A rear mech hanger (also called a derailleur hanger) is part of your bike’s drivetrain designed to absorb impact and prevent damage to the frame.
If your bike takes a knock, the mech hanger will bend or break. When this happens you’ll need to replace it.
Sometimes when you think your derailleur needs replacing it may be the case that a new hanger does the trick – a much cheaper job!
In this blog post we’ll answer all your questions about mech hangers, including:
- How to fix a mech hanger
- Why you need a mech hanger
- How to find the right mech hanger
How do you fix a derailleur hanger?
It may look fiddly but replacing your rear derailleur hanger is actually fairly painless. This is what you’ll need to do:
- Remove your back wheel
- Remove the derailleur from the hanger
- Remove the hanger inserts from the dropout
- Clean and lubricate the dropouts
- Install the new hanger
- Reinstall the derailleur
- Replace the back wheel
- Check it’s all working properly
And these are the tools you’ll need
- Allen keys
- Torque wrench (optional, to tighten things up to manufacturer spec)
- Alignment tool (optional, for diagnostics)
We recommend watching a Youtube video to see the process in action. This one from REI is simple and easy to follow.
If you have any problems with bolts and thread sizes, check out our FAQs for more info.
When should a derailleur hanger be replaced?
If you can tell by looking that your mech hanger is bent, it needs replacing. If it’s a little bit bent, you may be able to salvage it by realigning it.
How do I know if my derailleur hanger is bent?
The telltale sign of a bent mech hanger is trouble with shifting gears. If you’re experiencing this, check your mech hanger as part of your diagnostics.
First, just take a look. A mech hanger should be straight from top to bottom, and usually if it’s bent it will bend towards the frame (as this is most often the direction of impact).
If it’s not visibly bent but you’re still having trouble, you may want to use an alignment tool. This can be quite fiddly so we won’t go into full detail here, but there are plenty of instructional Youtube videos.
How do you fit a mech hanger?
Instructions for fitting a new mech hanger are given in a previous section. If you skimmed ahead to this part of the article, click here to go back.
What causes a rear derailleur hanger to break?
As a sacrificial part – i.e. one designed to break on impact – it’s not unusual for a rear mech hanger to break. The most common causes are:
- Impact from hitting an obstacle
- Impact from riding over a pothole
- Being in the wrong gear when climbing
- Being in the wrong gear on a stationary start
- Mech hanger goes into spokes (usually from poor configuration)
- Your chain is too short
As you can see, these are either related to impact or to putting too much strain on your bike’s drivetrain.
Why do I need a derailleur hanger?
You need a hanger to keep the rear derailleur correctly positioned, to absorb impact from any damage, and to protect your bike’s frame and drivetrain from damage.
Do all derailleurs need a hanger?
Not all derailleurs need a mech hanger. Some bikes have the attachment point built into the frame, rather than being a separate part.
As a general rule, if your bike has a hanger and it breaks, replace it with a hanger. If you’re replacing the derailleur on a bike without a hanger, don’t use one.
Are rear derailleur hangers universal?
No, rear hangers are not universal. Some mech hangers can accommodate a selection of different derailleurs, but there is no one-size-fits-all option available.
How to find the right derailleur hanger
Simple: head over to our Mech Hanger Finder. Just pop in your bike’s make, model and year, and the tool will show all compatible products.
This will ensure the perfect fit for your mech hanger, meaning you can be back out on the road in no time.
Hopefully this blog post has cleared up any questions about rear mech hangers and derailleurs. If you have any more questions drop us an email or give us a call on 0113 32 00 345 and we’ll help you get back on track.