Workshop: How to replace internally routed cables

Handy five-step guide

Does the prospect of replacing internally routed cables strike fear into your heart? Worry not – our mechanic George Ramelkamp's five-step guide will ensure the process is trouble-free.

When replacing internally routed cables, the trick is to have something threaded through the frame at all times that can be used as a guide.

1 Can you re-use old outer cable?

Check the old outer cable (the plastic coated housing). If it's in good condition you can re-use it. If this is the case, remove the old inner cable (the wire which goes through the brake lever or shifter and gets pinched by the anchor bolt), but not the outer. If the inner cable is damaged, cut off the offending bit first with a pair of wire cutters.

If the old outer is corroded or damaged in any way (including the Teflon liner) you'll need to replace it. In that case, you can either follow the step above or remove the old outer first and keep the old inner routed through the frame. Make sure it’s long enough and trim off any kinks or frayed sections from the old anchor bolt zone that might hook themselves on the way out.

2 Don't get caught out!

Avoid making the mistake of taking everything out! If you left the old outer in place, simply insert the new inner cable – a dose of oil or light grease keeps it running smoothly.

If the old outer needs replacing, make sure you leave the new inner routed through the frame when you pull the outer out. Then slide the new outer over the top. Add a few drops of oil with new outer.

If you left the old inner in place, simply slide the new outer over the top. Once that is in place you can then pull out the old inner and replace it with a new cable.

3 Make sure you have the right outer

Brake outer differs from gear outer with its tighter, corkscrew spiral winding, giving it more flexibility and greater resistance to fraying under high loads.

Derailleur cable inner is narrower (often 1.2mm), and the outer is a different structure: the cable wires are wound in a gentle helix, and resist compression. They’re called compression-less or “SIS” outer (Shimano Indexing System). Never use SIS gear outer on brakes.

Cap off outer cables with a ferrule (metal or plastic cap) whenever possible. Inner cable ends should be crimped to stop fraying. Use a rubber cable wiper wherever you can, at transitions between exposed cables and their entrance to the outer.

4 Cyclist's little helper

Carbon frames can be difficult, especially those with no internal guides, because of the debris left behind by the manufacturing process; bits of plastic bladder, uncompressed strips of carbon and other obstacles will conspire to block the cable’s path. A length of welding rod makes the perfect cyclist’s helper for threading through cables.

Available from any good engineering or hardware supply store, a 1.6mm copper rod will set you back 20p for a length about 3ft/1m long. A stretch of Teflon liner salvaged from a brake outer kit will fit perfectly over the rod, and can be threaded through the frame as pictured below. With the liner in place, you can then run an inner wire through it.

5 Go fish!

While the rod makes it easier to poke through obstructions, sometimes you end up having to go fishing. Poke the cable through the frame and hook it as pictured below; the perfect tool for this is a simple spoke, which you can shape a bit if needed.

Exit holes on frames will often have a guide or cap, which reduces the size of the hole and tidies everything up, eliminating noise by holding on to the outer. These can sometimes be removed on certain frames; you’ll need to look for them first, since their removal will make the job of threading cables a lot easier. They either slot into the oval hole in the frame tube or are held in place by a very small grub screw – usually a 2mm or 2.5mm Allen screw.

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