Gear slipping and then chain slip and broken derailleur.

gez747 Posts: 23
edited July 2011 in Workshop

On Sundays Etape I was at the last 1km marker in St.Flour when I tried to change down to my smallest 29 gear. My gears had been slipping a bit on the climbs but nothing major. This time my rear derailleur jammed and sheared off into my spokes rendering the bike broken. This happened around 6 months ago aswell.

I ride a Pinarello FP2 with Campagnolo veloce. 29/11 on the back.

The force has snapped the carbon insert and I am now really wary of getting the bike back and it happening again.

Does anyone have any ideas as to why this is happening?

Many thanks,



  • term1te
    term1te Posts: 1,462
    Just some thoughts... The obvious one is to adjust the high gear adust screw to prevent the mech moving to far over, but I guess this was set correctly.

    11 - 29 is a big range. Could it be that the top jockey wheel is butting up against the largest cog, obviously with the chain between them? I've an 11 - 28 and needed to adjust the angle adjusting screw on the rear mech to hold the top jockey wheel away from the 28 sprocket. If they do connect it is noisy and causes the mech and chain to jump about a bit. Maybe this was enough to derail the whole mech? Chain length is going to be crucial with that sort of difference, maybe the derailleur arm isn't long enough to accomodate it?

    Chain slipping on the other sprockets suggests it had stretched. Have you replaced the cassette, but not the chain recently? The 29 is probably the one you use the least, so will have worn the least as the chain stretched. This also may make it more likely to jump off the top and pull the mech into the wheel.
  • Monty Dog
    Monty Dog Posts: 20,614
    Check that your frame rear mech hanger wasn't bent in transit - your LBS should have a tool to check alignment / tweak it back into position.
    Did you extend your chain length when you fitted the bigger cassette?
    Whilst a worn chain might cause gear slippage, it's usually mis-alignment that causes mis-shifts.
    If the frame / hanger alignment is OK, then suggest you find yourself a competent mechanic 'cos your current one isn't very good!
    Make mine an Italian, with Campagnolo on the side..
  • gez747
    gez747 Posts: 23
    Thanks guys,

    The shop has mentioned that the 29/11 is on a lot of Pinarello bikes, and there should be no problem with running this set up. They also stated that it sounds more like the hangar was out of alignment and must have got bent in transit.

    It is in there being fixed at the moment, so fingers crossed it comes back alright this time.