Welcome to the forum.
I have a 1225 Berk also. One heck of an engine. I also have a 765 Berk.
What happened to the trailing truck.
I don't call these American Flyers. They are Lionel. I am not fond of most
Lionel S scale engines. The FlyerChiefs are an exception.
Pere Marquette 1225 and Nickel Plate Road 765 run side by side - YouTube
Here are the prototypes
Yes, these are definitely Chionel products. Old man Gilbert would not approve.
I figured at $250 for a loco, 3 cars, power pack, and track, it was a deal.
I need to put another $20 into getting the rear axle back in, but hey...
This is my first S size locomotive. I'll post more once she is rolling.
Chionel was absolutely no help, they told me I had to buy a complete trailing truck, then told me its not available.
I found the bearing number, myself, but its out of stock.
So, I'll buy a pilot truck, and harvest the parts. More on my 1225 Berk later.