Bike Repair & Maintenance For Dummies®
Page 21
Figure 14-8: Attaching the cable.
Figure 14-9: The cable cap.
Many rear derailleurs have a third screw called a B-angle screw. This is used to adjust the space between the upper jockey wheel and the cogs. Normally, you won’t need to adjust this unless you’re installing a new derailleur. If you do install a new one, adjust this screw until the upper jockey wheel is close but still has enough space to allow the chain to pass freely without making contact with the cogs.
Adjusting the rear derailleur
If you find that your chain is jumping back and forth between gears or getting stuck on a cog and needs an extra click or two to shift, you need to make an adjustment to your rear derailleur.
The easiest way to recognize that your derailleur needs adjustment is a rattling or clanking noise from the chain when you’re pedaling.
Here’s how to adjust the rear derailleur:
1. Use a bike stand or other mechanism to support the bike with the back wheel off the ground.
You’ll need to pedal the bike with one hand and shift with the other, so having the bike up off the ground is essential
2. Start by examining how well the derailleur shifts to lower gears or to the larger cogs: Shift the derailleur until it moves the chain onto the largest cog.
If it struggles to reach the largest cog, loosen the L-limit screw (refer to Figure 14-7) by a quarter- or half-turn until the chain easily reaches the largest cog. If the chain goes over the cog, tighten the L-limit screw to restrict the movement of the derailleur.
3. Shift the derailleur in the opposite direction to the higher gears, focusing on how well the chain shifts onto the smallest cog.
If it hesitates to drop down, loosen the H-limit screw (refer to Figure 14-8) by a quarter- or half-turn until the chain sits easily on the smallest cog. If the chain is thrown off the freewheel to the outside, tighten the H-limit screw.
4. After the limits for the derailleur have been set, shift through all the gears, making sure that the chain moves to another cog with each click of the shift lever.
If the chain hesitates or makes a lot of noise, you’ll need to use the barrel adjuster to do some fine-tuning (see Figure 14-10): Start with the chain on the smallest cog and, while pedaling, shift one click. The derailleur should move the chain instantly to the next cog. If it doesn’t, turn the barrel adjuster about a quarter of a turn counterclockwise. If the opposite problem is true and the chain shifted two places, turn the barrel clockwise. Repeat this procedure for each of the cogs on the freewheel until the chain is shifting smoothly for each click of the shifter.
Figure 14-10: The barrel adjuster.
If the derailleur is shifting well going up to the larger cogs and slow or hesitating coming down to the smaller cogs there may be a kink or problem with the cable not moving smoothly through the housing. Remove the cable, inspect it, and replace it if it is kinked, frayed, or damaged.
The rear derailleur is a very exposed part of the bike and is prone to being bent or damaged if the bike falls over on top of it. If this happens, all you may need to do is bend the derailleur back into shape. Here’s how:
1. Use one hand to insert an Allen wrench into the mounting bolt.
2. With the other hand wrapped around the body of the derailleur, leverage the derailleur back into place so it’s suspended in a straight line under one of the cogs.
If you have problems aligning your derailleur, make a visit to your local bike shop. Most shops have a specialty tool called a derailleur hanger alignment tool, which is made to perform this task and measure the positioning.
Cleaning the rear derailleur
Because the rear derailleur is so close to the ground and so exposed, it accumulates a lot of dirt and grit over time. If you do a lot of riding, especially any off-road riding, you may want to think about adding a rear derailleur cleaning to your monthly maintenance activities (see Chapter 17).
You can clean the rear derailleur on the bike by using a solvent and a brush to scrub it down. But for a more thorough cleaning, consider removing it and then soaking it in a strong degreaser solvent. After it’s soaked for bit, use a brush to remove any dirt and grit trapped in its inside parts. Use a rag and clean the jockey wheels — dirt and grime will normally be caked onto their surfaces. Rinse with warm water and then blow-dry with compressed air. Let the derailleur dry completely before reinstalling, and then lubricate the pivots in the derailleur and the inside and outside center of the jockey wheels.
A cassette cleaning brush is very useful for regularly clearing dirt and muck from the jockey wheels.
Most jockey wheels are made of plastic, so regularly inspect them for wear. When the teeth start to get pointed and sharp and they’re no longer nice, squared-off tops, replace them.
The front derailleur
Your front derailleur probably won’t give you as many headaches as the rear derailleur will over the life of your bike, but it will need occasional care and service. If you have a front derailleur that’s acting up, it probably needs a new cable or just a thorough cleaning and lubrication, which will be more effective if you perform it while the derailleur is off the bike. The following sections describe how to remove and then reinstall the front derailleur, as well as how to adjust it.
Removing a front derailleur
To remove a front derailleur, follow these steps:
1. Shift the derailleur to the smallest chain ring to remove tension on the cable.
2. Using an Allen wrench or a box wrench, detach the cable by loosening the anchor bolt that holds it in place (see Figure 14-11).
3. Use an Allen wrench or box wrench and undo the pivot bolt that holds the derailleur to the seat tube (see Figure 14-12).
