Lionel Legacy Berkshire tripping power supply breaker

It's time to remove the shell.  You have a dead short, and the damage should be painfully obvious.  Your description leads me to believe the motor was struggling against a physical bind causing it to draw more amperage until a wire melted and dead shorted.  Check the worm and gear train for binding, damage and signs of stress.  Look for lack of lube or old/caked lube. Replace/adjust as required.  Then repair the short and retest.  Hopefully your robust Pittman motor survived.

Great Engine, don't give up on it yet.  Take pictures as you take everything apart if you haven't done it before.  Do it on a soft blanket to protect the paint.  It might be something easy to repair.  I have even seen screws come out on the inside and get lodged in a bad place and that's all it was.  Let us know what you find.

Thank you for the suggestions guys but I tried everything, I think my best bet is to send it for repair.

Might be good to remove the shell and take some pictures. It is remarkable the details forum wizards see.

Ive noticed that this metal piece gets extremely hot to the point where I can’t even touch it.

Am not sure what that metal piece is - a bracket that holds a heat sink maybe?

FWIW: I had a similar occurrence with a Legacy 4-8-4 - in my case the engine collided into another train at a crossing; despite not jolting off the tracks, from that point on the train tripped the circuit breaker...fortunately it was under warranty and Lionel repaired it. I looked for the repair sheet but couldn't find it...mostly likely they replaced something that fried. I have to admit I was disappointed in the lack of robustness...the collision was nothing like Gomez Addams high-speed antics...in fact I recall the trains were traveling at slow to medium at best when they collided. Perhaps there was a voltage spike, don't know.

@TrainMan114 posted:

Ive noticed that this metal piece gets extremely hot to the point where I can’t even touch it.

Those are the Triacs that drive the motor. They must be shorted. Sometimes you can replace just the triacs and be all good. Probably what to make sure the motor is in good working order in case it took the triacs out. Seeing as it should have a Pittman that’s not very likely. Hopefully someone that might know what the part number is on those triacs pop in. Otherwise we needs some good pictures from the other side or you can just replace the DCDS