I have a Gary Fisher mountain bike and when shifting the rear derailleur from larger to smaller cogs, the shifter is extremely mushy and has lost any kind of defined click, consequently it misses. Shifting up the rear cogs to a lower gear is perfect with a well defined click. The gears have always been dialed in and adjusted correctly. The cable is taught.
I usually would suspect grime in a situation like this, but I have lubed the cables and housing and taken the shifter cover off and lubed inside of that. The bike is 8 years old though, and I have never actually replaced the cable and housing. The cable looks good, but I obviously can't see inside the housing. Would you suspect that I need to go new?
The RD is thoroughly cleaned and lubed in all moving parts. The bike did fall over a couple of weeks ago, but I can see no bend in the rear derailleur hanger and don't suspect this kind of behavior from the shifter to be a result of that.
Another possibility is the shifter lever return spring has broken. I'm not sure about pulling that thing apart to repair and the cost of a new shifter itself is a little high. Any advice on identifying the problem and what's wrong here first?
Appreciate your help,