@rplst8 posted:If I had to venture a guess, one of the two has a motor that came loose. Or maybe the tach reader and/or flyweel-tach. I’ve had the former happen on three other F units, all of different vintages.
P.S. These are Alco FA1s or FA2s. Not EMD F7s. I only point that out because it might help you determine the product number.
I think you’re right about the sensor equipment because it’s only at low speeds and the run fine independently.
I am not sure how much poking around I want to do, so looks like these might be taking a trip south to Lionel repairs.
Thank you for your help and the clarification on the identification. I Really appreciate this community.