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.

i've had that happen with some 5 speed freewheels.. the gears are just too far apart i think

Heliocomatic cogs had a groove on top of the teeth that was intended to improve shifting, but in my experience the chain would often land on the groove and fail to engage the teeth.

Is that what you're experiencing?

Yes, I believe so. I think I will get another wheel/hub and use Suntour or Shimano FW's. I suppose I could get a new Heliocomatic FW but isn't that system kind of crappy anyhow?

Yep, I've had this problem too, and I'm currently having it happen with the Huret freewheel on my Motobecane, though not quite as bad as the wheel I had with a Helicomatic. A new wheel is the best, and might even be the cheaper option too.