Ultegra 6800 FD - Piece of plastic?

Bozman
Bozman Posts: 2,518
edited April 2014 in Workshop
Does anybody know the purpose of the small piece of flimsy black plastic on the inner side of a 6800 front derailleur.
As soon as I changed up it fell off and it's only attached to the derailleur by a couple of small plastic clips.

Comments

  • The Mechanic
    The Mechanic Posts: 1,277
    I have just looked on the Shimano Tech docs site but they don't have a document for that front mech yet. Sorry.
    I have only two things to say to that; Bo***cks
  • arthur_scrimshaw
    arthur_scrimshaw Posts: 2,596
    I thought it would be a spacer for positioning the FD when installing it, used in conjunction with the large chainring?
  • majormantra
    majormantra Posts: 2,094
    If it's the one I'm thinking of it stops the chain rattling against the mech so you can set the limit very close. Obviously it won't if it's fallen off.
  • marcusjb
    marcusjb Posts: 2,412
    Arthur Scrimshaw wrote:
    I thought it would be a spacer for positioning the FD when installing it, used in conjunction with the large chainring?

    I'd have thought that to be the case as well (though I've not used a 6800 front mech, when installing other mechs like 6700, it had a plastic clip (bright green from memory) that you then take out once you've aligned the mech to the chainrings).

    Pictures might help with this query.
    Stuff about riding a bike a long way
  • Bozman
    Bozman Posts: 2,518
    It gives the impression that you've set the limit up but the chain is actually rubbing against the plastic so you don't get any noise/rub. The chain rubs against the plastic, the plastic pops off and then rubs against the derailleur, then you realise the derailleur wasn't set up correctly.
    The clips that attach the plastic to the derailleur are flimsy so I can't really see it being a permanent fixture, the chain will catch it how ever you set the mech up so it will eventually wear through. Maybe it is for setting the mech up.

    Sorry about the lack of pic, the plastic "was" black, roughly 40mm long, 5mm wide and is probably roughly 1-2mm thick and sits toward the front of the rear derailleur blade.
    Pointless description but I'm just hoping that someone can enlighten me to its purpose.
  • mitchgixer6
    mitchgixer6 Posts: 729
    Picture of the offending item included taken of my yet to be fitted 6800 FD. It's described in the tech document as a 'skid plate' so I presume is meant to touch the chain. A replacement is available to buy as a spare part so can only presume it's designed to wear out. Not sure if it would make much difference riding without it.

    Mine is pretty loose straight out the box, so can understand why it would fall off.

    11860811783_8aa7200d78_c.jpg
    11860953614_9cecbfa1e0_c.jpg
  • mitchgixer6
    mitchgixer6 Posts: 729
    Just had a mess about with mine whilst it was out the box to take the pictures. Mine was loose due to the middle clip not being far enough down to hook to the underside of the hole. I have fixed this by superglueing a very thin piece of plastic on top of the clip. This has made it much more secure but remains to be seen how long it will last once it's on the bike.

    The dura ace version only has 2 clips holding the same part on, so slightly different design. But I've seen reports of these coming loose too m
  • Bozman
    Bozman Posts: 2,518
    Thanks for the replies. I feel that if it had any real purpose it would be a little more robust, it seems to be there for silent running at extremes(50/23-25) but having set it up without it, it doesn't seem to effect anything.

    P.S I've set plenty of derailleurs up over the years but I really found the 6800 a pain in the a55(bad day?), thank god that it's worth it when it's finished.
  • marcusjb
    marcusjb Posts: 2,412
    Interesting. Wonder what it's about, especially being a part that seems to be designed as a consumable. Maybe it is to reduce wear on the chain side plates?
    Stuff about riding a bike a long way
  • Millidog
    Millidog Posts: 32
    looked on here earlier as the "Piece of plastic" came off...... Having read above I have replaced the said bit, it seems to clip on again albeit a tad fiddly and the only real benefit I can see is that it does make changing quieter and slightly slicker. The High/Low adjusting on 11 speed is quite fine and this part also aids any rubbing if you find yourself in an incorrect gear ie. Big ring to Big ring.
    Having said all this it all worked ok without the part !! :D
  • crankycrank
    crankycrank Posts: 1,830
    Here's a link to the Dealers Manual. http://si.shimano.com/#seriesList/38 Link, FD-6800, DM-FD0002-04 Pages 10-14 show cable attachment (not sure if your owners manual explains this) and the plastic "skid plate" is mentioned on pages 15 & 17. Doesn't offer up a huge amount of info but it looks like the plastic part is made to stay in place.
  • Bozman
    Bozman Posts: 2,518
    I can safely say that after covering roughly 1200 miles, the plastic thing does squat.
    There's a slight bit of rub in the forbidden zone(50/25, 34/12) but that's it, other than that it's slick.
  • dennisn
    dennisn Posts: 10,601
    mitchgixer6 wrote:
    Picture of the offending item included taken of my yet to be fitted 6800 FD. It's described in the tech document as a 'skid plate' so I presume is meant to touch the chain.

    Me thinks you would presume wrong if you're thinking that the chain should touch it or rub against it while you're riding. It is meant to help shifting.
  • mitchgixer6
    mitchgixer6 Posts: 729
    Well it will touch the chain if it helps with shifting. I'm not daft enough to think that it should constantly be in contact with the chain.

    Thanks for the update Bozman. Certainly doesn't look like it would be essential to the function of the FD.

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