Chain rubbing against front Derailleur

bus_ter

When the chain is on the last few highest gears at the back, the chain rubs against the front derailleur.

My understanding is that there should be a mm or so gap between the front derailleur and chain when the bike is in the top gear (smallest back, largest front). I've tried to adjust the limit screw but it already feels loose, and further undoing of the screw makes no difference. If I tighten the limit screw until I start to feel resistance I can see the derailleur start to move inwards, however at it's slackest (which seems to be how it was set) it's rubbing against the chain. I have to be in the 4th/5th gear before it stops rubbing.

The groupset is Shimano Ultegra 6700. The bike is only a few weeks old and seems to work fine. However after hearing excess chain noises I inspected further to discover the chain rub. The bike is mail order so it's not easy to take it back for readjustment

Boyzer

Same problem here, same groupset, same mail order issues. Im avoiding the offending gears at the moment, but plan on paying for a 6 week service at my LBS.

Twostage

Sounds like the gear cable needs a bit more tension so it pulls the DR further out. You should have a barrel adjuster either on the down tube or an in-line one. Twist it counter-clockwise.

bus_ter

Twostage wrote:

Sounds like the gear cable needs a bit more tension so it pulls the DR further out. You should have a barrel adjuster either on the down tube or an in-line one. Twist it counter-clockwise.

Wow Spot on! Seems to have worked perfectly. I'm now wondering what combination of barrel adjustment vs limit screws should be used to set it.

I even read through the Shimano tech document and it only mentioned the limiter screws :?

EDIT: Still not right. If I goto the inside gears it now rubs there. Even if I loosen off both set screws I can't get it so it doesn't rub at one side. I also think the cable is a little too tight now, it's like a guitar string on the down tube.

arlowood

Might be worth going back to first principles and doing a basic set-up from scratch.

The attached link shows you how:-

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

Seems reasonably comprehensive if you can put up with the chronic catarrh that the guy seems to suffer from.

Just a comment in that he does not mention checking the fore/aft alignment of the derailleur cage and it might be worth checking that it is completely parallel to the chainrings. If not you will have to release the derailleur clamp bolt and twist the mounting until the cage is correctly aligned. Thereafter you can proceed with his set-up.

sandyballs

You should do some reading into what the limit screws do, thats not tryin to put you down. They limit the travel of the front derailleur they do not move it. The barrel adjuster tightens or loosens the cable and so moves the derailleur. You should adjust the barrel / cable so that when in the big front small back you have no rub. When you move the rear up the cassette to the inside gears you will probably experience rubbing at the front. The shifters usually have a trim mode. By downshifting 1 on the front derailleur lever it usually moves the FD slightly enough to stop the rubbing but not enough to shift down to the small ring at the front. You should ensure that you readjust the limit screws so that the chain does not drop of the front rings. Hope that makes sense.

bus_ter

Thanks for the replies. It's getting past my tinkering skills. The bike has now done a 100 miles, so I'm going to get my LBS to tune the gears now any initial cable stretching and bedding in should have occured.

sandyballs

Please never get past your tinkering skills, its how we all learn. Stick with it a bit longer you will save money in the long run by not having to pay the LBS every time its goes out of trim.

Google and you tube help, and ultimate advice, if it feels like it going to snap, stop what your doing..

Twostage

Sounds like you've overcooked it. The shimano tech docs are good but you have to follow them exactly. Step 1 in the instructions assumes the gear cable isn't connected yet. And the bottom of the 1st column talks about ensuring that the cage is exactly parallel with the front cogs which is important.
If the cable is a bit too tight it will be holding the DR above the lower limit.
If you are confident enough disconnect the cable from the DR and go through the steps in the tech docs.

bus_ter

The more I look into this, the more wrong it looks.

Step 1 in the tech docs says to adjust the chain guide to be 1-3mm from the outer chain ring. Well mine is 6mm. I can't adjust it because it uses a braze on adapter, and it's already at the bottom of the slot on the frame (I have the compact chainset). I don't know if this is a fault with the frame or what the implications of being this far out are?

EDIT: Further to the above, the derailleur isn't an even distance away from the outer chainring as it goes round. At the front end it's 6mm, but by the back it's about 10mm from the chainring. I'm not sure if this is normal? The tech document seems to suggest this should be even, and that I should rotate the derailleur?

I think it's best I get my LBS to take a look. It's not quite right. All the set screws seem to be at their limits just to get it to fit.

Twostage

I think you're right. Once you have it back and working ok you can have a look at how they have set it up.

bus_ter

ok Update. My bike spent yesterday at the LBS having the gears redone. Quite a few things were adjusted front and back, including the derailleur angle, position and the cables redone too. It now seems to be shifting much better, much smoother and without rub on the derailleur at all. I haven't gone for a proper ride yet because of the icy conditions, but I will report back when I do.

There is some further good news and bad news too. Good news, they didn't even charge me?! The bad news, on inspecting the bike when I got home there is a nice scrape on one of the crank arms showing shiny metal (see my other post on touch up paint for Ultegra grey!). I wasn't happy about that, and I do wonder if that's why they didn't charge me..