The correct adjustment of a front derailleur is one of the most subtle bicycle maintenance procedures, as it is about a few millimeters. If you have trouble shifting gears or see the chain hitting the derailleur, you don't need to go to a bike shop to get it fixed. All you need is some basic tools and a good view. With practice and patience, you can become a pro at repairing this item.
Steps
Method 1 of 2: Solve problems with speed change
Step 1. Find out what a properly adjusted front derailleur looks like
The goal is for the front derailleur to sit comfortably on top of the chains, with the outer plate 2-3ml above the largest chainring. This element must be aligned in such a way that it curves parallel to the chainrings and must be parallel to the chain.
If the derailleur rubs against a chainring or gets caught in something, don't get on the bike. Instead, you need to restore the front derailleur
Step 2. Diagnose the problem
Place the bike on a repair stand or place it upside down on the seat and handlebars. Shift the front derailleur into a higher or lower gear while pedaling by hand. Can you reach 2 or 3 gears? Does it click, rub, or bump? Take note of problem areas and remember them as you go through adjustments. Make sure to check the cables and frame as well.
- If the front derailleur does not move when activating the shifter, the cable could corrode. If this is the case or you find cracks, chips or worn parts, you should replace the cable and frame.
- Put the chain over the smallest gear at the front and release all tension from the gear lever. Feel the cable and adjust the tension until it is just barely taut.
- Reposition the derailleur if it appears crooked. You should replace the derailleur or shifter if they are broken.
- Also, the rear derailleur needs to be properly adjusted before proceeding, so check to see if it shifts properly.
Step 3. Shift into a lower gear on the bike
Make sure the chain is over the center sprocket at the rear and the smallest plate in the front. This will ensure that the chain does not stretch diagonally and will loosen the derailleur cable to make it easier to manipulate.
Step 4. Loosen the cable bolt and adjust the derailleur cable
Just above the derailleur, there is a thin cable, hooked in place by a bolt or screw. Usually the derailleur is attached to the frame (the metal skeleton) of the bike. Hold the top of the cable and pull up, then loosen the bolt. Pull the cable up to make it snug, then retighten the bolt again. This way, the bolt will hold down the cable so that it cannot move.
This may move the derailleur slightly, but will adjust it again in a minute. Now, you need to make sure the derailleur cable is snugly snug so that everything runs smoothly
Step 5. Locate the limit screws
There are two small screws on the top or sides of the derailleur, one labeled "L" and the other labeled "H". They are likely not fully screwed in, and are coming off slightly up and out of the derailleur. These are the low and high limit bolts, and they control how far to the left or right the derailleur can move. They are tightened with a regular Phillips ("star" or "+") screwdriver.
- Screw L controls how far the derailleur can advance towards the bike. Screw H controls how far and how far you can go from the bike.
- If the screws aren't labeled, you can easily test them. Switch to the smaller plate in the front. Turn a bolt one full turn in each direction and look at the derailleur. If it moves, this is the lower limit (L), if it doesn't, you should try the other one. If it moves, mark it with an L for future reference.
Step 6. Align the lower end of the derailleur
Shift to the smallest chainring at the front and the largest chainring at the rear so that the chain is all the way to the left and closer to the bike frame. Turn the L bolt so that the derailleur has 2-3mm of clearance on each side of the chain.
You should see the derailleur move as you turn the screw
Step 7. Align the upper end of the derailleur
Pedal the bike and shift the front to the largest cog and the rear to the smallest gear. The chain should be completely to the right of the bike and farthest from the frame. Turn the H limit screw until the derailleur is 2-3mm on each side of the chain so you have plenty of room to move.
Step 8. Set the rear derailleur in the middle gear and then test the derailleur at the front
Shift the rear gears a little in the middle to prevent them from pulling the chain in any direction as you shift. Then pedal the bike and shift up and down through the front derailleur, making sure you don't have a problem. Adjust the limit bolts as needed and have fun with your bike.
Setting the limits too far on both sides can cause the chain to slip. However, you should be able to determine if they are too far away before starting the test
Method 2 of 2: Reset Bad Derailleurs
Step 1. Reset the derailleur if it is hitting the chainrings, bowing or leaning awkwardly
Limit bolts will not fix the problem if the derailleur needs complicated adjustments. If you feel the derailleur hitting the chainrings (it's tilted or too high) you'll need to reset it and start over.
Step 2. Switch to the leftmost plates
Switch to the smallest plate in the front and the largest in the back. You may need to place your bike on a stand or upside down to easily pedal and change gears at the same time.
Step 3. Loosen the barrel adjusters to relieve the tension on the cable
These adjusters are typically located at the end of the derailleur cable, near the handlebars. To find them, you need to follow the front derailleur cable until it reaches a small rotating cylinder. Turn it clockwise as far as you can.
Count the number of rotations you make on the barrel. You should put it back in roughly the same position when you're done
Step 4. Unhook the screw that holds the derailleur cable in place
Above the derailleur there is a cable that runs to the gear lever. It is held in place by a small bolt that prevents it from moving or slipping. Unscrew this screw enough that the cable can move freely if you pull it but it doesn't slide on its own.
Step 5. Unscrew the bolts that secure the derailleur to the bike frame carefully
You don't want him to move seriously, as any major movement will change the entire lineup. Unscrew the bolts enough that you can move and reposition the derailleur.
Step 6. Gently move the derailleur to the right place
If the derailleur is tilted, you should rotate it so that it is parallel to the chain, being careful not to change the height. If you touch the top of the chainring, move it up a few millimeters so that it is over the largest sprocket. The objectives are the following:
- get 1 to 3mm of clearance above the largest chainring (you should be able to comfortably fit a coin between the outer plate of the front derailleur and the chainring sprockets)
- make both plates parallel to the chain
- match the curve of the derailleur to that of the sprockets
Step 7. Retighten the cable and limit screws
Once you've made your changes, you need to readjust the front derailleur to run smoothly. To achieve this, you must tension the cable and re-hook it under the bolt. Then tighten the limit screws.
Make sure to lubricate the chain and keep it clean for the best gear shifting. Also, you need to readjust the barrel adjusters
Advice
- It is helpful to have pliers handy to help you tighten the wire.
- Do your moves slowly and then re-hook everything and give it a try. Don't try to make big, exaggerated movements or screw turns, as this can make it difficult to return to the previous setting if something goes wrong.
- For instructions on how to adjust a Shimano front derailleur, you can refer to the wikiHow article on How to adjust a Shimano front derailleur.