Thinking about it, Conrail locomotives had the toilet dump connection in that spot. I wonder...maybe an asthetic cover for a gunky pipe fitting?
Mark H
Modeling in HO...Reading and Conrail together in an alternate history.
I do not believe the tab is a jacking pad. I think the jacking pad is behind the tab and positioned above the center axle of the truck.
But if you look at this photo:
you will see an object that is in a similar position. It features a round device. It is in a similar position as the tab. I see it on a few SD40-2's, but not most. I believe there's a battery box directly above. Perhaps it's related to that.
Ed
Took me a bit to figure out what you are referring to...but I got it now. That is an odd little feature...and only on the front. My first thought was a cover of sorts to protect the truck air cut out. I remember some Conrail locomotives I worked on had the C/O around that location at the side sill. But that doesn't look like the case here.
I can only guess that maybe when the units were built that feature had an intended purpose...but they changed their mind later and never removed the feature.
CN enthusiasts might have a better take on this.
I was looking at pictures of SD40s and I noticed that CN ones had a trapezoid shaped 'tab' on the side of the frame. I don't see this on other rr's SD40s. Does anyone know why the CN ones have this?
Pictures for reference:
http://www.railpictures.net/viewphoto.php?id=549403&nseq=32
http://www.railpictures.net/viewphoto.php?id=546761&nseq=20
http://www.railpictures.net/viewphoto.php?id=541898&nseq=28