Author Topic: Using shim with front mech  (Read 421 times)

Using shim with front mech
« on: September 15, 2019, 12:36:13 pm »
Just bought a replacement second-hand front mech on fleabay without checking band size  ::-)  It's an Ultegra 6703.  Any downside to using with a shim or should I resell & get one the correct size?

Re: Using shim with front mech
« Reply #1 on: September 15, 2019, 01:01:04 pm »
a shim will work OK but any FD that sits in a different place has the potential to mar the finish on the frame such that it will show when the correct FD is fitted.

It can look slightly kludgy but, with 'road' FDs there is something to be said for using a braze--on type FD with a band-on adaptor; you are almost guaranteed to be able to fit any of your mechs to any of your frames this way.

cheers

Re: Using shim with front mech
« Reply #2 on: September 15, 2019, 01:04:51 pm »
Thanks Brucey.  It's an unfinished ti frame so no issues with marking.

Torslanda

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Re: Using shim with front mech
« Reply #3 on: September 15, 2019, 01:16:10 pm »
Most mech shims are now made of plastic (Delrin?) so, provided everything is clean, marking will not be a problem.

The largest size band is 34.9mm and the most common smaller sizes are 31.8mm and 28.6. Most LBSs will have a drawer full of the reducing shims. The difficult one is when you've bought a 31.8mm mech and need to shim it to 28.6mm because they're quite rare nowadays.
VELOMANCER

Well that's the more blunt way of putting it but as usual he's dead right.

Re: Using shim with front mech
« Reply #4 on: September 15, 2019, 01:59:29 pm »
Yes, it's a 34.9 than needs to go on a 31.8 tube. Sound as though it will work OK.  Thanks.

Re: Using shim with front mech
« Reply #5 on: September 15, 2019, 06:39:27 pm »
The difficult one is when you've bought a 31.8mm mech and need to shim it to 28.6mm because they're quite rare nowadays.

Surely the *really* tricky one is finding stock of the inverse shim required to let you go the other way.

FifeingEejit

  • Not Small just Far Away at the back
Re: Using shim with front mech
« Reply #6 on: September 15, 2019, 07:18:28 pm »
Most mech shims are now made of plastic (Delrin?) so, provided everything is clean, marking will not be a problem.

The largest size band is 34.9mm and the most common smaller sizes are 31.8mm and 28.6. Most LBSs will have a drawer full of the reducing shims. The difficult one is when you've bought a 31.8mm mech and need to shim it to 28.6mm because they're quite rare nowadays.

Had a quick check on SJS' site and it confirmed what I thought, if you order a 28.6 you get a 31.8 with shim.
https://www.sjscycles.co.uk/gear-spares/shimano-duraace-di2-fdr9150-smad91-clamp-band-adapter-318mm-smad91ms/

Oddly enough Shimano do a range of shims for front mechs including this one:
https://www.ebay.co.uk/i/202752337349?chn=ps&norover=1&mkevt=1&mkrid=710-134428-41853-0&mkcid=2&itemid=202752337349&targetid=522577447343&device=c&mktype=pla&googleloc=9046864&poi=&campaignid=1782815745&mkgroupid=70885937482&rlsatarget=aud-629407025025:pla-522577447343&abcId=1139356&merchantid=114921730&gclid=CjwKCAjwwvfrBRBIEiwA2nFiPbHm_zkZfg5uScsk2JG8H19DvTDZqbkTsdRGYes_aL9DFyFKjDD7BxoCS5YQAvD_BwE



I've had a similar nightmare with MTB mechs...

Re: Using shim with front mech
« Reply #7 on: September 15, 2019, 08:46:00 pm »
Surely the *really* tricky one is finding stock of the inverse shim required to let you go the other way.

IIRC you just keep tightening the bolt.

Re: Using shim with front mech
« Reply #8 on: September 16, 2019, 12:29:18 pm »
I think shimano do a lot of shims as they tries to streamline their range. This is however based on when they made a 9 speed front mech for mountain bikes that could be pulled from above or below and shimmed to fit. I might have some shims but don't think they would work as the band of the mech had cut outs for them fit in.