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Next time you are in the mountains and you hear someone shouting profanities deep in the forest, don’t rush to grab your mobile for a call to the emergency services. It might just be a mountain biker suffering the frustrations of a misbehaving gearshift.
Of all the things that can go wrong with your bike, a badly adjusted gearshift is one of the most frustrating. [Just ask our editor] A misaligned derailleur is like someone nagging over your shoulder as you toil up a steep hill, poised to spit you off at the crucial moment.
Unfortunately, brute force and primal rage rarely work when trying to get your gears to work, so here is the first part of the guide to sorting out some of the common problems:
PROBLEM: STICKY CABLES
Dirty or corroded gear cables are probably the most common cause of gear shift problems, especially for the rear derailleur. Do any of these symptoms sound familiar?
- Gears seem slow to engage with the next sprocket
- Shifting to a bigger sprocket is ok, but won’t shift smoothly to a smaller sprocket
- Shifting to a smaller sprocket is ok, but you have to ‘over-shift’ [push the lever too far] to go to a bigger sprocket
- The lever feels very stiff
FIX: Disconnect the cable and see how easily you can move the cable by hand. The best solution is probably to fit a new inner and outer cable, but if it looks ok, you can pull the inner out and coat it in light oil [WD40 or similar] If the cables are frayed, it’s definitely time to get some new ones, re-fit and re-adjust.
PROBLEM: BENT DERAILLEUR HANGER
If the gears suddenly start to skip or the chain gets jammed between the spokes and largest sprocket, it’s possible that the hanger hit some obstacle and got bent inwards.
FIX: Look in at the rear of the bike to see if the derailleur is in line with the sprocket. If you’re brave enough, just grab the derailleur and gently bend the whole lot straight. But this is very risky, as the hanger might break off in your hand, so if it’s badly bent, or if you’re not willing to take the chance, you’ll have to readjust the ‘L’ screw and cable tension till you can get your bike to a repair shop.
PROBLEM: WORN OUT CHAIN AND SPROCKETS
Chains stretch with use and sprocket teeth get worn into a hook shape. This usually causes the chain to jump or slip a couple of teeth when you pedal hard, most likely when climbing in a low gear. Hooked teeth can also cause the dreaded ‘chain-suck’ - the chain gets dragged up between the cranks and frame near the bottom-bracket.
FIX: When the skipping, jumping and sucking gets too much, it’s time for some more new parts. Keep in mind that a new chain won’t work very well on worn sprockets and an old chain will wear out your new sprockets faster. So buy at least the chain and block together.
PROBLEM: WRONG CHAIN LENGTH
If the chain is too long, the chain will be too loose when using the smaller sprockets. Shifting may be sloppy and the chain might jump off when going over bumpy ground.
If the chain is too short, you may not be able to shift into the largest sprocket on front and rear at the same time. If there is not enough slack, the drive-train comes under a lot of extra stress and the chain may even snap.
FIX: Shift to the largest sprocket on both front and rear derailleurs before fitting the chain. Thread the chain into place and pull it tight with the rear derailleur stretched all the way forward. Allow one extra link and join the chain with a good chain tool. Be careful not to leave a tight link.
On bikes with rear suspension, it is very important to leave extra chain slack, to allow for changes as the rear wheel moves through its travel. If you can’t find some guidelines provided by the frame manufacturer, the best way is to check the tension with the rear shock removed and the suspension compressed fully.
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