What is the difference between these trucks. Obviosly ones old and ones new, but when did the switch happen? Would you find both styles on trains?
Thank you!
I always forget whatever I knew on these details. Looks to me like the top photo shows a roller bearing truck, the one in the lower photo a bit earlier vintage.
See the history in a related December 2003 MR article that you can download.
https://mrr.trains.com/~/media/import/files/pdf/4/c/c/mr_pi_5-06_freightcartrucks.ashx
Here is a short article from Trains magazine.
https://trn.trains.com/railroads/abcs-of-railroading/2006/05/freight-car-trucks-and-carbodies
The truck in the bottom photo is a 50-ton AAR standard solid bearing type from Accurail. Solid bearing trucks were banned from interchange in about 1993, but cars thus equipped started to disappear quite a few years earlier.
The top photo is the old Model Die Casting roller bearing truck. It isn’t a particularly good model of a specific prototype, but probably is closest to a Barber 77-ton design. These showed up in quantity by the 1960s, and are still around today.