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.
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.
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.
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.
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.
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.
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.
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.
Most often if your shifting is sluggish in one direction you can improve it by turning the barrel adjuster.
Your upper derailleur pulley is likely too close to the cassette, and the B screw needs to be adjusted.
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.
A jumping or slipping chain is often caused by a mis-measured chain, worn drivetrain components, or a stiff chain link.
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.
That last bullet point was my problem. I actually broke a chain on a really steep paved hill. I believe the chain break cracked my chain stay and bent the frame. ASE didn’t want to warrantee my frame because they claim that kind of damage can only happen in a car wreck. Trying to figure out shifting problems with a bent frame was a nightmare until I finally found the crack and brought it back to the shop.
Great article. I wanted to point out a couple of things I do not think you mentioned. First do your rear derailleur downshifts BEFORE it is too late, in anticipation of very soon needing that lower gearing. If you wait too long for the downshift you will be putting too much force on the chain, making it harder to drag it sideways to the next larger cog. If you always back off your pedaling force a bit when downshiifting, the shift will go much more smootgly and quietly and requires less thumb pressure to accomplish.
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If when downshifting, the shift does not quite happen, try thumbing the lever a bit past the point where the detent in the shifter can be heard (or felt). If you get a downshift with a bit more lever movement, you need to adjust the barrel adjuster to take up a bit more slack, which moves the chain farther to the left.
Last night towards the end of my ride, I was suddenly unable to shift up to the 4 larger rings (1×11 drivetrain). I made do since there weren’t any super steep climbs and I’d already finished the long climbs and it was still a great ride, but it was annoying. I’m going to see if I can fix it by adjusting the high limit screw or the barrel adjuster. Thanks for the information!
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