Shifting down to small ring - won't engage
 

I've been building up a road bike for the past few weeks and it's pretty much done except that I am having some issues with shifting down in the front. Sometimes when I am in the smaller half of the cassette the teeth of the small ring don't latch onto the chain on the downshift and it takes a few revolutions for it to snag. The front derailleur seems fine otherwise. I made sure to check for rub in big/small and small/big combinations.

Back off The (L) screw on the derailleur 1/8 to 1/4 turn until it drop ,also check your cable's tension , it might be to tight .

Is the down shift issue when in the stand and/or when riding? Andy.

Check the clearance between the front derailleur's outer cage plate and the teeth of the large chainring. The gap should be very small, 3mm at most and much closer is better. I recently changed a very sluggish front shifting bike to a much more eager shifting bike by lowering the fd to just miss the chainring teeth.

while riding. it doesn't do it on the stand really

I expected you to say that. We see on stand and in the rider's hands differences in shifting (epically front) all the time. Even after all the limit range, height, rotation and cable adjustments that can be made you're still left with the ft der acting on the tensioned half of the chain run. We find that MANY ft shift problems go away with proper soft pedaling techniques. Part of this is also when you shift. Andy.

you might be misunderstanding what's happening. the chain moves from the big ring down but it does not get latched onto the small crankring so i end up sort of tripping over myself until it finally catches. this isn't an issue with shifting technique. i'll try what everyone has suggested so far though and see if that works.

Ah, stuck in what i call neutral. Chain width VS ring c-c dimension can come into play here. Chain angle as you shift too, you did say it's only when you're in the outsides of the cassette. I don't think that anythings going on that you don't already kind of know about. You're right in that i initially read into your OP what I wanted, sorry.

But as I've said before in other posts, my replies are also for those reading. While your problem is real to you it is not a frequent one for most. Inability to get the chain to derail off what ever ring it's on because of high pedaling pressure (often because the rider waited too long and has a low cadence to begin with)is a very common issue. one that "simple" skill improvements can go a long ways to fix. Andy.

Still having issues with this. I brought it into the shop to have them look it over and everything is adjusted correctly yet the chain seems to not want to move over. They couldn't figure out a solution themselves. The chain seems to be just to the right of where it should be. I'm starting to wonder if this might be an issue with the frame itself, possibly with the bottom bracket shell. Here's a video of what happens to the chain once I downshift. Keep in mind that the limits of the FD are adjusted correctly.

http://www.youtube.com/watch?v=d0aiA...ature=youtu.be

do i need a driveside spacer? i was under the impression that 66mm bbs on road bikes do not use them

MORE blind Guesses ..

maybe the BB spindle is too close and the FD hits the seat tube rather than travel in far enough .

that's kind of what i'm starting to think which makes me wonder if a spacer would help there.

I'm just guessing too but a LOT of front derailleur issues stem from less-than-perfect positioning of the derailleur on the seat tube. That's often overlooked on a bike that's shifting "pretty good" and, if that's the case, the only thing that limit screw and cable adjustments do is to create a new problem somewhere else.

Or bang a dent in the seat tube, so, then it wont hit. .. Ball Pein Hammer .. ball side ..

WELL, HOLD ON...Ignore what I wrote earlier (below) for the moment. I just thought to check that video again. Can't see the whole derailleur, but the height seems a bit too high, which would certainly make shifting less crisp. First order of business is to get minimal clearance between bottom of cage and chainwheel, as Hillrider noted previously, then try different rotation. If still a problem see my notes below.
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OK, basic troubleshooting comes first.

• Most bikes don't have this problem, so it's possible something out of the ordinary is going on.
• The chain deraills but just hangs between the chainwheels, so the problem may be more with the chainwheels than with shifting.
• One of the first things to ask is what happened when the problem started. The OP says he has been "building up a road bike.." We do not know what crankset he used, whether he has used it successfully on another bike, or even whether the chainrings were originally paired with the crank arm

.

So... for the OP:

• Where did the crank come from? If you rode it on another bike did you have the same problem?
• What brand are the cranks and the chainwheels if marked?
• Is the tooth count marked on each chain ring visible from the same side of the crank?
• Is the inner chainwheel symmetrical when viewed edge on, or does it have no shoulder on one side?
• Are there any shims installed between either chainwheel and the crank arm spider?

Is it my eyes or does the inner ring look fairly well worn? Andy.

just fixed it! thank you for all your suggestions. this morning i had an epiphany. before i moved the crank over to this bike i took it apart and cleaned it. i looked at the smaller ring and yes, i had installed it backwards. flipped it around and it shifts fine now. d'oh

See post #8 for this possibility. The rings c-c being off. Andy.

sorry, i didn't understand that term. thanks for your help though

some things need more than internet chat to fix. see what the LBS says.

As I pointed out in my previous post, the 1st thing to look at is the last thing you did before the problem occurred. That's why I asked about the orientation of the chainrings. Asking the right questions up front prevents a lot of irrelevant guessing.