I recently got an old bicycle for the sole purpose of using it on a trainer. It has old non-indexed levers for gear changing and they don't seem to work OK. The front one slips into lower after a while, and the rear one is now "locked" since it's plastic, I don't want to force it and break it.
I don't want to invest much into this bike, it was already more than I was planning to spend on it.
I was thinking to remove them and fix the derailleurs on a specific gear ratio. I would like to be able to adjust the rear one, but wouldn't mind if the process is somewhat cumbersome (ie: requires tools).
Is this possible? What would be the best path to do it?
Some pictures for clarification:
There doesn't seem to be any barrel adjuster on the derailleur side, just on the shifters.