Bicycle Mechanics - Why the need for a second "click"?
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01-26-06, 11:07 PM
When I shift my DA front der so that the chain goes from the small ring up to the large one, sometimes the chain rubs against the front der even when I'm in the middle cogs in back. (Note these are brifters.) When this happens, in order to get it to stop rubbing, I nudge the release lever for the front der to the right until it clicks again. Normally this would bring the chain back down to the small ring, but in the situations where the chain is rubbing when it shouldn't (and only in those cases), it just clicks, the rubbing stops and all is well (but the chain doesn't shift back down). Is this an adjustment issue, is there something wrong with the derailleur, or is this something that is typical (in which case sorry for the dumb question)?
BROKEN FIX IT
01-26-06, 11:39 PM
This is called a Half shift it use to adj. for the angle of the chain so you can use more gear combos. OR it could be your bikes Haunted!!!!!!! ok maybe not its cool just check out about half shifts. Camp. Sha. all the major companys talk about it. ------------Rubber side down
01-27-06, 01:44 AM
There is nothing wrong with your brifters nor with your derailleurs... you have just discovered the phenomenon called "trimming". You can see this discussed in the shimano website or in the "manuals" that came with your DA brifters...
01-27-06, 08:26 AM
Thanks guys. Believe it or not I checked the Shimano website before posting the question but didn't find a manual or other info regarding this. Guess I'll have to lok a little harder. No manual came with the bike.
01-27-06, 09:48 AM
It's working perfectly and doing what it is designed to do.
01-27-06, 10:10 AM
It's why its there! There's no way you'd get precise shifting Shimano-style without the trimming function.
01-27-06, 11:33 AM
OK, I still can't find literature on it. Trying to figure out whether it's working properly. Is the trim only supposed to kick in when I'm on certain rear cogs? For instance, it seems to be needed even when I'm on one of the middle cogs in the rear (it's a DA double by the way). There just seems to be no rhyme or reason on when I need to use it and when not. If you know of something online that explains how this works that would be great also.
01-27-06, 03:28 PM
Right. Forget looking for the literature, it really isn't that big a deal so I'll just explain it better for you.
When you shift from inner to outer cog, you can shift the brifter through the whole of its arc so that you hear two clicks, which are so close together it's barely noticeable other than one click. If you are towards the top of the block (i.e. the big rear cogs) then you'll find that the front mech catches the chain. if you then trim the brifter with the small lever, the front mech moves very slightly, so that it is out of the way of the chain, but not so much so that it shifts down.
The same goes for the reverse situation.
I must emphasise again, THIS IS PERFECTLY NORMAL OPERATION, and is referred to in the shimano service instructions for the DA, Ult, 105 and I think Sora brifters these days too. Without trimming, smooth operation of the drivetrain will never happen throughout the block on one ring. Also, bear in mind that the chain should always be as straight as possible as per the shimano documentation to avoid unnecessary wear to the chain and spockets and even the front chainrings.
Hope that helps.
01-27-06, 04:26 PM
Thanks Matt, that does help. Just seems to need an adjustment, since it happens even when I'm not anywhere near the top of the cogs in back.
01-27-06, 10:03 PM
I scanned the instructions that came with my Sora as the print was too small to read.
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