I had the same problem.It started last spring,I checked the clutch,free play was good.. This spring I removed the inspection cover, I reset the clutch again.I still had a chatter. I had had the problem for over a year The clutch had 30,000 miles on it and I do know how to drive my Model A . In June I found the chatter. I was on a tour and I lost all drive. The 4 rivets that hold the clutch together all broke off and the disc came apart. The disc was not worn. The clutch was made in U.S.A. and good quality. The flywheel and pressure plate were exellent. The loose rivets were the problem.