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So my rear derailleur and front shifter have stopped working together, my shift can shift once up and then nothing. My bike has essentially turned itself into a 2 speed.

The shifter is a 2300 shifter and the derailleur is a 105, both compatible with each other and my 8sp cassette (I know this because it has been working fine for a year).

So the other night I moved my cable because it was kinda blocking my light and then all of a sudden my derailleur and my shifter had disengaged and I was stuck in 1st gear.

I thought possibly the cable had slipped from the rear derailleur and that was the issue so I tried adjusting it with no improvement (in fact I made it slightly worse because I am now stuck in my highest gear).

My question I suppose is, how do I figure out if it is the derailleur or the shifter and does anyone have any idea how to fix it? The shifters seem like black magic since I can't really see what they do and all the mechanisms and screws are hidden away. I may need to replace the cable as I have kinda messed it up and got it all frayed and prickly (lost the nipple), how difficult a job is that?

Cheers

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Replacing a cable is not rocket science, but it requires some mechanical skill and intuition. It's hard to tell what you did to it (did you physically disconnect the cable?) but anytime the cable is disconnected (or somehow loosened such that it's tension changes) then it needs to be re-adjusted. Small adjustments can be performed with the "barrel adjusters" usually found inline in the cables or where the cable exits the shifter. Larger adjustments require loosening the cable clamp and moving the cable in/out. –  Daniel R Hicks May 19 '13 at 20:51
1  
Here is an extensive article on cables, probably more than you wanted to know, and another article on derailer adjustment, probably a better fit for your immediate needs. –  Daniel R Hicks May 19 '13 at 20:55
    
I fitted the new derailleur last year so I know about the indexing and stuff but this was something that left me scratching my head. I read through the article and decided to go check the length of the cable, I think I have managed to snap it inside the shifter, so I need to replace it. Cheers for helping me get there –  mark mcmurray May 19 '13 at 22:51
    
Does the derailleur move enough to the left and the right to hit the sprockets? Does it move freely? It could have been that it was improperly adjusted and you just knocked something loose. Without looking at it I can not tell from here. –  Chris Belsole May 21 '13 at 20:02
    
It's moving within the high and low stop all right, the indexing was a bit dodgy but it was all right too. I am almost 100% its a part of the cable has snapped inside the shifter. –  mark mcmurray May 21 '13 at 20:37

2 Answers 2

If you need to replace the cable, try this:

Shimano 105 Shifter Cable Removal

  1. Take the bike for a short ride and shift into the gear that gives the shifter cable maximum slack. For the front gear shifter, maximum cable slack corresponds with the lowest gear. For the rear gear shifter, maximum cable slack equals the largest gear.

  2. Loosen the bolt on the derailleur that secures the shifter cable with a 5-mm hex wrench. The shifter cable is attached at one end to the Shimano 105 shifter and at the other end to the derailleur.

  3. Cut the metal cap, called the "ferrule," away from the end of the cable, using cable cutters. Grab the cable where it enters the derailleur and pull it free.

  4. Squeeze the shift lever on the Shimano 105 gear shifter to expose the head of the cable. The cable head is located on the side of the top of the shift lever.

  5. Grab a portion of the cable and push it forward, forcing the head of the cable out of the Shimano 105 gear shifter. Grab the head of the cable and pull the cable free.

Shimano 105 Shifter Cable Installation

  1. Thread the replacement shifter cable through the hole in the Shimano 105 gear shifter. This is the same hole from which the old cable emerged. The cable has two ends, with a metal fitting at one end, which is designed to anchor the cable inside the shifter.

  2. Pull the shifter cable taught until the metal fitting is fully anchored.

  3. Pass the cable along the bicycle. The cable follows the exact route of the old shifter cable, passing through the cable housing and cable stops before arriving at the derailleur.

  4. Thread the shifter cable beneath the derailleur bolt and pull the cable tight.

  5. Tighten the derailleur bolt onto the cable, using the 5-mm hex wrench. The cable will be excessively long and will need to be cut.

  6. Cut the cable just past the derailleur bolt, using the cable cutters. Leave enough cable, approximately 2 to 3 inches, to allow for future adjustments of the cable.

  7. Press a new ferrule onto the tip of the cable. Squeeze the ferrule onto the cable using pliers.

from: http://www.ehow.com/how_7706040_replace-shifter-cable-shimano-105.html

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Shimano shifters are notorious for breaking cables off at the head inside the shifter. If all the individual wires that make up the cable completely break off it can be really difficult to to remove the head due to the frayed end. I think there's a good chance that this is what's happened to you. If it has, you'll need need tweezers and/or very slim needle nose pliers and/or metal picks, and a lot of patience to finagle the cable head out of the shifter- there's not a really great way to do it. Once you get it removed, follow the directions in Christopher Scott's answer.

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I've had my GIANT Boulder Shimano shifters snap my cables about four times over the last 5 years. Needle nose pliers will do the job. –  Deesbek Dec 5 '13 at 17:36

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