Indexing problem - front gears

[lulubel]

I've looked at it again.

The chainline is exactly 45mm, so that's fine.

I've had a good look and a poke around with a tiny screwdriver, and I can't find anything lodged inside.

Considering the chainline is correct, here's the weird thing. With the limit screws as far out as possible and no cable attached (ie the mech in "normal" position), if I put the chain on the middle ring and turn the cranks, the chain will not drop onto the granny ring unless I angle the back of the cage inwards towards the frame slightly. If I did that on my old bike (or any other bike, for that matter) the chain would be immediately thrown onto the BB.

Is it reasonable to deduce from that last paragraph that the mech is broken? (Or faulty, I suppose, but I have to assume broken after what I did to it.)

Have you built this bike up from scratch? Or what set up was it previously?
I have recently fitted a Tiagra triple chainset in place of a compact set up and it came with a black plastic spacer which sits on the axle on the drive side, this is to give the correct chainline for the triple and to ensure that the granny ring doesn't catch the frame. Is your Sora chainset the same? Did you fit the spacer?

There wasn't a spacer, but apparently I didn't need one. (I'ce checked the manual online.) The chainline is correct.

Lulubel, sorry assumptions made and terminology gets chucked about:-

Thanks for the definitions. Knowing terminology makes it a bit easier to explain things too. I can actually use the correct term rather than trying to explain what I'm attaching to what or which bit I'm measuring!

 

[Alun]

Is it reasonable to deduce from that last paragraph that the mech is broken? (Or faulty, I suppose, but I have to assume broken after what I did to it.)

I think it must be, if you can't find any bits of "alignment block" lodged inside, and the chainline is correct. Do you have another front mech you could try?

 

[Crackle]

I can't imagine you've bust the mech by leaving the thingdoodahwotsit in place. I'm pretty sure I've pinged one across a room too, They're only flimsy plastic.

It's odd this. Crank fully in place on that side? I'm struggling to think of anything.

 

[RecordAceFromNew]

I've looked at it again.

The chainline is exactly 45mm, so that's fine.

I've had a good look and a poke around with a tiny screwdriver, and I can't find anything lodged inside.

Considering the chainline is correct, here's the weird thing. With the limit screws as far out as possible and no cable attached (ie the mech in "normal" position), if I put the chain on the middle ring and turn the cranks, the chain will not drop onto the granny ring unless I angle the back of the cage inwards towards the frame slightly. If I did that on my old bike (or any other bike, for that matter) the chain would be immediately thrown onto the BB.

Is it reasonable to deduce from that last paragraph that the mech is broken? (Or faulty, I suppose, but I have to assume broken after what I did to it.)

If the chainline is 45mm, and if the front mech is indeed a triple, then there is definitely an issue if the front mech won't throw the chain inboard enough onto the granny with no cable and with limit screws back out all the way.

The weird thing is front mechs are stout things that can stand up to quite a bit of bashing and rarely go wrong, let alone a new one (despite being man-handled by an honorary man... ). It might be worth taking a good look to see what is stopping the spring pushing it going further inboard - once you are sure it is not the frame if necessary take it off the frame so it is easier to see inside the mech.

 

[Dayvo]

Found this

View: http://vimeo.com/5780736
yesterday whilst casually surfing.

Hope it helps.

 

[lulubel]

I think I might have finally won.

I took it off, wiggled it about, stuck a screwdriver in it and wiggled it about some more, and a tiny piece of plastic came out. I now seem to have access to all the gears I should have. It was still a pig to get aligned properly, and involved adjusting by about half a millimetre at a time until I got it just right. I've tested it on the trainer, so I just hope it's still behaving itself when I get it out on the road.

Thanks for all the suggestions and advice.

 

[MacB]

I think I might have finally won.

I took it off, wiggled it about, stuck a screwdriver in it and wiggled it about some more, and a tiny piece of plastic came out. I now seem to have access to all the gears I should have. It was still a pig to get aligned properly, and involved adjusting by about half a millimetre at a time until I got it just right. I've tested it on the trainer, so I just hope it's still behaving itself when I get it out on the road.

Thanks for all the suggestions and advice.

Superb, as mentioned FDs are pretty tough so hopefully you'll be good to go now.

 

[Crackle]

I think I might have finally won.

I took it off, wiggled it about, stuck a screwdriver in it and wiggled it about some more, and a tiny piece of plastic came out. I now seem to have access to all the gears I should have. It was still a pig to get aligned properly, and involved adjusting by about half a millimetre at a time until I got it just right. I've tested it on the trainer, so I just hope it's still behaving itself when I get it out on the road.

Thanks for all the suggestions and advice.

Result. I'll have to add that one to my list of weird FD problems and potential causes.