Troubleshooting Common Rear Derailleur Shifting Problems on a Bike By Brian Gerow

Once you have learned the basics of installing a 1X drivetrain, there are a host of details to fine-tuning and maintaining it. Eventually, it will start making annoying clicking sounds, or skipping out of the gear you select. From the first day a new drivetrain is installed until it is recycled, pieces stretch, loosen, wear, and become bent. The troubleshooting guide below will take you through some common shifting issues, followed by their most likely causes and solutions.

We will stick to problems that plague rear derailleurs, as 1X setups are common on most modern mountain bikes. For older bikes with front derailleur issues, the solution is quite simple: Remove the front derailleur and replace the chainrings with a single 1X-specific ring and wide range cassette. Boom! You just cut your drivetrain problems in half.

Drivetrain definitions

In all seriousness, we need to define a few key terms before starting. If you already know bicycle drivetrain nomenclature you can skip ahead to the troubleshooting section.

Low limit screw

The low limit screw adjusts the limit of how far a derailleur can move toward the lowest gear. The lowest gear is the big spinny one used to climb steep stuff, and it is located nearest the spokes.

The shift cable pulls against the derailleur’s spring to shift into lower gears and releases cable tension to allow the same spring to pull the derailleur into higher gears. When you shift into the lowest gear you are putting direct pressure on the derailleur via cable tension, and the limit screw is what keeps it from going too far and falling off the cassette. The ideal position for this limit is where it stops the derailleur’s upper pulley (a.k.a. jockey wheel) directly below the lowest gear and does not allow it to go any further.

High limit screw

The high limit screw adjusts the limit of how far a derailleur can move toward the highest gear. The highest gear is the little one near the bike’s seat-stay and chain-stay junction. Just like the lowest gear, the ideal limit adjustment places the derailleur’s upper pulley directly in line with the highest gear, preventing the chain from shifting off of the cassette and into the frame.

B screw

The B screw (a.k.a. body-angle screw) adjusts the amount of space between the upper pulley and the lowest gear, which affects chain wrap and low gear shifting.

Chain wrap is the amount of chain that interacts with any given cog in the cassette, from the point the chain first touches the cog until it leaves on its way to the chainring.

Most of the time a bike will shift properly with the upper pulley wheel 5-6mm away from the lowest cog. Turn the B screw clockwise to make the gap larger, and counterclockwise to close the gap.

Barrel adjusters

On modern mountain bike shifters, barrel adjusters are mounted on the shifter, right where the cable housing exits the shifter body. They essentially work like bolts that the cable housing sits against, allowing effective length adjustment of the cable housing. The shift cable passes through the hollow center of the barrel adjuster.

Barrel adjusters can be made of plastic or metal, and are usually black or polished alloy in color. On flat-bar, index-shifters (standard on all modern mountain bikes), they are always located where the shift housing exits the shifter.

Turning the adjuster counterclockwise (from a rider’s perspective) lengthens the cable housing slightly, which increases the tension on the cable. This added cable tension helps move the derailleur toward the lower gears. Turning the barrel adjuster clockwise shortens the cable housing, lowers cable tension, and allows the derailleur’s spring to pull toward the higher gears.

When cable tension is properly balanced the chain will stay in the selected gear, and will move up and down the cassette with equal ease, speed, and accuracy.

Derailleur troubleshooting

Ok, now we dig into the greasy issues.

This chain is In the low and slow gear.

My chain is falling off the largest cog of my cassette, and into my spokes

Likely the issue is either a bent derailleur hanger or the low limit screw needs to be adjusted.

• First, try to wiggle the cassette, then the derailleur and hanger to make sure everything is tight. If any of these components are loose your bike will not shift properly, and you will not be able to make accurate adjustments. Also, make sure the hub is properly seated in the dropouts (QR only) and that the skewer or through-axle is tight.
• If you have not recently changed or adjusted your drivetrain and your chain is falling off into the spokes, your derailleur hanger is most likely bent inward. If you have a spare hanger, this is its time to shine. If you are on the trail you can try to bend the hanger back by hand or continue your ride using higher gears to keep it from falling into the spokes. If you try to bend it back you will risk breaking the hanger, and unless it is extremely bent you will be better off shifting into a high enough gear to keep the chain on and finishing your ride.

The derailleur hanger is a piece of aluminum bolted to your frame that your derailleur is then mounted on. Hangers are unique to your frame, and it is a good idea to buy a spare when you buy a new frame. A hanger separates the derailleur from the frame and is designed to bend or break on impact, rather than damaging your frame or derailleur. Some steel frames, like the blue one pictured above, have integrated derailleur hangers, which can be straightened but not replaced.

