Troubleshooting: Rear Derailleurs & Hangers

Derailleurs are made for lots of use and if cared for, will last almost indefinitely. The jockey wheels will wear out over time with use and need to be replaced but the rest of the mechanism shouldn't see significant wear.

They are however by design incredibly exposed to knocks and bumps - when Mountain Biking you may snag branches or rocks; and while riding in the city, they may get knocked around in the bike rack or when loading into a car.

TIP: Always be mindful of the rear derailleur. When laying your bike on the ground, do it with the drive side facing up (the side with the gears/derailleurs). Be very careful when loading your bike into a car or with other bikes as this is also a potential risk.

The following troubleshooting guide is designed to help you understand any issues you might have with your rear derailleurs and hangers so you know what can be done and what needs to be fixed by a mechanic:

Problem: Why does my derailleur keep hitting my spokes?

Derailleurs must be perfectly in line, and if they are not, your bike isn’t going to work as well as it could. If you find your gears don’t work well or the chain is regularly skipping, it is more likely that this chain line isn’t correct.

The reason your derailleur will hit your spokes is that it isn’t where it should be and is leaning too far inside the wheel; so when you go into your lower gears, you start to hear a ting noise. This is not something you can safely allow to continue and will need to be addressed.

This could be a simple matter of adjustment (watch our video on How To Adjust Your Rear Derailleur https://youtu.be/GBsRcNPRK3g ) or it may have been knocked or damaged and will need a skilled mechanic to fix.

Problem: Why has my chain line moved?

So we know the reason the derailleur is hitting the spokes is that the chain line isn’t correct, but why does the chain line move? There are many reasons why this might happen, but here are the most common:

The most common issue to cause an incorrect chain line is a bent derailleur hanger. A derailleur hanger (or mech hanger as it is commonly known) is a small piece of metal that sits between the rear derailleur and the bike’s frame. Most derailleurs are unique to each bike or brand of bike. The mech hanger is normally made of aluminum and has a very important job. It is designed to be strong enough to maintain the chain line but also has to be weak enough that when the derailleur is hit, it will bend.

It’s much cheaper to replace a derailleur hanger than to buy a new derailleur. When the mech is bent, it causes the chain line to lean inwards and hit the spokes.

If the hanger isn’t bent, then more than likely, the derailleur will be bent. Sometimes this can happen after you fall or something has hit your bike.

This can have the same effect as the mech hanger being bent and cause the derailleur to lean in and hit the spokes.

The next issue you might have is the derailleur itself is broken.

It is very common for derailleurs to break and what can happen is the derailleur loses its adjustment, and then because it is poorly adjusted, it goes too far into the spokes. This could be something as simple as a loose screw or a broken cable.

How To Fix the Chainline

Firstly, remove the rear wheel and check the cassette/freewheel for tightness. Refit the wheel and tighten axle nuts/quick release/thru axle properly.

Step One: Inspect the derailleur

You first need to look at the derailleur and see if it has any broken parts or looks like it has taken any damage. If it has damage, that will likely be the issue.

Step Two: Check the Chainline

The next step is to check the chain line. It would be best if you stood by the bike on the drive side to do this. Then look above the chain and inspect the chain line to see if it runs straight from the front chainrings to the rear cassette. If it looks like it is twisted, then the mech could be bent.

Step Three: Fixing the problem

If the problem is a broken derailleur, this will need replacing, and we recommend replacing the mech hanger and the cables simultaneously to ensure that you won’t face problems later down the line. Add the new derailleur and adjust the screws to suit your cassette.

If your derailleur is fine but you’re still having issues, we recommend replacing the mech hanger. Mech hangers can be repaired if bent, but once bent are much weaker and might cause more issues later down the line. Once done, you will need to adjust the derailleur again to suit your cassette.