Why does the chain keep slipping

A common question that I see arise from new riders is: why does the chain keep slipping or skipping gears? We are going to address the possibilities of causes in this article.

The short answer is, its probably an issue with any one of the following things: chain, rear/front chain cassette, or the derailleurs.

What are the causes of a slipping/ skipping chain?

There are many things it could be, and some of them are simple adjustments.

Dirty Sprockets and Chain

A common reason the chain slips is too much build up on the sprockets. When the chain oil and dirt mix up on the sprocket it leaves a thick black mixture on your sprockets. If you go too long without cleaning your bike it will build up enough that it will cause your chain to slip.

Derailleur pulleys are out of alignment with the rear wheel cog that the chain is on

This will cause unnecessary tension on the chain, and can/ will cause the chain to skip gears while you are riding. It is easy to verify if this is the issue. Look straight on at your rear wheel. Identify the gear cog that your chain is on and look below it. Is the pulley cage(metal pieces on either side of the rear derailleur pulleys) perfectly in line with the gear?

Bent / Damaged Derailleur pulley cage

A bent derailleur pulley cage is going to provide the same kind of tension as the pulley cage being out of alignment. To verify if the derailleur is out of alignment look at the rear wheel head-on. Your visual inspection will verify whether the derailleur is out of alignment. However, if this is the issue, replacing the derailleur will stop the chain from slipping.

Some times the derailleur is damaged. You will want to determine if the derailleur is difficult to shift going up in gears (on the front) or down. To fix this you will follow the cable from your front derailleur shifter down to the derailleur. Near where it attaches there will be an adjuster. turn the adjuster counter clockwise to adjust up and clockwise to adjust up. As you are adjusting verify that you are fixing the issue and make sure you have smooth shifting through all gears.

Worn Chain

A worn-down chain is the third cause of slipping. The chain is where the majority of chain slipping comes from. The teeth on the gears won’t line up and it will cause the chain to bounce. A worn chain is essentially the stretching of the chain so that the distance between the links is no longer what it used to be. To measure that distance, you can use a chain checker tool. They look like this.

To use it you would slide the hooked end in under a link in the chain (do this on the upper section of chain between the pedals and the rear wheel). You want the other end of the tool to sit on top of a link. When the tool slides between links that will verify that the chain has stretched and is the cause of the slipping.

Worn cassette

The final cause is a worn cassette. A worn-down cassette is when the sprockets have been worn down far enough to reduce their effectiveness. Checking visually isn’t recommended because it requires a tool., however, there is a sprocket wear indicator tool to test if the cassette is worn. It looks like this one. To use this you would remove the rear wheel from the frame and chain. Place the chain links around the sprocket and use the flat part as a lever and pull down. If you can easily move the first couple of links off of the sprocket, as a result, you know cassette wear is not the issue.

How do I stop my chain from slipping?

The good news is that for most of these there is a simple solution. We will address each one below. Some of which I will address in upcoming blog posts, and eventually accompanying videos.

Cleaning the sprockets

Perhaps one of the easiest solutions would be to clean the sprockets on your bike. This is probably going to require some elbow grease and lots of persistence. However, once cleaned and re-oiled, verify that the de-railleurs are aligned over the sprockets. If they are not, continue on to the next section if they give your bike a try and see if the chain slips.

Derailleur out of alignment

If the derailleur pulleys are out of alignment, there is a nut that connects the shifter cable to the derailleur. Adjusting that nut will move the pulleys over one way or the other.

Bent Derailleur

A bent derailleur will have most likely happened on the trail. I would suggest trying to bend it back into alignment yourself. If the problem persists (bending it back is kind of a bandaid.. though it may do the trick.) you will need to replace the whole derailleur. I will post an article soon on replacing the derailleur.

Worn out or “Frozen” chain

Worn out chains are easy and cheap to fix. For this, find the master link on the chain. Remove it using master link chain pliers. Reroute the new chain and attach the two ends together using the pliers.

For a “frozen” chain, you can attempt to move all of the links on the chain individually and try to find the frozen section. Once you have identified the frozen section, you can put a little lubricant on it and work it back and forth until it frees up. Ensure that there is no other frozen section by finishing up the entire chain. Sometimes there are links that are frozen but remain anonymous. If that is the case, it may be time to just replace the chain.

Worn out cassette

The only way to fix a worn out cassette is to replace it. To do this you are going to need a lockring removal tool. Remove the wheel from the bike. Take the skewer out (the screw that holds the tire to the bike frame). Use the lockring removal tool to unscrew the lock ring. Pull the old cassette off, place each sprocket of the new cassette on individually matching the grooves up properly. (there is one extra wide groove that makes it easy to line things up.) Screw the lockring back on and place the “skewer” back in. Place the tire back on the bike tighten it down and place the chain on the new cassette. Here is a video showing the cassette replacement.

Some bikes have a freewheel assembly instead of the cassette. The process is much the same except that the freewheel actually screws onto the wheel itself instead of slides onto the bearing assembly.

1. Take the wheel off
2. Remove the chain from the sprocket
3. Remove the skewer
4. Use a lock ring removal tool that will match up with the grooves on the freewheel to unscrew the freewheel.
5. Remove the old freewheel
6. Place the new freewheel on
7. Screw it in using the lockring removal tool
8. Replace the skewer
9. Place the wheel back on the bike
10. Realign the chain.

Conclusion

All of these things can and do cause the chain to slip and skip gears. They are all fairly easy fixes. I hope that these tips will help you fix any issue like this on your bike.