• If your derailleur hanger is straight you may need to adjust your low limit screw to stop the derailleur just below the largest cog. Turn the low limit screw clockwise roughly half of a revolution, then gently turn the pedals to see if the chain stays put on the lowest cog. If you are using a bike-stand this will be far easier, as you can push the derailleur into the lowest gear by hand, and adjust the limit screw precisely, while looking at the cog and pulley. If you make incremental adjustments and hand pedal the drivetrain gently and slowly to check the alignment you can catch the chain before it falls off the cogs again, and adjust further as needed. On the trail, you can sometimes use a tree branch or a friend as a bike stand. Your own neck also works as a momentary bike stand, but I will let you figure that one out if you are so inclined.

My chain is falling off the smallest cog and getting stuck between the frame and the cassette

The chain is on the high, sprinty cog.

Again, this is likely due to a bent hanger, or the high limit screw needs to be adjusted.

• As above, make sure your derailleur, hanger, and cassette are tight, and your wheel is properly seated and tight.
• If you have not recently changed or adjusted your drivetrain and your chain is falling off toward the frame, your derailleur hanger is most likely bent outward. If you have a spare hanger, this is its day of glory. Out on the trail, you can try to bend the hanger back by hand or continue your ride using lower gears to keep it from falling off between the cassette and frame. If you try to bend it back you will risk breaking the hanger, and unless it is extremely bent you will be better off shifting into a low enough gear to keep the chain on and finishing your ride.
• If your derailleur hanger is straight you may need to adjust your high limit screw to stop the derailleur just below the smallest cog. Turn the high limit screw clockwise roughly half of a revolution, then gently turn the pedals to see if the chain stays put on the highest cog. If you are using a bike-stand this will be far easier, as you can let the derailleur’s spring pull it toward the frame while adjusting the limit screw precisely below the cog. You may need to push the derailleur slightly inward while making the adjustment to make it easier to turn the screw. If you make incremental adjustments and hand pedal the drivetrain gently and slowly to check the alignment you can catch the chain before it falls off the cogs again, and adjust further as needed.  On the trail, a tree branch or friend’s arms can be a great substitute bike stand and a nice way to keep your riding buddies warm while you wrench.

Paint damage from a bent derailleur hanger that caused the chain to drop between the frame and cassette.

My shifting is slow, up and down the cassette, and sometimes I have to shift past a gear and then back to it

Have you changed your cables and housing recently? Often sluggish and reluctant shifts are due to debris buildup between the shift housing and the shift cable, kinks in the cable and/or housing, or worn out housing.

• As above, make sure your derailleur, hanger, and cassette are tight, and your wheel is properly seated and tight.
• If your shifting is generally slow or stilted you likely need to replace your shifter cable and housing with a fresh set. Changing these bits is often a simple and quick way (internal routing aside) to make your drivetrain shift like new. For a detailed description on how to make the swap, you can check out either this video from GMBNor this one from Seth’s Bike Hacks.
• If you are on the trail and notice this kind of slow or sticky shifting there are a couple things you can try. First, look for kinks in the cable housing that may have occurred in a crash or when a stick flipped up and twisted between things. If you find bends or kinks, gently reverse any acute angles to let the cable pass more smoothly.
• If you are trailside and happen to have emergency chain lube (or any thin oil), you may be able to lube enough of the cable to get it to shift more smoothly. If your bike has full continuous shift housing, meaning the housing goes all the way from your shifter to the derailleur body without any exposed cable outside the frame, shift into the highest gear, lube as much of the cable as you can, and then shift back and forth from the highest to the lowest gear. This may dislodge whatever is gumming things up and allow you to shift smoothly for the rest of the day. If your drivetrain uses segmented housing you can take this lube technique a step further. First, shift the derailleur into the largest cog. Then, without pedaling or letting the derailleur move from the largest cog, shift all of the way to the highest gear. This will make the shift cable as loose as it can be without removing it from the derailleur’s pinch bolt. From here you may be able to remove segments if the cable housing, fully lube them, and slide them back and forth to clear debris.
• Removing the derailleur cable from the pinch bolt while out on the trail can cause problems, particularly if the cable is frayed or unwinding. Fortunately, there are not many cases where you would need to do so.
• An excessively dirty drivetrain can also slow down your shifting. Keeping your drivetrain clean and well lubricated will extend its performance in multiple ways.

My shifting is slow going into harder (or easier) gears

Most often if your shifting is sluggish in one direction you can improve it by turning the barrel adjuster.

• As always, make sure all drivetrain components are tight, clean, and properly lubricated.
• If shifting is slower toward easier (lower) gears your shift cable is likely too loose. Turn the barrel adjuster counterclockwise (from the rider’s perspective) by half revolution increments until the tension is balanced and your bike shifts perfectly.
• If shifting is slower toward harder (higher) gears your shift cable is likely too tight. Turn the barrel adjuster clockwise (from the rider’s perspective) by half revolution increments until the tension is balanced and your bike shifts perfectly.

