Sounds like the connection between the blades & the motor is worn. Separate the driven blades part from the driving motor part. Look at both the driving & the driven parts of that connection for wear & breakage. If there are broken/missing/severely worn parts of either connection, replace them. You may have to get a whole new section with the motor or a whole new section with the blades, if not both. If they both need replacement, just get another Cuisinart.