The front derailleur

Your front derailleur probably won’t give you as many headaches as the rear derailleur will over the life of your bike, but it will need occasional care and service. If you have a front derailleur that’s acting up, it probably needs a

new cable or just a thorough cleaning and lubrication, which will be more effective if you perform it while the derailleur is off the bike. The following sections describe how to remove and then reinstall the front derailleur, as well as how to adjust it.

Removing a front derailleur

To remove a front derailleur, follow these steps:

1. Shift the derailleur to the smallest chain ring to remove tension on the cable.

2. Using an Allen wrench or a box wrench, detach the cable by loosen­ing the anchor bolt that holds it in place (see Figure 14-11).

3. Use an Allen wrench or box wrench and undo the pivot bolt that holds the derailleur to the seat tube (see Figure 14-12).

4. To remove the chain from the derailleur cage, remove the nut and bolt holding the cage together, and pull apart the cage so that the chain will slide through (see Figure 14-13).

Some front derailleurs have a rivet holding the cage together, which requires you to first remove the chain from the bicycle and then proceed.

The front derailleur

The front derailleur

Figure 14-12:


the pivot


The front derailleur

Figure 14-13:

Pulling the cage apart.

5. Spread apart the derailleur mounting clamp and remove the derailleur from the seat tube.

Installing a front derailleur

Follow these steps to install a front derailleur:

1. Open the cage of the front derailleur and wrap it around the chain.

2. Replace the nut and bolt that holds together the cage.

3. Wrap the derailleur mounting clamp around the seat post, and thread the clamp bolt enough so that it isn’t tight but allows the derailleur to be moved by hand.

4. Align the derailleur so that its outside cage edge runs parallel with the chainrings.

Visually inspect the position by standing overhead and looking down on the derailleur.

5. Position the derailleur at a height that places it about 2mm above the teeth of the largest chainring.

6. After aligning and positioning, firmly tighten the mounting clamp bolt.

In order to limit the movement of the derailleur so that it doesn’t throw the chain off the chainrings, you need to set the H — and L-limit screws.

7. Set the L-limit screw so that the side of the cage closest to the bike is about 2mm inward of the smallest chainring.

8. Pull the derailleur away from the bike and over the large chainring.

9. Set the H-limit screw so that when you move the derailleur as far as it will go, it reaches to a position 2mm outward of the largest chainring.

10. After you’ve found the correct position for the derailleur, pass the cable through to the anchor bolt and, while holding the cable taut with a pair of pliers or a fourth-hand tool, tighten the anchor bolt.

Make sure you follow the correct route for the front derailleur cable. Some bikes are designed with the cable coming up from the bottom bracket, and others drop down the length of the seat tube.

11. For a new cable, shift the levers a few times to stretch and seat the cable. Then loosen the cable anchor bolt, pull the cable taut, and retighten if necessary.

12. If you have installed a new cable, cut off any extra and then attach a cable cap to the end. Crimp the end cap in place with pliers.

Always leave about 2 inches of cable on the outside or past the cable anchor bolt. This will make future adjustment to the cable and/or derailleur much easier.

Adjusting the front derailleur

One of the first things you need to do to adjust the front derailleur is to set limit screws so that the derailleur doesn’t move too far and push or pull the chain off the chain rings. There is nothing worse than hitting a steep hill, shifting to your smallest chainring, and having the chain fly off the chainring and become stuck in between the chainring and chainstay. A properly adjusted limit screw will ensure that the chain doesn’t go past the smallest chainring when shifting.

1. Shift the derailleur to move the chain onto the smallest chainring.

2. Set the L-limit screw so that the side of the cage closest to the bike is about 2mm outside the smallest chainring (see Figure 14-14).

3. Shift the derailleur to the largest chainring.

4. Set the H-limit screw so that the cage plate farthest from the bike is about 2mm outside the largest chainring.

5. Try shifting between the two or three chainrings on your bike.

If the chain doesn’t not move easily to the appropriate chainring or it rubs on the side of the derailleur cage, you may need to make some fine-tuning adjustments (see the following steps).

The front derailleur

Figure 14-14:

Adjusting the L-limit screw.

6. To fine-tune the front derailleur, try increasing the tension using the cable adjuster.

On front derailleurs, this is usually located where the cable enters the left shift lever. Make quarter — to half-turns of the adjuster and recheck.

You can also make small adjustments to the H — and L-limit screws to improve shifting or prevent the chain from rubbing on the cage.