Front derailleur problem

I'd be grateful for some advice. I've been having a problem with the front derailleur of my touring bike since I went on a 50 mile ride some weeks back which had a few off road sections (good tracks). I'd been riding the bike before then and also checked it over just before the ride and everything worked fine. During the ride, it rained for a bit and the off road sections threw up wet grit but not mud. The front derailleur then seemed to struggle with shifting down into the smallest ring even after being washed off with the help of my water bottle. It just kept sticking and wouldn't shift down without a fair amount of coaxing. I rarely use this ring but there were some long, steep climbs (for me) including one towards the end. Thankfully, it started playing up before I got to that point so I made sure I shifted down at the bottom of the hill in preparation - it's a well-known hill on a popular route.

Once I got the bike home, I cleaned it off, lubricated and re-adjusted the gears. The shifting was/is fine when I'm testing it at home (i.e no load) and most of the time when I'm riding on the flat but it sticks when I'm trying to shift down while applying a bit more pressure e.g. once I've started a climb. I went on a 30+ mile ride today and there were a couple of steep hills where it just wouldn't shift down. What do the mechanically minded among you think the problem is? My cable is in good condition but it's been on the bike for a while. Do I need to adjust the tension? I have to admit to being a bit obsessive about the cleanliness of my bikes and wash, degrease/relube at regular intervals.

Thanks.

It's a bit harder to troubleshoot if you can't replicate the problem at home, but the first thing I'd do is try to check if the lag is in the cable or the derailleur. If the derailleur moves smoothly back and forth by hand the problem is the cable or cable tension, if the derailleur movement feels sticky or if the cable slackens without the der doing anything, it's a sticky/gritty/rust spot in the derailleurs pivot points.

I'd liberally lube the pivot points and work the derailleur back and forth, then loosen the cables from the housing and lube inside any bends in the housing and check for rust and fraying.

It's a bit out there, but I once had problems with this for the longest time until I realized that the cable was sticking in the groove under the bottom bracket (it's routed underneath, over a guideplate). It had dug a v-shaped groove into the plate. I turned the bike upside down and drilled the groove into a u-shape :)

Thanks lph. Just turned the bike over to check. The cable routing is fine but I've just noticed that maybe the cable is not in as good condition that I thought as there is some rust down there.

I can feel the cable tension changing when shifting up but there doesn't appear to be movement as I shift down and the derailleur is sticking on the downward shift too. In fact I'm noticing that the shifter is also sticking. Instead of springing back up automatically, I'm having to nudge the thumbshifter then everything moves. I have lubed the derailleur but possibly not enough on the pivot points. Will try what you suggested.

Thanks again.

Is there grit inside the cable housing that could be causing a problem. I know that it might be unlikely, but just a thought. Hope you can get it resolved.

When a front derailleur won't shift to a smaller ring, it's often that the cable/housing needs to be replaced. LPH gave good advice about separating the effect of the housing from the effect of the derailleur itself. There are also small adjustment in the derailleur that could affects its shifting, eg, the stop screws and the cage angle and height. Shifters can also get sticky and stop working properly, so squirt in some lube, or soak in solvent and relube.

Thanks Velocivixen and DebW. I've relubed all the pivot points on the derailleur as lph suggested and the shifting has already improved, but it's still sticking a bit. I haven't checked the cable housing yet but will do that in the next day or two when I have time to remove the bar tape etc. I think you're all right about the cable/housing. Probably time to change it or at least clean it out. DebW, it didn't occur to me to lube the shifter. Thanks for that.