Over time gear cables can stretch. This will make gear shifting less smooth. If your shifting is feeling sluggish then it can be a good idea to replace the gear cable.
Note that it’s very important to not attempt this repair with a cheap pair of cable cutters. Gear cables in particular fray very easily and this will cause problems in your shifting.
Once again, special thanks to Lunar Cycles in Kentish Town for helping to demonstrate this repair. It will be added to the Bike Doctor app soon.
What you’ll need
- New gear cable – often cheapest to buy from the bike shop
- New housing (optional) – if there are kinks in the cable housing then it’s a good idea to replace them.
- Allen key
- Good quality cable cutters
How to replace a gear cable
1. Shift in to the smallest cog on the cassette. Release the old cable by undoing the clamp bolt on the rear derailleur.
2. Use a pair of cable cutters to cut the cable so that you can slide it out easily. Thread the cable through the system to remove it. Keep the outer housing to re-use it if it’s still in good condition or to measure the length of the new housing.
3. Remove the cable cover. This may require undoing one or two small screws holding it in place. Remember to re-install this after the repair is complete as it is important for prevent dirt from entering the system.
4. Push the cable out and release it from the clamp.
5. Reset both the barrel adjusters all the way in by turning them in a clockwise direction. When they are fully wound in, turn them back by half a turn. This ensures the adjusters don’t seize and also leaves you a little space for small tweaks. Spray GT-85 lube through the barrel adjusters on the derailleur and the shifter. This will clear out any dirt.
6. If you are also replacing the cable housing then use your existing housing to measure the new ones. Cut them to size using a quality pair of cable cutters. You may need to use a small screwdriver to prise apart the ends if they get squashed.
Thread your new cable in to the shifter being careful to not get it caught as you slide it in. Rotating it gently can help it slide in to position more easily.
7. If you are replacing the housing or you are replacing the ferrules at the end of the housing, then now is a good moment to fit these in to position.
Add some wet lubricant to the end of the gear cable and slide it through the cable housing. Note that some of the more expensive gear cable systems come pre-lubricated. The lubricant prevents the cable from getting stuck or seized up.
Thread the cable through the housing, the barrel adjuster and beneath the cable clamp bolt. Make sure it is tightly pulled and then loosely tighten the bolt to hold the cable in place.
8. You need to pre-stretch the gear cable. Do this by pulling a large exposed area of the cable. This will bed the system in to place, before making the final adjustments. Check that there is no slack in the cable. If there is, loosen the cable clamp bolt, pull the cable through tightly and then loosely tighten in.
9. Shift in to the smallest cog on the cassette. This will cause the cable to be fully extended to allow you to set the high limit. If as you pedal it feels as though the chain is trying to fall off the cassette then you can adjust the H screw. Check that the chain line is correct and adjust the derailleur if necessary.
10. Shift into the largest cog of the cassette. Now it’s time to adjust the lower limit screw. This will (hopefully) be labelled “L”. The screw will need to be adjusted to prevent the chain from falling off the top of the cassette. Test you’ve made the correct adjustment by pushing the rear derailleur with your hand to test whether it’s possible for the chain to fall off the end.
11. Now, it’s time to adjust the gears to be sure you can get the full range of them.
Shift back down in to the smallest cog of the cassette. Then, shift up one gear. If your chain doesn’t move across then you’ll need to add tension. Do this by turning the barrel adjuster by a quarter of a turn, anti-clockwise. Then, repeat the shift. Keep adding tension if the gears are not smoothly shifting. Remember to make changes in small increments.
If the chain shifts too far across and skips a cog, you need to reduce the tension. Do this by turning the barrel adjuster clockwise.
Repeat this until the gears are fully adjusted.
12. Finally, check that the cable clamp bolt is fully tightened. Cut away any excess cable and fit a ferrule to the end.
That’s how you replace a gear cable. Any questions, please feel free to leave a comment below!
You may also be interested in these repairs:
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As seen on The Guardian, BBC and The Independent.