OK I'm putting together a comutter bike and one of the new parts is the front derailer. I got a pretty good deal on it and didn't even think to check the clamp size. Well it's a 31.8 clamp and the bike is 28.6. So I was thinking of making my own spacers either out of rubber hose or lathing out some plastic. But I saw a derailer advertised with a shim for just this, but I can't seem to find just the shim. Does anyone know where I could buy one or should I just stay with plan A and make my own?
First try calling your LBS to see if they have them. If not, or if they want a ridiculous amount of money, then make your own, except make it out of metal, not rubber. Head to down to Lowe's, Menard's, or Home Depot, and a good wander around ought to find you what you're looking for. Looks like you'll need something roughly 31.8 - 28.6 = 3.2 mm thick. My first guess would be to look at hose clamps (hack saw off the part which bulges out that you won't need).
'75 Bertin, '93 Parkpre Team 925, '04 Kona King Kikapu, '05 Bianchi Vigorelli
I think that a lot of Shimano front deraillers now come as a 31.8mm with 2 shim sets to make up the two smaller sizes. Like the othber poster said, go to your LBS. If it is a shop of a reasonable size, they likely will have tons of leftover shim sets and won't need to charge much (hopefully). Bring your deraillerr to check the fit.
Ditto- don't use rubber. The deraiiler mount must be rigid or the shifting quality will suffer considerably. Poss. use hard, flexible plastic, say cut from a five gal. bucket or such. You need to find the right thickness, so that the deraiiler's band clamp does not completely close up when fully tightened.
Well if your LBS does not have shims from old school shimano FDs (they come with them standard). Take a Heineken or your favourite beer can and make one yourself. Cut strips out and layer it and hold them together with some thin tape. Sandwich it and tighten the bolt. and done.
Been using it like that for the last 6000 km and not a problem.
I was in exactly the same situation as you. I have a 31.8mm band front derailer on a 28.6 mm seat tube. I'm using the Shimano shims that my LBS had from new derailers they had but didn't need the shims for. Something important that I found is that you need 2 shims as they are only half size even though you may be told that you only need 1. With 1 fitted initialy it just didn't align properly or hold tight enough.
The Shimano shims are plastic but once mounted properly with 2 shims I have had no further problems.