Sunday, May 1, 2016

Trucks and snubbers, Part 3

In the first post in this series, I described truck spring arrangements, and some simple snubber designs (you can read it at the following link: ). The subsequent post described a variety of trucks with leaf or elliptical springs, substituted for the usual coil (helical) springs, as another method to accomplish some snubbing action (it’s at this link: ), through the friction among the individual leaves in the spring.
     But also in the 1930s, more compact and simpler ways to provide frictional snubbing were also being developed. The first one, and very influential, was the Barber stabilizer design (named for its inventor, John C. Barber), first produced by the Standard Car Truck Company but soon licensed by almost all other truck manufacturers. Thus the term “Barber stabilized” truck” does not designate a truck manufacturer, it only indicates the licensed snubbing design. The drawing below, from Railway Mechanical Engineer, December 1938, shows the operating principle. The sliding wedge, highlighted in red, was forced against the vertical wear plate to create friction whenever the bolster moved up and down.

The auxiliary springs (called out in the drawing as “special side springs”) which maintained pressure on the friction wedges were located behind the main springs and thus ordinarily invisible from trackside. But the distinctive pockets in the bolster end, in which the wedges were housed, are an easy spotting feature for Barber trucks, as in this example. This S-2 truck has a spring plank.

The photo is from the Richard Hendrickson collection.
     In subsequent years, most other truck manufacturers would develop their own versions of this bolster snubbing capability, marketed under such trade names as “Cushion Ride” and “Snub-Up.” The most successful of these was the “Ride Control” design by American Steel Foundries, designated the A-3 design, which along with the Barber S-2, were by far the most popular trucks of the transition era, and sideframes of both types are being produced today in 100-ton roller-bearing versions. Below is a photo of a transition-era ASF-A-3, produced for B&O, as indicated by those initials cast onto the sideframe (photo by ACF Industries, courtesy Edward Kaminski).

In this truck, you can see there are five spring pairs, not the usual four in a 50-ton truck, and that is because the springs which exert pressure on the friction wedges are inside the outer two main coil springs.
     Even more exotic truck designs were created to provide snubbing in other ways. One interesting example, which did sell in small quantities, was the Chrysler truck, using beefed-up automotive shock absorbers to absorb vertical motions. This truck, named FRD-5, looked like this (photo from the manufacturer), and had sideframes cast by Symington-Gould. The shock absorber is at the right, with a coil spring at left, in the spring opening.

I described a modeling approach to this truck in a prior post, about a PFE car group which had them. If you’d like to see it, here is the link: .
     We have good model versions of most of these trucks (a glaring exception is the Barber truck shown earlier in this post, which we need in a postwar version without a spring plank). But many model equivalents of the trucks shown in both these posts are provided in Richard Hendrickson’s summary, available from this link: .
Tony Thompson


  1. When later, i.e. bigger, cars started using 6 spring packs instead of four or five, the springs under the wedges were the same size as the rest of the springs. I am very familiar with these, since my former employer coated the friction surface of the wedges for ASF (later bought by Amsted Rail) with composition friction material. This improved the friction performance. These were used in their premium "SwingMotion" trucks.

  2. Thank you, Tim, an interesting comment "for the future," in that I model 1953. There have continued to be changes in the details of truck design, even for "conventional" trucks, down to today.
    Tony Thompson