how to replace a rear derailleur on a mountain bike

How to Replace a Rear Derailleur on a Mountain Bike

Replacing the rear derailleur on a mountain bike can seem daunting, but with the right guidance and tools, it becomes a straightforward process. The rear derailleur is a crucial component of your bike's drivetrain, helping to shift the chain between gears smoothly. Over time, it may get damaged or worn out, necessitating a replacement. This article will walk you through the steps to replace a rear derailleur, ensuring your mountain bike is in top condition for your next ride.

Tools and Materials Needed

Before you get started, gather the following tools and materials

- New rear derailleur - Allen wrenches (usually 5mm and 6mm) - A Phillips screwdriver - Chain tool (if you need to adjust the chain) - Bicycle stand (optional but helpful) - Lubricant

Step 1 Prepare Your Bike

First, secure your bike either in a repair stand or flip it upside down, resting on the handlebars and seat. This will give you easy access to the rear derailleur. Make sure to remove the rear wheel for better access, which usually involves loosening the quick-release lever or unscrewing the axle nuts, depending on your bike's configuration.

Step 2 Remove the Old Derailleur

1. Disconnect the Chain If the derailleur is heavily damaged, it might be easier to cut the chain using a chain tool. Otherwise, you can simply unthread the chain from the derailleur. 2. Locate and Remove Bolts Identify the bolts that attach the derailleur to the hanger on the bike frame. Use the appropriate Allen wrench to loosen and remove these bolts. Be careful not to strip the bolts during this process.

3. Disconnect the Cable Next, you’ll need to loosen the derailleur cable. Locate the cable anchor screw (usually on the derailleur body) and use a Phillips screwdriver or Allen wrench to loosen it. Once loose, pull the cable free.

4. Take Off the Derailleur With the cable disconnected and the mounting bolts removed, you should now be able to gently remove the old derailleur from the derailleur hanger.

1. Position the New Derailleur Place the new derailleur onto the derailleur hanger. Ensure it is oriented correctly; the jockey wheels should be pointing towards the rear wheel.

2. Secure the Derailleur Insert and tighten the mounting bolts. Make sure it’s snug but avoid over-tightening, which could damage the frame or the derailleur.

3. Reconnect the Cable Thread the derailleur cable through the appropriate guide and back into the cable anchor screw. Pull the cable taut and tighten it securely.

4. Reattach the Chain If you had to cut the chain, use the chain tool to reconnect it. Alternatively, simply thread the chain back through the new derailleur's jockey wheels if you left it intact.

Step 4 Adjustment

Now that the new derailleur is in place, it’s time to make some adjustments

1. Limit Screws Most derailleurs have limit screws (marked as H and L) that prevent the derailleur from shifting beyond the largest and smallest chainrings. Adjust these screws to ensure the derailleur moves freely within the designated range without overshifting.

2. B-Tension Screw This screw controls the distance between the upper jockey wheel and the cassette. Adjust it so that there is a small gap (around 3-5mm) between the jockey wheel and largest sprocket.

3. Test Shifting With everything secured, it’s time to test the shifting. Spin the pedals and use the shifters to change gears. Observe how smoothly and accurately the derailleur shifts between gears. Make further adjustments as necessary.

Conclusion

Replacing a rear derailleur on a mountain bike is a skill that can enhance your mechanical knowledge and improve your biking experience. Regular maintenance and timely replacements will keep your bike performing at its best. Once you become familiar with this process, you’ll feel more confident in handling other bike repairs. Enjoy riding, knowing that your bike is in optimal condition!