How to Fix a Broken Bike Chain

How Do Bicycle Chains Work?

A bicycle chain is actually a fascinating little piece of engineering. They are quite simple but made with extreme precision. Inner and outer plates are held together by pins. Between the inner plates, a roller rides over the pin. The roller provides the surface for the chain ring to contact and traps lubrication between the moving parts of the chain to ensure smooth, efficient operation. Check out the diagram below to get an idea of how these parts fit together.

Why Do Bicycle Chains Break?

Your bicycle chain goes through a lot of stress. It has to deal with dirt and grime, shifting between gears, and operating at an angle when on the inner or outer cogs while transmitting all the power you’re putting down to the wheel!

When tension is applied to the chain while shifting, the derailleur creates a side load on the chain against the next gear. This can create a situation where the cog can pry the link off of the pin, particularly on a worn chain. While one shift under load is very unlikely to be an issue, continually shifting under hard load on a worn chain can be a big problem. As the chain wears, the pins and the holes the pins ride in wear and make this type of failure much more likely.  The Shimano Ultegra 8100 and Dura-Ace 9200 drivetrains are said to be mush more resistant to this and can regularly be shifted under load, although at the time of this article's writing, there's not enough real world data yet.

It is important that you check your chain for wear regularly and replace as needed. Your components will last much longer, and you’ll almost certainly never break a chain. To keep an eye on your chain wear, we suggest the Park Tool CC 3.2 Chain Wear Indicator.

What You Need for Bike Chain Maintenance

We recommend the at-home mechanic have a few tools on hand to get you through most chain repair jobs. 

First, you’ll likely want a chain breaker. This tool is used to remove links when installing a chain or to push pins out for chain removal if you do not have a quick link. Park Tool makes a great chain tool that is sturdy and will last for years to come. 

More and more newer chains are held together by a quick link, also called a master link, which replaces the master pins. While they are convenient, they can be a real pain without a pair of chain link pliers. These handy little pliers allow you to remove a quick link and make sure your new link is fully seated when installing a new chain.

It’s also a great idea to have a chain wear indicator as mentioned above. This tool allows you to keep an eye on wear and replace a chain before it becomes a problem. We recommend the Park Tool 3.2 Chain Wear Indicator as it gives a repeatable measurement of chain wear by simply determining if the tool fits between the rollers. A loose fit means you definitely have a worn chain in need of replacement.

How to Fix a Broken Bike Chain: Step-by-Step

Worst case scenario: You now have a broken chain while out on the trail or on the road. Hopefully you have a couple of tools and a quick link or a spare rivet in your repair kit.

The first thing you want to do is remove any damaged links. This is where you’ll want a multitool like the Crankbrothers M20 that contains a chain breaker to push the pins out of the broken link. Now you need to reconnect the chain. Keep in mind that to connect the two ends of the chain with a quick link, you’ll need to have an inner link on each side for the quick link to attach to. Install the link with the arrows facing in the direction that the chain moves normally. If you are using a spare pin, you’ll need one end to have outer plates and the other end of the chain to be inner plates. Align the two ends and press a new link into the chain with your chain tool. Snap off the excess pin when complete. Be careful that your chain moves freely where you’ve just installed the link. If it's over tightened, sometimes the easiest thing is to flip the chain tool around to the other side of the pin you just installed, and apply the slightest bit of back pressure on the freshly installed pin.

Another thing to consider is that if you’ve had to shorten the chain it would be a good idea to stay out of the big cogs to make it back home or to the trailhead. Your rear derailleur will not be properly set up for the shortened length, and you could run the risk of damaging the derailleur and rear wheel if the chain is now too short.

In an extreme case, it's possible to reuse the pins, but in most cases this is only possible if the pin wasn't fully removed and is still held by one of the outer plates. This is really only a last resort option though as the process of pushing the pin back in will likely cause damage to the chain. But if you're stuck a long way from a ride, it beats walking!

How to Maintain Your Bicycle Chain

The most important thing you can do is keep your chain clean and lubricated. We generally do not get too carried away with degreaser, but we keep our bikes clean and lubricate after cleaning. Many new riders use too much lube. Best practice is to place a drop on each roller, spin the crank, then wipe off as much excess lube as possible. The lubrication is most important within the rollers and extra lube just creates a mess and attracts dirt. A chain lube we’ve found to work well in most conditions is Finish Line Dry Lubricant. If you're riding in wet or muddy conditions, then switch to a lubricant specifically formulated for this like Finish Line Wet Lubricant.

Another method of maintaining and keeping a perfectly clean drivetrain is waxing your chains. Stay tuned for an upcoming post about the benefits and how to wax a chain!

How to Avoid a Broken Bike Chain in the Future

The number one thing you can do to prevent a chain from breaking is to replace your chain when worn. Use a chain checker and replace as needed. An 11 speed chain on the road is good for 2-3,000 miles if properly maintained. Offroad, it is a little harder to judge based off of miles as conditions can vary greatly. We suggest using the chain checker and keeping an eye on things. When you reach 0.5% wear, get ready to replace the chain. Not only will that help avoid broken chains, it will also minimize excessive wear on your gears from a worn out chain.

You should also keep your chain properly lubricated to extend the life of your chain as mentioned above as well as minimizing shifts under load. When riding hard or racing, it is impossible to completely eliminate shifting under load, but a quick hesitation in the pedal stroke when shifting can go a long way towards preventing broken chains, especially if you’re a bigger or stronger rider. Also regularly examine your chain rings and cassette for damaged teeth that would cause unwanted stress on your chain.

With proper maintenance, broken chains are extremely rare, but when they do happen it can be a quick fix out on the trail as long as you have the right tools! It's always a good idea to have a spare chain at home. Browse our selection of chains and quicklinks here.