105 levers - not staying in the big chainring

[upandover]

Hi,

Thanks for everyone's advice earlier on the torque wrench. My new chainset arrived this morning, and is now fitted. It's an extremely cheap triple one, as a temporary measure so that I can ride my cross bike (the gearing on the double was to difficult for my knee issue). Nicer one to come after the summer.

I've been confident my 105 levers will manage three rings, as
1) the guy who sold it to me was telling me about it, after I paid, and it seemed genuine (and because that's not enough).
2) with the wire disconnected, I can get two clicks as it moves back to normal position. This was enough for me, and seemed to confirm my reading on the forum.

With the new crank fitted though, I can use the small ring, change to the middle ring, but while I can change-up to the big ring, it doesn't stay there, and returns to middle as soon as I release it.

So - I wonder if I've actually got levers that can only manage 2 rings, or if something else is going on? I can't really see what adjustments to make. The levers appear to be retro-fitted, as they go to point where the gears would used to have been, and then down to the crank.

I'll do some more reading now - but if anyone has any helpful advice please?

Thanks
Steve

 

[upandover]

A little late I've found a model number on the rubber hoods (st-1055), and answered my own question. Double only. I've also learnt about trimming which would seem to contradict measuring on the basis of clicks, which I'd read about on another forum.

Still, at least I can use it now, event if I can't go fast...