Campy 8 cog spacing is 5.0mm.and Shimano 8 is 4.8mm. That magnitude of mismatch works on in other senarios, one being shimano 8 speed shifters with a 7 speed shimano cassette which has the same cog spacing differences.
You need to get a "Wheels Mfg." spacing kit to replace your Campy spacers. They are a little thinner than the campy spacers, to make the wheel work great with the Shimano shifters.
Your LBS should be able to get them, or you can order them from branfordbike.com
Look under cassettes and spacer kits.
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