How to Adjust a Rear Derailleur – Limit Screws & Indexing

Summary

This video by Calvin Jones from Park Tool Company provides a comprehensive guide to adjusting mechanical rear derailleurs for optimal shifting performance. It covers the importance of setting the H and L limit screws, fine-tuning the indexing, and adjusting the B screw for proper derailleur alignment. Viewers are shown step-by-step how to correct issues like misalignment, noise, and poor shifting, with tips on using the barrel adjuster and ensuring correct cable tension. The video also emphasizes the importance of test riding to ensure proper function after adjustments.

Takeaways

• 😀 The most common shifting issues are when the gears don't shift fully or make unusual noises, and proper mechanical derailleur adjustment can help fix these.
• 😀 The rear derailleur is responsible for shifting the chain on the rear cogs, and is connected to the shifter by a cable that passes through housing.
• 😀 Limit screws on the derailleur prevent the chain from going into the spokes or the frame, and must be adjusted properly to avoid issues.
• 😀 The H limit screw is adjusted first to set the inward limit of the derailleur's movement, ensuring it doesn't go beyond the smallest cog.
• 😀 Indexing is the process of lining up the guide pulley with the cogs, so each shift corresponds accurately with each cog.
• 😀 The barrel adjuster is used to fine-tune the indexing by adjusting the slack in the cable, helping to avoid confusion with the limit screw settings.
• 😀 To properly adjust the H limit screw, it's essential to check for excessive noise while pedaling and adjust until there's no rubbing against the next cog.
• 😀 After setting the H screw, the indexing is fine-tuned by adjusting the barrel adjuster to ensure smooth shifting between cogs, with a focus on avoiding excessive noise.
• 😀 The L limit screw is adjusted after indexing, ensuring the chain doesn't move past the largest cog and into the spokes.
• 😀 The B screw controls the gap between the guide pulley and the cogs, which should be between 5-6mm for most bikes, and is adjusted to ensure proper shifting and performance.

Q & A

What is the purpose of the rear derailleur in a bike?

The rear derailleur is the mechanism that shifts the chain across the rear cogs, allowing you to change gears while cycling.

What does the H limit screw do on a rear derailleur?

The H limit screw prevents the derailleur from moving too far inward, which could cause the chain to go into the spokes or the frame. It sets the maximum inward position of the derailleur.

How can you identify which limit screw is the H screw if they are unmarked?

You can identify the H limit screw by turning each screw in and out while observing the derailleur. The H screw will cause noticeable movement of the derailleur.

Why is it important to adjust the barrel adjuster before setting the H limit screw?

Adjusting the barrel adjuster adds slack to the cable, allowing you to separate the shift position from the limit screw setting. This ensures you don't confuse the two when making adjustments.

How do you fine-tune the H limit screw for proper adjustment?

To fine-tune the H limit screw, tighten it slightly until you hear excessive noise, then back it out slightly until the noise stops. The correct setting avoids noise while shifting.

What is indexing in the context of rear derailleur adjustment?

Indexing is the process of aligning the guide pulley with the cogs so that each shift aligns perfectly with a cog, ensuring smooth and precise gear changes.

How do you adjust the barrel adjuster during indexing?

You turn the barrel adjuster clockwise or counterclockwise to fine-tune the shifting increments. This adjusts the cable tension to ensure the guide pulley aligns correctly with each cog.

What do you do if the rear derailleur doesn't shift to the next gear after one click?

If the derailleur doesn't shift, turn the barrel adjuster counterclockwise a full turn, and try again. Repeat until the derailleur shifts properly.

How do you adjust the L limit screw?

The L limit screw is adjusted similarly to the H screw. Tighten it until it causes issues like slow shifting or noise, then gradually loosen it until the derailleur shifts smoothly without excessive noise.

What is the function of the B screw on a rear derailleur?

The B screw adjusts the gap between the guide pulley and the cogs, ensuring the correct derailleur positioning. It helps with maintaining optimal chain clearance and smooth shifting, especially when the chain is on the smallest sprocket and largest cog.