There are three things that will cause a shifter to become hard to shift. This is a common occurrence and is not reason to panic. It’s also, normally, quite easy to fix. I fixed three in the last two days. One on my gravel bike (front derailleur), one on my wife’s gravel bike (front derailleur) – do you sense a theme? And one on my rain road bike (rear derailleur).
The three common causes are: dirty cable, dirty cable guides, dirty cable housing. A fourth, far less common cause for a sticky shifter is that the factory applied grease in the shifter itself has worn out. This is so rare, I’ve only had to have it fixed twice in ten years with seven bikes in common rotation (three for my wife, three for me, and one tandem – I maintain all of them). I feel it is important to mention, though. There are two ways to fix that and I’d recommend the GCN video on the topic – that’s how the shop fixed my two occasions. I didn’t know any better at the time, so I took the bikes to the shop.
Now, lets get to the common three, because we’re going to hit this with a shotgun approach and nail all three at the same time. You’ll need a damp towel (something that can get dirty and greasy), a pair of needle-nosed pliers (to remove and replace the cable end cap), and a 4 and/or 5 mm hex key/wrench, and a light lube (I prefer Finish Line Ceramic Lube – it’s super-slippery).
First, remove the cable end-cap of the offending shifter – let’s do rear in this example because there are more moving parts. For either derailleur, do not touch the set screws. If the bike shifted well before the shifter got sticky, it’ll shift fine after we clean it up. Next up, loosen the bolt that holds the cable to the rear derailleur, paying close attention to how the cable runs through the clamp. When we put this thing back together, you’ll have to replace the cable exactly as it was originally run through that clamp. If you go on the wrong side of the bolt, the bike won’t shift properly. Take a picture with your phone for reference if you must.
With the cable detached, if you’ve got internal shifting, take a long piece of cable liner and thread that over your cable until it comes out the guide at the bottom bracket (if you have a cable guide there, I do on my Venge), or the down tube of the frame. If you’ve got external routing (as I do on our gravel bikes and my rain bike), simply pull off the rear housing loop, thread the cable back through the cable guide and pull the housing and cable out of the cable stop on the down tube.
Now, roll back your shifter hood from the bottom to expose the hole through which your shifter cable is threaded (through the side on some shifters or the bottom for others). Don’t pull the cable all the way through unless you wish to install a new cable (sometimes this is necessary – if so, you may have to undo the top of your bar tape down to the hood to get access to the cable housing). Pull the cable until just an inch or two is showing at the down tube end cap. Get out your handy-dandy light lube and hit that part of the cable sticking out of the hood with a fair bit to make it slippy, the whole exposed cable, from the stop to the hood. Then pull it back through making certain the cable end seats properly all the way inside the shifter. You may have to help it, and if it won’t seat in the slot properly, you’ll have to pull the cable all the way through and shift all the way up for a rear derailleur (the smallest cog) or down for the front derailleur (the small ring) to get to the shifter pull in the proper location to accept the cable. This happened to me when I fixed my gravel bike the other day, so I just installed a new cable… if I’m going to the trouble of pulling the cable all the way out, I may as well insert a brand new cable.
Next, for an externally routed cable, unscrew the barrel adjuster at the down tube stop. Clean everything, including the stop, and lube the threads of the barrel adjuster being careful not to bounce the spring onto the floor and into some crevice in the floor, never to be seen again. Install the barrel adjuster and thread the cable through.
We turn our attention to the bottom bracket cable guide next. While we’ve got the cable on the floor, clean out the cable guide. If metal, add a dab of light lube before you thread the cable through. If plastic, clean any dirt out (I use a 1mm hex key), wipe it clean and slide the cable through. If you’re internally routed, you’re simply feeding the wire through the cable liner, the same way you took it apart, until you get it through the frame at the rear derailleur.
Before threading the cable through the barrel adjuster at the derailleur, unscrew and tighten down the adjuster. Any grit or dirt in the adjuster? Clean that up and lube the threads. Next, on the remaining exposed cable, add a fine coat of light lube and insert the end through the loop housing and thread the cable back through the derailleur making sure the cable housing is firmly seated in the frame and derailleur at the barrel adjuster.
Having threaded the cable back through the lock bolt on the derailleur exactly as it was when you unbolted it, pull the gable taught and tighten the bolt. Now, if I’m not working on a stand, I’ve got the bike upside down for this part because I need both hands to work this cheat… With the bike upside down or in a stand, operate the pedals forward and manually move the derailleur so the chain shifts down (up the cassette, down to easier gears) two cogs, then stop pedaling without releasing pressure on the derailleur so the chain stays on the bigger cog. This will leave some slack in the cable. Loosen the locking bolt on the derailleur and pull the slack out of the cable and tighten the bolt down again. Once that’s done, simply operate the pedals forward and the chain will shift down naturally to the smallest cog. Now adjust your derailleur so the shifting works up and down the cassette. If you did that last part right, you should be within one turn of perfection on the barrel adjuster (I’m usually within a half-turn).
Give your bike a few shifts up and down the cassette to make sure it’s right. You should be good to go.
If not, in the extremely rare occasion it’s still sticky, assuming your housings are all in good condition, it’s the shifter. At this point you might be cranky you did all of that work just to have to go back to clean out the shifter. Don’t be. You just cleaned out the entire system all the way from the hood to the derailleur. When you get that shifter cleaned up, everything will go back together in minutes and everything will be tip-top.