14
djusting Derailleurs

Derailleur Basics

The common rear derailleur designs all operate on the same principle. A moveable cage receives the chain returning from the chainwheel and directs it onto one sprocket of the cluster. Moving the cage sideways directs the chain onto a different sprocket. The cage contains two jockey wheels or rollers, over which the chain rolls. Because the cage is rotated by a spring, the rollers keep the chain taut no matter which sprocket is being used.

There are two methods of selecting the position of the rear derailleur: indexed shifting and friction shifting. With indexed shifting, the lever has a click-stop at the proper position for each of the gears. With some levers, the lever moves to the new position and stays there; with others, it moves to the new position and then returns to the neutral position to wait for the next movement of the cyclist’s finger. With friction shifting, the lever has no stops but can be moved to any position, where it is held by friction. Many indexed shifting levers also allow for friction operation when the derailleur isn’t shifting properly. When indexed shifting systems are working well, they are a joy to use. The manufacturers say that they work well only with the types of cog and chain for which they are designed. This may be just the manufacturers’ way of getting the whole sale, but there is some truth in it. This is one more manifestation of the combination of more models with fewer choices and less flexibility that afflicts the business today.

A front derailleur can be used only with a rear derailleur that takes up the slack in the chain. Therefore the front derailleur is merely a cage that moves the chain sideways as it feeds onto the chainwheels. All front derailleurs use friction levers because their operation is heavily influenced by which rear sprocket is being used.

Derailleur Selection

There are two types of derailleurs: narrow-range derailleurs for racing and wide-range derailleurs for touring and mountain bike use. The older narrow-range racing derailleurs, designed for five-speed rear clusters with double chainwheel, had ranges that were even narrower than modern racing derailleurs designed for nine-speed rear clusters and widely spaced chainwheels. Racing derailleurs give quick shifts over small differences, but can handle only a small difference between lowest and highest gears. Touring and mountain bike derailleurs can handle a large difference between lowest and highest gears but give slower shifts. A wide range of gears requires widely different sizes of both rear cogs and front chainwheels. Therefore, a wide-range gear system must be able to take up a lot of chain slack, and narrow-range systems can get by with much less take-up capacity. Rear derailleurs are typically rated by two characteristics: total chain capacity and largest rear sprocket. The length of the cage determines the chain take-up capacity, and the position of the upper jockey wheel determines the largest rear cog that it will clear. A characteristic that is harder to see when the derailleur is in its sale box is the changing height of the upper jockey wheel as the derailleur moves. Modern derailleurs are designed to lower the jockey wheel as the derailleur moves to low gear, to keep the distance between the jockey wheel and the active cog as constant as is possible. Wide-range derailleurs incorporate more of this change than do narrow-range derailleurs, because wide-range derailleurs must operate with large differences in cog size. Front derailleurs are rated by total chainwheel difference. A front derailleur designed for a very small inside chainwheel must have a cage that extends down much further than one designed for a large inside chainwheel, and it may have other differences also.

Derailleur Adjustments

To do any derailleur adjustments properly, you must have the bike on a stand so that the cranks and rear wheel can spin freely. See the section on workstands under “Tools” in chapter 2.

These adjustment instructions assume that nothing major is wrong, like a bent derailleur or bike frame, incorrect rear hub position, or incorrect chain length. First make sure that the derailleur mounting bolts are tight and that the derailleur has no obviously bent or broken parts.

Control Cable Troubles

If a cable inner wire breaks, the solution is obvious: install and adjust a new one. A kinked wire or housing can make shifting difficult—straighten or replace it. Indexed systems are so sensitive that they will work only with perfect wires and housings. The shift lever must be stiff enough so it won’t be pulled back by the derailleur spring when you release it. If the derailleur keeps shifting into higher gears, the lever friction adjustment is probably loose. Tighten the adjusting-lever screw until the lever moves when you want it to, but not by itself. If the cable is too long, it will be adjusted during derailleur adjustment.

Derailleur Body Position Adjustment

Some derailleurs are designed with a position adjustment that controls the angle between the derailleur body and the chain stay. Start by turning the adjusting screw to make the parallelogram mechanism parallel with the chain stay (unless the manufacturer provides other instructions). You may change this in the final adjustment, depending on the size of the largest sprocket.

