67tony 

Shimano 105 1056 clamp-on measures 27mm when closed up tight.
My seat tube measures 29mm, and it's pretty obvious that this ain't working!

Is there a 105 RD made with a larger clamp, or one with a larger diameter range?
Probably impossible to force the clamp into a larger shape, right?

bikemig 

longer screw? 28.6 was the dimension for seatposts for a long, long time. That is likely what your seatpost diameter is and what your FD is designed for.

3speedslow

I would think the 105 clamp has been pushed into the clamp shape it is now. Does Velobase list different clamping sizes. I would not try to force the clamp on that pretty frame but instead try to reshape it on a scrap frame.

Let us know how it goes.

bear_a_bug 

Outside the obvious, which is buy a new FD, you might be able to carefully clamp it into a bench press and light massage the inner diameter into a workable size, with likely a longer clamping screw, as @bikemig suggested. I have no problem making my components work for me, esp when they are common and relatively cheap to replace.

Chrome Molly

I have had this issue and carefully filed out the inside a bit. It then fit like a charm.

Andrew R Stewart 

Is it possible that the seat tube is not round at the location the ft der mounts to? If the seat tube is ovalized at the bottom and that is too high up the tube or the ft der is being mounted lower then OEM intended... I have seem ft ders that seemed to be too small a clamp but needed some "help" in closing the clamp. Usually only the front/hinged section suffers this too tight a curve. Andy

67tony 

I see a couple listed on the auction site, one with a 28.6 size and another with a 31.8 size. Also, I need it to shift a triple.

My seat tube is for sure 29mm...a '91 Schwinn Crosscut hybrid. Maybe the powder-coating adds a bit of diameter, but I'm more off than a just a bit. Too much to file, but I like the idea of a longer screw and trying to open it up on a donor frame.

67tony 

Problem solved...and rather easily I might add!

I used 3/4" copper x FIP adapter, and a longer screw, and stretched the clamp sides out nicely.
The alloy is way more malleable than I thought.

Thanks a ton for all the suggestions!