how to fix a rear derailleur on mountain bike

How to Fix a Rear Derailleur on a Mountain Bike

Mountain biking is an exhilarating activity that can sometimes lead to mechanical issues, especially with the rear derailleur. The rear derailleur is responsible for shifting the chain between the gears on the rear cassette, and when it malfunctions, it can be a major headache for riders. Fortunately, fixing a rear derailleur is a manageable task if you have the right tools and know-how. In this article, we’ll guide you through the steps necessary to diagnose and repair common issues with your mountain bike’s rear derailleur.

Understanding the Rear Derailleur

Before diving into repairs, it's essential to understand how a rear derailleur works. The rear derailleur consists of a cage, which holds the chain, and a spring mechanism that allows it to move laterally across the gears. It is controlled by the shifters on the handlebars, which pull a cable connected to the derailleur. The alignment of the derailleur in relation to the cassette is crucial for smooth shifting.

Step-by-Step Guide to Fixing a Rear Derailleur

1. Diagnose the Problem

Begin by identifying the issue with the derailleur. Common problems include - The chain not shifting properly between gears - The chain skipping or jumping - The derailleur hanger being bent - Loose or frayed cables

Inspect the derailleur closely while shifting through the gears. Listen for any unusual noises, like grinding or skipping, and observe how the derailleur responds.

2. Check the Cable Tension

One of the most common causes of shifting issues is incorrect cable tension. To check the tension, pull the shifter to change gears. If the derailleur does not move or moves sluggishly, the cable might either be too loose or too tight.

To adjust the tension - Locate the barrel adjuster, usually found on the derailleur or shifter. - Turn the adjuster counterclockwise to increase tension or clockwise to decrease tension. Make small adjustments and test the shifting after each adjustment until it operates smoothly.

3. Align the Derailleur

A misaligned derailleur can cause shifting problems and chain skips. Check the alignment by looking at the derailleur in relation to the sprockets. If the derailleur is sitting too far in or out, it may need to be adjusted.

To realign - Loosen the bolt securing the derailleur to the hanger (which attaches it to the frame). - Gently reposition the derailleur so the jockey wheel (the lower pulley) is about 1-3mm from the smallest sprocket. - Tighten the bolt carefully.

4. Inspect and Replace Cables

If you find that the cable is frayed or damaged, it’s wise to replace it. To do this - Shift the bike to the highest gear (smallest sprocket) to relieve tension, then disconnect the cable from the derailleur. - Remove the old cable from the shifter. - Thread the new cable through the shifter, around any housing, and back into the derailleur. - Adjust the cable tension again as previously described.

5. Check the Limit Screws

If the derailleur may move out of range and the chain might fall off the cassette, the limit screws need checking. There are two limit screws - ‘H’ (high) limit screw controls how far the derailleur can move towards the smallest sprocket. - ‘L’ (low) limit screw controls movement toward the largest sprocket.

To adjust - Shift to the highest gear, then adjust the ‘H’ screw so that the derailleur aligns with the smallest sprocket. - Shift to the lowest gear and adjust the ‘L’ screw accordingly.

6. Test Ride

After making all necessary adjustments, take your bike for a test ride. Shift through all the gears while pedaling to ensure everything operates smoothly. Pay special attention to any unusual sounds and make further adjustments if necessary.

Conclusion

Fixing a rear derailleur might seem intimidating at first, but with patience and practice, it can become a straightforward task. Regular maintenance and checks of your mountain bike’s components will lead to a more enjoyable riding experience. Remember, the key to successful bike repair lies in understanding how the system works and approaching each problem systematically. Happy riding!