Cage Travel Adjustment

All derailleurs have two adjustable stops that prevent the cage from moving too far left or right. The cage of a rear derailleur is pulled to the left, toward the spokes, when you pull on the cable with the lever. The left stop prevents you from dropping the chain between the largest sprocket and the spokes and from forcing the derailleur cage into the spokes. The stop screw inside the derailleur body prevents the cage from going too far left, toward the small sprockets, when you release the cable by pushing the lever. The right stop prevents the chain from dropping off the smallest sprocket, where it either slides uselessly over the axle or jams between the smallest sprocket and the seat stay. The front derailleur operates the same way, except that on most of them, the spring pushes the front derailleur to the small chainwheel and the cable pulls it to the larger. (This is called the low-normal type of front derailleur.)

Find the adjusting screws on your derailleur by twirling the cranks and moving the derailleur from high gear to low and back again. You will see that the cage mechanism bumps against one screw at its furthest left position and one at its furthest right. Different manufacturers and different models have slightly different arrangements for the stop screws.

Set the high-gear adjusting screw first. Twirl the pedals and shift to high gear (the smallest sprocket). If the chain won’t go onto the small sprocket, loosen the high-gear screw until it does. If it goes too far, tighten the screw. If loosening the screw doesn’t let the cage move further to the right, the cable may be too tight. Loosen the cable wire clamp bolt at the derailleur and leave the cable slack. Then adjust the high-gear screw until the chain feeds straight onto the small sprocket without noise. Adjust the cable length by loosening the cable clamp bolt and moving the lever all the way to its high-gear position. Then pull the cable taut at the derailleur and reclamp it. Then check the adjustment by turning the pedals and shifting out of high and back in several times. If the shift to the smallest sprocket is not quick, try unscrewing the adjusting stop a little more.

Next set the low-gear adjusting screw. Twirl the pedals and slowly move the lever to the low-gear position. If the chain won’t reach the largest sprocket, loosen the low-gear stop screw until the chain shifts easily onto the largest sprocket. Once the chain reaches the largest sprocket and feeds straight onto it, tighten the low-gear screw until you feel it touch the derailleur arm. Then recheck the adjustment by shifting out of low and back again several times. If the shift to the largest sprocket isn’t quick, try unscrewing the adjustment a little. However, watch that the derailleur cage does not touch the spokes—listen for a little pinging sound. You should be able to get a good shift into low using either the small or the large chainwheel without the cage pinging on any spoke. If it touches a spoke, first check to see if the spoke is bent or loose. Then just tighten the adjusting screw until the cage doesn’t touch it, even if the shift is slow.

If the derailleur cage still touches the spokes in low gear, look for other troubles. The chain may be a little too loose, which with a large sprocket makes the jockey pulley overlap the largest sprocket as it tries to climb onto it, which forces the cage to move too far to the left to get the chain to climb onto the largest sprocket.

The spokes may not be laced—that is, they may not be interlaced at the furthest-out crossing. Lacing narrows the cone of the spokes so they are further from the cage. The derailleur may be bent a little. You may have an unusual hub that requires a spacing washer behind the cluster to move it away from the spokes.

You also have a front derailleur to think about. First, make sure that it is in the correct position. The cage should be parallel with the chainwheel and no more than ¼ inch above the chainwheel teeth at the closest position. If the cage is not in this position, loosen its clamp bolts and reposition it. Many front derailleurs have cages that are wider at the bottom than at the top. Make the outside bar of the cage parallel with the chainwheel.

The front derailleur also has two adjusting screws. Find which screw is which by watching the mechanism operate as you shift back and forth. One screw is the left (small) chainwheel stop. The other is the right (large) chainwheel stop. Put the rear derailleur into high gear (smallest sprocket), and adjust the large-chainwheel stop of the front derailleur. It should be adjusted so that the front derailleur kicks the chain onto the large chainwheel without throwing it over the chainwheel and so that it doesn’t scrape the cage against the chain.

Then change the rear derailleur to low gear (largest sprocket). Now adjust the front derailleur’s small-chainwheel stop so that the derailleur kicks the chain onto the small chainwheel, but not off it, and doesn’t scrape the cage against the chain.

With the rear still in low, flick the front derailleur back and forth to see if it changes well. If necessary, loosen the large-chainwheel stop a little further to get a quick shift when the rear is all the way to the left. Then shift the rear to high gear and flick the front derailleur back and forth again to see if you get a quick shift onto the small chainwheel when the rear is all the way to the right. If necessary, loosen the small-chainwheel stop a little.

When you are using the maximum crossover positions of the chain—large sprocket and large chainwheel, or small sprocket and small chainwheel—the chain may scrape against the side of the front derailleur cage. Don’t worry. Once you have completed your shift, move the front lever just enough to stop the scraping, and it should run free without scraping. The movement should always be toward the center of its range.

You may also find that when you are using the small chainwheel with the small sprocket, the chain scrapes against the side of the larger chainwheel. This problem is most likely when the small chainwheel is considerably smaller than the large chainwheel. If this occurs, then decide to use this combination only rarely.

