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Like all mechanical components of the bicycle, the gearbox must be treated with care. The bicycle gear is the component that allows the chain to move from one sprocket to another, thus varying the ratio and the metric development of pedaling.
Being a highly-stressed component and working as a result of mechanical stress, it is therefore prone to failing. In this article we will see how to make the step-by-step adjustment of the rear gear box.
Here are the six steps you can take to fix bicycle gear step by step:
Before we can look at how to fix the bicycle gear, let’s look at its operation.
How does bicycle gear work?
Some bicycles are equipped with a derailleur-changing system that changes gears by derailing the chain, passing from one tooth or one sprocket to another.
The transmission system consists of all those parts of the bicycle that allow the derailleur to change gears, including the front derailleur or rear derailleur, the gearbox controls, the transmission cables, the transmission chain.
By reducing the ratio, by actuating the gearshift controls, the chain is moved towards the inside of the bicycle, allowing you to accelerate and ride easier and more comfortably.
Increasing the ratio, again by actuating the gearshift controls, causes the chain to move out of the bicycle, allowing you to acquire greater speed while pedaling.
To be able to vary the ratios correctly, it is always necessary for the chain to be tensioned. It is therefore necessary to always pedal forward to guarantee the exchange system to carry out its work correctly.
Warning: Operating the transmission system while pedaling backwards may cause the chain to fall, causing it to become jammed, thus causing serious damage to the bicycle and a possible loss of control resulting in a fall.
1) Front derailleur:
The front derailleur is controlled by the control on the left. Reducing the ratio by selecting a smaller gear makes pedaling easier. Increasing the ratio by selecting a larger gear, makes the ride more challenging but allows you to gain speed.
2) Rear derailleur:
The rear derailleur is controlled by the control located on the right. By moving the chain from a small gear to a larger one, the ratio is shortened, making the pedaling more agile with a lower requirement for physical effort.
By moving the chain from a large gear to a smaller one, the ratio lengthens, making the ride harder but allowing, through greater physical effort, to reach higher speeds.
A correctly adjusted derailleur system should not give problems. If an unusual noise follows every gear change, it is possible that the derailleur cable should be adjusted. If, after adjustment, the noise persists or increases in intensity, stop the bicycle and try to identify the source of the noise.
Refer to the dealer to identify and eliminate problems and set up a proper adjustment of the derailleur system. The adjustment of the front derailleur must be carried out with the bicycle securely held in a work support or with someone who keeps the rear wheel raised off the ground, so that the transmission and the transmission system can be activated while the bicycle remains stationary.
Adjustment of the low travel position of the front derailleur
1. Move the chain on the smaller front rim and on the tooth of the larger cassette.
2. Loosen the clamping bolt of the front derailleur cable until the cable is free.
3. Turn the low travel adjusting screw (marked with “L” until the inner derailleur chain guide is about 0.5 mm from the chain
4. Pull the end of the cable and shift downwards the left shift lever a few times so that it is in the position of the small chain crown
5. Turn the shift cable adjusting cylinder to its most extreme position clockwise.
6. Insert the cable into the groove next to the derailleur cable tightening bolt, tighten the cable and tighten it: check the “Tightening torques” table.
Adjusting the high gear position of the front derailleur
1. Move the rear derailleur to the smallest rear tooth.
2. Turn the high-speed adjustment screw (marked “H”) clockwise so that it cannot interfere with the movement of the front derailleur.
3. While turning the crank by hand, use the shift device to carefully move the chain on the outermost rim.
4. With the shift device, place the outer chain guide of the front derailleur approximately 0.5 mm from the chain.
5. Re-tighten the high-speed adjusting screw until it meets resistance.
If the screw has been tightened too much, the front derailleur will move towards the small chain ring.
Adjustment of the mid-travel position of the front derailleur, with three chain crowns
1. Move the chain on the larger front ring and on the smaller rear tooth.
2. Turn the cylindrical tension regulator of the chain (on the lower tube or lever) counterclockwise increasing the tension of the cable to align the inner derailleur cage until it touches the chain.
Test the various gear combinations to make sure that the chain is easily aligned with all chain crowns.
Note: some front shifter devices have a ‘tongue’ function. By moving the lever slightly to a lower gear, the derailleur moves slightly and should no longer touch the chain.
