I currently have a (frame) damaged TREK 1200, vintage approx. 2000, whose components I would like to be able to switch to a new TREK 1500 frame. The problem I need help with is the front derailleur.

My current set up is a clamp-on front Shimano RSX derailleur with a triple Shimano SG A 52-42-30 chainring. The set up in the rear is an 8-speed rear cassette (26T - 13T) on a Shimano RSX rear hub FH-A416. It is a Shimano RSX derailluer in the back. The shifters are of the double tap variety.

The problem is with the seat tube that I have to clamp the derailleur on. The 1200 seat tube is 27.1 mm and the 1500 is larger at 31.8 mm. I can't machine the clamp to accommodate the larger diameter as it would remove too much material. A new front derailleur seems inevitable. Went to the LBS and they think I am going to be out of luck due to compatibility issues (these days most of the rear cassettes are 10 speed clusters). They mention something about probable chain rub up front.

I am not sure how to best describe the chain, but when I measure the width I get a max outside width of 7.07 mm at the rivets, 6.73 mm at the outer links and 4.30 mm at he inner links.

Does anyone know of a compatible front derailleur or other (non-expensive) fix for this situation?

If anyone can help me with this dilemma I would be most grateful.

Thank you,
Chuck