Design and principle of operation of the front crossover
The design of the front derailleur is very simple. We will consider all its components, as well as their purpose below.
- Clamp. This part attaches the front derailleur to the bike frame.
- Parallelogram. Parallelogram-shaped hinged spring-loaded part. It is the main moving part of the front bulkhead, to which the frame is attached.
- A guide frame that has an outer and an inner part. A chain runs inside her.
- Adjusting bolts L and H (stops). There are two of them. They restrict the movement of the guide frame towards the frame (L) and away from it (H).
- Cable fixing bolt. Locks the gear shift cable.
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The principle of operation is based on a simple collision of the chain on the desired star. When the gear is shifted from a larger (in diameter) star to a smaller one, the cable tension is weakened, and the switch spring pulls the parallelogram with the guide frame a certain distance towards the frame. The outside of the frame pushes against the chain, causing it to bounce onto the smaller sprocket. When switching from a smaller star to a larger one, the opposite process occurs. The derailleur cable tightens and moves the parallelogram and guide frame away from the frame. The inner part of the frame presses on the chain, and thanks to the special shape of the frame itself, as well as special hooks on the sprockets of the front system, the chain engages and throws it onto a large sprocket.
This design provides limiting bolts (L and H) against which the parallelogram rests when reaching the end positions. If the setting of the front derailleur stops is not correct, the chain will jump off the carriage or connecting rod.
INTERNAL SWITCHING MECHANISM
This type of derailleur uses planetary bushings. In this case, the shifting mechanism is hidden inside the rear hub, which results in one sprocket on the front wheel, a chain, and one sprocket on the rear wheel.
The current planetary hubs have a different number of gears (from three to fourteen), they can also have a built-in brake.
Such mechanisms are mainly used on walking and road bicycles, very rarely on mountain bikes.
Consider the merits of these switches:
- increased resistance to weather and road conditions (the parts of the mechanism are in the case);
- the presence of a built-in brake;
- they are quite reliable and durable;
- such a mechanism allows you to change gears without pedaling;
- fairly simple maintenance.
However, such mechanisms also have disadvantages:
- quite heavy weight;
- complication of movement may occur due to strong friction of the nodes;
- it is impossible to repair the mechanism in field conditions.
How to adjust the rear derailleur
The rear derailleur is a machine that transfers the chain from one sprocket of the rear wheel to another. Today, the vast majority of high-speed bicycles are equipped with such a switch.
The rear derailleur consists of the following elements.
- Switch frame. The number of bike speeds depends on its length.
- Two rollers that are responsible for the direction of the chain: the guide and the tensioner roller.
- The mechanism itself (parallelogram).
- Fixing bolt.
- Low gear stop. screw marked L.
- Top gear stop. screw marked H.
- Cable guide groove.
- Tensioner adjusting screw.
Setting the rear derailleur is necessary if the mechanism is out of order, the chain jumps over the necessary stars, the speed does not switch, a grinding or loud sounds are heard. You can configure the mechanism and debug its work yourself. You will need a Phillips screwdriver and a hex wrench
First, make sure the derailleur is vertical and parallel to the bike. If everything is in order, you can proceed to the setup. For convenience, turn the bike upside down, placing it on the saddle and handlebars, this will give access to the switch itself and the adjustment screws.
- First, lower the chain to the smallest sprocket. Do this with the shifter on the right handlebar of the bike, it is she who is responsible for the rear derailleur.
- Loosen the screw holding the cable. This is done in order to unlock the switch.
- Prepare a screwdriver and find the screw with the Latin letter H.
- Move the switch so (adjust with the screw H) so that the sprockets on which the chain lies (one star on the cassette, two stars on the switch) are in the same plane, i.e. form one line.
Parallelogram Spring Problems
For better operation of the return spring, you need to wash it. Then lubricate after cleaning.
The front derailleur usually has more travel and requires less adjustment, so they usually start with that. In addition, the readjustment here requires less precision and is easier to repeat after the rear.
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Bicycle Rear Derailleur Adjustment
After we have eliminated all 5 possible problems with the rear derailleur, we can begin to configure it. I took a bike with a shimano rear derailleur and divided the whole setup into 8 steps:
On the shifter, we throw off to the highest speed (which corresponds to the smallest star on the block of led stars). We pedal so that the chain is on a small star. (now you understand why it is so convenient to work with the rack)
I do not show numbers on the shifter, but believe me the position of the indicator is on the “number” 9. Which corresponds to the smallest star on the cassette.
When adjusting the rear derailleur on the sprockets (front) the chain is best positioned where you use it most. This is usually the central star on a 3-star system.
Loosen the hexagon or bolt that holds the cable.
We twist it all the way, and then we return one turn back all the adjusting thumbs of the cable tension, which are located on the switch and on the shifter (sometimes there is only one adjustment screw on bicycles, most often it is on the switch, less often on the shifter).
In my case, the cable tension regulator is located only on the shifter. The photo shows how I twist the lamb.
We pull the cable with our hand (it is not necessary to pull with all our strength, the main thing is that it does not sag and be stretched along its entire length) and tighten the bolt holding the cable.
Align the center of the derailleur foot rollers with the center of the smallest chainring on the bike. Some people remove the chain for stages 5 and 6 to fine tune them. I do not see the need for this, you can not shoot, especially if you have a switch that is not of the top level, such as shimano tourney, acera or alivio.
Actually, all this movement of the switch occurs using the adjusting screws with the letters “H” and “L”.
We turn the screw “H” with a screwdriver until the centers of the rollers on the foot of the switch and the small star coincide and go on to the next step.
In the photo, I showed a red line, by which you can see that the switch roller is under a small star on the cassette, which means that the extreme position is set correctly.
We switch on the shifter to the lowest speed (number 1), which corresponds to the largest driven star. We twist the pedals so that the chain goes to the extreme sprocket. And also align the center of the presser foot rollers with the center of the largest sprocket. All this alignment takes place with the screw “L”.
On the shifter, the indicator for switching the speed to number 1, if there are no numbers to the most extreme position, which should correspond to the largest star on the cassette.
Essentially, the “H” and “L” screws act as end stops for your derailleur, which keeps the chain from flying off while driving and keeps you alive.
We drop again at the highest speed. Remember to pedal? The chain should be on the smallest star. Next, switch to one speed and turn the pedals, if the chain does not jump or does not jump right away, then you need to slightly unscrew the adjusting screw that adjusts the cable tension (it turns out we are pulling the cable).
Then again we check and switch from the highest speed one step lower (if an 8-speed cassette, then from 8 to 7 speed), if the switch happened immediately, congratulations you set the switch! You can check the remaining speeds will also easily and clearly switch both up and down.!
The chain should jump to the adjacent speed. In my case, this is a 9 speed cassette. Switching from 9 to 8.
Adjust the distance from the largest star to the derailleur roller. This distance should be about 4 mm, if the distance is greater, the switching clarity will be reduced. The adjusting screw on the switch is responsible for adjusting this gap. By unscrewing the screw, the distance decreases, screwing it in increases. tuning is done on the largest star corresponding to the number 1 on your shifter.
COMBINED GEAR SHIFTING MECHANISM
Such mechanisms are hybrids of a conventional shift mechanism and a planetary hub.
Such mechanisms are in most cases installed on city bicycles. On other types of bicycles, they have not received their distribution, since they have all the disadvantages that internal and external switching mechanisms have.