How to replace your front derailleur

Jul 06, 2023

Difficulty

Easy

Our guide to replacing your front mech and getting it shifting smoothly

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Shimano is a bike component manufacturer based in Osaka, Japan. The company is one of the industry’s most popular manufacturers and it makes up around three-quarters of the bicycle component market by value.

How to Steps

Change into the small chainring and remove the cable

Remove the chain

Remove the derailleur

Fit the new derailleur

Set the support bolt

Set the derailleur height

Attach the cable

Refit the chain

Set the L (low) limit screw

Set the H (high) limit screw

Set the cable tension

Cut and tidy the cable excess

Tools Needed

Step 1

Change into the small chainring and remove the cable

Shift into the small ring, and remove the gear cable. Unfurl it from the cap that holds the excess, pull the crimped end off with the pliers, then undo the cable clamp bolt with a 4mm Allen key. If you’re running Shimano Di2 electronic shifting, then you’ll need to unclip the cable, ideally using the Shimano TL-EW02 tool.

Step 2

Remove the chain

Next, remove the chain. If you have a master (aka quick) link, you can use your pliers to squeeze the link together and remove it. If not, you’ll have to break the chain using a chain tool.

Step 3

Remove the derailleur

Now the derailleur is free, we can remove it from the frame. You’ll either have a braze-on derailleur or a clamp mounted version. Whichever type you have, you’ll likely need a 5mm Allen key to undo the bolt and free the derailleur. Make sure to remember or note the original position of any parts that come off.

Step 4

Fit the new derailleur

To refit the derailleur, or to fit the new one, mount to the curved mounting bracket with the 5mm Allen bolt. Attach loosely, and don’t worry about what height to set – you’ll adjust that later. Some new derailleurs come with a ‘support bolt’, which needs to be un-threaded most of the way before fitting the derailleur.

Step 5

Set the support bolt

Once the derailleur is in place, the support bolt (if you have one) should be threaded back in to touch the bracket, and tightened until the derailleur runs parallel to the outer chainring.

Step 6

Set the derailleur height

Now, set the height of the derailleur. Using the 5mm Allen key, position the outer cage of the derailleur so that it sits between 1-3mm above the tallest teeth of the outer chainring. Also, double check that it’s totally parallel to the outer chainring.

Step 7

Attach the cable

With the derailleur in position, you can attach the cable. This is a good opportunity to swap your old cable for a new one. Guide the cable through the back of the derailleur and under the cable clamp washer.

Pull the end of the cable tight, and fix it in place by tightening the cable clamp.

Top Tip

If your cable is frayed or looking a bit tired, this is a good opportunity to replace it with a new one.

Step 8

Refit the chain

Now the cable is in, refit the chain by guiding it through the frame and front derailleur, over the cassette and chainring, and through the jockey wheels. Rejoin the ends with a master link. Just remember, most master links aren’t reusable, so use a new one to rejoin the chain.

Step 9

Set the L (low) limit screw

With the chain on, we can set the L (low) limit screw on the derailleur. To do this, put the chain on the small chainring and the largest sprocket of the cassette. Turn the L limit screw while pedalling the bike in the stand until you can hear the chain rubbing on the inside of the derailleur, then, then turn the screw a quarter turn anticlockwise. The derailleur should just about miss the chain.

Step 10

Set the H (high) limit screw

Next, set the H (high) limit screw. Before you can set it, you need to change into the smallest cog at the back and the big chainring on the front. Then, you can turn the H limit screw until you can hear the chain rubbing on the outer plate of the derailleur, then turn the screw back a quarter turn, just to leave 1mm or so of space.

Step 11

Set the cable tension

Now we’ve got the limit screws set, we can check the derailleur is shifting properly and add any cable tension if necessary.

Put the chain in the middle of the cassette and try using your shifter to move the chain to the large chainring. If it fails to shift, there’s too little cable tension. Increase the tension either with the barrel adjuster that is inline with your cables, or the micro adjustment bolt near the cable clamp.

Step 12

Cut and tidy the cable excess

Finally, tidy up the excess cable. Guide the end of your cable through the rubber cable guide piece, if you have one. If you replaced the gear cable, cut it to length and crimp a cap onto the end to protect it from fraying.