Nightmare with changing between the front chainrings

[Roadhump]

have you tried a different shifter

I think that is the next step tbh. Followed by the mech / derailleur, as they are the only bits that haven't been changed.

 

[roadrash]

you've already stated that the mech will actually go in the big ring so I would say shifter

 

[gbb]

Just a theory. You say you're 15 stone? That' a lot of power potential to put through the pedals...and the BB.
I had an old Bianchi that flexed in the frame quite badly, you could tell because if I really worked it, the chainrings and /or chain would rub the front much. As soon as I relaxed the rub stopped....and I'm a lightweight.
So try it just pedalling easy, does it shift ok ?
Try it as normal...is the result different ?

 

[Sharky]

When changing up at the front, which sprocket are you in at the rear? If on one of the smaller cogs, it might give a better "grip" than when on the bigger cogs.

 

[mjr]

So try it just pedalling easy, does it shift ok ?
Try it as normal...is the result different ?

^^ This. Derailleurs don't like much load when shifting. Front ones even less. Ease off and see how it moves.

 

[mrandmrspoves]

If you have a length of exposed gear cable running along your downtube you can pull it tight when riding. This will mimic the effect of changing up using the gear shift. If the derailleur moves up correctly when you do this, it demonstrates that the shifter is at fault (or the cable at the shifter)
If the front derailleur does not move up correctly it would demonstrate that the problem is with the derailleur. The front derailleur is such a simple piece of equipment that I am surprised it has caused so much grief but although it is simple, a small maladjustment can make a huge difference so it is worth checking that the derailleur sits parallel with the chain ring and hasn't rotated out of parallel. Likewise check that the derailleur hasn't slid up or down the downtube. With the derailleur adjusted so it is over the largest chain ring, the bottom edge of the derailleur should clear the top teeth of the chain ring by 2mm.

 

[Roadhump]

When changing up at the front, which sprocket are you in at the rear? If on one of the smaller cogs, it might give a better "grip" than when on the bigger cogs.

I thought of that, but it makes no difference whether the bike is riding on a high or low cassette cog.

 

[Roadhump]

If you have a length of exposed gear cable running along your downtube you can pull it tight when riding. This will mimic the effect of changing up using the gear shift. If the derailleur moves up correctly when you do this, it demonstrates that the shifter is at fault (or the cable at the shifter)
If the front derailleur does not move up correctly it would demonstrate that the problem is with the derailleur. The front derailleur is such a simple piece of equipment that I am surprised it has caused so much grief but although it is simple, a small maladjustment can make a huge difference so it is worth checking that the derailleur sits parallel with the chain ring and hasn't rotated out of parallel. Likewise check that the derailleur hasn't slid up or down the downtube. With the derailleur adjusted so it is over the largest chain ring, the bottom edge of the derailleur should clear the top teeth of the chain ring by 2mm.

The derailleur does seem to line up properly. There was a problem when the shifter was gunked up and it wasn't clicking into place when moved, so that the derailleur just fell back to the small ring, but when it was cleaned out and started to stay in the higher position, the derailleur stays in place over the large ring, but I wouldn't know if the gap at the bottom edge between the teeth is more or less than 2 mm. I would take photos of it in either position but as the cable is snapped at the moment, it won't operate at all/

Thanks for all your replies, much appreciated.

 

[alicat]

I'd echo what @gbb says. I ease off the power almost completely when changing.

 

[buzzy-beans]

There are quite obviously several different causes for this perplexing problem, the chain, the cable, the shifter but could it also be the rear derailleur not performing properly, i.e. not allowing enough slack in the chain, so it might be worth thoroughly checking out that the tensioning spring is allowing enough ease of movement.

 

[davidphilips]

Like jobjh i would be thinking of the cable? If the old one snapped perhaps it was on its way out also the new cable may be settling in. When you wrote that the problem only started when you changed the back wheel makes me wonder if the rear wheel is in line, dont know if this would have any effect with the front derailleur shifting but i know if the rear wheel is not in line you would have problems with the rear derailleur.

When you replaced the cable was it both inner and outer that where replaced or just the inner?

 

[Levo-Lon]

It sounds like the chain has worn out,Have you checked it?

As it plays up under load and works fine on the stand.
A "stretched chain" worn to limit will not align when going up as well ,so poor changes

 

[Cycleops]

It’s difficult to suggest more solutions at a distance. If you’re taking it back to your LBS let them try to sort it. Could be the shifter by the sound of it.

 

[Roadhump]

The outer and inner cable were changed about 3 weeks ago, so shouldn't have been worn, and both mechanics checked the chain and said it wasn't worn either. It's interesting to hear the suggestions re the rear derailleur. I will mention these to the LBS, but will have to be careful I don't come across as telling him how to do his job. I might just ask him to cost up replacing the whole drive train.

 

[iluvmybike]

Have you checked that the cable is routed correctly at the pinch bolt on the mech - if it is not it can cause problems?