most economical solution is to convert over to a separate set of brake levers compatible
with the type of brakes you have, and to use 7 speed SRAM Grip Shift shifters. They require much less maintenance, will work with Shimano drive trains,
and are less expensive than purchasing a complete set of integrated brake/ shift levers.
Alan
