Annoying front derailleur problem

mikehiggs

Hi all,

Help appreciated on this one, it's driving me mad!

The bottom bracket "went" on my Focus Cayo (FSA BB-6000 Gossamer MegaExo BB), I had it replaced by the local bike shop, with a service as well, and it's now quiet as a mouse. Problem is, now I can't change gear between the two front rings. I've stripped it down (after repeated visit to the ****** shop) and put it back together adjusting and setting up as I went. One thing I noticed was that the front derailleur was lower than it ought to have been so I lifted this a bit. On the workstand it works perfectly fine and changes gear really nicely.

Big BUT, when I get on the bike to ride it, it doesn't change! I take up the slack on the cable with the adjuster, and it'll change to the big ring, but then won't change down. If I slacken off the cable, it'll change down to the smaller ring but not back up.

It had new cables as part of the service and the rest of the bike is working fine.

I managed to resist throwing it over a hedge and when I put it back on the stand it' fine. :roll:

Thanks all

Mike

turnerjohn

try adjusting the limit screws...little bit at a time...do the smaller ring first.
also check the plates are parallel with the chainrings ?
should be a gap of 1 to 3mm between chainring and outer plates.

owenlars

It is difficult to explain quickly in words so I would look at one of the YouTube videos showing how to do it.

Key points, get the derailleur at the right height (2mm above the big cog), make sure that it is parallel to the chainrings, ensure that your limit screw are set right and the gotcha that stumped me for about an hor and a half once.

Make sure that the cable is tight enough so that when you pull the gear lever it actually pulls the derailleur far enough across to push the chain off the small cog onto the big cog.

Good luck

mikehiggs

Finally, I'll be getting to look at this tonight.

The bit that stumped me was that it's fine on the work stand but won't change when I'm on the bike, I don't see how that should make a difference but I'll see how it goes later and report back.

Thanks for the replies

Mike

mikehiggs

Just been through it again, changes fine when on the work stand, sit on it to ride and it changes to the smaller ring ok, won't go back to the big ring.

onbike 1939

mikehiggs wrote:

Just been through it again, changes fine when on the work stand, sit on it to ride and it changes to the smaller ring ok, won't go back to the big ring.

There is always some difference between adjusting on the work-stand and on the road. The main one is that the upper part of the chain is under tension when pedalling which means that in order to change up in the front it's necessary to release the pedalling tension momentarily at the time of the gear-change. This slackens the chain sufficiently allowing the chain to climb to the large ring.
Again on some light-weight frames there may be a degree of frame or chain-set flex which affects the gear-change. In this case the "H" screw needs to be backed off a little to allow for this (anti-clockwise) to allow for any flex.

Killit_Bang

Did you ever figure this one out, i'm having exactly the same issue,

Started by taking a tumble and smacking the derailleur, so took it the shop nice service seemed to be all working fine, couple of rides later, an annoying clicking sound from the front derailleur, followed by shifting down and not being able to shift back up, clicking sound even more annoying on the granny cog. Put the bike in the stand, nothing rubbing or showing wear, changes up and down nice and smooth, but again as soon as I'm riding the problem returns. Tried the going gentle on the pedals, at one point it was working if I went to the smallest cog at the back and then shifted up, but that has since failed as well.

Thanks for any feedback

964cup

As others have said, this is a combination of the high limit screw - which controls how far out from the centre line the front mech can move - and cable tension, which determines how far it tries to move. If you have the limit screw set too tight, it will still change up on the stand, because there's little tension on the chain, so nothing resisting either the outward motion of the derailleur or the acquisition of the chain by the upshift ramps on the big ring. When you're pedalling you need a greater outward motion to ensure a clean change - indeed Di2 mechs deliberately overshift, then trim themselves back. With a mechanical mech, try opening up the high limit screw half a turn at a time - you don't want to go too far, or you can drop the chain over the outside of the big ring. At the same time, make sure you have plenty of cable tension, either by using a cable puller or by adding an in-line adjuster - or, if you have strong fingers, just pull the bugger plenty tight before doing up the pinch bolt.