Originally Posted by
spd28
Hello, I知 hoping to find some help with a bike front derailleur function issue. I知 working on my brother痴 bike (Trek 1220 Road Bike). Just doing some general maintenance. Bike has a triple front derailleur. I completed making sure the rear derailleur was tuned well and moved onto the front. I noticed the front derailleur cable was slightly frayed at the end and decided to replace it. I have completed tuning the front derailleur and all works well while mounted to my work stand. Once I get on the bike for a test ride is when the problem starts. Shifts work well in the two smallest chain rings in front but when I move to the largest chain ring the shift is smooth but when I push on the pedal with any force the chain wants to drop of the large chain ring and makes lots of noise. I知 not seeing any indication that the derailleur cage is touching the chain once on the chain ring. Since I知 not able to replicate this issue while on my bike stand I知 having trouble diagnosing the problem.
Thank you,
where is the chain on the cassette when this is happening? Do you see the same behavior when on the large sprocket (crossed chain) vs on one of the smaller sprockets? If there痴 no evidence of FD chain rub, sounds like the chain is trying to derail all by itself