So I put together a bike a couple months ago. New chain, new chainrings (3 speeds), and new rear cassette (8 speeds). Used front and rear derailleurs from a bike co-op. The free wheel is old but seems to be working fine. All components are Shimano.
It had been plugging along just fine until recently. Now any time I stop pedaling, such as at a stop light or a bump, when I start again, the chain "skips" or "jumps". I'm not trying to change gears, it just feels like the chain is disengaging and then reengaging. It's infuriating and I think pretty dangerous.
When I'm pedaling continuously on a trail, no problem. When I'm standing up on my pedals going up a hill in 2 (front)/7 (rear), no problem. This info, combined with the fact that the entire drive train has to have less than 500 miles on it, and the fact that I went into another bike coop and the tech there measured my chain for wear and found that it wasn't worn makes me think this is not a worn drive train problem.
My guess is that the rear derailleur is properly keeping cable tension when I stop pedaling, which is somehow (?) causing my issue.
Any help is greatly appreciated, it's really my only form of transportation and it's getting to the point where it's unrideable.