New BB7 mechanical discs on my SC Superlight. The fork is a new Manitou Skareb 80 mm. from 2004 but never used. When I apply the brakes, they chatter, shudder, I'm not sure of the most descriptive word, but it's very pronounced. They're new and everything is fine mechanically. Could it be the fork not being stout enough for a disc or the brakes not broken in properly? It must be one of the two. Everything was OK with rim brakes. Thanks for any help.