I have a Helicomatic freewheel on my 84 Trek 560. If the shifts aren't perfect and the chain doesn't land on the next cog, up or down and the chain lands in between, or slightly off the cogs it will slip leaving me pedaling away in "neutral". Imagine pedaling away and your chain snaps, thats what its like. I'm using a new 6 speed chain and the FW doesn't look wore out but maybe it is?

I have 4 other bikes running Suntour, Shimano UG, 5,6,7 speeds and none of them do this. If I'm off on a shift, I just trim it a bit and its fine.

Any thoughts? Anyone else have this problem. Perhaps the FW is too worn or the hanger bent.