Cable Adjustment for Indexed Shifting

When the cable of a rear derailleur is slack, the derailleur rests against the high-gear stop and moves the chain to the smallest sprocket (that is, if the stop has been properly set). Each indexed-shifting derailleur requires a specific amount of shift-cable movement from this relaxed position to reach each gear. The indexing shift lever that matches that derailleur design has its click-stops set so that it pulls that exact amount of cable for each gear. As long as the designers have done a good job, all that the user needs to do is to adjust the length of the cable so that the cable is just taut when the lever and the derailleur are in their highest-gear position.

To allow for precise adjustment, the derailleur has a cable length adjustment similar to that on brakes. Unclamp the derailleur cable and let the derailleur move to the smallest sprocket. Move the lever to the highest-gear position. Screw the cable adjusting barrel to its furthest-in position. Pull the cable taut through the derailleur clamp and tighten the clamp. Then unscrew the adjusting barrel until the derailleur just starts to move. Move the lever through its various positions to see whether the shifting occurs just when the lever clicks into its stops. If the shifting occurs sooner or later, turn the adjusting barrel until the shifts occur exactly as the lever clicks into its stops. Make the same tests for all chainwheels, and readjust until the shifting is equally fast for all chainwheels.

The art in designing indexed-shifting derailleurs is in getting a derailleur that will always require a particular cable movement to shift to a particular gear, either going up or going down the gears, without regard to which sizes of sprocket and chainwheel are used and without regard for reasonable wear in the derailleur or in the chain. One requirement is a close and consistent spacing between jockey wheel and sprocket in all gears. Anything that upsets this condition will cause bad shifting in the index mode.

Encouragement

Getting your derailleurs properly adjusted pays dividends in easy operation. If nothing major is wrong, getting to know your equipment and keeping it adjusted is relatively easy, as has been covered thus far. Though derailleurs look complicated and cannot be operated unless the wheel is turning, they are relatively simple mechanisms.

Adjusting Chain Length

There are two limits to chain length. If the chain is too short, it will not fit over the large chainwheel and the large sprocket with sufficient slack for changing gear. Generally, attempting to shift with too short a chain will bend the derailleur out of shape—and it could do worse. If the chain is too long, when you are in the smallest sprocket and chainwheel the chain will be loose and likely to jump off sprockets and chainwheel or jam in the derailleur, and it will certainly shift badly from that gear.

Short-Chain Test

Turn the pedals slowly. Shift onto the large chainwheel. Shift onto the largest sprocket while turning the pedals gently as the chain climbs onto the sprocket. If you feel unusual resistance, stop turning—the chain is too short. The only resistance you should feel is the normal derailleur spring resistance as the chain climbs the sprocket. Observe the chain as it runs through the jockey rollers as you shift. The chain should not pull into a straight line, but should still have some bend in it at the lower roller. Repeat this test several times. Then, with the rear derailleur set on the largest sprocket, repeat this test as you shift onto the large chainwheel.

Long-Chain Test

With a double chainwheel, shift onto the smallest chainwheel and the smallest sprocket. The derailleur should keep tension on the chain. Examine the position of the cage. It should not be nearly horizontal, and if it has a stop it should not be against the stop. If it has either of these characteristics, it will not be able to rotate more to keep the chain taut.

With many triple-chainwheel setups, the derailleur cannot take up all the slack generated by a wide-range cluster and a small inner chainwheel. Shift the chain to the largest sprocket and then to the smallest chainwheel. Then shift to the next smaller sprocket, and make the long-chain test. If the setup passes this test, then shift to the next smaller sprocket. Continue until the setup fails the long-chain test. When riding with the small chainwheel, take care to use only the sprockets for which the derailleur can keep the chain taut.

Installing a New Chain

The chain may have the end rivet sticking out in preparation for joining to the other end. This end is too big to fit through the cages, so start with the small end below the chainwheel. Go upward around the front of the chainwheel, back through the front derailleur cage, and over the sprocket cluster. Rotate the cage of the rear derailleur counterclockwise, and lead the chain over the upper roller, through the cage, and around below the lower roller to join the first end. (On joining, see chapter 17.)

Derailleurs generally work better with the chain a bit longer than it must be, rather than shorter. If the differences in your sprocket sizes and in your chainwheel sizes do not use all the slack capacity of the derailleur, set your chain length with the chain around the smallest sprocket and the smallest chainwheel. But never neglect to do the short-chain test before riding with a new chain.

