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/diy/ - Do It Yourself

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The gears in my bike, on the left hand side are a bit defective. Whenever I shift to a higher gear it's fine for a while but then when I stop the hear will quickly snap back to a lower position. Not sure what I should do. It's an old bike and was "fixed" by my dad. Also a couple of times the chain just flew off the gears when I was switching gears. What do.
Probably need to adjust the derailuer. Should be pretty simple.
Well obviously it's not fixed if it's still defective.

you need to understand why its not working properly or needs adjustment. typically derailleurs come out of adjustment because the cable stretches just a little bit, maybe a 1/16 of an inch or a millimeter. This is what your barrel nut adjustment can be used for aside from initial setup.
Here's what you do.

>put your bike up off the ground, if you don't have a bike stand then throw the saddle nose over a low branch and tie it in place
>unseat the cable from the derailleur.
>turn the cable adjustment nuts at both ends of the cable housing all the way in.
>the derailleur has tension to pull to one end of its travel
>pedal the bike to get to the end of its range, be sure to put the chain on the front drive gear in the same end of travel
>i.e. you dont want the chain on the small gear up front and in back.
>your derailleur has two set screws, peak inside to see which one is currently engaged at the furthest end of its travel.
>pedal slowly and observe the chain climbing onto the sprocket, adjust that set screw to make a perfectly straight line for the chain
>shift the shifter into the appropriate position for that gear
>pull the cable tightly through the clamp and tighten the retaining nut
>shift ONE gear while pedaling
>the chain will chatter
>the housing adjustment nuts will allow you to take up this slack. If there are two, one on the derailleur and the shifter, then the derailleur one is course adjustment and the other is fine. If there is only one on the derailleur then ... well there's only one
>adjust the derailleur nut out while pedaling until the chain just jumps into gear
>while pedaling stil shift one more gear
>again adjust the cable nut until it just clicks into place and stays there
>work your way up through all the gears using the adjustments available
>if you're in the big gear up front worry more about the smaller half of the gears in back or vice versa
>once its good, shift to the next gear up front, and back to the resting home position in back
>repeat the shifting cycles and adjust as needed.
>if you've got a triple, shift into the third gear up front and repeat the back sequence
>finally set the second set screw for maximum travel
When you're riding on the small gear up front, stay on the biggest half of your rear cassette. If you're in the middle gear on a triple stay in the middle of the cassette. And when you're on the biggie, stay on the smallest half of the rear. This helps prevent chain and cassette wear to a minimum by keeping a straight line in the chain.
Throw derailleur shit away and install Nexus or whatever planetary gearset.
You're going to have to adjust / tune up the derailleur and/or shifters. It can be finicky and take some time, but it's not hard. I'm not going to write out the whole process here because I'm not sure what your exact problem is and there are lots of possibilities to try, from cleaning dirt out of the cables to adjusting derailleur alignment. Again all easy with minimal tools/skill, difficult to permanently break anything, but takes some time and patience. Go on youtube and watch tutorials or google/read written ones. Or google your symptoms and see if someone on some forum has had the same experience and gotten answers. There's lots of good info online. Look at a few guide then go for it.

The Sheldon Brown website is an excellent resource.

Parktool's "big blue book of bicycle maintenance" is pretty good too.
>The gears in my bike, on the left hand side are a bit defective.

that is simply a bike not worth fixing, even after you adjust it it will come out of adjustment since its poor quality. Go on /n/ ask for advice, you can buy very good used for up to 100$
Above suggestions are good. Also check that the hub, chain and shifter are all still the original ones or at least matched in numbers. i.e. a 9-speeed hub won't work correctly with a 7-speed shifter and the chains are different widths as well, so if your dad swapped in a different rear wheel or chain to 'fix' the bike, it may have left it in a fucked up state.
That screw on the top of your left shifter adjust how strongly it holds position. It sounds like it's too lose. The spring in the derailleur wants to pull into a lower gear; the shifter needs to be stiff enough so that doesn't happen on it's own.

I agree with this guy. It looks like a friction shifter on left and those dont really care much about cable tension. But they are prone to slipping if they arent tightened.

Worst case take it to your LBS. I usually stick a stupid tax on extra work i have to do because someone googled the wrong response and made it worse(on my 9th year in a shop). Dont be the guy to get a stupid tax. This looks like way quick work

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