The speedometer needle on my 76 300D (115 chassis) fluctuates intermittently by up to 5 mph between 25 and 80 mph, and it is doing it more often lately. The greatest fluctuation is when the car is slowing down (the needle bobs up and down by 10 mph or more between 25 and 10 mph).

When the needle is fluctuating and I engage the cruise control (pneumatic CC actuator), the car "pulses"...I may eventually develop whiplash!

When the needle is not fluctuating, the CC (new amp) is also steady (the speed sensor is in-line and the 2 halves of the speedometer cable are joined at the sensor).

Is the fluctuation more likely the result of the cable or the speedometer - or both? Or is the speed sensor the likely culprit?

If it is the cable, what is involved in replacing the lower half of the cable (from trans to in-line speedsensor) - unfortunately there is almost nothing in the paper and CD manuals I have about the transmission).

Robert