Adjustment of the high gear position of the rear derailleur
1. Move the chain on the smaller rear tooth and on the larger front chain.
2. Loosen the cable tightening bolt until the cable is free.
3. Stand behind the bicycle to check that the smaller rear ring and the two front derailleur pulleys are aligned.
4. If not, turn the high-speed adjustment screw (usually marked with “H”) until the alignment is created.
5. While pulling the cable, engage a higher gear until the gearbox is in the small tooth position.
6. Turn the adjustment cylinder all the way clockwise onto the gearshift device, or the down tube. Turn the adjusting cylinder completely clockwise on the rear derailleur and then turn it one turn anticlockwise.
7. Insert the cable into the groove of the clamping bolt on the rear derailleur, tighten the shift cable and tighten it.
Adjustment of the low travel position of the rear derailleur
1. Turn the low travel adjusting screw on the rear derailleur (generally marked with “L”), counterclockwise enough to not restrict the movement of the derailleur.
2. Move the chain to the smaller front chain ring and the larger rear tooth. Do not move the rear derailleur too much or the chain may lock between the large tooth and the spokes.
3. Align the pulley of the rear derailleur with the largest tooth.
4. Turn the low gear adjusting screw clockwise until it meets resistance. If it is turned too far, the derailleur moves towards the outside of the bicycle.
5. Test the various gear combinations. Make sure the chain does not fall when changing gears.
Align the indexed system of the rear derailleur
1. Move the chain on the larger front ring and on the smaller rear tooth.
2. Change one step with the rear derailleur.
3. Check that the chain moves easily to the next gear.
4. If the chain makes too much noise or does not move, slowly turn the cylindrical governor counter-clockwise and check again that the transition is easy.
If the chain moves to the third smallest ring, turn the cylinder regulator clockwise until it is aligned with the front derailleur pulleys and the second smaller tooth. Inspect the various gear combinations to make sure the chain aligns easily with all the rear teeth.
If the derailleur could not be adjusted in this way, the derailleur hook could be misaligned; bring the bicycle to your dealer for assistance.
How is the gearbox made?
The gearbox consists of two main parts: the barbell and the cage. The first is the actual body, on which the transmission thread acts: at each variation of the ratio the tension of the cable acting on a spring, which keeps the barbell in position, will change.
The gearshift controls are indexed, i.e. with each click of the lever corresponds the alignment with a certain pinion of the cassette. The derailleur does not move linearly but has a movement defined as a parallelogram, since it always maintains the same distance from the pinion, even if the diameter of the pinion is changed.The cage instead is a metal body formed by two steel blades fixed together with two screws. The same screws act as a pivot of the pulleys, the two toothed wheels that intertwine with the links of the chain and always keep it taut.
The derailleur is fixed to the dropout by means of a screw, which usually tightens with a 5mm Allen wrench or with a 9mm wrench.
The dropout has a protrusion on which it is made to rest what is called “the nail” of the derailleur, or a small plate that has the task of pressing against the dropout allowing the bar to have the proper resistance to move.
When to adjust the gearbox
During a bike exit the derailleur moves hundreds if not thousands of times (especially in off-road) and this leads to a progressive loss of regulation. There is no expiration date or a precise interval of time between one adjustment and another, simply done every time it is necessary. The symptoms that denote the need for a gearbox adjustment are:
- Difficulty of changing: The chain does not rise or does not flow smoothly between the various sprockets, or the gearshift is very slow and the chain takes several turns of pedal before moving from one sprocket to the other;
- Chain hopping: When you are pedaling, you feel that the chain “dances” on the sprockets, making it difficult to mesh;
Fall of the chain: When you pedal using the smallest or largest sprocket the chain falls on the frame or between the spokes of the wheel;
- Poor response: When you operate the gearshift lever, you feel it too soft or too hard and the derailleur’s response is slow;
- Fall: After a fall or a blow taken on the transmission side, it is advisable to check all the adjustments of the gearbox, to verify that there was no serious damage;
Regulation: equipment, timing, difficulty
To adjust the gearbox you need:
- A suitable cross-head screwdriver;
- 5mm Allen wrench or a 9mm wrench, depending on the type of fixing for the cable on your derailleur;
- Cotton degreaser and cloth;
Adjusting the gearbox correctly requires no more than ten minutes of work. Obviously the first few times can be more difficult and having to deal with all those screws and registers can scare but once you have stored two basic principles and learned the technique, the adjustment becomes almost automatic.
