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  Last updated: 12/6/2009

brake and shifter

Q. I broke a shifter cable this morning and it got me thinking about the brake cables. Given that brakes are critical to safety, should their cables be replaced as a matter of course, say every 12 months or at some mileage interval? My bike is 8 years old but was not ridden much before the last year when I started commuting to work. R.G.

A. (From "If your bike was stored inside during those years of little activity, I bet the brake cables are fine. The things that cause problems are corrosion (from exposure to the elements) and abuse (severe riding or crashing).Shifter cables are more likely to break than brake cables. They get more use because you shift more than you brake. And shifter cables are thinner -- 1.1 or 1.2 mm in diameter vs. 1.6 mm for brake cables. That's a significant difference.

To check your brake cables, squeeze the levers firmly and feel the action. Assuming there are no problems with the levers or calipers, the cable movement should feel silky smooth. If it does, it's unlikely there's cable corrosion or a housing problem.Also check at the sections of uncovered cable, particularly at the anchor bolt where the cable attaches to the brake. Any signs of rusting or fraying? Replace the cable. If not, it's probably fine.

When you replace any cable, be sure to inspect the ends of the housing and anything the cable passes over, under or though. Make sure there aren't burrs or sharp edges that can cause the cable to wear and break.Lubricate the head of the cable (with a dab of grease), the sections that pass inside housing (with drip lube)and those that contact cable guides (drip lube).

You might come across a recommendation to replace cables yearly. However, modern Campagnolo and Shimano cables and housings are so well made that they'll last years longer -- if you lubricate them occasionally and don't abuse the bike."

Adjusting a "stretched" cable.

Have a new bike and the shifting has become a bit balky - the chain isn't climbing onto bigger cassette cogs as quickly or smoothly as it once did? This is a common problem as the gear cable stretches. The fix is easy and you can do it without tools. Look at the rear derailleur. You're almost certain so see a fitting (often called a "barrel") where the cable enters. It can be turned with your fingers to adjust cable tension. To make it properly taut again, turn the barrel half a revolution counterclockwise. Try some shifts (best done with your bike in a repair stand or hanging off your car's bumper rack). Better but not perfect? Give it another half turn. Keep testing until shifts are instant. Don't overdo it and degrade shifts to smaller cogs. If the chain doesn't drop down quickly, you've turned the barrel a bit too far. Back off (clockwise) until you find the sweet spot.

This works for tightening brakes (those cables stretrch too) and the front derailleur as well. A loose cable is common after riding a new bike for a few weeks or replacing your cables.

Replacing brake cables

You can replace your own brake cables. The tools you will need are a

  1. cable cutter
  2. diagonal cutters (for the housing)
  3. an awl
  4. a flat file

The diagonal cutters are for trimming the coiled wire inside the housing if it gets bent when you make the cut. The awl will open the end of the cable housing after it's been cut. Often, cutting the housing crushes the Teflon liner inside so you will use the awl to make it round again (so it doesn't cause any friction). And the flat file will smooth and square off the ends of the housing so it sits flush against frame stops (and so the housing caps seat fully). It's hard to cut housing perfectly square, but it's easy to file ends (don't use a bench grinder on housing ends. It can easily heat and melt the plastic cover and the Teflon liner. Hand filing won't do that.)

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