A broken or bent derailleur hanger is a much more common bike maintenance issue than you might think.
It can cause havoc on your bike, sending your gears all over the place and, in the worst case, pushing your derailleur into the wheel.
As an experienced bike mechanic, I have had to fix many, and always recommend carrying a spare. In this article, I’m going to tell you everything you need to know when it comes to fixing and replacing derailleur hangers, covering:
What Is A Derailleur Hanger?
Credit: Glory Cycles, CC BY 2.0. Modified from the original.
A derailleur hanger is a small piece of metal that connects the rear derailleur to the bike’s frame. It’s usually hook-shaped and painted either black or silver.
The derailleur hanger is intentionally built from softer material than the frame and derailleur. It’s designed as a fail-safe for the rear derailleur; if the derailleur gets hit, the hanger will bend and break before the derailleur or frame, protecting them from damage.
It’s much easier and cheaper to replace a derailleur hanger in the event of an accident than to have to replace the whole derailleur and reindex it all. Hangers are designed to bend and break and can be quite flexible.
When regularly servicing the bike, it is a good idea to check the hanger is straight.
The majority of bikes have them, but some come without derailleur hangers, in which case the derailleur attaches directly to the frame.
Hangers are typically unique to each frame model, meaning you probably won’t be able to mix and match or borrow one from a friend if yours breaks while on a ride. For that reason, it’s a good reason to carry your own as a spare.
How Can You Tell If Your Derailleur Hanger Is Bent?
It can be surprisingly difficult to tell if your derailleur hanger is bent, especially if it is only slightly deformed.
The first symptom you can look out for is to visually inspect whether either the rear derailleur or chain look skewed or bent, or are no longer perpendicular to the ground.
The second symptom you will find is gears not changing properly, no matter how much you try to index them. This is a common issue that comes from a bent derailleur and something that you can sort once the hanger is straight.
How To Fix (Or Replace) A Bent Derailleur Hanger in 6 Steps
When it comes to dealing with a bent or broken hanger, you have two options; you can choose to replace the hanger completely, or you can attempt to repair it by bending it back into shape.
In this section, we will show you how to do both. The process for most of the steps is the same, but you’ll see the two different options deviate at Step 4 (4.a to replace the hanger, or 4.b to repair the existing hanger).
If possible, I would typically recommend replacing the hanger instead of repairing it, based on my own experience as a mechanic and long-distance racer.
Once hangers are bent and then repaired, they tend to become weaker and more brittle, increasing the risk that they will suddenly snap or shear. This carries the risk of sending your expensive derailleur tangling into your spokes, causing much more expensive damage.
However, it’s still worthwhile to know how to repair a bent derailleur hanger, as there will be times that a direct replacement isn’t immediately available.
For example, on a bikepacking trip, you’re more likely to find someone with a derailleur hanger alignment tool than your specific model of derailleur hanger. Likewise, if your bike shop doesn’t have the specific part in stock, you’ll need to wait while they order it in.
What Tools Will You Need to Fix or Replace a Bent Derailleur Hanger?
- Allen Keys
- Replacement Derailleur Hanger (if replacing)
- Derailleur Hanger Alignment Tool (if repairing)
- Bike Stand (optional)
If you have a bike maintenance stand, this will make the task much easier. I would set aside around 30 minutes to complete the job if you’re replacing the hanger entirely, or 45 minutes to repair the bent derailleur hanger.
Step #1. Preparation And Investigation
The first step is to get prepared. Give the bike a quick clean and get it into the stand. Then, get the tools and anything you might need close at hand.
I highly recommend double-checking the hanger you have bought as a replacement to ensure it’s the same. The last thing you need is to take the bike apart and then realize the parts won’t fit!
It’s also a good idea to have a check around the hanger area to ensure the bike frame isn’t damaged, and the hanger is bent and not the derailleur itself.
Step #2. Remove The Wheel
Now, remove the rear wheel. Undo the quick release or thru axle and push the hinge on the derailleur forward. The wheel should drop out with a little encouragement.
Put this somewhere safe and out of the way.
Step #3. Remove The Derailleur
Next, you are going to need to remove the derailleur.
Take the Allen key (typically a 5 mm) and unscrew the bolt on the hanger, turning anti-clockwise. Keep the bolts somewhere safe so you don’t lose them.
Then, you can leave the derailleur hanging on the chain.
Step #4. Replace or Repair The Bent Derailleur Hanger
4a: Replacing The Derailleur Hanger
Most hangers are secured to the frame with either an Allen key bolt or two micro Allen key bolts. Undo the bolt(s) anti-clockwise, and the hanger will fall out.
Then, just like you took the hanger off, you simply need to add the new one. If the manufacturer specifies a torque figure, go to that. If not, ensure it’s fairly tight without putting too much force into it.
4b: Repairing The Existing Bent Derailleur Hanger
If you plan to repair the hanger, first put the wheel back in the frame. Don’t worry about putting the derailleur or chain on.
Insert the derailleur hanger alignment tool into the derailleur hanger, where the derailleur typically sits. Without applying any pressure, rotate the lever to the bottom (6 o’clock) and align the small rod with the rim’s surface.
Then, rotate the lever to the top of the wheel (12 o’clock). If the hanger is bent, you will see a gap between the end of the rod and the rim’s surface (as in the photo below).
It’s worth checking the 3 o’clock and 9 o’clock positions too.
The next task is to bend the derailleur back into shape. You have to be really careful when doing this not to break the hanger.
With the derailleur hanger alignment tool in the 12 o’clock position, lightly push the bar so the rod hits the rim’s surface. Repeat this process until it stays there when the pressure is lifted.
Now, repeat the process at the opposite side (6 o’clock), and then at the 3 and 9 o’clock positions. Once finished, ensure that wherever the lever is on the wheel, the rod touches the rim’s surface.
Once you have got to this point, your derailleur hanger will be straight.
Take the rear wheel back out to make it easier to re-install the derailleur in the next step.
Step #5. Re-install the Derailleur And Rear Wheel
Whether you replaced or mended the bent derailleur hanger, the next step is to re-install the derailleur.
Ensure that when you put it back on, it’s in the correct position far enough back that the derailleur sits on the small ridge.
Next, re-install the rear wheel.
Step #6. Adjust The Derailleur
The final step is to adjust the rear derailleur. If you haven’t adjusted it since the derailleur bent, it might just work as it should. If you have adjusted it, I recommend starting fresh.
Shift into the smallest cog on the rear derailleur. Fully screw in the adjustment screw at the base of the cable. Undo the pinch bolt to release the cable tension, then pull it finger tight and tighten it back up again.
Then, click the gear shifter to move up the cassette. More than likely, it won’t, so you will have to undo the adjuster until it does. Once it jumps up, try the next and repeat the process until you get to the end of the cassette.
If you struggle with this step, we have a whole article dedicated to installing and adjusting a rear derailleur.
Then you’re done! Your derailleur hanger should now be straight, with the gears all working properly.
Robbie’s Video Guide: How To Repair or Replace a Bent Derailleur Hanger
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