Thursday, June 18, 2020

The enigmatic PRR 2D-F8 truck

T. S. Martorano Collection
One of the interesting things about the Pennsy was its trucks. Like everything the Pennsy did, they were different. The trucks used on the X29 (and X28) illustrate this. The 2D-F8 (PRR designation) truck had a pronounced droop at the bottom of the sideframe, lending the trucks a distinct shape. This was similar to the ARA Type Y cast sideframe design. However, the Pennsy also employed several different types of bolsters, resulting in a dog's breakfast of combinations after cars were shopped. X29 572110 shown above is a fine example, with what I am calling an "ARA" bolster on the left truck and a "box" bolster on the right truck (click on images for larger views). Here are views of a few others, along with HO scale truck references

This is an early bolster with a notably sloped face in the bolster end. This is the truck included in the Red Caboose HO scale X29 model.

This and the following image illustrate the "box" bolster. This truck was offered by Sunshine Models as a set of white metal castings to be assembled by the modeler.

This bolster is what I have dubbed the "ARA" bolster. I am not aware of an HO scale offering for this. Should Kadee get around to offering an 'HGC' version of their 2D-F8 truck, I would lobby for this as it could be used as a Type Y stand-in, most notably for several PFE reefers. That beer can-like thing where the outer right hand spring is supposed to be located is a Miner snubber, which was supposed to reduce harmonic oscillation and improve ride qualities. There were other flavors. See the CP chapter in your 1932 ARA box car book.

This is the last and most "modern" of the bolsters with a vertical web cast in the center of the outer portion. This truck has been reproduced in HO scale by Bowser.

Note that while I have highlighted these as shown on X29s, they were used on many, many others classes of 50 and 55-ton PRR cars, so having representations of all of them in HO scale is a good thing, even for non SPFs*.

*Slobbering Pennsy Freaks


  1. Ted, I agree the variation in the bolster ends is interesting, but also note the variation in the shape of the side-frame. The 2D-F8s that came on the 1924-25 X29s had that distinctive "droop" above the journal boxes, and the Red Caboose trucks are an exact match. All subsequent PRR 2D-F8s are flatter along the top, and the Bowser trucks are closer (but maybe not perfect).

    The former are often termed "ARA Type Y" trucks because the sideframe shape matches some ARA drawings from the 1920s. But two points: (i)the ARA standard was for dimensions and engineering standards, NOT the exact shape of the sideframe, and (ii) the exact shape seems to vary a bit from the earliest 1923 drawings to those published into the 1930s.

    Thanks for the interesting post, and best regards.

  2. Please consider that you might be referring to differing PRR classes of trucks and not variations of the 2D-F8. See which links to diagrams of most of the freight trucks the PRR used. According to this document, the X29 and its various sub-classes, used eleven different 2D-f* classes of trucks.

    In particular the last image in your post is really a PRR class 2D-F22 truck.


Comments always welcome!