Braze-on Front Derailleur - Washer Front and Behind?

[type2sam]

All,

Braze-on front derailleur newbie here...

I'm attempting to use a Shimano 600 tri-color front derailleur on a Serotta with a braze-on mount, however I can't seem to get the FD cage parallel with the chainrings as the body of the FD hits the seat tube (or more specifically the part of the braze-on that wraps around the seat tube). If I space the FD back about 2mm I can get enough clearance to twist the FD such that the cage is parallel.

I understand that there's a concave washer that goes on the front of the mount (I need to source one), but should there be one behind to perform these spacing out duties?

I'm sure I can fab something up, but wondering if there is an official part I am missing or if the mount is just bent a bit.

I can post pics in a bit.

[pcxmbfj]

On my Tarmac the bolt and washer go into braze on, derailleur body other side.

[type2sam]

Thanks - that's what all the pictures I have seen would indicate. Perhaps I need a different model of derailleur.

[Lewis Moon]

Pics would help.

[type2sam]

Indeed. At first, I thought the cage of the FD was bent, but turns out I have 2 of that model and they are identical.

[rwsaunders]

It appears that you're missing the concave washer behind the mounting nut, which allows you to adjust the position of the derailleur.

http://blog.treefortbikes.com/wp-content/gallery/front-derailleur-post/frontderpost-2.jpg

[Mark McM]

The front concave washer allows the derailleur to be clamped more firmly, but it won't change the seat tube getting in the way of the derailleur rotation.

The derailleur tab appears to be held on by some type of band - can this band be rotated on the seat tube? Or is it fixed in place?

Several manufacturers make derailleur shims, although these are usually tapered (different thicknesses top and bottom), and are intended to vary the vertical angle of the derailleur to accommodate different seat tube angles. But one might work for you, if the taper isn't too extreme - or maybe you can use two of them in opposite orientations to cancel out the taper angle.

Here are a few of them:

http://shop.osymetricusa.com/ANGLED-WEDGE-SPACER_p_47.html

http://www.artscyclery.com/SRAM_Braze-On_Front_Derailleur_Shim/descpage-SRFDSH.html

http://www.slowtwitch.com/articles/images/8/75168-largest_1_SRAM_shims.jpg

[type2sam]

It appears that you're missing the concave washer behind the mounting nut, which allows you to adjust the position of the derailleur.

http://blog.treefortbikes.com/wp-content/gallery/front-derailleur-post/frontderpost-2.jpg

Yes, understood that I am, but that would still not solve the issue of the alignment. I need the body of the FD to move towards the rear of the bike so that I can rotate it enough clockwise so that the cage is parallel with the rings.

[type2sam]

The front concave washer allows the derailleur to be clamped more firmly, but it won't change the seat tube getting in the way of the derailleur rotation.

The derailleur tab appears to be held on by some type of band - can this band be rotated on the seat tube? Or is it fixed in place?

Several manufacturers make derailleur shims, although these are usually tapered (different thicknesses top and bottom), and are intended to vary the vertical angle of the derailleur to accommodate different seat tube angles. But one might work for you, if the taper isn't too extreme - or maybe you can use two of them in opposite orientations to cancel out the taper angle.

Here are a few of them:

http://shop.osymetricusa.com/ANGLED-WEDGE-SPACER_p_47.html

http://www.artscyclery.com/SRAM_Braze-On_Front_Derailleur_Shim/descpage-SRFDSH.html

http://www.slowtwitch.com/articles/images/8/75168-largest_1_SRAM_shims.jpg

You describe the problem exactly and this is just what I was looking for! The hanger is not a band but instead a brazed on fixture - like this:

http://www.cycle-frames.com/bicycle-frame-tubing/FRONT-DERAILER-BOSS-INV.-CAST.html

Thanks Mark!

[David Kirk]

The large 1 3/8" seat tube Serotta used played havoc with some derailleur designs that were designed around a 1 1/8" tube.

I'll bet you can shim it rearward and have it work or pick a different style of changer that works well with the big tube.

dave

[rwsaunders]

^ and there you have it.

[type2sam]

Awesome. Thanks David!