While riding today, the gears started jumping from high to low during shifts and then completely stuck in the low gear setting. Had to pedal back in this setting-which was brutal.
So, the lever stays in the forward position now at all times, even after shifting.
I took the lever off and notice that some pieces of metal had sheared off of a small sprocket inside it.

Although a vintage bike--its a great ride.
What do I need to replace on this to fix it? Can it be fixed?

Thanks for helping.

Joe

Sounds like time for a new shift lever. But without more details who really knows? Brand, is it indexed, photos, which side, do you mean that the chain can be derailed to the next cog but the lever returns to the default position and the chain stays where it was shifted to? Andy.

I had this exact bike..assuming it is in fact the 1987..you can get new down tube shifters or..as i recently did.switch to barend shifters..8-speed ultegra is super cheap..and I find them way more convenient than downtube ones.

If it shifts to the up position on its own..it could just be that the screw was loose..I remember something similar happening to me.

Brand is Shimano. lever is rt side as I'm sitting on it. Shifting lever all the way down and let go-it returns to forward position and derails to last cog-hardest to pedal. Again, removed the lever and saw sheared off small chunks of metal. Would prefer a newer handlebar mounted shifter. Suggestions?

Get a flat bar thumb shifter then. NBD. Andy.