USA F3s - Close Coupling
The USA F3 diesels have been out for several years, and they are real beauties in both appearance and performance.  They come with soft rubber diaphragms between units as did the prototype when new.  These often were removed by many railroads as the units gained mileage and use, since they were a problem to maintain and repair.  I wanted to keep mine, but have never been happy with the space between units.  The locomotives are very unrealistic looking with the space that two diaphragms between each unit produce.  The correct prototypical distance is actually one diaphragm spacing between these units.  Since I will always run mine as an A-B-A set, I decided to remove one diagram from each end of the "B" unit and pull the couplers between the units in as close as I could make them.  I did not realize what a job this would entail.
    I first went to the Kadee home page to see what they recommended in their "Conversions" section.  Their conversion to Kadee couplers put the units at the same spacing as the original USA couplers.  I e-mailed them with a question about closer coupling, and surprisingly, they still could not help other than recommending body mounting rather than pedestal mounting.  I decided that my best course of action was to body mount a shortened coupler to get the distance that I required. 
    I removed the coupler mounting pedestals on all the units.  I then used Kadee's instructions and built mounting blocks out of some oak scrap that I had in the garage. The mounts are 1 25/64" long, 53/64" wide, and 35/64" tall.  I notched out the sides where the mounting screws go so that the truck swing would not be restricted on curves.  I used the original mounting pedestal as a template and drilled holes for mounting screws. These new mounting blocks were sanded and screwed to both ends of the "B" units and on the rear of both "A" units. I painted them black so that they would not show from the sides as the locomotives were viewed.
    I chose a #789 coupler because I did not want any offset, and  had several sets in my parts box.  I cut the coupler draft gear off at the mounting hole, and screwed it to my new mounting blocks. When mounted and viewed from above, you can barely see the coupler on the "B" unit, and it is under the diaphragm on the two "A" units.
    Now when the diesels are coupled, there is only one diaphragm space between units.  The square part of the coupler lift bars overlap but do not interfere with each other.  The spacing is now what I wanted.  The coupling is very secure to the point that it may be difficult to uncouple the diesels when you want to remove them from the layout. The following pictures to illustrate the conversion, and how the units now look with their closer coupling and single length diaphragms. 
F Units with two daiphragms as they come from the USA factory.
F units with one diaphragm and close coupling using Kadee #789 couplers.
Note: wires shown between units are jumpers which provide for the directional MARS light option on both "A" units via the Sierra Sound System.
More Conversion Photos