Shimano front mech issue

Had a look at a bike today that refused to change gear cleanly. it was a standard, shop supplied machine that had not been altered since sold. The front mech was reluctant to change from the inner to the middle ring but didn't make a fuss of the middle to large change. the front mech was spot-on for angle and height above the chainring.
After a lot of head scratching I noticed that, with the chain on the inner ring, the gear cable was touching the lower inner pivot of the front mech and was deflected slightly. When the shifter was operated the mech would start to move, the pivot would move out of the way and the chain would slacken off. With the mech using part of it's movement taking up this slack it wasn't moving the chain far enough to get it onto the next chainring. Once it was there though, the offending pivot was out of the way and the next change up was hunky dorey.
The solution was to get the cable to follow a wider path as it left the bottom bracket shell. The bike had a nylon cable guide so I threaded a self tapper into the underside of it, lifting the end away so it was 2-3mm clear of the BB shell.
I hope this proves useful information for somebody. Given that the bike was as supplied there must be other instances of this problem.

2 Attachments

Useful! Thanks... I've got a very reluctant FD-6600 where it sounds like a similar fouling problem and I can't get it to shift all the way to go from the small to the large ring. I'm going to experiment now.