There's nothing worse than being out on the open road or hitting the trails, only to discover that your rear derailleur has no intention of smoothly shifting gears for you, or doing it at all.
If you're looking to save a little bit of money or time then you can replace your rear derailleur yourself. And luckily for you, we've put together this article to talk you through how to do it.
In this article, we'll be going through how to tell when you need a new rear derailleur, what tools you'll need to do the job, and how to do it like a professional.
Carry on reading to learn everything you'll need to know to install a rear derailleur.
How to tell when you need a new rear derailleur
A rear derailleur is a mechanism that's function is to shift the chain into the rear sprockets. This is part of the gear-changing process.
It is made up of two pivots (an upper and a lower) that are coupled by a linking system. The shifter cable and chain are both fed through this system. The G pulley and T pulley work together to raise or lower the resistance in the chain as you change gears.
The rear derailleur is so important because it controls your gear system. It is one of the most important parts of the bike, second only to the brakes and the wheels.
So, how can you tell when your rear derailleur isn't functioning properly?
Well, firstly your bike will feel different when you change gears. There will be tension in the gearbox and the chain will jerk as you make the change. This is very hard to miss.
Secondly, you may hear a loud grinding or clicking whenever you try to change gears.
The good news is that it is totally possible to change your own rear derailleur, and whilst you're at it you should change your shifter cable and cable housing too.
What tools will you need to install a rear derailleur?
There are some cycling repairs that you can do on the side of the road on a ride. Sadly, replacing your rear derailleur is not one of these jobs.
As well as the following tools, you will need to acquire the correct type of rear derailleur for your bike and some shifter cable.
When replacing a rear derailleur you will need these tools:
- A chain-breaking tool
- (alternatively) a set of chain pliers
- A set of classic pliers
- A Phillips head screwdriver
- Chain oil
- A set of rags and soapy water
- (alternatively) a pressure washer
- A set of Allen keys
- Cable housing
- A length of shifter cable
Once you have these tools and the right parts then you are ready to begin installing your rear derailleur.
How to install a rear derailleur
We suggest that you wear a pair of safety gloves whilst doing this, as not only can you catch your fingers, but it is also a very messy job.
Step 1 - Using your chain pliers, remove your chain, and set it aside.
Step 2 - Remove and dispose of the old rear derailleur.
Step 3 - We recommend changing your shifter cable and housing at the same time as the rear derailleur. So you may want to remove these too whilst you're there.
Step 4 - Check that your derailleur hanger is still functional. It should be hanging straight, with no damaged threads or cracks on its body. If it is damaged replace it. If not, on to the next step.
Step 5 - The lock threads on your new derailleur should match the ones on your hanger, if not you will need to get a different part.
Step 6 - Place the derailleur in the correct position, and use an Allen key to mount it on the bike.
Step 7 - Replace your chain. See our article on putting on a chain for more information
Step 8 - Using a Phillips head screwdriver (or Allen key, depending on the model) adjust the upper and lower limit screws. Doing this will give the derailleur enough flexibility to absorb the movement of the bike (if it is too tight it will snap off) whilst being stable enough not to throw off the chain.
Each derailleur is different so check what measurements the manufacturer recommends. Loosen the screws in small increments. Turn the wheels and change gears as you go to check your progress.
Because you have removed the shifter cable when you do this you will have to manually change the gears on the derailleur.
Shifter cable and housing
Step 9 - Measure the needed amount of cable housing, and cut to size using your cable pliers. Do not crimp the ends.
Step 10 - Remove the case at the base of the shifter gears and feed through the cable. Attach the case again. You may need to use your Philips head screwdriver to do this.
Step 11 - Feed the cable through the cable housing and seal the ends.
Step 12 - Set the derailleur to its hardest gear and then feed through the newly housed cable.
Step 13 - Pull the cable tight, then clamp it down before cutting it to size. Remember to leave yourself 2 inches of leeway past the cable clamp.
Step 14 - Now you can crimp the ends of our cables. This will prevent them from splitting during use.
Adjusting the cable
Step 15 - Turn out your barrel to heighten the tension in the shifter cable. You can also use a barrel adjuster to do this.
Step 16 - Starting at the highest gear, switch down to the lowest gear. With each gear check how the cable copes. If it is struggling, use your barrel adjuster to add or remove the tension as necessary.
This step may take a little practice to be able to do perfectly.
Step 17 - With either the rags and soapy water or the pressure washer clean your chain, shifter cable, and new rear derailleur.
Step 18 - Re-oil the chain and new rear derailleur.