The first thing to do, before “tweak” directly on the gearbox, is to verify the perpendicularity with the ground. Put the bike on the stand (without this tool lean it straight to a wall) and stand in front of the rear wheel.
Look carefully at the front derailleur cage: is it parallel to the wheel or is it crooked (usually bent towards the wheel itself)?
If the cage is folded, it certainly happened as a result of a blow or a fall. There are two symptoms that can explain this situation:
The dropout is the kind of stirrup that is integrated into the frame in the bike of a certain age, while in the new generation it can be removed by means of a screw.
The wheel pin is inserted into the dropout and the derailleur is screwed on. Usually a blow, a gearshift under tension or the breaking of the chain tend to force on the dropout, bending it towards the wheel. There is only one way to check that the dropout is folded. We need to equip ourselves with a tool called caliber.
The derailleur is removed and the caliper is screwed into place. The rear wheel is rotated until the valve is at its highest point and the gauge body is approached.
This is equipped with a pawl that allows you to measure the distance between the dropout and the wheel. The gauge is then moved to the opposite point of the wheel and the measurement is resumed. If the latter is smaller than the first, then the dropout is bent and must be replaced.
The caliber is not an expensive tool and is very useful but if you are not a “geek” as the undersigned does not make sense to buy it, better bring the bike from a shopkeeper to make it check:
Folded derailleur cage
Following a fall or impact with a root, a stone, the sidewalk, the cage of the derailleur, being without protection, can bend. In this case the pulleys would be located offset from one another, causing the chain to work badly.
A derailleur with a folded cage is to be replaced, because trying to straighten it back bringing it in line by force with a key can trigger a crack at the bend point.
From this cricket a process called “fatigue of the material” will start which will progressively thin the wall of the cage, until it reaches a section that is not able to bear the applied loads and will break.
Adjust the gearbox step-by-step
Step 1: Reassemble the derailleur and clean
The control of the dropout should always be carried out, so remount the derailleur in its seat, paying attention to match the “nails” of the two components.
Then take the degreaser and spray on the whole transmission. Always use products designed for use on bicycles and avoid universal degreasers that are too aggressive. Finally clean everything with a cotton rag.
Step 2: Bring the derailleur on the hardest relationship
The perfect adjustment of the gearbox starts by lowering the chain onto the smallest sprocket. On the other hand, if your bike is fitted with a single crank set, there is no problem, if the crank is double you can use them indifferently while if you mount a triple you have to place the chain on the intermediate crown.
Step 3: Free the cable
The steel cable allows to connect the gear lever to the gearbox and to give power to the system. Release the tension cable by using a 5mm Allen key or the 9mm wrench on the appropriate nut.
Check that there are no folds, cracks, fraying and there is no trace of rust on the cable, as sometimes the loss of efficiency of the gearshift is due to the wear of cables and sheaths. If you find it difficult to pass, you can participate in one of our basic mechanics courses to have an experienced mechanic guide you personally in this operation.
Step 4: Eliminate the residual voltage
The gearbox is a system that works in tension, where the cable is stretched more or less intensely to allow the derailleur to move on the various sprockets. The intensity of the voltage is assigned to a pawl, called the voltage register.
On racing bikes and on many trekking bicycles, the log is installed directly on the balance of the gearbox (from which the gear cable passes).
Screw the register to the end of the stroke. Remember this scheme:
- I screw the adjusting screw = I decrease the tension
- I unscrew the adjusting screw = increase the tension
Learn it well because it will be essential to know it to carry out further operations.
Step 5: adjust the limit switch H
On the back of the derailleur there are three screws:
i). The first, called H, is the register that adjusts the lower limit switch , that is when you pedal with the longest or fastest ratio (H stands for High speed). Basically it allows aligning the derailleur pulleys with the smaller pinion, avoiding that the chain exceeds the frame;
ii). The second one, called L, is the register that acts on the upper limit switch that is when we pedal with the shorter or slower ratio (L stands for low speed, low speed in English).
