Front Derailleur

[Minnsy]

Chaps.

New front derailleur on bike. Adjusted high and low settings, so shifts to all the chainrings smoothly however when on middle ring, with chain either on largest or smallest gears on rear cassette it scraps the front derailleur (the part that the chain travels through). Googling has suggested that the way this is sorted out is by playing with the adjuster on the shifter on the bars... have tried this, but not a great deal happens...

Any ideas?

David

[neil_bolton]

Possily is a smaller caged front mech, as newer ones (Microdrive I think Shimano call it) are smaller based on the fact that the chainrings are smaller.

Based on your prognosis, there's not a lot you can do:

Have you:

1. Got the Mech set at the right height - 2mm from the chainring when in the largest sprocket?
2. Angled the mech correctly based on the chainline

Other than that, going on your symptoms, I'd say you've replaced a non Microdrive front mech with a newer one that isn't the same.

Can you list out the components you're using with the age/model?

[Parrot of Doom]

The adjuster will simply move the derailleur up and down the chainrings, nothing more. I think Neil is probably correct. How does the new mech compare physically to the old one?


BTW, if the bolt that clamps the cable is made of dark grey metal, be careful how much you tighten it. I've had 2 of those break on me, they're little swines. I'm replacing them with steel bolts.

[Minnsy]

Bike is Epic.

replaced Deore with XT. Positioning is 2mm above, as instructed - derailleur has sticker to help with alignment, and it is aligned 'true' as you describe.

have just compared cage sizes.. and the new one is a couple of mm narrower than the old one. Which might explain the chain bashing on the sides... so basically unless I now replace again with non microdrive, I am stuffed...

[neil_bolton]

Minnsy said:

Bike is Epic.

replaced Deore with XT. Positioning is 2mm above, as instructed - derailleur has sticker to help with alignment, and it is aligned 'true' as you describe.

have just compared cage sizes.. and the new one is a couple of mm narrower than the old one. Which might explain the chain bashing on the sides... so basically unless I now replace again with non microdrive, I am stuffed...

Sounds like you're running a 9spd mech with an 7/8spd chain?

Doesnt usually cause an issue, however seems it is. Apart from the rub, it won't cause any issue to be honest.

[Parrot of Doom]

Minnsy said:

Bike is Epic.

replaced Deore with XT. Positioning is 2mm above, as instructed - derailleur has sticker to help with alignment, and it is aligned 'true' as you describe.

have just compared cage sizes.. and the new one is a couple of mm narrower than the old one. Which might explain the chain bashing on the sides... so basically unless I now replace again with non microdrive, I am stuffed...

Which model of XT derailleur do you have, and which do you require? I have a spare M770 XT here (Mega 9 drive train, sans cable tightening bolt and plate) that I could let you have for a tenner, just depends which model you need.

[Minnsy]

Derailleur is Shimano XT Front Derailleur Top Swing M770 31.8-34.9 Dual Pull
Chain is Sram pc 971 9 speed

So right chain... new derailleur... and rubbing like crazy. It is not so much the 'damage' it won't cause to the cage... it is the noise... (old one was silent... until it broke.. )


Thanks for offer of M770 though..

Mighe just amble off to the LBS to see what they say..

[neil_bolton]

Minnsy said:

Derailleur is Shimano XT Front Derailleur Top Swing M770 31.8-34.9 Dual Pull
Chain is Sram pc 971 9 speed

So right chain... new derailleur... and rubbing like crazy. It is not so much the 'damage' it won't cause to the cage... it is the noise... (old one was silent... until it broke.. )


Thanks for offer of M770 though..

Mighe just amble off to the LBS to see what they say..

Very odd.

Once you've been, can you let us know what it was? Or, take a pic, so we can see

I'm a geek, I hate not working out stuff like this

[Minnsy]

Well matey in the LBS (who is a mate!) fiddles with this, fiddles with that.... re tensions the cable. Fiddles with the handlebar adjuster, pokes it prods it, takes it out on the road, brings it in again, repeats all of the above, and even though it still scrapes (beit on the lowest gear on cassette) it is a vast improvement...) so in asking him what he has done he replies 'tweaked this, fiddled with that, etc...

So the moral of the story is... if you can't fix it, get someone else to do pretty much exactly what you have already done and that normally works..

So no magic wand!

Cheers

[Parrot of Doom]

He probably stuck a big screwdriver in the cage and widened it

[neil_bolton]

Parrot of Doom said:

He probably stuck a big screwdriver in the cage and widened it

I've never done this. Ever.

[Zead]

Parrot of Doom said:

He probably stuck a big screwdriver in the cage and widened it

+1, read this post and came to same conclusion. Cage could easily have been squeezed in transit. There is nothing a big screwdriver cant fix