I'm guessing its the rear brake that needs centering? if so then you need to do this with a thin 15mm spanner. Campagnolo rear brakes are a single pivot, differential design, which work brilliantly but are prone to getting moved out of position when changing wheels. So to align this use the 15mm spanner on the nut on the caliper to centralise.
Thanks very much, will try that.
Just did that. Perfect. The spanner just centres the caliper, yes? It's not a question of loosening the bolt? It didn't loosen, just moved the whole caliper to a central position.
Seems OK. Thanks again.