Engineers have spent more time and resources perfecting the trucks than just about any other part of rail cars. Yet these vital parts are easy to overlook when we think of the cars themselves, especially when modeling.
Trucks are actually composed of many different components. Most modelers generally only really study only one, the sideframes. Structurally speaking, the sideframes transfer the weight of the car and its lading from the bolster, which runs perpendicular to the rails in the center of the truck, to the journals on the ends of each axle. Each truck includes a pair of sideframes which run parallel to the rail. Most sideframes also include a method for inserting springs of some design to cushion the ride.
The sideframe itself is the most obvious, and most distinctive feature of just about any truck. What is less obvious is all of the factors contributing to its design. Not only must the part be able to support the weight of the car and load, its connections to the axles, bolster, and other truck parts must also be made in such a way that the truck can adjust to changes in track and load conditions. A rigid truck would be relatively easy to design, but very ineffective in service.
There have been more than 100 patented truck sideframe design variations in the past 200 years. While you could write a lengthy book on the subject, for the focus of this blog, let’s look at a few of the common prototypes used under Lionel cars.
The Arch-bar truck was first patented in or around 1857 and became common by the 1870s. Its distinctive characteristics include a sideframe made up of heavy steel straps bolted together. The journal boxes were also bolted to the side frame and the bolster was supported by coil springs (most commonly two per side.) You’ll find this truck on many of our older steam-era rolling stock.
The Arch-bar was easy and inexpensive to construct. No large foundry or pattern was necessary. In fact, a decent Arch-bar truck could have been fashioned by any competent blacksmith. The bolted sideframes also offered a little extra flexibility for handling the rough track conditions common in the 19th Century. Construction of these trucks was common for at least 50 years – up into the 1920s.
Unfortunately, those same bolts never grew tighter with age. These were the weak link in the design and could fail almost without notice. With the high risk of derailment, Arch-bar trucks were outlawed for interchange service in 1940. The trucks could still be used on cars that did not pass between railroads however, and many lasted decades longer in company service.
The next step in the evolution of the sideframe was the “Andrews” truck. These trucks used a solid steel casting for the sideframe itself, but the journal boxes were still separate pieces which were bolted on. In addition to being stronger and safer, the Andrews design allowed railroads to recycle the boxes from their retired Arch-bar trucks.
Lionel does not currently make any models of this style of truck.
The commonly and usually incorrectly named “Bettendorf” truck was the first to use a fully integrated casting which included both the sideframe and journal boxes. The design was first patented by the Bettendorf Company in 1903. Although their name has been widely applied to the design, they readily shared parts of the design with other builders. In other words, all Bettendorfs weren’t Bettendorf’s. Generally however, the name is used for any sideframe with integral journal boxes.
Nor were all Bettendorf trucks identical. The most dramatic change came when the original “T” shaped cross-section of the sideframe was replaced by “U”-shaped steel. This doubled the strength of the truck. Later, the “U” was filled in for even greater strength. Beyond this major change, there were more subtle revisions in shape, size and springs based on the necessary carrying capacity, builder, etc.
The Bettendorf, or perhaps more accurately called AAR Type Y, truck became the defacto standard design for freight cars from WWII to the end of the steam era and formed the basic form for most of the common trucks that followed.
The addition of roller bearings to railroad wheels dates back long before they became mandatory or even standard practice for freight cars. Since 1980, they have been the requisite standard on all cars in interchange service in the United States. In overall form and function, there is little difference between a modern roller-bearing equipped truck and the solid-cast Bettendorf designs of the 1940s except of course for the journals themselves.
Lionel’s roller bearing trucks are based on a 100-ton Barber S2 truck. This is one of the most common in use today. Close examination of any car however is still likely to reveal some variations from car to car, even on the same car or truck, between smaller details of the sideframes, spring packages and journals. Since parts have been standardized, in many cases it is possible for a shop to replace worn-out components with those of a different builder for faster repair.
Cabooses, express cars, passenger cars, and of course heavy-duty cars all have unique truck designs tailored to their needs. We’ll cover these in more articles down the track.
Until then, take a closer look at what’s holding up the freight cars the next time you’re watching a train go by – in any scale. There’s a lot more going on down there than you probably thought.