Seeing your derailleur at a weird angle or even worse, broken off, isn’t a pretty sight. But luckily you can easily replace them in contrast to the old frames where the hanger was welded to the rest of the frame. The damage is usually not limited to the derailleur hanger so we’re also briefly going over installing the rear derailleur, chain and doing derailleur adjustment.
Getting the right derailleur hanger for your bike might need a bit of investigation. Derailleur hangers are bike specific, usually make, model and sometimes year specific, so make sure you order the right one. In some occasions you have the choice of two hanger types, the standard dropout and the direct mount hanger. The standard drop-out hanger is generally the one you’d go for. The direct mount hanger is a newer standard by Shimano that places de derailleur about 25mm further back compared to the standard dropout. But only Shimano Shadow derailleurs and some frame manufacturers support this standard. The Shimano Shadow derailleurs have a B-Link for installing the derailleur on the standard dropout, remove the B-Link and you can install it on a Direct Mount derailleur hanger.
For installing a derailleur hanger you barely need any tools. You will need:
Hex keys (for installing the derailleur hanger and derailleur)
Torx keys (for installing some of the SRAM derailleur)
Additionally, for installing the chain and the derailleur adjustment:
Chain tool (for splitting the chain)
Master link (for linking the chain, also called Powerlink, Powerlock or chain link)
Philips screwdriver (for adjusting the derailleur)
PREPARATION & REMOVAL
The damage to the derailleur hanger is usually caused by some impact to the derailleur. But also check the other important parts of your bike if they did not sustain any damage. Inspect the frame, derailleur, chain, shifter cable and rear wheel for any damage and fix it before continuing.
Now remove any remaining parts of the old derailleur hanger with care. Remove the rear wheel to gain better access to the derailleur hanger and use a hex or Torx key depending on your derailleur to remove it from the hanger. A smaller hex key is used to remove the derailleur hanger from the frame, which in my case is a 4mm hex key. Be careful not to damage the frame and clean the derailleur hanger mount afterwards.
INSTALL THE NEW DERAILLEUR HANGER
Get your new derailleur hanger and put some Loctite on the threads of the screws since you can’t really torque the screws in the aluminum derailleur hanger. Now place the derailleur hanger on the frame and screw the derailleur hanger in place. It should only fit one way with the notch positioned to the rear of the bike. Prevent cross threading and don’t tighten the bolts too tight, about 2Nm is enough.
INSTALL THE DERAILLEUR AND WHEEL
The derailleur can now be installed when you have a standard dropout hanger. If you have a direct mount derailleur hanger you need to remove the B-link from the derailleur if you haven’t yet. Now mount the derailleur on the derailleur hanger with a hex or Torx key and torque it to about 8-10Nm. If you have a B-link there shouldn’t be any gap between the B-link and the notch of the derailleur hanger. In other cases the b-screw needs to touch the derailleur hanger. Here turn the derailleur a bit so the b-screw applies some force to the notch of the derailleur hanger.
Now that the derailleur is installed, put it in the mode where it lowers its tension. Not all derailleurs have this option, but for Shimano’s Shadow Plus derailleurs you have to put the clutch mechanism in the off position and SRAM derailleurs with Cage Lock in the locked position. Now install the rear wheel and we're ready to go to the next step of installing the chain.
INSTALL THE CHAIN
For the chain installation I’ll be running through some basics. For more in depth information about chain installation, removal, connection types and chain length check out the article: How to replace the chain on a mountain bike.
The chain that I’m using to install is used and worn, matching the state of the chainring and cassette. If the wear on your chainring and cassette is still limited, then using a new chain is a good choice. But a new chain on worn chainrings isn’t a great choice since it decreases performance and increases chain wear. For connecting the chain I’m using a master link, a 2-part outer chain link that makes installing and removing the chain a lot easier and can be reused depending on the type you buy.
