Velocivixen

I am replacing the Shimano 200GS Grouppo on my 1992 Hardrock Ultra. I bought a great used Shimano FD-M730 derailleur on ebay - won the bid for $2.79! I got it on the bike, set it up perfectly then decided to tighten the fixing bolt on the clamp. I heard a "pop" then decreased tension on the bolt. I cracked the clamp!!!!https://www.bikeforums.net/images/smilies/cry.gif! It's a hairline, but I'm not willing to take my chances, so it now sits in a bag with a note that says "Do not ride. Parts only". I really want a Shimano FD-M735 to match my rear derailleur, and those come in 28.6 & 31.8 clamp sizes. Most of the ones online are the larger clamp size. 3.2 mm doesn't seem like much, but I know on bicycles it can mean a lot. So....has anyone tried shimming a 31.8 to fit a 28.6 and how did it work?

Also, anyone know the torque specifications for a front derailleur band?

brockd15 

You can definitely shim it. Most new derailleurs come with shims. You might want to check at your LBS to see if they have any.

Velocivixen

OK, great. Universal Cycles, where I do a lot of shopping has them I see. I just wondered what the success rate is? If they're more a pain in the b@tt, then I'd rather not attempt it.

Velocivixen

So my seat tube is 28.6 and I'm considering a derailleur with a 34.9 clamp size. Is that difference too much to effectively shim? I'd appreciate some thoughts & opinions. It may be possible to do from a technical standpoint but does it WORK?

busdriver1959

I usually buy my shims from the beer store. The advantage there is that I get a beer and a shim, not just a shim.

Henry III

You'll have to use the whole can to shim that. The shims that normally come with most shimano derailleurs are a good 1/8 if not more. I've got some in my tool box. They also have double sided tape on the shims to hold them in place on clamp.

cs1

Amen!

brockd15 

It works just fine and you'd never know there was shim there if you didn't look at it. In my mind the biggest downside to using a shim to go from 34.9 to 28.6 is the look, but just day to day it's probably not something you'd notice.

fietsbob

Buy a Braze on FD and you just change the Band mount for a bike with a different seat tube diameter.

tight enough , but not too much ..

busdriver1959

Hopefully it would take more than a whole can. Sounds like a good excuse to drink another beer.
Seriously though, 28.6 to 31.8 is a 1/8 inch difference. The shim would only be 1/16 thick.

Velocivixen

Ok great. I'm looking for a specific Shimano Deore XT circa 1988-1993 model and they are not brazed on as far as I can tell. So buying one with a braze on type clamp mount wouldn't work, I believe. OK, so I'll see what I end up with on auction site. Ive scoured 3 bike coops today with none.

rhm

Busdriver nailed it. Don't think in millimeters, think in inches. Home depot sells aluminum stock 1/16" thick. A full ring around a 1 1/8" tube makes a shim for a 1 1/4" derailleur. Two rings and you're up to 1 3/8". Bending such a thick bar into a ring will distort the section, so you will need to file it flat again. First form each ring around a gaspipe frame or other pipe, and then file it flat. Then it is best to cut each ring into two pieces so you don't change the curvature. The more care you put into it, the better it will work out.

CroMo Mike 

3.2 mm is .128" so you would need a shim half that, or .064" thick. 1/16" is .0625", should be close enough. The thickness of a beer can varies, but is likely about .010", so it would take about 6 wraps to do it. A piece of 1/16" aluminum stock could be cut and bent around, but would be handful to cut using household tools. Scissors won't cut it; stout tin snips would.

Dfrost 

I'm using a Wheels Mfg FD plastic shim, purchased from Universal, on my Marinoni for a 31.8 clamped FD on a 28.6 DT. Works great!

The problem I've had with multiple layers of beer can aluminum is keeping them lined up, and not scratching the DT paint.

brockd15 

I've gone the route of making a shim from aluminum stock and it can work just fine, but the pre-made shims are so much easier and cleaner. Since you're still shopping for a derailleur I would just order one and be done with it.

John E

Does anyone else remember the great anecdote from "Zen and the Art of Motorcycle Maintenance," in which Pirsig advocates making one's own shims from beer cans, whereas his traveling companions insist on buying the "real thing" from a motorcycle mechanic's shop?

onespeedbiker

If your looking for the shim online, search for "derailleur shim 31.8 to 28.6"; generally these shims are not sold by thickness, but the difference in diameter..When buying older derailleurs make sure you check the pull direction is the same as your bike. While the wrong pull direction can be made to work, it's obviously better to have the correct version if it's available

To answer your other question, Shimano® front derailleur bolt 5~7 Nm 44~60 in lbs.

Jeff Wills

I shimmed a 28.6mm seat tube to match a 31.8mm clamp (an Ebay purchase goof) with a short piece of Schedule 40 PVC pipe. This is really close to 1/16" thick, so it worked perfectly. It was still working when I sold the bike, 6 years after the modification.

PVC is nice because you can paint it to match the bike very easily.

seedsbelize 

Some of us just use duct tape, or a piece of innertube. We don't run with the meticulous crowd though.

eschlwc

^ exactly. or use the hard cardboard stuff in the center of a roll of rim tape. it doesn't squash like a rubber tube, and if it's too thick, you can tear it apart to thin it.

i've had to do this with first gen suntour cyclone on two '70s motos.

Velocivixen

Thanks for all the suggestions. Since I practically LIVE at Universal Cycles I'll get one of the Wheels Mfg. front derailleur shims for $9. The derailleur I'm trying to find, either at a coop or ebay, needs to be bottom pull and, ideally, 28.6. I will get it in a 31.8 and shim if necessary. I know where I can get a NOS one, but it's a little steep, so holding off on that one for now.