The question: Is there any significant difference between the trucks (disc-brake) used under pre-war Budd cars and those used after the war?

From what I've been told, you cannot take a truck from, say, a 1949 Budd car and put it under and older (1939) car without some significant modifications. I use these model years only because I am familiar with some cars built in these specific years. I've never seen the trucks side-by-side out from underneath the cars.

Any enlightenment from the sage experts here would be appreciated! :>)

My recollection is:
6" difference in wheelbase (8'6"postwar, 9'0"prewar).
Double eqalized prewar truck, single equalized postwar.
Different location of truck mounted brake cylinders.
Differences in springing and snubbers.

Sorry I don't have more detail, but this is just off the top of my head.

There weren't that many pre-war Budd-built cars that had disk brake trucks, but the ones that were disk almost always had double drop equalizers, as artshwartz noted, as well as numerous other different details.

Most pre-war Budd cars had 5 1/2 x 10 trucks, while post-war cars could be 5 1/2 x 10 or 6 x 11, depending on the weight of the car and/or the speed which the car would be traveling.

I terms of interchangeability, the primary issue is center plate compatibility. That can be a major project, or maybe not so major, depending on what's on the carbody bolster and what's on the truck bolster. As usual, there were a number of different types of center plates used over the years, depending on the RR, car builder, and truck type. A second issue to be addressed, but usually not as involved, is side bearing compatibility. Also, changing trucks almost always should include a review of all the springs to make sure they are reasonably close to what is appropriate for the weight of the car.

There have been some good articles over the years in some of the modeler magazines, such as the 2 part series in Mainline Modeler back in the 1980's (I think), that gave a decent overview of most all lightweight truck types, including photos.

Thanks for the feedback, Topfuel & Artschwartz. Sounds on the face of it that it would be a fairly extensive and expensive proposition to put the more modern trucks, whether disk or tread brake. I did a quick Google search and found reference to the Mainline Modeler articles. They appeared in Volume 3, Nos. 1 & 2. Not sure what year that translates to, but I'll have to dig out my print copies and see if I just happen to have them. There is a basic passenger car truck primer available as a PDF file from the RPCA:

http://www.google.com/url?sa=t&rct=j&q= ... Ww&cad=rja

Hopefully, the Mainline Modeler articles will be much more detailed.

In case anyone else is interested, the Mainline Modeler articles are in the 1982 January/February (v. 3, No. 1) and March (v. 3, No. 2) issues. I did find my copies in my collection. I also found copies of these issues currently available online at that big auction website, in case anyone is interested. Glad I have my originals, cover price $2.75!