My ****ing 105, brand new on my opera bernini has been giving me the ****s since I got it, about 2 1/2 months ago.
I have a (stock, unfortunately) 12-27 cassette, and I really don't use the 27 or 24. I'm mainly interested in grinding and sprinting.
I'll describe the behavior:
Limit screws are set correctly. (Really, I have to affirm this!)
Cable tension is set so that in cog 5 of 10, when in little ring, the top der. pulley is aligned with the bottom of the cog. (As it should be!)
Result: Great shifting across the range, a little hesitant to hit the 27 when in the big ring. Whilst sprinting, shifts nicely and quickly down the stack up until the 14t. When I try and engage the 13t, it hesitates, sometimes taking 2-7 seconds to engage, even if I vary my power input, same result. Same thing but worse when trying to hit my 12t.
I tried re-indexing the gears, exactly the same. I tried lessening the cable tension so I'd have quick engagement going down the stack. Same behavior in 13 and 12t. GRRRRR!!!!. So I adjusted the limit screw, so it should be throwing the chain into my dropout instead of landing on the 12t. Nope. Still doesn't want to grab the 13.
I've played with the B tension, adjusting it up, from it's relatively lax initial setting. Nada.
I tried indexing it to be optimized in 5 of 10 cogs whilst in the big ring up front. No cigar.
I'm a trainee cert III bike mechanic, and all the guys at work say "is the derailer hanger straight, hows the cable tension, it must be your limit stops" but these things have been checked over and over and over.
It works fine in the stand with no load. I'm getting ready to blow this 105 up and get campy like the guys at work told me too in the first place. For the record, my old Tiagra (2004) gave me full range in the bottom and top chainring, and shifted under full load in any combination. My 105 just won't perform, it's supposed to be an entry level race group...whats the point in trying to race when you have to wait 7 seconds to get in your top end sprint gear?