First we need to determine the correct chain length. The easiest way is to match the length of your chain with the old chain. If you don’t have the old chain you can use another method. A common way to determine the chain length from scratch is to wrap the chain around the large chainring and the large sprocket without running it through the rear derailleur. Bring both ends together and check where the chain starts to overlap. From this point add 2 links and that is how long your chain needs to be. Since the master link also counts as one link, add only adding one link to the length of the chain. When using the master link both ends of the chain need to be inner links. If that’s not the case, add one more link. This is the point where you split the chain.
Get the chain tool and position it above the center of the pin and drive the pin out of the chain. It requires some force to get it started. When the pin is out, remove the tool and install the chain correctly. Wrap the chain around the chainring and cassette, through the rear derailleur and front derailleur if you have one. Pay special attention to the rear derailleur, the chain needs to run in a straight line between the guide pulley and tension pulley, not rubbing on the tab of the derailleur cage. Now place one part of the master link on each end of the chain and bring both ends together. Align both sides of the master link and push the sides together. Apply tension on the chain so that the master link will snap in to place. If you link requires more force you can position the master link between the cassette and the chainring, apply the rear brake and turn the crank.
The last step is to engage the clutch mechanism of the derailleur again. Put the clutch mechanism in the on position or disable Cage Lock depending on your derailleur.
THE DERAILLEUR ADJUSTMENTS
Since you were probably using the derailleur before replacing the derailleur hanger, chances are that your derailleur is still setup right and only needs some minor adjustments to the cable tension. Derailleur adjustment may seem complicated, but knowing what the adjustment screws do makes it a lot easier. In this part I will discuss the basics, but check the How to adjust your dedailleur article (coming soon) for more in depth information.
We’re going to start with the derailleur in its base position under the smallest sprocket. Shift your chain to the largest chainring and the smallest sprocket. Without any cable tension the derailleur sits against the top limit screw indicated by an H. Turn the limit scew clockwise to move the derailleur left (towards the spokes) or anti-clockwise to move it to the right. The center of the guide pulley should be aligned with the outside of the smallest sprocket.
Now turn the barrel adjuster clockwise all the way in and then back off one turn. The barrel adjuster can be placed on your shifter and/or rear derailleur. Next remove excessive slack from the cable at derailleur’s cable fixing bolt and tighten it. Turn the crank and check if it shifts to the next gear. If it’s not fully shifting to the next gear, then you’ll have to turn the barrel adjuster anti-clockwise. This moves the derailleur’s position a bit more to the left for all the gears. Continue adjusting the barrel adjuster until it properly shifts between the first gears and it’s not rubbing against the next sprocket when in gear.
The Top limit is now set and shifting in the higher gears should work properly now. To set the low limit you have to shift to the largest sprocket and the smallest chainring. If you feel a resistance in your shifter when shifting to the largest sprocket, like the gear is blocked, turn the lower limit scew, indicated by the letter L, anti-clockwise until it shifts to the largest sprocket. Whe center of the guide pulley should be aligned with the center of the largest sprocket. Turn the lower limit screw clockwise to move the derailleur to the right and anti-clockwise to move the derailleur to the left.
The last adjustment scew is the B-tension adjust screw. This adjusts the distance between the guide pulley and the cassette. Shift to the smallest chainring and the largest sprocket. If the guide pulley rubs against the sprocket you have to turn the B-screw clockwise to increase the distance. The distance between the guide pulley and the largest sprocket should be about 6mm. If you distance is bigger than 6mm you can turn the B-screw anti-clockwise to decrease the distance.
Now that the limits are set, run through all the gears and check if it’s shifting properly. Minor adjustments can be made with the barrel adjuster. When the chain wants to skip to the next larger sprocket you’ll have to turn the barrel adjuster anti-clockwise. If it wants to skip to a smaller sprocket turn the barrel adjuster clockwise. And lastly check these settings while riding on your bike, a few clicks of the barrel adjustment should be all that you need.