Front mech - shim?

[Blue Hills]

I am planning to take some bits off an old bike to put on an old frame I have acquired.

The front mech on the old bike still appears to be in decent shape and I am keen to use it if I can as I have goos reason to think it will work particularly well with the new crankset I am planning to use (as it is effectively the same as the one on the old bike) but I have a question about mounting it.

The diameter of the down tube it is mounted to on the old bike is I think about 32.5mm but the corresponding measurement on the target bike is in the order of 28.75 to 28.9mm (CORRECTED AFTER INITIAL MIS-POST)

So I assume that once off the old bike it won't secure to the target bike?

I know that new mechs very often come with shims to take account of this but of course I don't have any shims for this mech as it came fixed to the bike.

The mech is around ten years old but is good quality.

What do folks do? Cobble together some arrangement using snipped beer cans or something?

If so, any particular advice?

 

[alecstilleyedye]

if it's a banded shimano type, it's possible to swap the bands over. anyone who has ordered a groupset and not paid attention to the band circumference will be relieved to find that out

 

[PhilDawson8270]

And if it's brazed on, you can just buy a clamp in whichever diameter you need.

 

[chriswoody]

I popped down the friendly LBS before, they often have some lying about.

 

[Nibor]

If it is shimano they have dedicated shims in the main sizes.

 

[Ajax Bay]

This is unlikely to be successful: the difference in seat tube diameter is too great to be coped with by a shim (we'd be talking 3+mm thick shim here), but others' MMV. Surprised you have a seat tube as slim as 25.2mm dia. Unusual. My steel (531) bike seat tube is 28.9mm.

Is this for a double or a triple, btw?

 

[Blue Hills]

If it is shimano they have dedicated shims in the main sizes.

By dedicated, you mean specific to the mech? If so, that will be a problem won't it in view of the age of the mech?

Also, knowing the economics of these things i could see a specific shimano shim bought separately being disproportionately expensive.

 

[Blue Hills]

if it's a banded shimano type, it's possible to swap the bands over. anyone who has ordered a groupset and not paid attention to the band circumference will be relieved to find that out

By swapped over, you mean swapped with a separate pair of bands supplied in the box the mech came in?

 

[Ajax Bay]

disproportionately expensive

This. And perhaps Alec can give a link to replacement bands, if possible to do this (DuraAce?).

 

[Blue Hills]

This is unlikely to be successful: the difference in seat tube diameter is too great to be coped with by a shim (we'd be talking 3+mm thick shim here), but others' MMV. Surprised you have a seat tube as slim as 25.2mm dia. Unusual. My steel (531) bike seat tube is 28.9mm.

Is this for a double or a triple, btw?

DOH!!!!!

Bit of serious mistyping up above or general brain rot.

It is in the order of yours, say 28.75 to 28.9.

Sorry.

Does this change your view on the possibility of a shim working?

If so, how would you shim?

It's for a triple.

New bike is tange chromo, old an aluminium bike with oversized tubes, hence the diiscrepancy.

Off to correct the mistake above.

Apologies again.

 

[Ajax Bay]

Sheldon: There are 3 different (clamp-on) mounting types for front derailers, depending on the seat tube diameter of your frame:

• 1 1/8" (28.6 mm) clamp-on. (This is the traditional, standard type for most road bikes and older MTBs).
• 1 1/4" (31.8 mm) clamp-on for mildly oversized seat tubes.
• 1 3/8" (34.9 mm) clamp-on for oversized seat tubes, common on aluminum frames.

I have used a shim to fit a FD-5503 with 31.8mm clamp to my seat tube (which I measure at 28.9mm). I actually used some bits of inner tube - the FD has stayed put for 6000km so far. But that's only 2mm (ie 1mm thick). I suggest you measure the old bike's seat tube again. If it's the 1 1/4" then it can be done. If it's 1 3/8" then the drop to 1 1/4" is, I suspect, rather more challenging, but I guess there's a shim out there - wouldn't be so easy to bodge. LBS help to source, perhaps.

 

[Nibor]

What make and model is the dérailleur I have just changed a Shimano from a steel bike to and OS aluminium bike you would be welcome to the Shimano shim if it was the right one for your dérailleur do you have a picture of it?

 

[Blue Hills]

What make and model is the dérailleur I have just changed a Shimano from a steel bike to and OS aluminium bike you would be welcome to the Shimano shim if it was the right one for your dérailleur do you have a picture of it?

Very kind offer from a fellow lancastrian will try and take pic tomorrow and also get more info on the model if possible. It is definitely shimano though.

 

[Blue Hills]

Sheldon: There are 3 different (clamp-on) mounting types for front derailers, depending on the seat tube diameter of your frame:

• 1 1/8" (28.6 mm) clamp-on. (This is the traditional, standard type for most road bikes and older MTBs).
• 1 1/4" (31.8 mm) clamp-on for mildly oversized seat tubes.
• 1 3/8" (34.9 mm) clamp-on for oversized seat tubes, common on aluminum frames.

I have used a shim to fit a FD-5503 with 31.8mm clamp to my seat tube (which I measure at 28.9mm). I actually used some bits of inner tube - the FD has stayed put for 6000km so far. But that's only 2mm (ie 1mm thick). I suggest you measure the old bike's seat tube again. If it's the 1 1/4" then it can be done. If it's 1 3/8" then the drop to 1 1/4" is, I suspect, rather more challenging, but I guess there's a shim out there - wouldn't be so easy to bodge. LBS help to source, perhaps.

Many thanks for the sheldon ref ajax. It rather looks as if i am trying to do the same as you did then, in which case I assume that it will work, and I assume that there is a certain amount of leeway in the original clamp, particularly for a hamfisted sod like me wbo tends to overtighten stuff/screw stuff down hard (one reason amongst many why I will never go carbon)

I may also have some thin strips of metal around from an old fixing bracket which could prove useful.

 

[youngoldbloke]

I've used a plastic shim with an oversized dog fang - don't see why a similar shim made from plastic shouldn't work with a FD clamp.