How to Install a Rear Derailleur On a Mountain Bike

Bikes are great fun. Bikes will make you healthier, more fit, better at work, and help you to get out in the great outdoors. Everybody should have a bike. As great as bikes are, they can often break, and it’s natural for that to happen. It’s like cars. There’s only a certain amount a moving part can work before it breaks, no matter how strong it’s made. It is also common for bikes to be dropped or thrown, which can cause damage.

Rear derailleur brakes are a common problem. Rear derailleur braking is fragile and has many moving parts. The rear derailleur controls your gears and also takes the entire pressure of the chain. It is also in a place where it can be easily damaged, and if you fall on the side of it, there’s a good chance it will need changing. This article will demonstrate how to mount a rear derailleur onto a mountain bike.

What is a rear derailleur?

Image by Farbsynthese, Pixabay

Rear derailleur: This is an accessory that allows you to shift gears on your rear cassette. It sits on the bike’s rear in front of the rear wheel and is generally on a derailleur hanger, but sometimes can be directly on the frame. They hold the chain and connect it at the shifters to the front. These are typically controlled with a cable. However, some can also be controlled electronically.

What do you need?

When it comes to installing a rear derailleur, you won’t need much and don’t need any special tools for this job.

  • Allen keys
  • Chain tool
  • Wire cutters
  • Bike stand
  • Derailleur


  • New Cable and External
  • New Rear Derailleur Hanger
  • Torque Wrench

If you are going to do this job, it is important that you take your time. You will also need a safe area and a bike stand to help you get through the process.

Rear Derailleur Removal

rear derailleur
Pixabay image by danielkirsch

You will first need to replace the broken derailleur if it is already there. You can ignore the following steps if it is not broken. Sometimes you might find it helpful to take the old one apart so you can understand how it fits back together.

Step 1: Break the chain

You will first need to put the bike on the stand. You will need to either use the chain tool, or if you have a quick link on your bike, remove it first.

Step two: Take out the derailleur

You will need to remove the mounting bolt that holds your derailleur on. This will place the derailleur hanger. The cable that holds the derailleur in place will remain attached to it. To remove the cable end, you will need to use your wire cutting tools. Next, undo the Allen key bolt that holds it in place. It is possible to save it or put it in a bin.

Rear Derailleur Installation

rear derailleur installation
Image by LUM3N at Pixabay

Step 1: Recommendations (Not Necessary)

First, let me make some suggestions. Start by taking a look at your hanger. Make sure it is straight. Get another hanger if yours is bent. You can bend it back straight but it will be less strong after this.

I recommend that you change the shift cable, and the housing that runs from the derailleur to the shifter. You can take the shift cable and put it in a bin. Then, remove the outer sections and keep them. The new outers should be cut to the same dimensions as the ones that you removed. Once the shift cable is connected, attach the new outers to the end of the cable.

Step 2: Attach the rear derailleur

Take the new derailleur, and then you will need to mount this to the hanger with the derailleur’s mounting bolt provided. It is important to use the recommended torque or tighten it.

Step Three: Connect the cable to your rear derailleur

You will now need to attach your cable to the new derailur. Make sure to be in the lowest gear (Highest), before you do this.

Step 4: Attach the chain

You will now need to rethread your chain into the drivetrain. You must ensure that the chain is properly threaded. Many people commonly make the mistake of not putting it through the rear derailleur cage correctly, and although it still works, it isn’t quiet. Make sure you connect the chain again with the quicklink and turn the pedals to verify you have done it correctly.

Step Five: Low limit screw and high limit screw

Next, you will need to install the high- and low limit screws. These screws can limit the range of the rear derailleur, so your chain doesn’t fall off the cassette. Start with the high limit. This will determine how far the rear derailleur is able to move the chain to the smallest rear shaft. While turning the pedals, screw the H screw in clockwise so it skips up one gear. Then slowly turn it anticlockwise until the original cog is reached. This is it.

You can now adjust the low limit screw settings by turning the pedals. The rear derailleur should be pulled so that the chain runs up to the lowest gear (Biggest Cog). If the chain is too long, the derailleur will tingle the spokes and cause the chain to go too far. You will need to push the derailleur towards the top cog, but turn the L screw clockwise to bring the chain to the center of the cog. To test it is in the correct place, turn the pedals and push the derailleur to the top and provide it goes to the lowest (Biggest) Cog and doesn’t go past into the wheel and the spokes don’t ting it will be fine. We can now move on if our limit screws have been verified.

Sixth Step: Adjust the index screw

Indexing our gears correctly is essential to ensure they shift correctly when we ride. This is done by adjusting the cable tension at the rear derailleur. You would now loosen your gear cable. Make sure it is in the highest (Smallest Cog) gear, and then pull it finger tight. Then tighten it up using the cable pinch bolt. We do this again to ensure it’s in the right place before we start doing this job and there’s not too much cable tension.

Your index screw is the one where the cable enters into the derailleur. You will find a small barrel adjuster. Turn the pedals to select the next gear. More than likely, you will find it won’t move. You will now need to turn the barrel adjuster counter-clockwise so that it skips to the next gear. Click to move to the next cassette gear. If it skips, it is great. Adjust the barrel adjuster to make it move up. To correct it, turn the barrel adjuster clockwise if you are going too far.

Once all the gears are working properly and the cable shifts as expected, you will know that the tension is correct. Next, you’ll need to cut the cable two inches below where it connects to your derailleur. You can then attach a ferrule to it. Your bike is now ready to go with the new derailleur.

Frequently Asked Question

Is it simpler to replace a Derailleur

Yeah, it’s relatively easy, just take your time and follow each instruction in this guide. When replacing a rear derailleur, we recommend that you use a new one.

I have replaced my Derailleur and my gears still skim?

You will then need to make sure your hanger is straight and that the derailleur is good. Also, ensure the gears and index are correct. Make sure the inner and outer cables are in good condition. It is likely to be one of them that is causing the issue.

How much does a Derailleur cost?

On low-end bikes, you’re looking at roughly $20-$30, and on high-end bikes, you’re looking realistically at $150 to $400.

Are Mountain Bikes the same as Road Bikes in terms of Derailleurs?

These are two different derailleurs, but they attach and work the same.


Fitting a new derailleur isn’t a difficult job. It’s easy to take your bike back on the road. The bike should be shifting flawlessly, and hopefully, you won’t need to replace it again anytime. It is always a good idea for you to ask the bike shop for help if you are not sure.

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