Chain rub on ultegra FD

jimwocko
jimwocko Posts: 34
edited September 2013 in Workshop
I'm hoping for some help on this - so any advice or ideas would be gratefully received!

I have a new set up and keep getting chain rub on the front derailleur - which I can't solve. I've replaced the cable and added inline barrel adjusters (which for some reason Ultegra doesn't come with) which improved the situation, but it still isn't right.

This doesn't seem to be a result of cross chaining or anything obvious. Using the small ring allows use of the full cassette (using the trim for the highest gears in the sequence). The rubbing only happens when on the big ring at the front, and smallest 4-5 cogs. It seems as though the rubbing is the result of the derailleur not coming quite far out enough, but adjusting the cable tension means that the chain rubs when on the small ring.

Adjusting limit screws to allow the derailleur to move further means that the derailleur starts to move into the big ring.

The set up is:

FSA SLK-lite Compact 172.5mm crankset
Ultegra Front derailleur
Ultegra Rear derailleur
Ultegra chain
Ultegra 11-25 cassette

Could it be something to do with this set up or am I missing something obvious?!

Comments

  • Monty Dog
    Monty Dog Posts: 20,614
    Can you physically move the front mech further outboard than the shifter allows - unscrew the H screw if necessary? Maybe you're starting with too much slack in the shifter cable - did you ensure the inner shifter lever was released a few times before you started?
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  • jimwocko
    jimwocko Posts: 34
    I released the shifter completely before attaching the cable.

    If the H screw is released the shifter will let me pull the derailleur further than it should go (ie into the chain rings). Is this not what the H screw is supposed to do though?
  • montyburns56
    montyburns56 Posts: 70
    "Adjusting limit screws to allow the derailleur to move further means that the derailleur starts to move into the big ring."

    But I thought that the problem was when you were in the big ring? Adjusting the H limit screw should have no effect on what happens when you are in the small ring. It sounds like you need to slacken off the H limit screw a little bit.
  • jimwocko
    jimwocko Posts: 34
    Sorry, should have been clearer - the derailleur itself moves so it starts to scrape into the big ring - slackening the H screw means that there is more pull in the shifter than there should be.
  • desweller
    desweller Posts: 5,175
    Double check that the derailleur is parallel to the chainrings. If it is pointing across them even a little bit then you're effectively narrowing the path that the chain can travel through.
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  • jimwocko
    jimwocko Posts: 34
    Thank you all for the replies.

    I seem to have solved it - for now at least.

    When tightening the derailleur bolt to the clamp the action of tightening pulled the derailleur away from parallel.

    I've slightly raised the derailleur on the clamp and then braced my finger against the derailleur to stop it pulling out of line. Hopefully this should sort it and raising it shouldn't cause additional problems (it is still within the 1-3mm specified in the manuals).

    Thanks again!

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