Jim’s Tech Talk
By Jim Langley
Tool Up to Fix a Loose Cassette
The other morning on my short almost all-downhill commute to the office my Cervelo S5 started making an awful rattle. I knew straight away what it was because nothing else on road bikes makes quite as loud and metallic a sound. What had happened is the cassette lockring had loosened. That’s the small part that threads onto the rear wheel’s hub to lock the sprockets in place. The whole part, lockring and sprockets, is called the “cassette.” And the individual sprockets are called “cogs.”
It’s a simple design and easy part to work on and fix as long as you are capable of removing your rear wheel and have the right tool for the brand of cassette used on your bike. You can have a bicycle shop mechanic do it for you because it’s a quick and inexpensive repair. But, if it happens the day before a bike event, it’s nice to have the tools to do it yourself to take care of it ASAP. I always keep the tools in my traveling toolbox for use at events, too, just in case.
Cassette Tools to Have on Hand
The two most common tools fit Campagnolo and Shimano/Sram cassette lockrings respectively. The tool to fit Campagnolo lockrings is Park Tool’s BBT-5/FR-11 and the one for Shimano and Sram lockrings is Park’s FR-5.2 Cost is less than $10 each.
To use the tool you will also need a way to turn it. A large adjustable wrench works nicely. But you can use anything you have that grips the tool, such as water pump pliers, also known as “plumber’s pliers.” If you do a lot of cassette work, you can get a type of lockring tool that has a built in handle (so you don’t need the large adjustable wrench). Park Tool makes one of these, too, for Shimano/Sram cassettes, their FR-5H (about $42).
Loose Lockrings Can Affect Shifting
When a cassette lockring loosens you will experience the loud rattling noise and you will probably feel it, too. Because the cogs are steel and if they’re really loose they’ll be jumping around enough to sound like rocks in a rolling tin can.
The other issue loose cogs can cause is poor shifting. Because the cogs are moving out of position the chain doesn’t land on them perfectly when you shift. Don’t try adjusting your derailleur to fix this because it won’t help. You have to fix the cassette.
Using the Lockring Tool
To tighten the lockring, remove the rear wheel. Depending on which type of lockring tool you have and the type of quick release on your bike, you might be able to slip the tool right over the quick release. If not, you’ll need to remove the quick release.
That’s as easy as holding one end while you turn the other counterclockwise until the QR comes apart and you can pull it out of the axle. Don’t drop and lose the little springs. And note that they go on either side of the hub with the narrow end facing in. Take a photo before you take the QR apart if you think you will need it.
Once you can get the tool on the lockring, all you have to do to tighten it and fix the loose rattling cogs is to turn the tool clockwise with your large adjustable wrench (or whatever other tool you had to turn the lockring).
Many lockrings have indentations on their surface that mate with similar ones on the last cog. This helps keep the lockring tight. This features makes tightening and loosening the lockring sound and feel notchy as if it’s ratcheting on, which it is. It feels a little strange but keep turning until the lockring is tight.
In the rare event that the lockring has come off the cassette and is loose, start it gently by hand turning it clockwise. The threads on some lockrings can be delicate so be careful not to crossthread it or force it. Be patient and keep trying until it starts threading on correctly and straight.
To make sure the lockring has done its job and tightened the cogs, hold onto the largest cog with one hand and try to jiggle, turn and move the smaller cogs with your other hand. They should all be rock solid as if they’re one piece now. If not, you may need to investigate further.
Other Issues You Might Run Into
Sometimes dirt gets in between the cogs and spacers if you ride with loose cogs long enough. This can make it impossible to get the cogs tight until you clean the dirt off the cogs. Once that’s done, tightening the lockring will lock the cogs down tight.
It’s possible to have a broken spacer on a cassette, too – the little black plastic pieces between cogs. In that case, you will need to replace the spacer because without the exactly correct spacing the cogs won’t tighten.
Once you have the right tool and have the procedure down, fixing a loose cassette is an easy and fun job. You’ll also be ready to replace worn out cassettes or switch to different ones for hillier or flatter terrain, too.
In this video, ace mechanic Calvin Jones of Park Tool shows all about cassettes. He demonstrates tightening the lockring in the very first part of the video.
Ride total: 8,863
Jim Langley is RBR’s Technical Editor. A pro mechanic & cycling writer for more than 40 years, he’s the author of Your Home Bicycle Workshop in the RBR eBookstore. Tune in to Jim’s popular YouTube channel for wheel building & bike repair how-to’s. Jim’s also known for his cycling streak that ended in February 2022 with a total of 10,269 consecutive daily rides (28 years, 1 month and 11 days of never missing a ride). Click to read Jim’s full bio.