Bike Repair & Maintenance For Dummies®
Page 21
Rear derailleurs (shown in Figure 14-1) have been known to give even experienced bike mechanics headaches at times. They do double-duty: keeping the chain under tension and guiding it back and forth between the cogs as the rider shifts. Slight changes in tension of the cable to which the derailleur is attached can cause shifting to become out of whack. Just as with the front derailleur, you can improve its functioning and longevity if you keep it clean, lubricated, and adjusted as needed.
The following sections describe how to remove and reinstall the derailleur.
Figure 14-1: A rear derailleur.
Removing the rear derailleur
To remove your rear derailleur, follow these instructions:
1. Shift the rear derailleur to the smallest cog.
2. Using an Allen wrench or box wrench, loosen the bolt that’s holding the cable in place.
Note that if you don’t shift the rear derailleur to the smallest cog, it could spring back at you because it’s under tension from the cable.
3. Use an Allen wrench or box wrench (as shown in Figure 14-2) to remove the bolt that is holding bottom jockey wheel in place.
Spray some lubricant on the jockey wheel if the bolt will not budge.
4. After the bolt is removed, lift out the jockey wheel.
5. Use an Allen wrench or box wrench (as shown in Figure 14-3) and reach around the derailleur to loosen the bolt that holds the top jockey wheel in place.
Figure 14-2: Loosening the bottom jockey wheel.
Figure 14-3: Loosening the top jockey wheel.
6. After the bolt is loose, you should be able to separate the cage (as shown in Figure 14-4).
7. With the cage separated, lift the chain off the top jockey wheel and away from the derailleur.
Rest the chain on one of the cogs, letting the slack hang down.
8. Use an Allen wrench to remove the pivot bolt (see Figure 14-5), which will allow you to remove the derailleur.
Figure 14-4: Separating the cage.
Figure 14-5: Undoing the pivot bolt.
Installing the rear derailleur
To install the rear derailleur, follow the steps in this section.
1. Position the derailleur so that the chain wraps around the right half of the top jockey wheel (as you’re facing the right side of the bike).
2. Align the mounting bolt with the gear hanger on the frame.
3. Insert the mounting bolt and tighten with an Allen wrench.
4. Pull the chain through the cage and, while holding the cage and chain with one hand, insert the bottom jockey wheel so that the chain wraps around the left side of the wheel.
5. Close the cage so that the holes align with the hole in the bottom jockey.
6. Insert the bolt and tighten both jockey wheel mounting bolts securely.
7. Adjust the H limit screw (see Figure 14-6) and the L limit screw (see Figure 14-7) so that they limit the derailleur from throwing the chain off the bike or, even worse, into your spokes.
Tighten both screws in a clockwise direction two turns. This will restrict the movement further than it was before.
Figure 14-6: Adjusting the H screw.
Figure 14-7: Adjusting the L screw.
8. To stimulate shifting with the cable, practice turning the pedals with your right hand while pushing inward and upward on the derailleur with your left thumb. Wrap your index finger around the cage and push on the cage with your thumb.
Note: These steps are for the most common type of rear derailleur. If you have a rapid-rise rear derailleur, the spring is opposite and pulls the derailleur toward the low gear. Therefore, you’ll need to reverse the process when moving the derailleur with your hand.
9. Using the method in Step 8, try to shift the chain to the largest cog. (It won’t succeed on the first attempt because you tightened the L limit screw as a safety precaution.) Loosen the L limit screw by a slight amount, about one-quarter to one-half a revolution, and then begin turning the pedals again.
Do this in incremental steps until you’re able to shift the chain onto the largest cog. The chain should spin smoothly on the largest cog and not make any grinding sounds.
10. Perform Step 9 in the opposite direction making incremental adjustments to the H limit screw until the chain arrives on the smallest cog.
You won’t need to move the derailleur with your hand because the spring in the derailleur will pull it down and outward. Now you’re ready to attach the cable and make finer adjustments to the shifting.
11. Run the cable through the cable-adjusting barrel hole and through the cable anchor bolt clamp.
There should be a notch in the cable anchor bolt clamp where the cable is designed to sit when the clamp is tightened.
12. Tighten the clamp with an Allen wrench or box wrench (as shown in Figure 14-8).
13. To make the cable taut, use a pair of pliers or a fourth-hand tool, and pull the cable as you tighten the cable clamp bolt.
14. Test the shifting of the derailleur down onto the highest gear.
Sometimes when you’re tightening the cable, you can pull the derailleur over just a little and then it’ll not drop down onto the highest gear.
15. Attach a cable cap (see Figure 14-9) to the end of the cable and use a pair of pliers to crimp it into place.
This will prevent the cable from fraying.
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.
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.
11. For a new cable, shift the levers a few times to stretch and seat the cable. Then loosen the cable anchor bolt, pull the cable taut, and retighten if necessary.
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 als
o 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.