If your sprocket and chainwheel differences use nearly all of the derailleur’s slack capacity, then set your chain length with the chain around the largest sprocket and the largest chainwheel. Then make both the short-chain test and the long-chain test before riding. You may have to change the length by a link or so to get it exactly right.

Derailleur Theory and Expert Adjustments

Fast, accurate shifting from one sprocket to another depends upon two things: establishing the proper distance between the jockey wheel and the sprockets, and ensuring that when the cage moves left, it immediately moves the chain.

In old-fashioned derailleurs, there was no adjustment of these matters. The jockey wheel moved only laterally. Therefore, it had to be positioned sufficiently far forward of the cluster to clear the largest allowable sprocket, which meant it was an excessive distance from the smaller sprockets. These derailleurs gave slow and inaccurate shifts between the smaller sprockets, which required moving the lever first too far, so the chain would shift, and then back again, so the chain would run smoothly. Modem derailleurs have several means of moving the jockey wheel vertically so that it remains close to sprockets of different sizes, making shifts faster and more accurate. The derailleur action invented by Suntour is the easiest to understand. The pivots of the parallelogram are tilted to the average angle of the “cone” formed by the sprockets so that when the jockey wheel is moved right for smaller sprockets it also moves up, staying closer to the smaller sprockets than it otherwise would. This system two disadvantages: a wide-range cluster has a greater “cone” angle than a close-ratio cluster, and a proper cluster doesn’t form a cone but forms a logarithmic curve like the horn of a trumpet. Therefore, this system cannot be perfectly adjusted for all sizes of clusters, but it is available with different tilts. Derailleurs that are intended for wide-range service have long cages with lots of tilt; those that are intended for narrow-range service have short cages with less tilt.

Campagnolo adjusts the slope of the parallelogram to suit the type of cluster being used. Several designs adjust the derailleur to clusters with different ranges by changing the angle between the derailleur body and the chain stay. Most modern derailleurs use a cage design in which the cage pivot is forward of the jockey wheel. As the chain moves to smaller sprockets and the cage rotates to take up the chain slack, the jockey wheel rises, thus staying close to the sprockets. This design adjusts to sprockets of all sizes, but not quite perfectly, and its adjustment is upset when you shift to a different-size chainwheel.

Shimano counters the problem of different-size chainwheels by allowing the whole derailleur to pivot slightly as the chain changes effective length when you switch from one chainwheel to another. The Huret Duopar (meaning “dual parallelogram”), an older design renowned for its suitability to wide-ratio systems such as tandems require, has the jockey wheel carried on a second parallelogram motion, which rises and falls with uncanny accuracy as the chain changes effective length.

If you understand these principles, you will be better able to make the next three adjustments. These adjustments are changing the length of the chain, adjusting the axle positioning stops, and adjusting the upper pivot spring or stops. You use these adjustments to ensure that the jockey wheel is as close as possible to the sprockets without being too close at any one position. You see, there is a catch. If the jockey wheel is too close, it won’t shift the chain to a larger sprocket. You don’t position the jockey wheel relative to the sprocket that the chain is on, but relative to the next-larger sprocket. The critical shift where clearances are tightest is from the second-largest to the largest sprocket. Shift to put the chain on the second-largest sprocket. Then sight across the jockey wheel to the largest sprocket. The jockey wheel must just clear the largest sprocket. The best clearance is just over ¼ inch. Then, when you pull the cable to shift to the larger sprocket, the jockey wheel can move in line with the larger sprocket to lay the chain onto it. If there is no clearance, the jockey wheel presses the side of the chain against the side of the sprocket, producing lots of clatter but no shift until a rivet head catches a sprocket tooth. You can’t tell the correct adjustment when the chain is on the largest sprocket, because then the sprocket has taken up more chain, so the jockey wheel has moved down and everything looks perfect, even though there wasn’t enough clearance to allow a good shift into that lowest gear.

Examine your derailleur’s operation in all gears. Then change the position of the axle and the angle of the derailleur body (if it has this adjustment) to try to get equally small distances from the jockey wheel to the next-larger sprocket in all gears. You may then try adding or removing a link of chain to see whether this makes an improvement, but first perform the short-chain test to see whether you have made the chain too short.

Narrowing the chain by eliminating the rivet heads has made two more expert adjustments more necessary than before. When the front derailleur moves to a larger chainwheel, or the rear one to a larger sprocket, the chain has to be pushed against the chainwheel or sprocket by the derailleur cage. If the cage is too wide, it must move too far before it presses against the chain. For many years, cyclists have bent the tip of the front derailleur cage slightly inward to get quicker shifting. At the rear derailleur, the problem is worse. If there is a lot of space between the chain and the top of the derailleur cage when the jockey wheel is aligned with a sprocket, the cage has to move a long way before it presses against the chain to shift to a larger sprocket. Then, when the chain jumps, it can jump right over the next sprocket and move to the third sprocket. Running a narrow, flush-riveted chain for a six- or seven-speed cluster through a derailleur designed for a normal chain just makes the problem worse. To get quicker, more accurate shifts, bend the top of the rear derailleur cage until it just clears the side of the chain when the jockey wheel is aligned with a sprocket.

