Postby Kid_Carbine » Fri Mar 14, 2008 8:34 pm
Ok, so now it shifts back when going in one direction only & not both like you said before.
Now you say it shifts back when you shift "up"
Is that "up" to a higher ratio, [smaller sprocket] or "up" to a larger diameter sprocket [downshift to lower ratio]
OK heres what's happening to your older bike.
The derailleur is spring loaded to derail the chain out to the smaller sprocket [upshift to higher ratio.]
The derailleur is pulled towards the wheel by the cable which is connected, in your case, to a lever on the downtube. [so far so good?]
This lever has some friction discs in the round part of the base of the lever & there is some sort of central screw that holds it together. Sometimes this screw has a means to tighten it right on the shifter & sometimes you need a screwdriver. Whatever the method, this screw is not as tight as it should be & the friction at the lever is not enough to overcome the derailleurs spring pressure. This means that the derailleur simply obeys the stronger force, that being the spring, & returns to the higher gear position. [smaller sprocket]
Like all springs, it's power or strength diminishes as it gets closer to it's 'at rest' position & there may be enough friction in the shift lever to prevent it from going all the way to the smallest sprocket.
The Fix
Tighten the central screw in the shifter a little to see if it helps as this should increase the friction, but not too much as it makes it harder to shift, so the right tension is a setting where the friction is just enough to hold the derailleur in the lowest gear [largest sprocket,.... next to the spokes]
If this doesn't fix it, come back to us with a make of the shifter. You never know, new parts may be available or someone may have another to swap over.
Carbine & SJH cycles, & Quicksilver BMX
Now that's AUSTRALIAN to the core.
