Why won't these (old) gears index?

[Globalti]

None of the above.

The cable outer at the rear derailleur is crudded and rusted up thanks to the bike being left out in the wet. Change it or better still change inner and all outers and it will shift well.

 

[rogerzilla]

Any 5 speed block you find won't necessarily index. It has to be a block designed for it, with the appropriate ramps and cutouts. Otherwise you will need to overshift to get the chain to move to the next sprocket. Indexing requires shifter, mech, block/cassette and cabling (constant-length outer, prestretched inner) all designed for it. It is not simple.

 

[gbb]

I seem to remember I had the same problem when I tinkered with an old bike, 5 speed , new cheap derailleur, good cables and routers...I struggled to get it to shift well, not sure I ever got it right. To back up what rogerzilla says, old 5 speed blocks tended to be straight cut, not ramped to aid shifting plus they tended to be used with friction shifters so you'd 'feel' in into gear. Some later 5 speed blocks may be ramped in which case the above needn't apply.