New chain ring...problems with the front mech

FlyingSchnitzel

As I decided to make my 2 bikes identical in terms of gearing, I decided to swap my chain ring on my training bike. I used to ride a 46T on my training bike an bought a 52T. I have a new chain (longer one) and reinstalled the front mech (higher) and replaced the shift cable too. As I thought, I'd be quite experienced, this shouldn't have taken too much work. But now I have some issues with the front mech. I adjusted it to the new chain ring (height, alignment and limit screws). I set the tension and there is my main problem. After tightening the clamp bolt of the shift cable with tension, the front mech won't shift into the big chain ring. So I adjusted the cable tension and it will shift. However, the chain will rub against the front mech when I shift to the small sprocket on the back (11T). This means that there isn't enough cable tension. So I adjust the cable tension with the barrel adjuster (the limit screw won't stop the front mech) and everything works just fine. However, when I shift back to the small chain ring and the big sprocket (28T) on the back, the chain will rub against the cage of the front mech. So I'll reduce the cable tension which will cause again rubbing when I'm in the big chain ring and the small sprocket.
What can I do? I have Shimano Ultegra leavers, front an read mech.
Thanks.

dj58

Read trailflow's guide to setting up Shimano FD's and balancing cable tension. Taken from the thread below.

viewtopic.php?f=40004&t=13004287&p=19295647&hilit=6800+FD+chain+rubbing+FD+6800#p19295647

Here's a set up guide i posted on another thread. So ive copied and pasted it. This guide also applies to the 105 5800 and Dura Ace 9000 front derailleurs.

Here's the Shimano 6800 set up pdf aswell
http://www.google.co.uk/url?sa=t&rct=j& ... 24&cad=rja

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The ultegra 6800 front derailleur has a trim function on both the big AND the small ring. So big lever and little lever. (if you dont know what the trims functions are - they are lever clicks that allow you to move the cage slightly to eliminate chain rub)


To set up the 6800 front derailleur correctly an inline barrel adjuster should be used. It will make set up much easier. if you dont have one, install one. Make sure it is screwed all the way in too, before starting.

Start off by making sure the outer limit screw is screwed outwards but not all the way that it pops outs (the limit screw closest to the chain rings)

Start over. undo the cable

When clamping the front derailleur to the frame make sure the gap between the big chainring teeth and front derailleur cage is around 2 to 4mm.

Toe the rear of the cage in slightly (around 5mm) when clamping. Then use the support bolt to align the cage with the big chainring. The support bolt is a small screw that pushes up against the seat tube to add stiffness to the front derailleur when shifting. It also moves the front cage outwards as you screw it in. See page 8 of the pdf below
http://www.google.co.uk/url?sa=t&rct=j& ... 24&cad=rja

So first , with the cable de-attached. Put the chain on the small front ring and 25t (or biggest) back cog. -

Adjust the inner limit screw (closest to the frame on the front derailleur) so the gap is 0.5mm from the chain and the front derailleur's plastic plate,and not rubbing on the chain.

Make sure to down click the left shift lever into its lowest position. Press it 4 times

Clamp the cable (pull the cable fairly tight with pliers and clamp). Then shift the chain onto the 11t cog (or smallest) at the back, and shift the front onto the big ring. (if it doesnt shift up - add more tension by loosening the bolt and pulling more cable ,then re-tighten the bolt). Now when in the big ring there should now be some chain rubbing on the cage if you spin the cranks.

Now wind the inline barrel adjuster (adding more cable tension) until there is a 0.5mm gap between the outer cage and chain, and no chain rub. Look down at the front derailleur cage as you do it, and spin the crank until the rubbing stops.

Then wind the outer limit screw in until it touches the stop. (If the outer limit screw is in too much it wont shift up - this is why you screw it out at the beginning.)

Next shift the front down onto the small ring and keep the rear on the 11t (or smallest) cog. Then click into the front small ring trim position. now whilst in the trim position,add a little bit more tension with the barrel adjuster, until there is also no chain rub. This will eliminate any slop in the trim and make it feel more positive to click.

Now it should all be set. Check all gears and trim settings. Make sure the chain isnt being thrown over off the big ring.

If you find the small ring trim click isnt very positive. Start over and try the second cable routing tab position. (remember to wind the barrel adjuster in again before starting.)

There will always be rub in the big/big combo. This is cross chaining