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Picture of Tuning a rear derailleur on any bicycle.
One of the most important mechanical components of a bicycle is the rear derailleur. It allows the changing of gears and a smoother more efficient ride. Keeping this component in good working order is essential for any cyclist from commuters to competitive racers. 

Most expensive bike shop visits can be prevented just by doing small maintenance and knowing how to prevent bigger problems in the future. Also less frequent visits to shops will decrease the chance that an employee will try to sell you new parts that you may or may not need. 

This instructable will go over the basic steps to get your bicycle back in working order. With practice, following these steps will have you tuning the rear derailleur with high quality in no time at all.
 
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Step 1: Gather Necessary Tools.

Picture of Gather Necessary Tools.
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One of the most important things in being efficient in tuning a bicycle is to gather all of the proper tools and materials. Having them at hand will make sure that you only spend a few minutes to get your bike back in working order. 

A list of necessary basic tools:

1. Phillips Head Screwdriver.
2. Allen wrenches. Necessary sizes, 4, 5, and 6. (metric). Also a three way tool as shown can be used.
3. Open ended wrenches, can vary by derailleur model. Metric sizes 8 or 10. combination wrenches can be used.
4. Cleaning materials. A simple degreaser, a one step clean and lube, and a shop rag. Note: do not use WD-40 as it will clog up the pulleys.

Optional Tools:

1. Flat nose pliers to aid in pulling cables.
2. Cable cutter to cut excess cable as needed.
3. Bicycle stand. I am using a park tool portable stand.

Step 2: Optional Step: place the bicycle in the stand.

Picture of Optional Step: place the bicycle in the stand.
Properly set up the bicycle in the stand. This can be done in one of two locations. Either the seat tube or on the frame. 

In the image it is on the frame. 

Step 3: Clean the derailleur and gears.

Picture of Clean the derailleur and gears.
The first step in getting a proper tuning is to clean the pulleys and gears to ensure there is nothing inhibiting a clean shift.

Using your cleaning equipment ensure that all excess grease and dirt is removed from the components. 

Once the equipment is cleaned you are now ready to start tuning the derailleur.

Step 4: Remove tension from the cable.

Picture of Remove tension from the cable.
The first step when actually working on the bicycle is to have the proper cable tension. The way to do this is to remove all of the tension first. Shift the chain into the smallest ring to take tension out of the cable. Then loosen the bolt holding the cable tight. In this situation you will either need an allen wrench or one of the open ended wrench sizes. For this derailleur it is a size 10 wrench that is needed.

Step 5: Tension the cable.

Picture of Tension the cable.
First turn the barrel adjuster all the way in until it stops. Once that is done turn it back out 2 full turns. This will allow for fine adjustments in either direction later on.

The next step in properly adjusting the cable is to add tension back into the cable. This is where the flat nose pliers will help. 

Pull the cable to a moderate tension. Pulling too tight will cause the derailleur to not have full range of shifting and not enough will cause the shifting to be very slow or not work at all. While holding the cable at moderate tension tighten the bolt that will hold the cable. Note: ensure not to tighten the bolt too much or the cable may begin to fray or even break.


Step 6: Set the limit screws.

Picture of Set the limit screws.
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There are two limit screws on every derailleur.(image 1) A high and a low limit. The low limit screw prevents the chain from getting stuck between the frame and rear chainrings while the high limit screw will prevent overshifting which will cause the chain to get stuck in the spokes and can be very expensive. 

Properly setting the low limit screw labeled with L:

Turn the screw either in or out to align the derailleur pulleys with the small chainring. (image 2)
The bicycle must still be able to shift to the small ring, test until it is properly set.

Properly setting the high limit screw labeled with H:

Turn the high limit screw in to prevent the chain from jumping over the top of the chain. Ensure that the chain will still reach the large chain ring. To test, push on the derailleur while pedaling to move the chain over by hand. (image 3)

Step 7: Fine tuning the shifting.

Picture of Fine tuning the shifting.
The final step is to fine tune the shifting to proper working order. 

Currently the bicycle should shift into all the gears although it may be slow or clicking in certain gears. This will be resolved by adjusting the tension with the barrel adjuster. Turning the barrel adjuster into the derailleur will remove tension from the derailleur shifting into a smaller ring. Turning the barrel adjuster away will add tension, shifting the bike into a larger chainring. 

Proper shifting will occur when the chain is in the next ring in under one full revolution of the pedals. This will take practice and is not always necessary for all applications depending on what type of riding you will be doing. 

An optional final step is to take the bike for a test ride. Occasionally there will be a difference in how the bicycle shifts when it is on the stand and when it is in use.