22. How to Replace Cable Housings
Measure, cut, lubricate and replace your old seized or damaged cable housings.
If your cable housing is old and stiff, or damaged, it's a good idea to replace them to improve your braking and shifting. So how do you know how much length you will need? It's easy if your old cables are still attached as you can simply measure them, but sometimes you’ll need to measure them manually.
It's quite difficult to evenly cut cable housings with regular pliers, so I'd recommend picking up a proper cable cutter before you begin. However, you will need some regular cutters on hand to cut off any sheared spiral housings, and a scribe or some kind of sharp poking device is handy to poke out the inner lining clear. You'll also need to install ferrules on each end of your housing, so you'll need two for each section of housing.
It's also very important to know that there is a big difference between brake and shift housings. Brake cable housings have a coiled metal spiral embedded in them, while compressionless shift cables have a series of tiny round wires running parallel along the length of housing. If you were to use brake cable housings on shift cables the result would be very poor shifting.
As I mentioned before, if your old housings are intact you can simply take them off and measure them for the exact replacement length. However, if there are no existing housings, you'll have to buy more than you think you'll need and then trim it down. For example, if I needed to replace the rear derailleur housing, I would take a ruler and move it along the estimated path and then add another few inches just to be safe.
Housings should make a smooth curve, with no sharp bends. For example, the length shown here is ideal. This would be too short, and this would be too long. The sections that run from your handlebar to your frame shouldn't be too long, but there should be enough room to turn the handlebar all the way in both directions.
Once you've measured twice, cut the housing clean across using the cable cutter. The inner spiral on brake housings will sometimes shear leaving some metal poking out. Trim this with your wire cutters until the end is flush. Then clear a hole in the plastic lining with your poker. Shift cables usually cut clean and just need the lining poked through.
Once all of your housing sections are cut and trimmed, slide a ferrule on the end of each. I like to also squirt a drop of Tri-Flow into the housings to keep them operating smoothly. Now you're ready to install the housings and reinstall the inner cables. I'll demonstrate how to replace your inner cables in an upcoming tutorial.