Modern chains are often labeled with the number of sprockets in the cluster that they are designed for. Use the appropriate chain with each derailleur setup.

Chain Deflectors for Triple Chainwheels

When there is a large difference between the middle and the smallest chainwheels, the front derailleur cannot work properly and will often dump the chain inside the smallest chainwheel, often jamming the crank movement and perhaps damaging the chain and the chainwheel. This is a normal effect of the design and cannot be avoided by better adjustment of the front derailleur, but it can be prevented from causing damage.

Chain dumping on the inside occurs as follows. When the front derailleur tries to move the chain to the smallest chainwheel, it bends the chain sideways until it climbs off the middle chainwheel. At this point, the chain is operating at an angle. As the chainwheels continue to rotate, the point where the chain leaves the middle chainwheel moves forward and down until the chain drops to the level of the small chainwheel. If the small chainwheel is only a little smaller than the middle chainwheel, the distance from the point where it leaves the middle chainwheel to the point where it joins the small chainwheel is short and the chain drops directly onto the small chainwheel. If there is a large difference between the middle and the smallest chainwheels, as with a half-step-and-granny system, the chainwheels have rotated much further and this distance is long. The angle of the chain takes it inside the small chainwheel before it drops to the level of the small chainwheel. The chain then has to drop inside the small chainwheel, where it jams rotation and causes other damage.

The cure is to close the space between the smallest chainwheel and the seat tube. Several devices sold are the Chain Watcher, Dog Fang, Jump Stop, or similar.

Selecting and Modifying Front Derailleurs

Front derailleurs have two important design characteristics, but the only one that is shown in the catalogs is the total range, given in teeth, between the largest and the smallest chainwheels. Obviously, when the derailleur is mounted to clear the largest chainwheel, the cage must extend down far enough to clear the chain when the chain is on the smallest chainwheel. A small total range (small capacity) indicates a derailleur designed for racing use; a large capacity indicates a derailleur designed for touring or mountain bike use with triple chainwheels.

Equally important is the difference between the largest and the middle chainwheels. A front derailleur should operate so that as it moves, the outside of the cage just clears the tips of the largest chainwheel and the inside of the cage just clears the tips of the middle chainwheel. Then you get clean shifts without dumping the chain. Most large-capacity front derailleurs today are designed for a large difference between large and middle chainwheels. If you have a smaller difference between large and middle chainwheels, as with a half-step-and-granny system, you have to mount the derailleur high enough for the inner side of the cage to clear the middle chainwheel. This setup puts the outer side too high, producing irregular shifts that frequently dump the chain outside the chainwheels, jamming it between crank and chainwheels and causing trouble and damage.

The cure is to grind away the inside cage plate so that it just clears the tips of the middle chainwheel when the outside cage plate just clears the tips of the largest chainwheel. Remove the bolt that closes the lower end of the cage so that you can slip the derailleur off the chain. Start with the chain on the large chainwheel. Slide the derailleur down the seat tube until the inner side of the cage touches or overlaps the middle chainwheel. If the outer side is higher than just barely clear of the large chainwheel, the derailleur should go down further. Mark the curve of the middle chainwheel on the inside cage plate, remove the derailleur, and grind the inside cage plate to the mark using a small grinding wheel in an electric drill or a die grinder. Then replace the derailleur a little high and check its operation while shifting back and forth. The outside cage plate should just clear the largest chainwheel and the inside cage plate should just clear the middle chainwheel. Lower the derailleur until there is interference with the middle chainwheel, and mark again. You will probably have to grind a bit more to get it right, so repeat until it is right. Then you can get quick, reliable shifts that won’t dump the chain.

Major Derailleur Repairs

Major repairs to derailleurs consist of either replacing parts or straightening them. When repairing derailleurs, the important things to ensure are that the sideways motion is free, that the cage rotates smoothly, that the bearings of the rollers are greased, and that the whole derailleur (when mounted on the bike) holds the cage parallel to the chainwheel throughout the motion of the cage. Derailleur work takes a bit of mechanical flair. If you have that, you can repair derailleurs with little extra instruction. If you don’t, the scope of this book doesn’t allow for the detailed instructions that you would need.