Gears Shifting Back

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Gears Shifting Back

Postby kernotmi » Fri Mar 14, 2008 9:19 am

Hi
i am new to this site and to roadcycling and i have been having a bit of a problem with my rear derailer. For some reason when ever i try and shift it up or down it changes gears and then as soon as i let go of the lever it changes back straight away. I have tried searching this problem on this forum and on the internet but i have come up with nothing so far, so if anyone can help me fix this problem it would be very appreciated. :D
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by BNA » Fri Mar 14, 2008 9:47 am

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Postby sogood » Fri Mar 14, 2008 9:47 am

More detail required. Which combo of gears? Any noise? Derailleur adjustments?

Otherwise there's a possibility that your chain is over-worn (stretched) and needs replacing, with or without the cassette.
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Postby Kalgrm » Fri Mar 14, 2008 11:27 am

Hi Kernotmi,

Welcome to the forum.

As sogood said, we need more information. I assume you are pushing the lever beyond the "click". Does this happen when you shift more than one gear at a time (in either direction)

How old is your bike? We know you are new to it, but was it bought recently from a shop (AKA LBS)?

If it is an old bike, you might need to service or replace your gear shifter.

Cheers,
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Re: Gears Shifting Back

Postby Kid_Carbine » Fri Mar 14, 2008 11:41 am

kernotmi wrote:Hi
i am new to this site and to roadcycling and i have been having a bit of a problem with my rear derailer.

For some reason when ever i try and shift it up or down it changes gears and then as soon as i let go of the lever it changes back straight away.

I have tried searching this problem on this forum and on the internet but i have come up with nothing so far, so if anyone can help me fix this problem it would be very appreciated. :D


Let me make sure I understand.
The chain is on a certain sprocket on the rear cluster, lets assume it's the middle one on a 9 speed for example.
Whenever you shift up or down, it shifts to the next sprocket, ... & on releasing the control device, the chain returns to the [nominal] middle sprocket that you just shifted from. In effect, you are stuck on a single sprocket & despite the fact that you can change up or down it always returns to the same one again.
Is this an accurate description of your problem?
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Postby kernotmi » Fri Mar 14, 2008 4:12 pm

My bike is quite old, it is an avanti kona there is no loud noise when i am shifting. What happens is whenever i shift up the chain moves up one sprocket and then moves back down to the same one.
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Postby Hawkeye » Fri Mar 14, 2008 5:03 pm

Do you know if your shifters are indexed or or are they the old friction type?

Indexed shifters have definite detents or clicks at the position for each of the gears. Sometimes found on teh downtube or headtube, they are usually located on the handlebars.

Friction shifters don't have those detents and you have to judge for yourself, usually by listening for quiet operation. When it stops making a racket you're in he right spot. They're usually found on the frame's downtube or headtube.
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Postby Kid_Carbine » Fri Mar 14, 2008 7:34 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.
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Postby kernotmi » Tue Mar 18, 2008 6:32 pm

okay, i will try that and get back to you if i cant figure it out or it doesnt work
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