I just found the instructions for the Sunshine kit, and now understand what you are referring to.  Neither the instructions for the Speedwitch kit or Ted Culotta’s article on the cars showed this part, so I didn’t include it on the model.  I don’t know if this part was unique to the later cars that were modeled by the Sunshine kit, or if it was used on all series of Soo sawtooth boxcars.  I also looked at a number of photos of Soo sawtooth boxcars.  The few that showed the brake cylinder did not seem to contain the mechanism shown on the Sunshine instructions.  Hopefully one of our Soo Line experts can shed more light on this subject.

Sincerely,

Rich Remiarz