I bought a carerra tdf road bike as my first road bike and i took it to halfords for a service and they broke the left 16 speed Shimano ST-2300 shifters, when i try to move the chain onto the larger ring it will move but the it doesnt click and the second i let go it moves back to the smaller ring... ive seen many cheap replacement sti shifters on ebay however i dont know which ones will fit my bike i was wondering if anyone here could help my out as im not very experienced with this sort of stuff.. kind regards.