The rear derailleur

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.

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.

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 14-9: 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.

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.