Rear Derailleur - Mountain Bike Zen
Rear Derailleur
You are likely to need to adjust your derailleurs from time to time as your gears can get knocked quite alot from riding, falls, and transportation.
Your gears will need attention if your gear changes are constantly clunky, you hear chain noise when in a gear that should run smoothly, your chain keeps falling off when in your highest or lowest gear, or worse - you cannot access a gear at all.
First check your cable - if this looks damaged or defunct it may need replacing. You also need to check the chain, watch your rear derailleur while turning the crank, if you see a jerk from the rear derailleur check the chain for `
Minor adjustments can be made using the barrell adjuster which is found at the end of the cable shaft next to the rear derailleur. If you are having problems with the gears changing up then you need to tighten the cable - you can do this by turning the rear barrell adjuster anti-clockwise. For problems with gear changes down then you need to loosen the cable a little by turning the barrell adjuster clockwise.
If this does not solve your problem then you need to proceed to a more advanced level of adjustement. When changing gear to the lowest gear, if you find the chain jumps off into the spokes then you need to use your low gear adjustment screw. You will find two screws on the derailleur that are labelled H and L. H is for high gear and L is for low gear. If your chain is jumping over into your spokes you need to turn your L screw clockwise until you reach a point where the chain is resting happily on the largest rear sprocket and no longer wants to jump. Similarly for the highest gear, if the chain is jumpping off or looks like it wants to you need to adjust the H screw to adjust this. You can do this so the rear derailleur hanger is just slightly further out from the bike than the bottom sprocket, turn the screw in quarter turns until you achieve the correct alignment.
If this does not work check your rear derailleur for more severe damage as it may be out of shape, buckled, or seized. This may be repairable by a bike shop or may need replacing.
The you tube video top right of this page is the best resource we can find to give you instruction on rear derailleur adjustment. Don't forget you can pause it!