Ask a Mechanic | Troubleshooting Rear Derailleur Tuning

Welcome to our Ask a Mechanic column where our expert mechanic Daniel Slusser answers your bike maintenance questions. If you have a question for Daniel, please post it on our Facebook Wall or e-mail Daniel directly at Today’s column offers some tips on Shimano mechanical road rear derailleur tuning that came in response to the above video Daniel made and posted on the Art’s Cyclery YouTube Channel.

Question: My 105 rear derailleur will not shift into the largest cog. Should I completely unhinge the cable, loosen the H screw all the way out and adjust from there? Or should I just walk through this video and mess with the H screw? From: sentient02970 (YouTube handle)

Shimano 105 Rear Derailleur

Mechanical derailleur tuning is straightforward whether you are tuning 105 or Dura-Ace, all the steps are exactly the same.

Answer: It might be best to go through the whole process, but here are some troubleshooting tips. See if you can push the rear derailleur into the large cog with your hand. Use this process to set the L (low gear) screw (H is for the small 11t gear). If it will shift manually with your hand, then your cable tension is the problem. The cable is likely very loose and you are missing your first shift. Loosen the cable anchor, pull the cable tight, and clamp it down again. Use the barrel adjuster to fine tune it after that and you should be good to go. If all of this fails, just follow the steps in the video from start to finish.

Question: I installed a new rear derailleur and at the same time, a set of Dura Ace pulleys with sealed bearings. I have gone through the settings over and over. The problem is hesitation going into 9th gear. And the worst part is that the chain jumps around in 1st gear. Oh, and it only shows me this awsome trick when I am going into a steep climb. I believe the pullys are possibly too wobbly. I am going to switch back and try the original pullys.What’s your take on this? It’s a Tiagra 9 speed setup. From: J

Shimano Derailleur Pulleys

Pulleys usually aren’t the problem unless they are oddball aftermarket offerings.

Answer: It sounds like you might have the cable anchored on the wrong side of the anchor bolt. The other possibility is that it’s the pulleys. Make sure that you have the pulleys mounted in the correct locations. The upper pulley should have side to side play, but the lower one should not. Switching to Dura Ace pulleys is probably not the issue if installed correctly, but I’m not sure because I’ve never tried that combination.

The only remaining possibility is that your cassette or shifters could be mismatched. Tiagra recently switched to 10-speed so your shifters may be 10-speed and your cassette is 9-speed or vice-versa. The rear derailleur should work ok whether it is 9 or 10-speed. Of course the 9-speed one will work better with 9-speed shifters and 10-speed derailleurs with 10-speed shifters, but a mismatched shifter and cassette will never work. I’ve run into this problem on customers’ bikes that are pieced together from spare parts. One notable example was on an X-Games star freestyle motocross rider’s bike that I worked on while living in Temecula, California five years ago. So if this is what went wrong in your case, don’t worry, because it happens to famous millionaires too!

Daniel Slusser is a professional bicycle mechanic with over ten years of experience. He holds a bachelor’s degree in business administration from HSU and a master’s degree in history from Cal Poly. When he is not riding, wrenching, or writing he enjoys spending time with his wife and two children.