There are few things that will affect a bicycle’s mechanical shifting as much as the cables. Get one little thing wrong and your bike can shift horribly until that tiny mistake is fixed. In many cases, the affect may be worse; it’ll be minor. Not enough to bother with changing the cable, but the bike just doesn’t quite shift as well as it should. Even something as simple as a frayed cable end can pooch your shifting. Relax, though, even the vaunted internally routed shifting cable is fixable in minutes with the right tools, equipment and knowhow.
A front derailleur’s main cable problems that will require a new cable are:
- The cable was installed/looped incorrectly at the derailleur bolt which can cause the cable to fray when it’s tightened down, among other problems. If the cable is frayed at the bolt this can/will cause the pull to be slightly off when the shifter is engaged and this will cause problems in shifting and adjusting the derailleur. A frayed cable can even affect the trim feature in your shift levers, meaning you’ll get chain rub on the derailleur cage at the big and/or little cogs of the cassette (you’ll likely think this is a set screw problem… check for a frayed cable where the cable is clamped to the derailleur, first).
- A kinked cable… if your shift cable is kinked, shift quality will be affected – and the cable can also kink inside the shift lever if cables aren’t changed every couple of years or so (the end can also break off inside the shifter which is not good).
- The cable/housing is old, rusted, dirty, grimy, etc. etc. Dirt, grim or rust will cause the cable to develop friction in the housing which will ruin shift quality.
- As a bonus, if the housings are too long or too short, this can adversely affect shift quality, but this gets a little tricky in that the shifting problems aren’t glaring. A bit slow going up the cassette, or maybe down… often just enough to make you wonder what’s going on.
A rear derailleur’s cable issues are a little more diverse. They are:
- See 1 through 4 above.
- The housing loop at the rear of the bike is too big or too small.
- The cable guide(s) are gummed up underneath the bottom bracket (sports drink leakage and sweat are the main culprits here).
- Item 1 is particularly daunting with the rear derailleur. The cable must be on the correct side of the screw for the derailleur to work properly. Typically, look for a little groove for the cable to rest in on the derailleur nub where the bolt goes into. Look up your derailleur type and download the setup instructions if you’re not sure. I searched “Shimano 105 10sp Rear Derailleur installation instructions”:
Now all that’s left is to complete the switch of an offending cable. First, if you can afford a few extra bucks for better cables, I recommend the stainless steel cables. They’re the cat’s pajamas and improve shifting immensely. To me, they’re well worth the money. Second, for interior cable routing I like to use cable liner (not cable housing, cable liner) to make the process painless and simple (amazingly so). I’ve got a 10 meter roll of the stuff and use it often.
First, we’re going to undo the bar tape down to just under the hood. There’s no need to unwrap any further – all you’re looking for is access to the bottom of the hood, where the cable housing enters the hood lever body. This is easier if you’ve got access and can see what you’re doing. Next, undo the cable from the derailleur and if there’s a frayed end, snip it off far enough up that you hit good cable. Then, slide the cable liner over the cable and keep feeding it till the liner comes out the other hole in the frame. If the liner won’t easily feed over the cable, you can fasten the liner to the cable with a piece of electrical tape and pull the cable and liner through that way. Tape the liner to both holes where it enters and exits the frame to secure it. Next, with your hood rolled up from the bottom, feed the cable out paying attention to the hole where the cable will go back in. This step will vary between shifters – if you run into questions, search online for the owner’s manual for your shifters.
With the old cable out, take some light lube on your fingers and wipe down the new cable (this step can be skipped if using stainless cables – most manufacturers actually recommend not using a light lube on the cable with new housing – this might need its own post and a pro interview it’s so controversial). Feed the end into the lever hole until it pops up by the cable housing end. This can be a touch on the tricky side getting the angle right. Then, carefully guide the cable end into the housing – I like to use an ultra-thin pair of needle-nosed pliers, they guide the end of the cable perfectly into the housing so I don’t have to mess with pulling the housing from the hood to guide the cable in by hand (a 2 mm hex key works well, also). Once your cable is through the first section of housing, you simply run the cable through the liner you ran through the frame earlier. You don’t have to worry about fishing for the wire or using magnets (and good luck with a magnet and stainless steel btw). Properly connect your cable to the derailleur and adjust the barrel or in-line adjuster. Wrap your bar back up, clean up, and Bob shall be your uncle.
Changing a cable is a daunting task when you’re new to bike repair. It’s a scary undertaking. You will improve with practice, though. New cables used to take me hours – it was a task reserved for a rainy weekend day when I had a clear stretch of time. After years of practice, I can change a shifter cable after work and before my regular evening ride.