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Bicycle Rear Derailleur Monday, September 19th, 2011

Shimano RD M410 Alivio Rear Bicycle Derailleur 7 8 speed Black
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US $22.05

NEW BICYCLE REAR DERAILLEUR HANGER PARTS 88
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US $.99

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Bicycle Rear Derailleur

Rear Derailleur Adjustment

These instructions should solve all shifting issues, however they may be overkill for most users. Most new bikes come with straight rear derailleur hangers, properly adjusted b screw, and properly set H & L screws. Hence stage#1-#3 are not required for for most new bike owners. However going through all the steps should solve shifting issues if simply going through #4 is not sufficient. Stage #1 Make sure the rear derailleur hanger is straight Check the rear derailleur hanger. Visually, one can see the below hanger is bent inward toward the frame. A rear derailleur hanger alignment tool is required to adjust it perfectly. However when a tool is not available it can be adjusted by pulling the derailleur with ones hand away from the cassette until the derailleur is perpendicular to the ground. The stock hanger is very soft and can be bent several times. Below we use the Park DAG-1 too to straighten the hanger. We will remove the derailleur, then use the tool to check if it aligned properly, if it is misaligned we will use the tool to bend it back into place and repeat until we are finished. From geometry we know two points define a line, and three points define a plane. Our goal is to place the hanger on a parallel plane with respect to the cassette. We will use the tool to place the hanger on a parallel plane as the rim. We will assume the rim and cassette are on parallel planes. We will use the DAG-1 tool to measure the distance from the rim at 3 different points and to bend the hanger until the distance from three points to the rim is the same. Step #1 Remove rear derailleur from the hanger with an allen wrench. Step #2 Install the DAG-1 hanger tool onto the hanger as shown Step #3 Test the distance from the DAG-1 tool to the rim at three points. If this distance is the same the hanger is in the proper plane and the job is done. Step #4 If the distances are not the same at all points around the rim use the tool as a lever bending the hanger to make the distances closer. Repeat the steps #3 & #4 as often as needed until the distances are the same. Stage #2 Adjust the b Screw We will assume the rear derailleur H & L screws are pulled out. Hence there should be no restriction on the derailleur's movement. The b screw adjustment is required when either: A). In the largest cog there is an issue with chainsuck ( when the chain wraps around the largest cog instead of going directly to the rear derailleur). B). One experiences shifting issues in the smallest cogs. As a general rule of thumb the b screw should be about 6mm away from the largest cog. Step #1 If you experience chainsuck issues in the biggest cog turn the b-screw clockwise to pull the rear derailleur back. Step #2 If you have problems shifting in the smallest cogs turn the b screw counterclockwise to push the rear derailleur in. Stage #3 H & L screw adjustment H & L screws limit movement on the rear derailleur. The rear derailleur should never be allowed to move inside the inside face of largest cog, this risks the chain getting caught between the spokes and rear cog. Once this happens you may need to rebuild your rear wheel. Additionally the rear derailleur should never be allowed past the outside face of the smallest cog. This could allow the chain to get wedged between the frame & cog possibly tearing up the frame. The H and L screws will limit motion by the rear derailleur past the biggest & smallest cogs to minimize the probability of problems occuring. These instructions are for a single chainring drivetrain. Our procedure ( algorithm ) is very quick and proper for our bicycles, but allows for some variability. Do not use these instructions for a multi chainring bike. Step #1 Check the rear derailleur. View the H & L screws Step #2 H screw has a yellow oval around it. L screw has a blue oval.. Note the H screw is out & L screw is in. Step #3 Place the chain on the largest cog. Pull the cable with your hand to create tension, if this causes the derailleur to move inside the largest cog you must turn the L screw clockwise until the derailleur is below the biggest cog, then back off counterclockwise a bit ( not to restrict range ). This will keep the rear derailleur from coming off the largest cog & backing off will not restrict the range of motion. Step #4 Place the chain in the smallest cog. Relieve all tension from the cable, if this causes the derailleur to move outside the smallest cog you must turn the H screw clockwise until the derailleur is below the smallest cog, then back off counterclockwise a bit ( not to restrict range ). This will keep the rear derailleur from coming off the smallest cog & backing off will not restrict the range of motion. Stage #4 Cable tension adjustment We will assume you have gone through stages #1 to #3 in adjusting a rear derailleur. This is the last and possibly easiest step. You will require a bike stand or a person willing to hold the rear wheel in the air. Due to spring tension the rear derailleur prefers to stay in the smallest cog ( assuming there is no cable tension ). Cable tension lifts the derailleur into the larger cogs. Hence if the derailleur does not move into larger cogs it needs more cable tension, achieved by turning the barrel adjuster counter clockwise. If the derailleur does not move into smaller cogs it has too much cable tension, and the tension must be relieved by turning the barrel adjuster clockwise. In short our procedure ( or algorithm ) for adjusting the shifter is as follows. If the shifter is in a smaller number gear than the chain ( for ex. chain is in #2 cog while shifter in #1 ) one should turn the barrel adjuster clockwise. On the other hand. If the shifter is in a larger number gear than the chain ( for ex. chain is in #2 cog while shifter in #3 ) one should turn the barrel adjuster counterclockwise. Step #1 View the barrel adjuster on the rear derailleur. Step #2 Put the bike in a stand or have a partner hold up the rear wheel. Step #3 Put the shifter in 1st gear and rotate the pedals. If the chain is not in the biggest cog we will assume it is in a smaller cog due to the limiting ( H & L ) screws do not allow it anywhere else. Turn the barrel adjuster counterclockwise & rotate the pedals until the chain is in the largest cog. Step #4 Run through the gears on the shifter from 1 to 9 if the rear derailleur does not shift properly follow the procedure above Step #5 Run back through the gears on the shifter from #9 to #1 if the rear derailleur does not shift properly follow the procedure above Step #6 Test shifting through the gears several times to make sure it is proper. One can adjust the derailleur while riding by turning the barrel adjuster on the shifter clockwise or counterclockwise ( as explained in the procedure ).

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