I'm not sure if this query is best served by this group, Classic & Vintage, or Mountain Bikes, but as it's technical in nature I figured I'd start it here.
The situation: I'm in the middle of refurbishing an old Bianchi Nyala mountain bike. Shifting is Shimano Altus C10's, and it's using the ST-CT15 shifters (3 x 7). At present, the bike's about 75% reassembled, and I'm down to cleaning and resetting the dérailleurs and shifters. Messing with the shifters before I disassembled the bike (when I got the bike the chain was completely rusted, there was no way I was going to try the drivetrain under normal operating conditions), they climbed the gears step by step very nicely, but when I pulled the lever to reverse the action, it shot to the small sprocket immdiately.
Is this normal action, are the shifters broken, or am I missing something? I'll admit to very little experience with MTB's, having only had a Trek 930 (nothing odd about that indexing) and my current Raleigh Seneca (no indexing) and Schwinn Ranger (SRAM twist grip) to fall back on.
Any advice would be greatly appreciated.