Any ideas what would cause a jerking at cruise on a 69 4 sp? The jerking goes away under load but at cruise it seems to jerk a bit. I have replaced the vaccum advance as well as changed and flushed the rear diff oil. I also installed a Petronics ignition but am wondering if my non-stock cam needs more fire? Thoughts are much appreciated.

 

Try looking at your front differential bushing that goes between the diff and the frame...I was caught by that one years ago.Same symptom. A cheap bushing and not hard to change .Your diff will rock with any play, that bushing is right in line to degrade with any oil leaking from the motor.

 

hey bp...........is the "jerking" the engine cutting out or does it feel like something in the suspension??