If the cable is frayed, kinked, or worn, it probably needs replacing. When you go to buy a new cable, make sure you buy cable and housing (the rubber coated sheath) that is made specifically for derailleurs — it’s normally a little thinner than brake cable, which has to be able to handle greater force.
You’ll be able to tell that it’s derailleur housing because the inner core wires run linearly with the length of the housing, which makes for a much more rigid housing and doesn’t allow any compression, resulting in a more precise shift. Brake cable housing has the inner core wires wound around like a coil, which allows more flexibility in the housing and a more controlled brake-lever feel.
Before you remove the shifter cable, take a moment to observe how it’s routed around the frame of the bike. Pay attention to the location of the cable housing, where the cable housing meets the cable stops, and the how the cable exits on the other side. You’ll need to route the cable and cable housing in the same manner when you reinstall it. You want the housing to be as short as possible. The housing should have gradual curves without any binding or sharp angles.
Follow these steps for removing the derailleur cable:
1. Shift the chain onto the small cog for the rear of the bike or the small chainring for the front.
This will put the index ratcheting system in the relaxed position and allow you to remove the cable.
Very few bicycles have reverse springs in either the front or rear derailleur; if yours does, you’ll need to shift into the large cog or the large chainring to put the derailleur in the relaxed position.
2. Unfasten the derailleur cable by loosening the cable anchor bolt where the cable attaches to the rear or front derailleur.
3. To remove the cable, you need to push it through the other side of the shifter.
To do this, look for where the cable enters the shift lever and pull back on the cable housing to expose the cable
4. For STI shifters, squeeze the brake lever and press the shifter inward at the same time.
This will open up the center core of the shifter where the barrel at the end of the cable is seated. You should be able to see the barrel.
5. Push the cable into the shifter so that the barrel is forced through and out the other side.
Handlebar shifters have different ways of concealing the barrel end of the cable. On some, there may be a screw-in plug or rubber cap that hides the cables. On the popular Shimano STI-style shifter, where the shift lever is integrated into the brake level, the cable runs sideways through the shifter. When the chain is on the smallest gear and you pull back on the brake lever and shift lever at the same time, you can see the barrel on the end of the cable.
Use pliers to grab the barrel and pull the cable the rest of the way out of the lever.
6. Collect any ferrules that were holding the cable housing in place at the anchor points or cable stops.
You’ll use them when you reinstall the cable.
It’s a good practice to change the cable housing when you replace cable wires. Manufacturers often sell cable with the housing included in the package. They normally give you more housing than you need, so you’ll have to cut it to fit your bike.
Follow these steps to install the derailleur cable:
1. To install new cable and housing, you first need to prepare the cable housing.
Assuming that the old housing was the proper length, use the older pieces of cable housing as guides for cutting the new pieces. Use a cable cutter for this procedure — they cut the housing without compressing the end too much.
Even if you use cable cutter, you may need to file the end if it has any sharp edges. You may also need to open up the end of the housing with an awl or another pointed instrument if the end is closed up after cutting.
2. When you’re ready to install the new cable, use a rag to apply a light coating of grease to its surface.
3. For STI-style shifters, squeeze the brake lever, push the shifter to the inside to expose the hole for the cable, and insert the cable.
You may have to wiggle it around to pass it through the shifter.
4. Pull the cable out the other side of the shifter.
Some trigger shifters and most grip shifters will require you to open the shifter body to load the cable. This may be challenging, especially on grip shifters.
5. Attach the ferrules that came with the cable housing to the ends of each piece of housing where needed.
6. Insert the cable into the proper cable housing and pull it out the other end.
7. Route the cable and cable housing around the frame of the bike in the same position as it was before.
The ferrules at the ends of the cable housing should fit snugly into the cable stops on the frame.
8. Run the cable through the cable anchor bolt on whichever derailleur is correct for that cable and tighten the cable anchor bolt.
If you’re installing cables for the first time, they’re likely to stretch a little after you’ve used them. It’s a good idea to shift them though the full range of gears a few times after connecting them. Then pull the cable taut and reconnect the cable anchor bolt if necessary.