Buy top quality replacement shift cables and housing
Because it’s the highest quality, works the best and lasts the longest, I recommend using the same brand of cable and housing that came with your bike, which usually means — in alphabetical order: Campagnolo, Shimano or SRAM.
I stick with a brand’s cables and housing because, over the years, I’ve seen many companies introduce supposed “super” bicycle cables that are said to be better than stock cables. Usually, these firms do a great job marketing their better cables and housing, and sometimes they introduce something new and intriguing in the way of features or technology.
However, I’ve purchased, installed and tried just about every one of these “super” cables. And, what I’ve learned from this experience is that the component manufacturers do a better job engineering cables and housing for their own components than outsiders do. Which is why I recommend sticking with the cables made for your components.
Tip: If all you need is the cable (AKA “inner wire”), you can purchase it alone. If you need the housing, too, get a cable and housing set because it will come with the matching cable and housing, plus any ferrules needed for the housing ends, and a cable crimp for the end of the cable to prevent fraying (don’t lose these small parts when you open the package).
Sizing the new cable housing
If the housing section on your bicycle is still in good shape, there’s no need to replace it. Proceed to the Cable Installation section below.
The first step in replacing a shift cable is sizing the housing, which is as easy as matching the length of the old pieces of housing. Be sure to cut the new housing with a cable cutter so that you get a clean, square cut. Cutting usually crushes the end. Poke a sharp tool like an awl in to reopen it.
Trick: If you save some shift cable scraps about 12 inches/30 cm long, you can use them to get square and non-crushed housing cuts every time. Just put the sacrificial cable piece inside the housing and cut/size the housing while the scrap is inside supporting the housing, and the cut will be perfect. Then poke out the remainder of the scrap left inside the housing with the other cable.
You can test your cuts by pushing the new cable into the just-sized housing sections and feeling how smoothly it moves in there. There should be minimal resistance.
Once you’re satisfied with the housing section, install any housing ends required (the ferrules supplied with the housing). Usually, for the housing section that travels from the shifter to the frame, there is only a ferrule on the frame end of the housing. But, look carefully and copy what’s on your bike. Refer to the housing section still on you bike if you’re not sure. On some setups, there might be a perfect-sized holder on the frame for the housing requiring no ferrule.
Tip: Sometimes the new ferrules may not match what’s on the housing section that’s still on your bike (black plastic versus silver metal, for example). If you want matching ferrules, you can usually remove the ones from the old piece of housing and put them on the new one. This is another advantage of using stock cables. With a different brand, the ferrules may not fit the housing.
Grease the head of the new shift cable so that it won’t get stuck inside the shifter and feed the new cable through the shift lever. If you can’t see the cable holder inside the lever, operate the lever as if you were shifting onto your smallest cassette cog and the holder will come into view.
As you feed the new cable through the lever, pay attention that the cable goes into its holder inside the lever and travels the right path out of the lever on its way to the housing section. Once in place, you can pull on the cable and operate the shifter and test that all’s well.
Tip: Most housing is lined with friction-reducing plastic, but it’s still a good idea for performance and longevity to lubricate the cables with a light lube like Tri-Flow. Also, be sure to lube the housing ends so they don’t get stuck in frame housing stops/holders.
Thread the new cable through the housing sections and frame stops in the correct order and path all the way to the rear derailleur. Before pushing the cable through the derailleur anchor bolt pinch point, wipe off any lube on the cable.
Feeding cables through housing beneath tape
If your housing section is wrapped beneath the handlebar tape, a trick that can help get the cable to make it around all the bends in the trapped piece of housing is to twist/spin the cable between your thumb and forefinger as you feed it through. Sometimes it takes a few tries, twisting and pulling and pushing, but if you’re lucky it’ll keep feeding into the housing and come out the end and you won’t have to remove the tape and housing section.
Tip: If you can’t get the cable through, try bending its end into a slight curve. Sometimes, the cable is too stiff and straight on the end, and if you put a bend in it, it helps it follow the curved housing path beneath the handlebar tape.
Attach the shift cable
When the cable is in place, check carefully that all the housing ends are in place on the housing, that the ends are firmly seated in any frame stops and that the cable is routed correctly. Then, pull on the end of the shift cable with pliers to remove any slack and tighten the derailleur cable anchor bolt.
New cables can stretch a little at first, and the housing sections can compress and seat into the end caps, which can create slack. So shift repeatedly to get this to happen. Then use your adjustment barrel to remove the slack and perfect the shifting.
If a lot of slack is created during this cable breaking-in process, you’ll want to loosen the derailleur anchor bolt and remove the cable slack rather than use up most of the barrel adjuster’s range to address it (save that for fine adjustments as needed later).
The finishing touch is to trim the cable to a nice length (match the front cable) and install the cable end to prevent fraying. Use pliers to crimp the cable end in place.
Now, go enjoy your perfectly shifting bicycle!