Front mech shifting issue

deveng

Having issues with my front mech - when out riding I cannot get it to shift from the small ring to the big ring. I have had it on a stand several times and set it up repeatedly - it shifts perfectly on the stand, but once I'm out riding it just won't go, unless I rotate the pedals very very slowly, applying virtually no load whatsoever. Is this a sign that the chainring is worn/damaged and the shifting ramps can't lift the chain up any more? No issues getting into the small ring from the big ring. Bike has done about 2500km and chain was replaced about 200km ago. I think it would sometimes do this before the chain was changed, and over the past 50-80km has gone from occasionally not shifting to not working at all.

dgunthor

sounds like the cable tension is too slack, try tightening it a little with the barrel adjuster

in my experience shifts in the stand are not the same as on the bike, so i set up on the stand then tweak on the bike itself

dj58

From the trouble shooting table 9.1 in the Park big blue book,

"Chain shifts slowly or not at all to the largest front chainring.
Front derailleur cable tension too loose, H-Limit screw too tight,
and/or rotation of derailleur cage is off."

In addition check that the inner control cable is not starting to fray and restrict full movement.

deveng

Plenty of cable tension and the limit screw is far enough out to allow it to move as far as it needs to. Derailleur height and alignment are okay - apporx 1.5mm gap to chainring and alignment seems okay as there is no rubbing/contact to chain unless at the extremes of crossing the chain (big ring/big cog and little ring little cog there is a big of rubbing but no other gear combos) and when on a stand it works perfectly, so I can't see how it can relate to the set up of the front mech. I've got a colleague bringing in a spare, virtually new set of chainrings for me to try to isolate that, and if that's not the case I'll re-do the front mech set up.

sungod

is the cage ok? if there's a screw at the trailing end, make sure it's tight

if there's any flex in the frame/crankset (and there'll always be some on even the stiffest bike), the chainring will move slightly wrt to the cage, the effect increases as you apply more force

this matches your description of symptoms, find on stand, problem on road unless you apply little force on pedals

so if the front mech is aligned correctly you'll need to adjust limit screw and/or increase cable tension

kajjal

Oil the pivots on the front mech and do a few changes. Without doing this now and then they will stick.