4. To remove the chain from the derailleur cage, remove the nut and bolt holding the cage together, and pull apart the cage so that the chain will slide through (see Figure 14-13).
Some front derailleurs have a rivet holding the cage together, which requires you to first remove the chain from the bicycle and then proceed.
Figure 14-11: Removing the cable.
Figure 14-12: Removing the pivot bolt.
Figure 14-13: Pulling the cage apart.
5. Spread apart the derailleur mounting clamp and remove the derailleur from the seat tube.
Installing a front derailleur
Follow these steps to install a front derailleur:
1. Open the cage of the front derailleur and wrap it around the chain.
2. Replace the nut and bolt that holds together the cage.
3. Wrap the derailleur mounting clamp around the seat post, and thread the clamp bolt enough so that it isn’t tight but allows the derailleur to be moved by hand.
4. Align the derailleur so that its outside cage edge runs parallel with the chainrings.
Visually inspect the position by standing overhead and looking down on the derailleur.
5. Position the derailleur at a height that places it about 2mm above the teeth of the largest chainring.
6. After aligning and positioning, firmly tighten the mounting clamp bolt.
In order to limit the movement of the derailleur so that it doesn’t throw the chain off the chainrings, you need to set the H- and L-limit screws.
7. Set the L-limit screw so that the side of the cage closest to the bike is about 2mm inward of the smallest chainring.
8. Pull the derailleur away from the bike and over the large chainring.
9. Set the H-limit screw so that when you move the derailleur as far as it will go, it reaches to a position 2mm outward of the largest chainring.
10. After you’ve found the correct position for the derailleur, pass the cable through to the anchor bolt and, while holding the cable taut with a pair of pliers or a fourth-hand tool, tighten the anchor bolt.
Make sure you follow the correct route for the front derailleur cable. Some bikes are designed with the cable coming up from the bottom bracket, and others drop down the length of the seat tube.
12. If you have installed a new cable, cut off any extra and then attach a cable cap to the end. Crimp the end cap in place with pliers.
Always leave about 2 inches of cable on the outside or past the cable anchor bolt. This will make future adjustment to the cable and/or derailleur much easier.
Adjusting the front derailleur
One of the first things you need to do to adjust the front derailleur is to set limit screws so that the derailleur doesn’t move too far and push or pull the chain off the chain rings. There is nothing worse than hitting a steep hill, shifting to your smallest chainring, and having the chain fly off the chainring and become stuck in between the chainring and chainstay. A properly adjusted limit screw will ensure that the chain doesn’t go past the smallest chainring when shifting.
1. Shift the derailleur to move the chain onto the smallest chainring.
2. Set the L-limit screw so that the side of the cage closest to the bike is about 2mm outside the smallest chainring (see Figure 14-14).
3. Shift the derailleur to the largest chainring.
4. Set the H-limit screw so that the cage plate farthest from the bike is about 2mm outside the largest chainring.
5. Try shifting between the two or three chainrings on your bike.
If the chain doesn’t not move easily to the appropriate chainring or it rubs on the side of the derailleur cage, you may need to make some fine-tuning adjustments (see the following steps).
Figure 14-14: Adjusting the L-limit screw.
6. To fine-tune the front derailleur, try increasing the tension using the cable adjuster.
On front derailleurs, this is usually located where the cable enters the left shift lever. Make quarter- to half-turns of the adjuster and recheck.
You can also make small adjustments to the H- and L-limit screws to improve shifting or prevent the chain from rubbing on the cage.
The derailleur cable
If the cable is frayed, kinked, or worn, it probably needs replacing. When you go to buy a new cable, make sure you buy cable and housing (the rubber coated sheath) that is made specifically for derailleurs — it’s normally a little thinner than brake cable, which has to be able to handle greater force.
You’ll be able to tell that it’s derailleur housing because the inner core wires run linearly with the length of the housing, which makes for a much more rigid housing and doesn’t allow any compression, resulting in a more precise shift. Brake cable housing has the inner core wires wound around like a coil, which allows more flexibility in the housing and a more controlled brake-lever feel.
Before you remove the shifter cable, take a moment to observe how it’s routed around the frame of the bike. Pay attention to the location of the cable housing, where the cable housing meets the cable stops, and the how the cable exits on the other side. You’ll need to route the cable and cable housing in the same manner when you reinstall it. You want the housing to be as short as possible. The housing should have gradual curves without any binding or sharp angles.
Follow these steps for removing the derailleur cable:
1. Shift the chain onto the small cog for the rear of the bike or the small chainring for the front.
This will put the index ratcheting system in the relaxed position and allow you to remove the cable.
Very few bicycles have reverse springs in either the front or rear derailleur; if yours does, you’ll need to shift into the large cog or the large chainring to put the derailleur in the relaxed position.
2. Unfasten the derailleur cable by loosening the cable anchor bolt where the cable attaches to the rear or front derailleur.
