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How to Adjust the bike rear derailleur ?

If you find that your chain is jumping back and forth between gears or getting stuck on a cog and needs an extra click or two to shift, you need to make an adjustment to your rear derailleur.

The easiest way to recognize that your derailleur needs adjustment is a rattling or clanking noise from the chain when you’re pedaling.

Here’s how to adjust the rear derailleur:

1. Use a bike stand or other mechanism to support the bike with the back wheel off the ground. You’ll need to pedal the bike with one hand and shift with the other, so having the bike up off the ground is essential.

2. Start by examining how well the derailleur shifts to lower gears or to the larger cogs: Shift the derailleur until it moves the chain onto the largest cog. If it struggles to reach the largest cog, loosen the L-limit screw by a quarter- or half-turn until the chain easily reaches the largest cog. If the chain goes over the cog, tighten the L-limit screw to restrict the movement of the derailleur.

3. Shift the derailleur in the opposite direction to the higher gears, focusing on how well the chain shifts onto the smallest cog. If it hesitates to drop down, loosen the H-limit screw by a quarter- or half-turn until the chain sits easily on the smallest cog. If the chain is thrown off the freewheel to the outside, tighten the H-limit screw.

4. After the limits for the derailleur have been set, shift through all the gears, making sure that the chain moves to another cog with each click of the shift lever. If the chain hesitates or makes a lot of noise, you’ll need to use the barrel adjuster to do some fine-tuning: Start with the chain on the smallest cog and, while pedaling, shift one click. The derailleur should move the chain instantly to the next cog. If it doesn’t, turn the barrel adjuster about a quarter of a turn counterclockwise. If the opposite problem is true and the chain shifted two places, turn the barrel clockwise. Repeat this procedure for each of the cogs on the freewheel until the chain is shifting smoothly for each click of the shifter.

If the derailleur is shifting well going up to the larger cogs and slow or hesitating coming down to the smaller cogs there may be a kink or problem with the cable not moving smoothly through the housing. Remove the cable, inspect it, and replace it if it is kinked, frayed, or damaged.

The rear derailleur is a very exposed part of the bike and is prone to being bent or damaged if the bike falls over on top of it. If this happens, all you may need to do is bend the derailleur back into shape. Here’s how:

1. Use one hand to insert an Allen wrench into the mounting bolt.

2. With the other hand wrapped around the body of the derailleur, leverage the derailleur back into place so it’s suspended in a straight line under one of the cogs.

If you have problems aligning your derailleur, make a visit to your local bike shop. Most shops have a specialty tool called a derailleur hanger alignment tool, which is made to perform this task and measure the positioning.

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