chain alignment
 

I've discovered a problem on my new road bike. I'm new to road bikes and new to vintage bikes so it's a double wammy. I've been riding it for a week now with no rear mech cable. I decided today it's to hard to ride up hills in my top gear so I bought after searching and scrounging I found a local place I can get classic cables. Now that I'm able to shift the rear when I shift the front the chain falls between the sprockets. Having to stop to fix this every time I downshift made slow progress home. Any ideas? Is my chain just to narrow?

Sounds to me like you need to adjust the derailleurs limit stops.......
http://sheldonbrown.com/derailer-adjustment.html

It falls between the rear sprockets when you shift the front derailler?

between the sprockets?

did you make sure the chainrings on the cranks are tightened down properly and that they are facing the correct direction?

if chain is falling off the rear f/w or cass cogs, you need to adjust the low gear stop screw on the rear deraillur; you limit screws. falling off the rear when the front is shifted? check you front deraillur limit adj screws as well. bottom line, something is pulling the chain beyond its adjustment points, so check your limit adj screws.

the chain falls between the gears on the crank when I downshift from the large gear to the small one.

might be the wrong chain. Might be bent chainrings. Check the rings by measuring the distance to a spot pn the frame and rotating the crank. the ring should be the same distance from that spot all the way around.

Here is a laundry list of things that would help:

What front crankset are you running?
What chain are you running? Is it a new replacement, and if so, was it a Shimano-compatible "9-speed" or "10-speed" chain?
Are the bolts that hold the chainrings to the crankset flush with the ring, or do they stick out?

-Kurt

What chainring combination are you using? The smaller the size difference, the narrower the horizontal spacing should be. You should be OK with any standard "8-speed" chain, such as an SRAM PC-58, but, as others mentioned, do avoid 9- or 10-speed chains.

Also, check the length of your chain. 24 half-links should measure no more than 12-1/16".