Help! - problem with front derailleur alignment

FrankGrimes

I was working on fine tuning my gears for the first time earlier on as I was getting gear slipping when on the small front ring and the big (easy) cogs at the back. I was following the instructions in the Zinn book but just couldn't get it so that there was no chain rub. DuraAce front derailleur by the way.

I was getting chain rub either on the outside when in the small cog on the big ring or on the inside when on the big cog on the small ring; I could sort either side out by adjusting the limit screws but not both at once.

I ended up having the brainwave of undoing the bolt holding the cable in place and trying to adjust the tension on it but I totally messed things up. After a lot of trial and error (with no coherent plan - didn't really know what I was doing or should be doing), I've managed to get just about working but it's definitely not fully right and it's giving a lot of skipping and chain rubbing on the front ring.

So it's just about cycleable at the moment but I want to get it sorted out - any ideas on how to approach it? What's the theory about how to align the cable in that bolt?

Planet X

Try this.

http://www.youtube.com/watch?v=ngm6dr-1na0&feature=related

bcmf

start from scratch.This is the way I did mine.
on the extremities of gears ie inside front with outside rear (eg39x12)/outside front inside rear (eg52x 25) you will get rubbing no matter what way you have your mechs set up.
Release the cable from the bolt.Align the mech so it is sitting in line with the botttom (inside) ring at the front.
.
Now with your chain on the biggest/inside sprocket at the rear see where the front mech is.If it is rubbing on the inside use the adjusting screws on top of the mech gently until it stops rubbing.GENTLY otherwise you will round the screws.
Now when thats done use your hand to see if the mech will move up and clear the outside/large front ring.You should be able to push the mech a good deal.If not then use the other adjusting screw until it does.You now have the parameters of your mech almost set.
Reattch the cable getting as much tension as possible on the cable then tighten the bolt.Remember the whole thing works on tension so make sure the bolt is firmly tightened.
test it with your brifters and will probably need to be tweaked with the adjuster screws.Remember if it doesnt work from inner /smallest chainreing to outer with your brifters YOU DO NOT HAVE ENOUGH TENSION ON YOUR CABLE.
Be carefeul when adjusting as too much leeway and you chain will drop off when you shift.take your time.

victorcarrera

I remember getting similar symptoms while trying to adjust derailer with cable connected. Cable tension is critical for correct operation of shifters with trimming. First ensure derailer is is straight and in line with chainrings. That Utube clip is generic but it doesnt describe trimming which your dura ace has. The tech specs are on the shimano site.

FrankGrimes

Right, big thanks for all those pointers. I followed bcmf's advice and I now have it operational though it's not perfect. Had lots of trouble with it - got the bottom ring sorted easy enough but then the chain was falling off the outer edge of the big ring when I changed up. I'd change the limit screws to sort that but then when I went to down shift back into the small ring nothing happened so I had to undo the bolt and start from scratch.

Eventually have it working but despite my best efforts the screws got pretty rounded off - the outer screw can barely be used now so I'm wary of pushing it. Assume I can pick up replacement screws in any lbs?

I could clearly see adjustments as a result of turning the inner limit screw, but didn't notice much from the outer screw.

Situation it's at now is that when in the big ring the derailleur is a bit further out than it needs to be - I got it so that the chain no longer slips off but it's rubbing on the inner edge on most cogs. Ideally that outer limit would be brought back in a bit without affecting the inner limit - is that what the outer limit screw should control?

I'll be in Cycle Superstore next week for a bike fitting so might ask them about it, but would prefer to get new screws and be able to sort it out myself. Think I'm on the right track but can't go any further for fear of damaging the screws too badly....if I knew what to look for when adjusting the outer screw, I think I'd get it sorted. The cable end got quite frayed as I was using a pliers to pull on it to get tension so I just taped up the end of it - anything to worry about there?

Thanks for the help - happy enough with the rear derailleur now and am close on the front so I've enjoyed learning that bit but want to get it fully sorted out.

Freddy687

If you are having this much trouble then it could be that the derailleur is not parallel to the chain.
Get new screws and align the outside of the derailleur with the outer chain ring, make sure that it is aligned less than 1mm front to back .
Then as bcmf was saying:
Remove the cable and set the lower stop screw so that there is 1mm of clearance when in the small chain ring and your biggest rear sprocket.
Attach the cable taking up as much slack as possible.
Adjust the cable tensioner, either at the STi or on the frame depending on your bike, to remove the remaining tension.
Move the derailleur to the big chainring and the smallest rear sprocket. Adjust the other screw so there is 1mm of clearance on the out side of the derailleur.
That should get it to 95% perfect. After that it is a case of adjusting the cable tension if needed.