Turn those F’s upside down, you’ll note that your trucks’ swiveling can interfere with the stepladders, but only a small detail part on the trucks actually makes contact; it’s the flat, squared-off “brake hardware”. Maybe it’s meant to be a brake line? Not accurate to a Blomberg B truck anyway. CUT IT OFF! See the left side, the red shaded area, that’s the culprit. There are 4 per bogie, you’ll have to decide which ones are right for your lead/trailing bogies based off interference by checking it (or cut them all off for uniformity?)

Seems like trucks on all of the F-units (not FT’s as fas as I know) can benefit. From what I can tell, the cast-on detail is so far from the real brake hardware I don’t see it as a “loss”. At this scale, it’s almost impossible for them to cast the part properly (in appearance) anyway.

For me this modification (just cutting/beveling off a tiny bit of delrin) fixed two issues. Not only the immediate end of some mystery derailments on grades, but also it appears I can tackle about an ~8″ radius curve with my F units now. WIN!

Check out the “where to cut” photo below, and the Wiki link on Blomberg B bogies.

Cheers!

http://en.wikipedia.org/wiki/Blomberg_B

Cut off those “brake hardware” corners, you’ll be glad you did!