Maintenance Monday’s – Drivetrain Issues (Gears)

Drivetrains are one of the most vital aspects of any bike, and to a lot of us gears in particular can seem extremely complex. In reality gears are a relatively simple piece of kit once you understand how they work. There are a few initial check that should be done that are often the cause for a lot of shifting issues:

  • Check your inner cables are well lubricated. If your inner cables are creating friction against the housing you’ll never achieve instant changes, use a water displacing lubricant on the inside of the housing to ensure they’re running smooth and replace any visibly worn cables.
  • Hanger alignment – your rear mech is connected to the frame by a hanger, if this is bent or damaged your shifting will begin to fail until it’s replaced.
  • Wheel alignment – often overlooked, if your wheel isn’t sat straight in the drop outs or is out of alignment, this will wreak havoc with your gears.
  • Chain wear – if you’ve put some miles on your current chain it’s worth investing in a wear indicator. As the pins begin to wear down over time and create stretch in the chain, this will damage other components and cause you to drop a chain

Shifting Issues

By understanding the following key points it can be easier than you think to diagnose your shifting issues.

  • Drivetrains rely on cable tension to work correctly
  • Gears must be indexed to achieve accurate shifting
  • Alignment must be correct for gears to work sufficiently

There are a few key words in there that may seem daunting so let’s explain further.

Tension

Your standard drivetrain is key to making sure you can cycle through a range of gears to adjust your speed whilst riding. The Rear and Front (if you run 2X or 3X) Derailleur or ‘Mech’ is a cage that uses springs to cycle through a range of chainrings. The mech moves by connecting to your shifter via a cable. This cable must be tensioned correctly to make sure that the correct amount of movement is allowed between each gear.

Adjusting Tension

The most common reason why cable tension is incorrect is due to ‘cable stretch’. After some use, new cables tend to relax leaving some play in the system. To resolve this, use the barrel adjust on your shifter, by turning this anti-clockwise you can re-apply tension to the system. If your barrel adjuster is already unscrewed as far as it’ll go, the method would be to shift into the highest gear, reset your barrel adjust to 2 turns off all the way in, then pull the cable taught by the mech and retighten.

If your up shifts are slow it’s likely there’s not enough tension in the system, alternately if downshifting seems slow this may be too much tension. Use your barrel adjuster to find a happy medium.

How to Index your Gears (Alignment)

If you’ve already checked (and more importantly adjusted) your cable tension, lubrication and mech hanger, it’s definitely worth re-indexing your gears

Firstly make sure your limit screws are set correctly by manually moving the cage gently to each extreme and making sure that it doesn’t carry the chain over your largest chain ring into your wheel, or off the smallest cog. If this needs adjusting then have a play with the limit screws until this is correct. More on this further down

If you run a 2X or 3X set up make sure you’re in the smallest or middle chainring you front. Using your shifter move into the smallest chain ring (highest gear) then loosen the retention screw so you can pull the cable taught then tighten the retention screw. Slowly rotate your pedals whilst manually pushing the cage so your chain moves into the second smallest gear. Re tension the cable and then let go of the cage, and as you’re pedalling you should see the chain move back into the highest gear.

Use your barrel adjuster and shifter to find that sweet spot in cable tension between the smallest and second smallest cog, this is when it runs smooth In the second smallest without jumping up an extra gear. You should be able to cycle correctly through each gear.

Limit Screws

Your derailleur system uses ‘limit screws’ to restrict the movement of the mech, stopping it from tangling with your wheel or going too far away from the bike and dropping a chain. Limit screws are usually located next to each other on the mech and can be identified by ‘L’ and ‘H’ to indicate the lower and higher limit.

Starting with the lower limit (largest cog) screw this all the way in to ‘limit’ the movement of the mech. You’ll then need to manually move the mech towards the largest cog whilst turning the cranks, you want to adjust the limit screw by bringing it back out as you go until you can move the cranks and the chain sits comfortably in the largest cog without slipping.

Higher limit screws are set using the same logic reversed. So you want to unscrew this all the way so there is essentially no limit, then gently move the mech as far away from the bike as you can with your hands whilst turning the cranks. Now begin to tighten the limit screw until the chain sits comfortably in the smallest cog.

Make sure your jockey wheels have the correct clearance from the cassette by using the B-adjust screw and if you have one, a guide provided by the component manufacturer.

The B tension determines the amount of space between your top jockey wheel and the cassette teeth. In the highest gear this should be around 2mm unless manufacturers specifications say otherwise. Adjust this by tightening the screw to increase the gap and loosening it to decrease the gap.


This guide should give you all the knowledge you need to adjust your gears, be sure to watch your fingers near moving parts and if you’re unsure show some love to your local bike shop or drop us a line with any questions!

Happy Trails – Ben

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