When the Rapido Trains HO scale models of Southern Pacific box car classes B-50-15 and -16 were first released, I posted a description of the prototype class histories and some details about the models (that post can be found at this link: https://modelingthesp.blogspot.com/2023/07/the-new-rapido-sp-box-cars.html ). In the present post, I address the brake gear on the models.
[I have also posted a description of the background to six of the paint schemes offered by Rapido (the seventh is too late for my modeling era). See the post here: https://modelingthesp.blogspot.com/2023/08/the-rapido-sp-box-cars-models.html .]
When these two car classes were built in 1925 and 1927, the standard freight braking system was what is known as the K brake, with air reservoir, cylinder and valve all in one component. Some of the Rapido models were manufactured with this brake, as I show below.
Starting in 1933, new freight cars were required to be equipped with a new air brake system, the AB brake, in which reservoir, cylinder and valve are three separate parts. It was further required that at any “major” shopping or repair, that existing K brakes were to be replaced with AB brakes. For that reason, by the end of World War II, cars with K brakes were becoming unusual. They were finally banned in interchange in 1953.
The AB brakes performed much better with longer trains, with both quicker application and quicker release than K brakes. They also had two reservoirs instead of one (though the two were combined into one component in the AB brakes), better for emergency applications. So replacement of K brakes with AB was not some bureaucratic detail but a significant technical improvement.
Rapido made some choices as to which of their paint scheme cars would have K vs. AB brakes which are hard to understand. For example, post-1946 car lettering was applied to a Class B-50-15 body with K brakes. But in all such cases, a small envelope was in the box, containing AB brake parts for the modeler to install. As I model 1953, I don’t wish to operate any of the cars with K brakes, except for the SPMW car. On-line cars such as MW cars could still operate with K brakes, they just couldn’t be interchanged.
The change to Rapido AB brakes is pretty simple. I sliced off the K brake component from below (its peg was inserted into the car floor) and discarded it. Important point: before removing the K part, snip the linkage to the lever right at the crossbearer (tip of the cylinder). See below. This retains the “chain” part of the linkage already on the car.
Then as stated above, slice below the K part and remove. You should then have a clean floor (except for the scar where the K gear was).
The AB parts provided have an insertion peg or two for ease in factory model assembly. One can either drill holes for these pegs, or slice them off and simply glue the parts flush to the floor. With a strong and tenacious glue like canopy glue, the latter approach is quite practical, and easier. But first, let’s see where each piece goes.
In the photo nearest above, you can see at the leftmost of the two cross-bearers that there is a lever, which in turn is connected to another lever behind the other cross-bearer to the right. These two levers are correctly located for the AB brake, so they remain where they are. The new AB cylinder will be located to connect with the left-hand lever (above).
Below is a photo of a Rapido box car underbody with AB brakes as manufactured. This is the arrangement to be reproduced using the AB brake parts supplied with K-brake models.
The value of the view above is that it clearly shows which piece of piping is which, looking at the envelope of AB parts in the model’s box. Here are those parts, arranged roughly as above. All three components, reservoir, cylinder and valve, have nice receptacle holes for the piping. (The piping is wire.)
I decided to first glue the cylinder and its pipe onto the car floor, then, using canopy glue, fit the other two pipes into the intended holes in the reservoir, and then arrange onto the car underbody. The last step is to fit the three pipes into the valve, which is touchy, but possible. I confess that in one case I just omitted the pipes altogether. In a side view, they are invisible anyway. But the AB brake components are visible from the side, so they are the minimum to install.
The cars with the newly-installed AB brakes are headed for the weathering bench, from which they will go into layout service. I like these cars and congratulate Rapido for choosing them to manufacture.
Tony Thompson
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