[KR500]

I agree with some as to the disc possibly causing the chatter. If a disc became overheated and weakened the torsional springs or if the springs were never up to tension in the first place, I would want to try a different disc. I was under the impression that a clutch disc should be included in the balancing job when doing the pressure plate and flywheel. If you have ever driven a vehicle with an oil or grease soaked disc you know how they can chatter.