By acting on this end, the derailleur pulleys are aligned with the largest sprocket, avoiding that the chain falls between the spokes. This eventuality is quite unfortunate because if it happens while we are pedaling we risk tearing the derailleur away from its seat, splitting the spokes and incising the pendant of the frame;
iii). The third is the spring tension screw, which brings the upper pulley closer or further away from the sprockets. Later I will explain what it is used for and how it is regulated.
If there are no H and L markings on your derailleur, in order to avoid mistakes, always remember that the H screw is the topmost and next to the frame and the L screw is the lower and furthest.
Take the screwdriver. With the left hand, turn the pedals while with the right hand act on the screw, screwing it or unscrewing it until the chain rotates without noise and the pulleys of the derailleur are not parallel to the pinion.
A good trick is to screw the whole screw, then turn the pedals and start to unscrew until you hear more the typical noise of the chain that rubs against the face of the upper pinion.
Step 6: Insert the cable into the housing
Take the cable again, slide it into the appropriate seat and stretch it with your left hand. Do not exaggerate, it should only be stretched by hand (so put away those pliers), because the true tension will be adjusted later. With the 5mm Allen wrench or the 9mm wrench, tighten the screw that secures the cable, tightening it firmly so that the cable does not escape.
Step 7: Adjust the voltage
Spin the pedals and try to change. If the chain does not rise, it means that there is no voltage in the system and therefore you will have to tension the cable, turning counterclockwise, and then unscrewing the tension register.
Unscrew until the chain rises correctly. Try with all the sprockets until it goes well on all, and then try to climb the sprockets. If the chain is struggling to go down, then there is too much tension and you will have to screw the register slightly.
Always remember this mirror:
- Chain does not rise = insufficient tension = unscrew the register by turning it counterclockwise
- Chain does not come down = excessive tension = screw the register by turning it clockwise
Try several times to get up and down all the sprockets, until the shift is smooth. I remind you that on the register you work with 1/4 of a turn at a time, since it is a very fine adjustment.
Step 8: adjust the limit switch L
Take the chain on the largest sprocket and on the smaller crown on the front. If the chain does not climb on the largest sprocket but can climb all the others well, loosen the L limit screw slightly, as it is too tight and prevents the derailleur from climbing.
Now that the chain is on the largest sprocket, check that the pulleys are parallel to the sprocket and try to push the derailleur with your hands while you spin the pedals. The chain must never go beyond the big pinion and you must never move towards the spokes and obviously must not fall.
If it does, you must tighten the L screw 1/4 of a turn at a time until the chain turns without noise but cannot go beyond the pinion. Try again to scale all the ratios 2 or 3 times.
Step 9: adjust the tension of the spring
We carry the chain on the largest pinion and on the smaller crown. Always with the screwdriver, we act on the screw that adjusts the tension of the rocker spring.
Unscrewing the screw, we bring the pulley closer to the pinion. The light between the pulley and the derailleur must be minimum (about 3mm), because the greater the light between the two, the larger the portion of the chain that is not stretched by the pulley, making the gearshift less fluid and faster.
Once approached the pulley to the pinion, try turning the pedals: if the gearbox starts to vibrate it means that you have gone too close and you have to move away.
Now try to climb a relationship. If you feel a tear-like noise or if the chain rises above the pinion teeth before going down, it means that you are still too close and you have to move away. Also in this case we are talking about 1/4 turn operations at a time.
Step for demanding: very fine regulation
This step I insert for the most demanding, like me, who want to add further finesse to the regulation. With the steps we have seen so far we reach an excellent level of regulation but with this passage the regulation will be perfect.
I recommend it only to those who use high-end components, as this type of process only affects groups with very precise mechanical processes.
Return the derailleur to the small pinion, screw the tension register back to its end and pull the cable towards us (without removing it from its seat, I recommend!).
In this way we eliminate the tension on the cable and essentially repeat the operation of adjusting the tension going to unscrew the register and passing the chain several times on all the sprockets.
This operation is used to eliminate the first tension we have given to the cable, which is countered by the elastic behavior of the steel which, when stretched, tends to return to the starting position. In this way we overcome this elastic limit, allowing the system to balance the tension and lengthening the period of the first retention.
Final step: Lubrication
Remember, once the adjustment is finished, to lubricate the chain following the instructions that we have reported in the dedicated article.