Front derailleur shifting issue

feelgoodlost

So I've been having issues with my front chainring shifting for a couple of months now, ever since I replaced the gear cables. Basically, I can't seem to get the allignment right when shifting up onto the top chainring and it's causing chain rub in almost every gear, even when the trim is being used. So.... I thought the remedy to this would be to tighten the cable via the adjuster barrel so it shifts up smoothly and gives enough room to run through the cage without any rub... rather than needing to make any sort of adjustment with the actual derailleur?

The problem I seem to have is that I can end up using the barrel adjuster 2 or 3 times in one ride and we're not talking about a quarter turn each time, it's more like 4-5 turns in order for the chain to run smooth on the chainring and then also give me a little bit of space with the trim on too, once I'm in the big gears. This seems to remedy the issue but as I've said, I end up needing to do this quite a few times during one ride, every time I go out on the bike - it's almost like the cable is stretching every time and loosening the pull on the derailleur in order to shift the gears???

So what could the issue be? Are the replacement cables just naff and need to replace with some better ones? Do I need to take it to a LBS to have them index the gears properly? Or do I need to start fiddling with the derailleur? Something I'm not massively confident doing.

You'll have to forgive me if I'm not explaining myself properly!! It's all very frustrating!! :x

sparklehedgehog

100% setup of it.

http://techdocs.shimano.com/media/techd ... 612827.pdf

Page 5 & 6

Semantik

Front mech adjustment can cause problems but shouldn't be too difficult to sort out.
First, I should clarify that I am a Shimano user.
1) Make sure mech is mounted at right height and orientation relative to chainrings- guess you've probably got no issues there.
2) With no cable yet fitted, adjust the low limit screw so that chain just clears the inner edge of the mech cage when in bottom gear.
3) Fit cable while mech is in small chainring position and set the cable tension so that there is a little slack (not much) in the cable. The cable tension at this point should not affect the static position of the mech cage which you have just set.
4) Check the shift onto the big ring (don't worry too much about the cable tension yet)and set outer limit screw in top gear in same way as with inner ring.
5) push the large sti shift lever as far as it will go so mech cage is as far out as it will go. Now test for the trim function. If cable tension is not right the trim function won't work properly and the cage will hardly move inwards at all when trying to trim. If this happens, NOW you should play with the cable tension using the barrel adjuster until the trim function moves the mech cage inwards by the right amount(1-2mm).
I have found that when the trim function is set properly then front shifting is usually spot on. The problems encountered are nearly always caused by incorrect cable tension.
Should add, that making adjustments to cable tension is best done with the mech back in the small ring position, then test again by shifting onto big ring.

feelgoodlost

Thanks for the replies, folks! I'll take a proper look at it this weekend :-)