My chain makes noise when I am in the lowest gear (largest cog)

Your upper derailleur pulley is likely too close to the cassette, and the B screw needs to be adjusted.

• If your derailleur was adjusted properly when the bike was built, this issue should only arise when you switch to a cassette with a larger low gear. If this happens “out of nowhere” your derailleur hanger may be bent forward.
• To adjust the derailleur body further away from the cassette, turn the B screw clockwise until the upper pulley site 5-6mm from the largest cog.

The B screw adjusts the space between the top pulley and the largest cog.

On some modern cassettes with large gear jumps, like Shimano’s 11-46 cassette, you will need to adjust the B screw further, adding space between the upper pulley and the largest cog, in order to make the final shift to the lowest gear possible. First, make the normal 5-6mm adjustment. Then shift between the lowest two gears, turning the B screw a full revolution until your derailleur shifts smoothly from one to the other.

The 9-tooth difference between the final two cogs will require more of a gap between the largest cog and the upper pulley wheel in order to shift properly between the two lowest gears.

I’m getting a clicking sound when the chain jumps around between two gears

Often called “ghost shifting,” this can be caused by a number of things.

• Make sure all components of your drivetrain are tight, clean, and properly lubricated.
• Turn the barrel adjuster a half revolution either direction to see if that solves the problem.
• Your chain may be too long or have stretched over time. This video will help you properly measure your chain length.
• You may have incompatible components. Tight tolerances are key to making drivetrain parts work together.
• Your derailleur hanger may be slightly bent.
• You may have debris in your cable housing and will need to replace it.
• If you have tried everything else, your drivetrain is likely worn and in need of some replacement components. Time to hit the bike shop!

Chain jumps or slips when I pedal hard

A jumping or slipping chain is often caused by a mis-measured chain, worn drivetrain components, or a stiff chain link.

• Your chain may be too long or have stretched over time. This video will help you properly measure your chain length.
• You may have a stiff chain link. If you inspect your chain and find a stiff link you can easily loosen it by holding the adjacent links and gently applying lateral pressure to the stiff link to free up its plates. Do this as close as possible to the stiff link to avoid bending other links.
• Your chainring or cassette may be worn and in need of replacement. If you recently replaced your chain and it is jumping all over the place this is an indication that your cassette or chainring need to be replaced as well.

This Black Locus made a fantastic bike stand. Hardwood trees like this one won’t be bothered by a little bike weight.

I’ve adjusted everything and my bike still isn’t shifting correctly

• Some shifting systems require different amounts of pressure and speed applied to the shift paddle. If nothing else works, try changing the speed and/or pressure you apply to the shift lever.
• Worn parts eventually don’t work as well as they once did. The plastic gears inside your shifter wear out, chains stretch, gear teeth wear to “shark teeth,” derailleur pulleys become crunchy and less responsive, springs stop springing, and derailleur cages get bent out of whack. Some shifting issues can only be remedied with new components.
• Drivetrain parts are designed by skilled engineers to work with great precision and tight tolerances. If your mix of components is not designed to work together you will not be able to achieve perfect shifting. For example, if you have a derailleur designed for a cassette with a maximum range of 11-42t and you are running an 11-46t cassette, you will likely hear a lot of noise in the lower gears, among other issues.
• Chains are far less expensive than cassettes. An inexpensive chain-wear tool will let know exactly when it is time to swap the links, keeping your cassette in top shape as long as possible. For reference, I change my chain roughly 4 times per season on my daily driver, and a cassette typically lasts two or three years.
• Loose or worn pulley wheels can greatly affect shifting. If your pulleys wobble, the teeth are worn, or the bearings/bushings are sticky you will need to replace them so the derailleur can properly do its job.
• Chainrings bolts occasionally work loose. Along with all of the component tightening and placement checklists above, make sure your cranks and chainring bolts (or direct-mount lockring) are tight. Excessive movement from the chainring can cause poor shifting, dropped chains, and a host of other issues.
• Some frames have more flex than others, just as some riders are stronger than others. If you have a particularly flexy frame or are brute strong, or both, you can cause the frame to flex enough that your bike will shift or drop its chain. In this case, you need to trade out your frame for a stiffer one, or chill out. The solution here depends on your budget.

If the above solutions don’t fix your problem, your local mechanic certainly can.

Have you experienced shifting issues that are not listed above? Do you know of possible solutions we didn’t mention? Please share them with us in the comments.

For more rear gear goodness, check out this video on trailside derailleur hanger adjustment, and this one on how to use a derailleur hanger alignment tool.