I'm curious. What does the missing plank look like. In other words what's the difference between a plankless and a "planked" truck. Google is no help.
Jim
You are going to have to clarify more, especially since Trans-Atlantic railroad terminology might be messing up the results.In American English a truck in railroading refers to the bogie/bolster that holds the axles a railcar rides on. In British English a truck refers to a goods wagon; and talking about planks on it can refer to how many wooden beams a truck has on the side (i.e. a three plank truck has three wooden beams on it's side while a taller seven plank truck has well, seven). This is one specific case where the change in language across both sides of the Atlantic drastically changes what people are talking about in railroad terms, and is worth accounting for when searching for the subject.
Very likely to be referring to 'spring plank' in the truck -- plankless might mean 'bolsterless'.
In earlier truck design the bottom of the spring rested upon a 'plank' that traversed both side frames. It can be seen here below the bolster:
8571004 by John W. Barriger III National Railroad Library, on Flickr
Later 'plank-less' designs used a beefed up bolster which added support for the 'spring package' and eliminated the plank. You can often see the ends of the spring planks as an inverted channel that is under the spring package, seen here under these eliptical springs:
9433 003 by John W. Barriger III National Railroad Library, on Flickr
The spring plank can be seen here just above the axle and below the bolster:
226-006094 by John W. Barriger III National Railroad Library, on Flickr
Spring planks were sometimes made of stamped steel and common channel. I witnessed the cleanup of a wreck on the B&O at Ravenna, Ohio caused by a broken spring plank on a gondola that was found to have used 'reconditioned' spring planks that had cracked and failed.
Plankless designs have fewer parts and are easier to repair or make wheel changeouts. The sideframe has a recess for the spring bottom and beefier bolsters for more support of the sideframe.
ACF Lot 3623 by John W. Barriger III National Railroad Library, on Flickr
Part of the brake beam can be seen here and might be confused for a spring plank but it is not. Model trucks rarely include a spring plank but I seem the recall one manufacturer in HO, perhaps Train-Miniatures that did have some semblance of a spring plank bolster.
Perhaps the moderator would want to move this thread to the 'prototype information' category?
I have considerably more information on spring plank design if the OP is interested.
Regards, Ed
Thanks Ed for the pix, I see the plank. Thanks to all. Jim