My late 1970's Lotus Odyssey road bike has shifters on the down tube and non-indexed shifting. There is a wire bail on the shift lever pivots - increase friction by tightening. This also makes it harder to shift. I really hate (HATE!) when the the bike changes the rear gear without any lever shifting! It will shift up one or two gears unless I have the friction bail adjuster set really tight. Naturally this happens when I'm grinding away on an uphill, exactly when I don't want to be reaching down and shifting back into a larger rear cog. This problem has existed since I bought the bike new.
Any suggestions beyond get a new bike (I actually have one, but the rear derailleur broke off and I'm waiting parts).