Folks, I am desperate to fix my sister's bike before I leave to go back to my studies this winter; I have only a few more days and then it will be history -- she might take it to a (*gasp*) bike shop to get it worked on, and then all will be ruined. The problem is this:
The rear deraileur is inclined only to stay in a select group of gears at a time. If it is in the smallest cog (highest gear), it can't go any lower than sixth gear. All attempts at keeping it in fifth gear are futile: it just want to drift back to six or seven. I reset the cable tension, and readjusted it numerous times (like 40), and it was to no avail. The limits are set fine and are not interferring.
Earlier, before I reset the cable tension, it was stuck in gears 3 and 4, because I had jacked the tension up with the deraileur barrel adjuster while out on a bike ride, away from a functioning 10mm wrench. It basically has a 'window,' if you will, of gears it's capable of working in. Shifting down doesn't work, because seemingly there isn't enough tension, which leads me to this conclusion:
I think the shifters are to blame. The bike hasn't been used in years, but it's a decent Yokota girls' mountain bike, with Shimano Alviro parts. The shifter in question is one of those 'rapid fire' style shifters with the lever that has two parts, one for your thumb and one for your index finger. It doesn't seem to be pulling enough cable when the time comes, I notice -- it just pulls a little, while your thumb is pushing on the lever, and the display reads what gear you should be shifting into, but then when you take off the pressure from the lever, it reverts back into the higher gear you were trying to get out of. Could this be the culprit? A janky shifter?
Do you guys read me at all? This is my first post here, and I haven't read any of the other ones so I don't know how they are supposed to go as far as tech talk goes. I hope someone here can give me some advice as to what the hell is going on with this thing, because it's driving me crazy. Thanks.