Cable Replacement Made Easy

Let’s face it, the thought of getting new gear cables fitted doesn’t really get the blood pumping. In the bike-glamour stakes it rates right alongside buying a spare inner tube and most would be far more excited at the prospect of upgrading their run of the mill derailleur to a bling XX or XTR unit. In reality, replacing moderately worn cables will provide a far bigger performance improvement than swapping from an X.7 or SLX derailleur to a range-topping model. With worn cables, it becomes harder to push the shift lever when selecting an easier gear on the rear cassette and the indexed ‘click’ that accompanies a shift gets lost with the cable added friction. Upshifts become slower and less precise as the derailleur spring struggles to pull the cable back through the outer housing. Of course this wear usually doesn’t happen overnight; it comes on progressively and often goes unnoticed until you get a new cable and realise how much better your shifting should be!

If you’re going to the trouble of fitting new cable, it’s important that you don’t cut corners—replace both the outer casing and the inner wire or you’re pretty much wasting your time. Some inner wires may feature special slippery coatings but it’s the outer that really makes a difference. Modern gear housing is lined with low friction material; it’s the nylon sleeve that you’ll see inside when cutting the outer cable. This material helps the inner wire slide smoothly but it also wears out over time. The wear accelerates rapidly if you get dirt inside the casing—something you’ll discover soon enough if you do a few wet and muddy rides.

If you’re getting a store to do this, make sure that you ask them to renew both the inner cable and the housing. With a good set of bike-specific cable cutters and a few common tools (plus a little patience) it’s easy enough to do it yourself. We’re focusing on replacing the rear derailleur as it’s the most frequently used, therefore the first to wear out, and with numerous small movements it’s the most likely to suffer a performance drop due to cable friction. If you do need to replace the front derailleur cable, the procedure is very similar. 

Before you get stuck into removing the old cables, survey your existing setup. Make sure that you are happy with the cable lengths and that nothing is wearing due to cable-rub. New bikes are commonly delivered with a bird’s nest of ugly over-length cables. On the other hand, fitting wider handlebars and other modifications can leave you with cables that are too short. In either case, this is your chance to get it right and tidy things up. In general, you want the cables long enough to allow for turning the bars all the way in either direction, as well as taking any suspension movement into account. It’s also important to route the cables to avoid excessive rubbing on the frame—you may be surprised how much a rubbing cable can damage a metal frame over time. Aim for gently radiused curves without excessive length.

Release all the tension from your gear cables by shifting into the smallest cog. Use your nice sharp cable cutters to snip off the cable end—that’s the small alloy cap that stops the cable from unravelling at the end. If there’s no end-cap, just snip off any frayed cable so it slides out easily (this will also ensure that you don’t jab yourself). Take note of how the cable is routed within the derailleur and which side of the anchor bolt it sits (take a photo if you think that you may forget). Now undo the anchor bolt with an appropriately sized allen key or torx tool and pull the inner wire free.

Pull the inner wire through each length of outer housing until you reach the gear lever. If you were happy with the existing routing and cable lengths, place each length off to the side to use as a reference when cutting the new outer housing. Removing the inner wire from the shifter will vary depending on which brand and model you have. On most Shimano Rapidfire units, the cable simply pushes out through a hole (see inset – note that this hole may be hidden under a threaded nylon plug). Current generation SRAM X.5, X.7 and X.9 triggers employ a similar exit-port with a rubber grommet. On the upper-end X.0, XX and XX1 triggers, the entire top cover of the trigger comes off to access the cable. Where you have direct mounting Match Maker clamps and a lack of space between the shifter and brake lever (as was the case here), it may be easiest to unbolt the shifter to gain access to the top cover. In any case, always double-check that the smaller ‘release trigger’ has been pushed a number of times before pushing the inner wire out (it should be in the small-cog position).

If using your old casing lengths as a guide, line them up next to the new outer and cut accordingly. Always use anti-compression gear outer as opposed to the more flexible brake outer. It generally comes in a long length then is cut to size with bicycle specific cable cutters—good quality cutters are very sharp and won’t crush the outer casing. When purchasing the new housing, ensure that you get the end caps to match.

Once you’ve cut the lengths of outer casing, inspect the ends to check that they are nice and square with no splitting in the plastic outer sheath. Also check that the nylon inner part isn’t squashed—open it up with a pointy tool if required (something like a small nail will do the trick). Once the ends are tidy, slip on the end caps. Never use gear outer without the end caps as it will split and break apart.

Wind the barrel adjuster almost all the way in—this can make it a little easier to guide the new inner wire through and means you can take up the slack if the cable stretches over time. Give the small trigger a few presses to ensure that it’s still in the small-cog position and thread the new inner wire through the gear lever (then remount the lever if required). New inner wires are easy to thread through, as the end will be tightly wound and unlikely to fray. It should slip easily through the mechanism but on levers where you have to pass the cable through a small port, it may require a few tries. Never force it through and if it’s proving troublesome, shine a torch back through the barrel adjuster and direct the inner wire towards the light.

With the end caps in place on the outer casing, thread the inner wire through and back to the derailleur. The inner wire should slip through with ease. If there’s excess friction or if the wire sticks at the casing exit, remove the end caps and double-check that the housing isn’t squashed and closed over. The tightly sealed end caps can also cause some restriction and may need sliding on separately. While some people would choose to put oil or grease through the cable housing, I’d be inclined to leave them dry on a mountain bike with split outer hosing. While the lube may make them feel extra nice when new, it’ll also attract dirt which will then speed cable wear. This will be less of an issue on bikes that run full length outer housing—they are better protected from contamination so feel free to lube them up.

Route the inner wire through the derailleur and place it on the correct side of the anchor bolt. Pull the wire snug and go back along the entire length of the cable to check that each section of outer housing is seated properly within the cable stops. Now tighten the anchor bolt whilst gently pulling the slack out of the cable (don’t pull too hard). Whilst it’s not essential at this point, cutting the inner wire will ensure that the excess doesn’t get in the way when adjusting the gears. Use your good cable cutters again and crimp an alloy end cap on the inner wire to stop it fraying.

Now for the gear adjustment… pedal the drivechain forward and click the main trigger once. If it doesn’t shift across to the next cog you’ll need more tension on the cable; turn the barrel adjuster anti-clockwise (when looking from the cable and back towards the shifter). Hit the smaller release trigger and wind the barrel adjuster out a little, then try to shift again. If the derailleur moves the chain more than one cog across, or it shifts one gear but leaves the chain rubbing up against the third cog, back off the cable tension a bit (turn the barrel adjuster clockwise). The aim is to get the chain shifting across to the second cog with one press of the main trigger—it should run smoothly with no rubbing against adjacent cogs. With that first shift sorted, the remaining shifts up the cassette should fall into place. However, if the chain attempts to climb up too far and into a bigger cog, back off the cable tension, and if it fails to shift promptly into a bigger cog, add some cable tension. Once you are familiar with this tuning process, it’s easy to adjust your gears if you need to compensate for cable stretch. Now go ride and enjoy your light and smooth-action gear shifting!

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