The speedometer in my '70 Duster worked just fine, no jumping and accurate. I had to pull the cluster to install a new dash pad. When I drove it after putting everything back together the speedometer was fine. After a few miles it started jumping all over the place and making a noise like hitting a little bell. So, I slowed down and headed back home not wanting to break the speedometer. It still bounced from below zero to more than max. It finally went to below zero and just started quivering. The strange thing is the odometer is still working fairly accurately. Speedometer or cable?