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8 reasons of a rear derailleur not shifting to lowest or highest gear

I’ve restored quite a number of bikes and the most important issue you can run into is of a rear derailleur not shifting or not shifting properly to either the lowest or highest gear. So in this article I’m going over everything I encountered that can cause issues with your rear derailleur and how to fix them.

I’m going into a couple of more exotic issues than simply correctly setting up the cable tension on a completely new drivetrain. Some of you might have older bikes with varying degrees of wear and tear, which might cause different issues.

1. Clean your drivetrain

rear derailleur 1

The first thing you need to look into is also the most obvious one, and that is that you have to make sure that your drivetrain is clean.

It goes without saying that a dirty drivetrain can cause all kinds of issues with shifting. And whether it’s your chain, your rear derailleur, or your cassette, the dirtier your drivetrain the higher the likelihood of your rear derailleur not shifting correctly.

best bicycle chain cleaner

I always take apart the entire drivetrain for an initial deep cleaning when I start with a new restoration project. If you don’t want to or you can’t because you don’t have the necessary tools, you might consider buying a chain cleaner tool and a brush.

2. Ensure your derailleur cable is correctly configured

rear derailleur2

Index shifters shift at predetermined intervals. A cable pull at the shifter represents a certain amount of movement up or down the cassette at the level of the rear derailleur.

If there’s not enough initial tension on the shifter cable it could mean pulling the shifter first takes up cable slack before moving the rear derailleur.

Another thing could be that there is an ever so slight misalignment of the rear derailleur with the sprockets of the cassette. Especially with big jumps between sprockets and moving to a lower gear this could result in the chain not jumping to the sprocket it’s supposed to.

By applying or releasing tension to the shifter cable you’re able to take up cable slack and/or correctly realigning the rear derailleur. This can usually be achieved at 3 points which are:

  • Mounting point at the rear derailleur
  • Barrel adjuster at rear derailleur
  • Barrel adjuster at shifter

Use the barrel adjusters after you’ve set the initial cable tension, not the other way ’round.

3. Ensure your limit screws are correctly configured

limit screws rear derailleur

There are 3 screws on your rear derailleur, 2 of them are limit screws and sit next to each other. They “limit” the extent of movement at the extremes of the cassette, left and right.

This is to prevent the chain from being moved off either the smallest or largest cog and causing havoc. Either by getting jammed in between spokes and cassette or frame and cassette.

If you have trouble moving the chain on one or both of these sprockets, give the rear derailleur more wiggle room by moving the correct screw outward until the chain is able to correctly move onto the cog.

4. Ensure your b-screw is correctly configured

b-screw rear derailleur

The b-screw configures how far the guide pulley sits from the cog. When screwed more inward it moves the guide pulley away from the cogs. More outward means the guide pulley moves closer to the cogs.

Usually this setting is only an issue when you change the cassette and the largest sprocket is either larger or smaller than what was on the original cassette.

A larger sprocket that’s incompatible with your derailleur will immediately result in rubbing between the guide pulley and the sprocket. If this is the case you’ll need to change either the cassette or the rear derailleur. You can’t configure this away with the b-screw.

A smaller cassette, where the largest sprocket has significantly less teeth, can result in the guide pulley being too far removed from the cogs, resulting in poor, sloppy shifting.

5. Ensure your derailleur cage or derailleur hanger isn’t bent

bent derailleur

Another issue which could be the cause of a rear derailleur not shifting correctly is a bent or broken derailleur cage or a bent derailleur hanger.

If there ever has been an impact the derailleur cage could sit at an angle with respect to the cassette. It could also be that the rear derailleur is fine but the derailleur hanger is bent.

fix bent derailleur hanger

If the cage is bent or sloppy it’s best to swap out the rear derailleur entirely. If the derailleur hanger is bent but not the rear derailleur itself, it’s possible to bend it back if the hanger is part of the frame. Or if it’s a separate hanger, you could buy a new one.

6. Renew your drivetrain

removing cassette

When you look at a cassette, chances are that 1 or 2 sprockets have been used 80 percent of the time and are more worn out than the rest of the sprockets on the cassette.

Especially with one-by drivetrains the smaller sprockets are used more often, and because a similar force from the chain is applied to a lower number of teeth, these smaller sprockets wear out more easily. The result is that shifting to a lower gear has the highest risking of not going smoothly with a cassette that’s worn out.

The obvious remedy is to replace the cassette. If you do, ensure you also replace the chain as well, because you should never use a worn chain on a new cassette. If you do, the new cassette will wear faster, because the teeth don’t fit well into the worn chain. And shifting will be just as bad, if not worse because of it.

7. Make sure you use parts that are compatible with each other

Shimano Dura-Ace RD-7700 rear derailleur

Compatibility is a thing in bicycle components, especially the drivetrain. So if you change or upgrade parts of your drivetrain ensure they work with each other.

The classic example is Campagnolo parts that don’t mix at all with Shimano, but especially with a drivetrain of 10-speed and up it’s more nuanced than slapping parts together and expecting them to work without issues.

The easiest way to prevent issues in this area is too simply not mix brands and stick with the configuration original to the bike.

8. Ensure your shifter works correctly

adjust shimano thumb shifter

Especially with older thumb shifters the lever might slowly be pulled into a lower gear because of increased cable tension. This is most noticeable in the lowest gear where the most tension is applied to the cable.

When the lever is pulled back the rear derailleur moves as well, which in turn might cause a rattling sound because it’ll sit in between sprockets. You can do nothing about this except keep the lever into position with your thumb or replace the shifter altogether.

bio vanseijen

Johan van Seijen

Founder Restoration.bike

Johan van Seijen is the founder of restoration.bike. His cycling career has seen him at the starting line of classics such as the Amstel Gold Race and Liege Bastogne Liege. Realizing his racing capacity would fall short of what was needed he obtained a MS from the University of Amsterdam in engineering. His love for cycling changed into riding in an amateur capacity with his local cycling club TFC Weesp as a roadie and supporting MTB Noordwest as a mountain biker. He repairs, restores, and builds bicycles and shares his knowledge on YouTube, Facebook and this website. 

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