As I mentioned in my other threads, I am going through checking, repairing and maintaining all of my long stored MTH locos and also checking out and running for the first time my newly acquired Lionel Legacy/VL locos.
This is a PRR DD35A legacy model. I placed it on the track and programmed it with the Legacy remote. It did not smoke well and when I tried to run it, it would run and stop and jerk and then suddenly it took off almost at full throttle while making "clicking sounds" from the rear gearbox. Luckily I caught it in time and lifted it off the track before, well, before it destroyed itself and left me drinking a whole bottle of Black label 
Took it apart and found a loose board where the antenna plugs in, I also found a piece of metal stuck in between one of the gears in the rear gearbox causing the clicking sounds and jerking motion. I was not able to remove the debris piece of metal so I had to push it inside the flanged wheel away from the gears. I also added a thin piece of tape to hold that board where the antenna plugs in, this seems like it can easily move out of its pins while in shipping and causing a potential issue as I think it may have done in my case. Anyway, Re assembled and test ran it, all is well. Thank for looking!
Before repairs, barely smoking 
Caffeine highly required
Internals
I adjusted the heat element to be in the center of the bowl. No sensor here.
Offending G'box, removed motor
Only two driven sets of wheels??
Note the shiny piece of metal lodgged in between the gear teeth
Zoomed in but not clear, best an iPhone 4S can do
Test and break in on rollers!
Runs great, smokes great now
Tie wrap to hold board down interfered with plastic body
Found a pinched coupler wire!
Electrical tape took care of the issue.
Thin Piece of electrical tape to hold down the board instead of the thick tie wrap...work ok.
Note the green tie wraps to clean things up a bit and may prevent pinching of wires.
Note the dual speaker plastic box, great for bassy sounds!