3. To remove the cable, you need to push it through the other side of the shifter.
To do this, look for where the cable enters the shift lever and pull back on the cable housing to expose the cable
4. For STI shifters, squeeze the brake lever and press the shifter inward at the same time.
This will open up the center core of the shifter where the barrel at the end of the cable is seated. You should be able to see the barrel.
5. Push the cable into the shifter so that the barrel is forced through and out the other side.
Handlebar shifters have different ways of concealing the barrel end of the cable. On some, there may be a screw-in plug or rubber cap that hides the cables. On the popular Shimano STI–style shifter, where the shift lever is integrated into the brake level, the cable runs sideways through the shifter. When the chain is on the smallest gear and you pull back on the brake lever and shift lever at the same time, you can see the barrel on the end of the cable.
Use pliers to grab the barrel and pull the cable the rest of the way out of the lever.
6. Collect any ferrules that were holding the cable housing in place at the anchor points or cable stops.
You’ll use them when you reinstall the cable.
It’s a good practice to change the cable housing when you replace cable wires. Manufacturers often sell cable with the housing included in the package. They normally give you more housing than you need, so you’ll have to cut it to fit your bike.
Follow these steps to install the derailleur cable:
1. To install new cable and housing, you first need to prepare the cable housing.
Assuming that the old housing was the proper length, use the older pieces of cable housing as guides for cutting the new pieces. Use a cable cutter for this procedure — they cut the housing without compressing the end too much.
Even if you use cable cutter, you may need to file the end if it has any sharp edges. You may also need to open up the end of the housing with an awl or another pointed instrument if the end is closed up after cutting.
2. When you’re ready to install the new cable, use a rag to apply a light coating of grease to its surface.
3. For STI-style shifters, squeeze the brake lever, push the shifter to the inside to expose the hole for the cable, and insert the cable.
You may have to wiggle it around to pass it through the shifter.
4. Pull the cable out the other side of the shifter.
Some trigger shifters and most grip shifters will require you to open the shifter body to load the cable. This may be challenging, especially on grip shifters.
5. Attach the ferrules that came with the cable housing to the ends of each piece of housing where needed.
6. Insert the cable into the proper cable housing and pull it out the other end.
7. Route the cable and cable housing around the frame of the bike in the same position as it was before.
The ferrules at the ends of the cable housing should fit snugly into the cable stops on the frame.
8. Run the cable through the cable anchor bolt on whichever derailleur is correct for that cable and tighten the cable anchor bolt.
If you’re installing cables for the first time, they’re likely to stretch a little after you’ve used them. It’s a good idea to shift them though the full range of gears a few times after connecting them. Then pull the cable taut and reconnect the cable anchor bolt if necessary.
Gear Shifters
There are a variety of different shifters available today but they all do pretty much the same thing: pulling a cable to move a derailleur in one direction and then releasing the cable to allow the derailleur spring to move it in the other direction.
Most bikes these days use index shifters that are mounted on the handlebars. Index shifters make a click each time a gear change is made, which prevents riders from missing a shift. They’re much easier to use than the traditional friction-type shifters, seen mostly on older bikes. Friction shifters are usually mounted on the down tube as two levers that the rider moves up or down to move the derailleurs. For someone not used to friction shifters, it can be a little unnerving to take your hand off the handlebars to make a shift.
Most shifters today, such as the one shown in Figure 14-15, do not require much maintenance and are not designed to be dissembled. In some cases, worn levers can be replaced, but if the internal mechanism of the shifter starts to wear out and the clicks become less distinct, it’s probably time to replace the levers.
The one thing you can do with shifters is give an occasional spray of a light lubrication into their internal parts. Operate the shifter a few times after the application, and wipe off any excess grease.
To adjust the position, loosen the clamp bolt if there is one, and move the shifters to a more comfortable position (as shown in Figure 14-16). If the shifters are on a road bike and are wrapped with tape, instead of removing the tape, you can loosen the clamp holding the handlebars and rotate the handlebars forward or backward slightly.
Figure 14-15: Gear shifter.
Figure 14-16: Adjusting the position of the gear shifters.
Removing shifters
In this section, we tell you how to remove shifters on road bikes, with a focus on STI-style shifters, where the shifter is integrated into the brake lever. To remove the shifters follow these steps:
1. Unscrew or remove the handlebar end plugs and then remove the handlebar tape.
2. Locate the bolt that holds the shifter onto the handlebars.
The position varies on different types of shifters although in many cases you need to roll back the rubber hood to find it.
3. After pulling back the rubber hood and finding the bolt, use an Allen wrench to loosen the bolt without removing it.
This will loosen the bracket and allow you to slide the shifter off the handlebars.
4. Repeat steps 1 through 3 for the other shifter.
5. The final step in removing the shifters is to remove the brake (see Chapter 8) and shift lever cables (see “The derailleur cable,” earlier in this chapter).
Installing shifters
To install shifters, follow these steps:
1. Slide the bracket that holds the shifter onto the end of the handlebar and move the shifter toward the top of the handlebar.