liqquid

Hello fellow cyclists,

I recently bought a used bicycle. I learned about gear shifting on the internet and tried it today. I was in a high gear cycling before a hill, and then I immediately twisted the switches to the low gear for the hill and the bike went *CRANK* and the bike stopped. I was puzzled as to what just happened, but I continued my way up the hill in a fairly low gear.

As I rode back home, I discovered the "rear gears" were not responding, but the "front" was fine.
Later on after supper, I played around with the derailer and wheels and came to a conclusion that the rear derailer is not able to shift UP but is able to shift down (I forced the chain onto the smallest sprocket and was able to shift down no problems). I also played with the limit screws which had no affect.

Any help is appreciated, and incase if you need any pictures let me know. Thank you.

BCRider

As a starter to check things I would suggest you find someone to hold up your bike or prop it up or flip it upside down onto the bars and saddle and then while pedalling forward work the gear shifter for the rear and see if the derraileur moves normally or if something odd is happening.

Keep in mind that when on the big ring in front it is not good to shift to the three innermost big sprockets on the rear. And similarly when on the "granny gear" small front ring it is not good to try to use the three smallest front rings. The middle front ring is generally considered to be fine for the whole rear range with the possible exceptions of the smallest and largest but it's not a crime to use them from that middle ring.

If the derraileur isn't moving and shifting the chain smoothly then there is something wrong and it's not the limit screws. Those only affect the derraileur when at the biggest and smallest rear sprockets.

When you say you "forced" it to the smallest rear sprocket why did you have to do that? When you try to shift to that small sprocket does the derraileur not move fully down to that point? Is it moving at all?

liqquid

Yes, I forced it to the smallest sprocket to experiment, and found out that it is able to shift down from there. Shifting up from the bigger sprockets does not work, as the derailer does not move at all.

Day-5

I dont know im not sure but i think that a spring inside the deraileur is broken,..

tippy

... used bike ...

In one shift direction, the derailleur is moved by the shifter pulling on the cable ... which sometimes can overpower sticky cables.
In the other shift direction, the shifter simply releases cable. It is up to the derailleur spring tension to pull the cable back in order to make the shift.

If there is not enough spring tension to overcome the cable friction (ie weak broken spring or large amount of cable friction), the derailleur will not shift correctly (or not at all in that direction).

Do like the other posts have suggested. Check for cable friction and check for derailleur spring strength/function.

RonH

You're hosed.
Take it to a bike shop and if no parts are needed, they'll adjust everything for a few dollars. They'll even let you watch and you can ask questions.

Day-5

Man I think he wants to repare it himself... if he didnt he wouldnt post it to the bike forums..

Joshua A.C. New

Liqquid, you'll want to check out the Park Tool site as well as the compendious and posthumous Sheldon Brown.

It sounds to me like you need new cables, though. Not a big deal. First time, that's maybe a 45 minute job with no specialized tools required.

BCRider

If the rear derrailleur is not returning to the smallest sprocket then it could be a few things.

• Loosen the cable from the clamp screw on the derraileur. Pull on the end of the cable while shifting at the bars. Can you feel the cable moving in and out as you shift each way? If not then your shifter is busted.
• The shifter cable often has smaller sections of housing with exposed cables between. Unhook these sections and make sure the cable moves very freely in the housings. If they stick enough that you can't easily push the cable through then you need new cable and housing.
• With the cable disconnnected lever the derraileur over to the biggest rear sprocket while pedalling. The chain should follow up and run on the big sprocket. Now let go while still pedalling. The derraileur arms should pull to the outside taking the chain with it and end up running on the small outer sprocket. On the slight chance that your derraileur is one of the oddball Rapid Rise ones do this last test backwards by forcing the derraileur to the smallest sprocket and then let go. Does it shift all the way in to the big rear sprocket?
• If the derraileur didn't pass the second test and it just sits there when you let go then the return spring in the derraileur is busted. At this point the quick and easy fix is to buy a new derraileur rather than fuss with trying to replace the spring but it's your dollar. Whichever compromise between riding and waiting and spending you want.

If it turns out that your rear derraileur IS one of the rare Rapid Rise ones I believe that those needed a special Rapid Rise shifter. If someone slapped on a part at either end just to sell the bike they may be mismatched. The shifter used for normal "spring to the outside" derraileurs pulls the cable shorter as you shift to a bigger number.

liqquid

Thanks for the help. The spring inside the derailer is completely gone. Unfortunately, I now need to buy a new bike since a new derailer costs the price of my bike.

Now I don't know why the spring broke because the bike is old or my shifting was careless.

defiancecp

Really? You can find "OK" rear derailleurs for as little as $15-$20... Must've got a pretty good deal on the bike! I think if it were me I'd fix it anyway