May 16, 2020

Bicycle Repair - derailleurs

I am working on adjusting a Shimano 105 rear derailleur on a road bike. It seems to like to shift two gears at a time. I also just replaced an 8 speed cassette with a 10 and need to know what derailleur adjustments may be needed for this new wheel.

• Video: how to adjust Shimano rear derailleurs (5 minutes)
• Video: Park Tool - Rear Derailleur - limit screws and indexing (16 minutes)
• Adjust a rear derailleur in 5 steps

The bottom screw (perhaps marked L) controls the travel of the D into the spokes. You absolutely do not want that, but you also don't want the chain chattering and unstable on the biggest cog. Don't adjust this though until you have fiddled with the cable tension and indexing.

People recommend turning the barrel adjuster all the way clockwise (inward) to give as much slack as possible, then reclamping the cable screw as the first step.

After this, you can use the barrel adjuster to tune up indexing. Move the chain to something like the third cog in and visual adjust the D to be directly below the cog. Then some trial and error along with shifting will let you fine tune it. Once this is done, adjust the L limit.

The last thing is to adjust the B screw, which is up near the dropout (the top of the D). The idea here is to have the D as close to the big cog as possible without touching it.