Mushroomed front derailleur - am I doing something wrong?

k-dog

Last night on my way home I was taking it easy and changed down to the small chainring before a hill - about the middle of the cassette - when everything locked up and my front derailleur got bent out.

I straightened it up as best I could just now and the shifting is okay - not perfect as I'm not sure the shape is just right but it works. I'm going to order a new one to fix that.

This is the second time it's happened to me - I replaced the old front derailleur a few months ago when it did the same - but it was at least 3 years old. This one probably only has 1000 miles on it. The chain and cassette have been on together and the chain just got to 0.75. Chain rings aren't too old and look okay (bit hard to tell with the Shimano teeth). Chain was cleaned and lubed last weekend.

Last time I adjusted the old one I moved it down a little but I was suspicious that caused it so this time I put it up so there was about 3mm clearance - looked right according to the sticker that comes on the derailleur.

Is is just chain suck and a coincidence or is there something I need to do to stop it happening again? I'd rather get more than a few months out of a FD.

Crankset is 105, shifters are 105, both derailleurs Ultegra. All same generation stuff, 50/34 and 12-25.

Thanks.

me-109

When you set the height make sure that it is measured against the tallest teeth on the outer ring. If it isn't then it will probably work but you'll get a regular clicking as the tall teeth or the chain clip the mech. Only other suggestion would be to ensure the clamp was tight. If it has loosened off them the back of the mech might swing out into the path of the crank.

k-dog

Yeah, I did that - the sticker has the different tooth profile so you can check that.

veronese68

If it was whilst changing down is it possible one of the outer chain plates may be damaged and has snagged the derailleur as it passed?