One last thought: I have not opened my Hudson #5415 engine, but did open my Santa Fe Northern #3759 when the DOG BONE linkage came out of the U-joint cups and the engine would not go forward. It would run smoothly in reverse, but not forward.
Other owners of the ATSF Northern engine put a packing on either end of the Dog Bone to keep it centered in the U-joint cups. Perhaps the clicking is the Dog Bone pins clicking inside the U-joint cup as it rounds the pins and eventually fails to turn. The clicking pins would interrupt the smooth rotation of the drive train, causing the stuttering. In reverse, the dog Bone is pushed back into the U-joint cup and runs smoothly.
I contacted Lionel about the previous Santa Fe Northern, to tell them about the "Dog Bone" linkage being too short to fit properly between the U-joint cups. I don't believe the newest Santa Fe Northern engines have arrived yet. Only some previous Northern engines had this problem.
The "Dog Bone" linkage may be the problem. If it is, it will wear until the pins round and no longer mate with the U-joint cup, ending forward movement.
I am not a technician. This is just one of my experiences.
Sincerely, John Rowlen
