Repair notes

Indexing Your Rear Derailleur When Shifts Go Mushy

I spent half of last winter fighting with my rear derailleur because I kept adjusting the wrong thing. Shifting felt vague, the chain would hesitate between gears, and I'd hear that awful grinding sound that means something's not quite right. Turns out indexing a rear derailleur is actually pretty straightforward once you understand what's happening, but nobody explains it in plain English. This is what finally worked for me in my freezing garage, and hopefully it'll save you some frustration.

What Indexing Actually Means

Indexing is just making sure that each click of your shifter moves the derailleur exactly far enough to line up with the next cog. When it's indexed properly, each shift is crisp and the chain drops right onto the gear you want. When it's off, you get ghost shifting, hesitation, or that terrible grinding noise that makes you wince. The derailleur itself has a spring that pulls it toward the smallest cog, and your shift cable pulls it the other way toward the largest cog. Each click of your shifter releases or pulls a specific amount of cable, and the barrel adjuster is how you fine-tune that relationship. I always thought this was complicated, but it's really just about getting those increments to match up.

The Actual Adjustment Process

First, shift into your hardest gear, the smallest cog in back. This releases all the cable tension. Now here's what I wish someone had told me earlier: you're only adjusting the barrel adjuster during this process, not the limit screws unless your chain is literally falling off the cassette. The barrel adjuster is that cylinder where the cable housing enters the derailleur or sometimes on the shifter itself. Turn it counterclockwise to add tension, which moves the derailleur toward easier gears. Turn it clockwise to reduce tension, moving it toward harder gears. Start by shifting up one click to the second-smallest cog. If the chain hesitates or doesn't shift, turn the barrel adjuster counterclockwise a half turn and try again. If it shifts past the gear or feels too eager, turn it clockwise a quarter turn. Once that first shift is clean, work your way up through all the gears. If the shifts are good in the hard gears but get worse in the easy gears, you probably have cable friction or a bent derailleur hanger, not an indexing problem.

Common Mistakes I Made

I used to start fiddling with both barrel adjusters when my bike has them at the shifter and the derailleur, which just made everything confusing. Pick one and stick with it, I use the derailleur one because it's easier to reach while the bike's in the stand. Another thing: I kept trying to fix indexing when my cables were old and gunked up. If your cables are rusty or the housing is kinked, no amount of adjustment will make shifting crisp. Replace them first, it's a fifteen dollar fix that'll save you hours. I also learned the hard way that you need to check your derailleur hanger alignment before you start. I bent mine slightly in a tip-over and spent two evenings adjusting things that were never going to work right. A hanger alignment gauge is like twenty bucks and actually useful, or your local shop will check it for a few dollars. And this is important for safety: make absolutely sure your high and low limit screws are set correctly before you start. The high limit keeps your chain from going into your spokes, and the low limit keeps it from falling off into your frame. Test them carefully before you ride.

What to Do When It Still Won't Work

Sometimes you do everything right and it still shifts like garbage. Here's my troubleshooting list from actual experience. Check if your derailleur hanger is straight, I mentioned this already but it's usually the culprit. Look at your cables for any fraying, kinks, or rust, especially where they exit the housing. Make sure your chain isn't worn out, a stretched chain will never shift cleanly no matter what you do. Check that your cassette isn't worn either, you'll see shark-fin shaped teeth if it is. Sometimes cable housing gets compressed inside the ferrules and you need to pull the cable taut and reseat everything. And honestly, if your derailleur itself is bent or the spring is weak, adjustment won't fix it. I rode a derailleur for months that had a slightly bent cage and only figured it out when I finally compared it to a new one. One last thing: do your indexing with the chain on the middle chainring if you have multiple up front. Cross-chaining makes everything shift weird and you'll chase your tail trying to fix it.

Questions people ask me