My Rear Derailleur Won't Shift Down

Written by matthew ferguson
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My Rear Derailleur Won't Shift Down
A rear derailleur requires proper cable tension to down shift. (a downhill mountainbike gear wheel and gearshift mechanism image by Stephen Gibson from

A cable attaches a bicycle rear derailleur to a hand control, called a shifter. When shifting gears, tension on the derailleur cable will either increases or decrease, depending on the gear desired. The sudden change in cable tension causes the derailleur and chain to suddenly pivot to the selected gear. When shifting down to an easier gear, the derailleur positions the chain onto a sprocket closer to the inside of the bicycle. These sprockets are larger but produce a smaller gear ratio, allowing for easier pedalling. The derailleur will fail to pivot in this direction, however, if cable tension is inadequate.

Skill level:

Things you need

  • 5mm Allen key

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  1. 1

    Use the rear gear shifter, on the right side of the handlebar, to shift the derailleur and chain to smallest rear sprocket. To complete the shift, lift the rear of the bicycle and turn the pedals forward.

  2. 2

    Lean the left, non-drive side of the bicycle against a stable surface, such as a wall.

  3. 3

    Identify the derailleur cable pinch bolt on the underside of the rear derailleur. This bolt attaches the cable to the derailleur.

  4. 4

    Use a 5mm Allen key and loosen the pinch bolt, causing the cable to go slack.

  5. 5

    Locate the barrel-shaped nut at the rear of the derailleur. The cable passes through this nut before entering the derailleur.

  6. 6

    Twist the barrel-shaped nut clockwise until it stops. Then turn the barrel-shaped nut two times in the opposite, counterclockwise direction.

  7. 7

    Pinch the end of the cable and pull it tight. Use the 5mm Allen key to tighten the anchor bolt back onto the cable.

  8. 8

    Use the rear gear shifter to pivot the derailleur and chain onto the next largest sprocket over. As in Step 1, turn the pedals forward to complete the shift.

  9. 9

    Turn the barrel-shaped nut counterclockwise if the derailleur and chain failed to shift onto the sprocket. Try shifting again.

  10. 10

    Shift the derailleur and chain onto each of the successive sprockets. Whenever the derailleur and chain fail to respond, turn the barrel-shaped nut counterclockwise as needed. Turning the barrel-shaped nut in this direction adds tension to the cable.

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